HVACReducation.net's Tech Tips

How to Charge An Air-Source Heat Pump In Winter

2011-09-18T07:54:00.001-05:00

By Phil Rains
HVACRedu.net
About Phil!

Much interest has been shown in the correct requirements and/or procedures necessary for winter heat pump charging. The correct method(s) necessary for accomplishing winter charging are often included in an overall charging description, typically devoted to summer charging. In this article, we discuss only winter charging criteria.

Always remember that the ASHP (air-source heat pump) must contain the correct refrigerant charge to be able to transfer heat appropriately and meet the structure needs.

An ASHP will achieve its rated energy efficiency only when it contains within a few ounces of the proper refrigerant charge per original equipment manufacturers’ (OEM) criteria. An ASHP that is either undercharged or overcharged cannot achieve its rated capacity. And, an improper refrigerant charge places an ASHP under additional stress and may shorten its service life. When the charge is correct, specific refrigerant temperatures and pressures listed by the manufacturer will match temperatures and pressures measured in the field.

Today’s ASHPs typically will include two metering devices. These may be orifices/pistons or thermostatic expansion valves (TXVs) in most applications. There even may be two orifices/pistons, two TXVs, or one of each in some ASHPs. Most modern ASHPs will have at least one TXV, and most likely prior to the indoor coil. In fact, most new R - 410A systems will specify a TXV prior to the indoor coil. These systems will either have an orifice/piston at the outdoor coil, or another TXV.

Adequate refrigerant charge for matching coils and 15 feet of line set is typically supplied with most split-system ASHPs. However, because each installation is different in terms of indoor air flow, refrigerant line length, and duct variations, etc., the manufacturer’s charge may not be correct for every application. To assure the best performance from the ASHP, the refrigerant charge should be checked and adjusted when needed on each installation. NOTE: Some manufacturers provide different line set lengths so always check with the supplier and the installation and operation manuals. In most cases where the line set exceeds 15 feet in length, refrigerant should be added at.3 to .6 ounces per foot of liquid line (again, check the installation and operation manuals). Weighing in charge is recommended, but, “topping off” is allow in most cases. If less line is used you should recover the excess refrigerant.

Always be aware that all refrigerant in an operating ASHP is under pressure. Plus, some ASHPs will use different refrigerants. Many ASHPs have R-22, but newer systems will use R-410A. You must guard against any refrigerant spraying into your face or on your skin. Always wear protective equipment, i.e. safety glasses or goggles and gloves, when working with any refrigerant.

When charging or checking charge, always check for clean coils, clean filter(s), and proper air flow. Indoor air flow should be 350 to 450 CFM per ton of cooling, based on the size of the outdoor unit. This approximate CFM amount should also be moving during the heating mode as well. The most common way of establishing indoor air flow of an ASHP is the emergency heat temperature rise method. Indoor air flow will then be: [(heating output of electric heater in Btus) / (1.08 x Temperature Rise between supply and return)]. In other cases, measurement of external static pressure is helpful.

When you must charge an ASHP during the heating mode, you must always use the “sub cooling” method of charging.

Only liquids and solids can be sub cooled. Sub cooling is any temperature of a liquid or solid below its saturation temperature. As an example, consider water. Liquid water at sea level and atmospheric pressure (14.7 PSI) has a saturation (boiling) temperature of 212ºF. At this boiling temperature (and pressure) and above, the water will be in a vapor state (or “superheated”). At any temperature below 212ºF (and atmospheric pressure in this case), the water would be in a liquid state. The resulting temperature of the water would be below the boiling temperature for water of 212ºF. If the water was at 200ºF, we would say that it is actually sub cooled 12 degrees. Liquid refrigerant can be under the same situation within an operating heat pump. In the condenser (the indoor coil during winter), after the vapor refrigerant condenses to a liquid, it will continue to decrease in temperature as more heat is rejected, or be sub cooled.

When referring to sub cooling, we are always concerned with the amount of liquid refrigerant that is in the “condenser”. During winter, the “condenser” is the indoor coil, not the outdoor coil as in summer (for either heat pumps or air conditioners). Inside a heat pump system’s “condenser” (indoor coil) during winter, conversion of vapor to liquid involves removing heat from the refrigerant at its saturation condensing temperature. Any additional temperature decrease is called sub cooling. Finding liquid line sub cooling requires determining the condensing pressure and two temperatures - the condensing temperature at the measured condensing pressure, and the temperature of the refrigerant at the outlet of the “condenser” on the liquid line. The liquid line temperature involves measuring the surface temperature of the refrigerant line at the outlet of the “condenser”.

Utilize the following steps to determine the refrigerant sub cooling value (remembering that the condenser is the indoor coil during winter). You don’t have to find entering wet bulb during winter as when finding superheat during summer, but, you do have to determine entering dry bulb at the return. You must take pressure readings at the service valves at the outdoor coil (as no service valves are typically located at the indoor coil), but the liquid line temperature is taken at the liquid line leaving the indoor coil. If the manufacturer provides you with winter sub cooling targets use them. If not, typical sub cooling targets can be utilized, if you understand they are not precise. The following values have worked in most cases:

The basic requirements for checking charge and/or proper charging using the sub cooling method (assuming a TXV prior to the indoor coil (operating as the evaporator during the cooling mode) are:

· First, purge your manifold gauge lines. Then, connect the gauge manifold to the base-valve service ports. Run the ASHP at least 10 minutes in the heating mode to allow pressures to stabilize. Install a reliable temperature analyzer (thermometer) on the liquid line leaving the indoor coil with adequate contact and insulate for the best possible reading.

· Measure and record the outdoor ambient temperature with a reliable temperature analyzer.

· Measure the entering dry bulb temperature at the indoor coil (at the return grille). Use manufacturers’ extended performance data to determine the pressures expected at the inspection conditions (heating mode). You should be within ± 5 PSIG if the system is correctly charged. An example of heating data is shown below:

· Find the liquid line temperature (leaving the indoor coil) and subtract it from the discharge saturation temperature from the saturation scale on the discharge gauge, or a P/T chart for the refrigerant being used. Subtracting one from the other, the difference is the amount the refrigerant gas has condensed and cooled past its saturated temperature, or sub cooling within the condenser (indoor coil).

Sub Cooling = Discharge Saturation ºF - Liquid Line ºF

· Refer to the manufacturer’s data sheets for required sub cooling target operating values. Sub cooling during winter should be typically 8 to 15 degrees ± 3 ºF (manufacturers will typically determined a target sub cooling operating value for various combinations of equipment and publish these values in the installation and operation manuals, or provide sub cooling charts). Contact your supplier or manufacturer if no target values are provided.

· If sub cooling is low (and superheat is normal due to the TXV working correctly), add refrigerant while checking sub cooling until normal levels are reached.

· If sub cooling is high (and superheat is normal due to the TXV working correctly), recover refrigerant while checking sub cooling until normal levels are reached.

· If you need to remove R-22 or R-410A from a system, you must recover the refrigerant based on EPA criteria. Never vent it into the atmosphere!

When charging an R-410A system, you must charge from the refrigerant cylinder in the liquid form (pull the liquid from the canister in the upside-down position), and charge into the low side of the system. Throttle the refrigerant to a vapor either by “hand-throttling” using the hand valve and the compound gauge, or use a commercially available throttling device in the low side line. This method assures the zeotropic blends in the R-410A refrigerant will not fractionate, and is required by the EPA and UL.

Copyright © Phil Rains

About the Author: Phil Rains is Master Trainer/Lead Technical Writer for HVACRedu.net. He has over 38 years of HVAC and Refrigeration experience in installation, service, and training. He is NATE-certified in all areas, a member of ASHRAE and RSES, and ACCA EPIC-certified in Residential and Commercial Design. He also holds a Universal classification in EPA 608. For information concerning online HVACR courses, please our website at HVACRedu.net.

R410-A Refrigerant Charging

2011-09-18T07:44:00.002-05:00

by Phil Rains

An R-410A air conditioner’s ability to operate as designed is dependent upon the amount of refrigerant it contains. U.S. Environmental Protection Agency (EPA) studies suggest that approximately 75 % of installed air conditioners possibly have incorrect refrigerant levels, which can reduce system capacity and efficiency by 20 percent or more.

The level of refrigerant charge is unique to each R-410A air conditioner and is determined by every component, including the outdoor coil and compressor, the indoor coil, and the refrigeration lines that carry the refrigerant between the coils. Correct refrigerant charge and proper refrigerant line sizing protect the compressor from damage, ensure efficiency, and improve performance. You should always verify the refrigerant charge for proper installation of an R - 410A air conditioner.

R-410A air conditioners should be leak-checked during the installation and during each service call. Most R-410A air conditioners are charged with refrigerant at the factory, and are seldom incorrectly charged. R-410A air conditioners that have the correct refrigerant charge and airflow typically perform very close to manufacturers listed cooling efficiencies. Over-charging or under-charging refrigerant however, reduces R-410A air conditioner performance and efficiency.

For satisfactory performance and efficiency, an R-410A air conditioner should be within a few ounces of the correct charge, specified by the manufacturer. You must measure airflow prior to checking refrigerant charge because the refrigerant measurements aren't accurate unless air flow is correct. Several simple methods have been utilized in the field for years by technicians to estimate the Cubic Feet per Minute (CFM) per Ton crossing the evaporator. They include velocity multiplied by area for registers and grilles, and pressure drop across a system or coil. These particular types are useful when you check for airflow across an evaporator during cooling and you should become familiar with these in lieu of simply guessing. Airflow should be between 350 and 450 CFM/Ton per Air-Conditioning, Heating and Refrigeration Institute (AHRI) standards.

When the charge is correct, specific refrigerant temperatures and pressures listed by the manufacturer will match temperatures and pressures measured in the field. Always verify these measurements. If the manufacturer's temperatures and pressures don't match the measured ones, refrigerant should be added or recovered, according to standards specified by the EPA.

R-410A air conditioners charged with refrigerant at the factory are shipped with the refrigerant charge typically noted on the unit nameplate. This charge is for a typical application of between 15 to 25 feet of equivalent line length, depending on the particular manufacturer. Occasionally, you may have to field charge or adjust charge when servicing existing systems. The best method to insure that the R-410A air conditioner is properly charged is by weighing in the amount of refrigerant specified on the outdoor sections nameplate, or per installation and operation manuals. Many contractors and technicians utilize the superheat method (for orifices/pistons), and the sub cooling method (for TXVs) when charging in the field.

R-410A air conditioners installed with more than 25 feet of refrigerant line should be charged following the charging method described in the installation and operation "long-line application" instructions provided by the particular manufacturer, or the superheat method, and/or sub cooling method, as necessary. No additional refrigerant oil charge is usually required for these applications.

Many field variations exist which may affect the operating temperature and pressure readings of an R-410A air conditioner. Some R-410A air conditioners utilize fixed orifice refrigerant control devices prior to the evaporator. The following procedure is for this type of refrigerant control device:

1. Check the condition of coils, blower wheels, and the blower motor speed. Measure airflow. The airflow calculation is very important because it helps you determine evaporator load, and therefore will have a significant effect on system pressures. Correct airflow if necessary prior to performing this check.

2. With both valves fully open, connect a set of manifold gauges to the valves' service ports, being careful to purge the lines.

3. Allow the system to operate at least 10 minutes or until the pressures stabilize.

4. Temporarily install a thermometer on the suction (large) line near the condensing unit's service valve. Make sure that there is good contact.

5. Determine the systems superheat as follows:

a. Read the system's suction pressure on the compound gauge.
b. Using the compound gauge (or a P/T chart) determine the system's saturated
suction temperature.
c. Read the suction line temperature with a temperature measurement device.
d. Superheat = the suction line temperature - the saturated liquid temperature.

6. Adjust the charge as necessary to meet the manufacturer’s requirements by adding refrigerant to lower the superheat, or recovering refrigerant to raise the superheat. Superheat charts are provided by manufacturers.

Most R-410A air conditioners manufactured today are equipped with a TXV prior to the evaporator. You can’t check a unit’s charge by using the previous Superheat Charging Method if this is the case. You must use the Sub-Cooling Charging Method.

TXVs control refrigerant flow by maintaining a constant superheat (for instance, 8ºF to 10ºF). With constant superheat values, the condition of the system charge cannot be determined using superheat. You must look to the condenser and the liquid side to verify proper charge. The following procedure is for this type of refrigerant control device:

1. Check the condition of coils, blower wheels, and the blower motor speed. Measure airflow by using the temperature rise method. Check pressure drop across coils using the manufacturer’s coil specification sheets. Or, use the velocity pressure to calculate airflow. The airflow calculation is very important because it helps you determine evaporator load, and therefore will have a significant effect on system pressures.

2. Check the system operating pressures. Connect the hoses from your manifold gauge set to the pressure taps on the liquid and suction service valves. Measure and record the liquid (discharge) and suction pressures.

3. Measure and record the outdoor ambient temperature.

4. Measure the wet bulb and dry bulb of the air entering the indoor unit in the return duct. This step is very important because it also helps you determine the evaporator load, and therefore will have a significant effect on system pressures.

5. Measure the liquid-line temperature so that sub cooling can be calculated. Use a good thermometer with a probe that can be strapped tightly to the line. Install the probe on the liquid line about 6-in. from the liquid service valve, then measure and record the liquid-line temperature.

6. Measure the high side pressure at the liquid-line service valve pressure tap. Using the discharge gauge (or a P/T chart) convert high side pressure to saturation temperature. Then simply subtract the liquid-line temperature from the saturation temperature of the refrigerant in the condenser to determine the sub cooling value.

Always refer to manufacturer’s data sheets to find the proper operating pressures for the conditions of the air that you’ve measured. Do the same for required sub cooling levels. Some manufacturers have tested their systems in laboratories and developed specific sub cooling requirements. If this has been accomplished, the sub cooling target will typically be visible on the label on the condenser. You should attempt to stay within 3 degrees of the target sub cooling.

If sub cooling is too low, there may be an insufficient amount of refrigerant. Add refrigerant as necessary.

If sub cooling is too high, there may be too much refrigerant in the outdoor coil. Recover refrigerant as necessary.

Zeotropic refrigerants like R-410A must be charged as a liquid from a canister due the possibility of fractionation of the blend of refrigerants it contains. You must consider its temperature glide, which refers to the range of temperatures at which components in a blended refrigerant boil or condense at a given pressures. R-410A’s temperature glide is < .3 º F, making it a near-azeotropic refrigerant mixture. Liquid charging is much faster than vapor due to the density of liquid refrigerant. R-410A must be “liquid charged” into the high side of the system if it is empty, so the components in the blend do not separate. Charging by weight is the preferred method of admitting the liquid charge. If you are “topping off” the charge, it is necessary to charge R-410A refrigerant into the low side of an operating system. You will need to invert most R-410A refrigerant cylinders, as most do not have dip tubes anymore. This will allow liquid refrigerant to flow freely from the cylinder. Connect the service hose to a commercially available throttling device and then to the suction service valve to charge the system. Using the throttling device is recommended, but some technicians have simply “hand throttled” the refrigerant into the system with the low side valve, with very little problem. Either way, you must avoid the possibility of fractionation. Pressures are 50% to 70% higher within an R - 410A air conditioner than what you were used to finding with R-22 refrigerant air conditioners. Always practice safe procedures when working with R-410A refrigerant. For more information about our R-410 online course, Click Here.

Copyright © Phil Rains

About the Author: Phil Rains is Master Trainer/Technical Developer for HVACReducation.net. He has over 35 years of HVAC and Refrigeration experience in installation, service, and training. He is NATE-certified in 5 areas, a member of ASHRAE and RSES, and ACCA EPIC-Certified in Residential and Commercial Design. He also holds a Universal Classification in EPA 608.

LADDER DIAGRAMS

2010-05-29T08:06:00.018-05:00

By Roger Desrosiers
HVACRedu.net
About Roger

Ladder diagrams are specialized schematics commonly used to document industrial control logic systems. They are called "ladder" diagrams because they resemble a ladder, with two vertical rails (supply power), and as many "rungs" (horizontal lines) as there are control circuits to represent. If we wanted to draw a simple ladder diagram showing a lamp that is controlled by a hand switch, it would look like this:

The "L1" and "L2" designations refer to the two poles of a 120 VAC supply, unless otherwise noted. L1 is the "hot" conductor, and L2 is the grounded ("neutral") conductor. These designations have nothing to do with inductors, just to make things confusing. The actual transformer or generator supplying power to this circuit is omitted for simplicity. In reality, the circuit looks something like this:

Typically in industrial relay logic circuits, but not always, the operating voltage for the switch contacts and relay coils will be 120 volts AC. Lower voltage AC and even DC systems are sometimes built and documented according to "ladder" diagrams: Notice that the right side of the 24 volt secondary is grounded.

So long as the switch contacts and relay coils are all adequately rated, it really doesn't matter what level of voltage is chosen for the system to operate.

Note the number "1" on the wire between the switch and the lamp. In the real world, that wire would be labeled with that number, using heat-shrink or adhesive tags, wherever it was convenient to identify. Wires leading to the switch would be labeled "L1" and "1," respectively. Wires leading to the lamp would be labeled "1" and "L2," respectively. These wire numbers make assembly and maintenance very easy. Each conductor has its own unique wire number for the control system that it’s used in. Wire numbers do not change at any junction or node, even if wire size, color, or length changes going into or out of a connection point. Of course, it is preferable to maintain consistent wire colors, but this is not always practical. What matters is that any one electrically continuous point in a control circuit possesses the same wire number. Take this circuit section for example, with wire #25 as a single, electrically continuous point threading to many different devices:

In ladder diagrams, the load device (lamp, relay coil, solenoid coil, etc.) is almost always drawn at the right-hand side of the rung. While it doesn't matter electrically where the relay coil is located within the rung, for reliable operation, it does matter which end of the ladder's power supply is grounded.

Take for instance this circuit:

Here, the lamp (load) is located on the right-hand side of the rung, and so is the ground connection for the power source. This is no accident or coincidence; rather, it is a purposeful element of good design practice. Suppose that wire #1 were to accidently come in contact with ground, the insulation of that wire having been rubbed off so that the bare conductor came in contact with grounded, metal conduit. Our circuit would now function like this:

With both sides of the lamp connected to ground, the lamp will be "shorted out" and unable to receive power to light up. If the switch were to close, there would be a short-circuit, immediately blowing the fuse.

However, consider what would happen to the circuit with the same fault (wire #1 coming in contact with ground), except this time we'll swap the positions of switch and fuse (L2 is still grounded):

This time the accidental grounding of wire #1 will force power to the lamp while the switch will have no effect. It is much safer to have a system that blows a fuse in the event of a ground fault than to have a system that uncontrollably energizes lamps, relays or solenoids in the event of the same fault. For this reason, the load(s) must always be located nearest the grounded power conductor in the ladder diagram.

Proper Air Distribution and Air Flow

2010-05-29T06:32:00.038-05:00

By Phil Rains
HVACRedu.net
About Phil!

Residential and light-commercial heating, ventilation and air-conditioning (HVAC) equipment distributes air throughout a residential and/or light-commercial structure by using an air distribution system. Designing a delivery system for air to flow in is critical. The proper operation of any heating or cooling system depends upon the duct design and layout. Poor design results in inadequate heating and/or cooling in some or all spaces in a structure. Poor heating and cooling is commonly attributable to insufficient equipment size even though the real problem is the conditioned air “delivery system”. When we say “delivery system,” we are actually talking about the duct work system (air distribution system).

If properly designed, the supply air and return air distribution is even and an approximate uniform temperature is maintained throughout the structure. Field studies have indicated that in some instances, the efficiency of air distribution (duct work) systems is over 50% less than it could be, because of poor design and leaks in the ducts. Many of these mistakes and problems can be corrected for little or no extra cost. However, proper air distribution can alleviate these problems from occurring in the first place, and if corrected after the fact, often increase savings for the occupant(s).

Leaks in air distribution systems can cause energy bills to rise and system capacities to be reduced. Leaking duct work can also cause unbalanced temperatures within a structure. Leaks in the return air duct work can result in dirty coils which can reduce system capacity and increased humidity levels (during summer). Return duct leakage can also allow contaminants to enter the air stream.

Improper design can result in oversizing or undersizing duct work. Undersized duct work can result in low air flow. Also, low air flow can result from too many unnecessary turns rises and drops in the duct layout which all lead to increases in pressure within the system. Additionally, noise can become a problem and the efficiency of the system can also be affected. Oversized ducts can also cause low air flow in some cases, as well as uneven temperatures throughout the structure. Oversized ducts also negatively affect the equipment efficiency.

Good air distribution design leads to occupant comfort, proper air flow, economical cooling and heating, and an economical duct installation. These are established by the duct design process. The final layout is called a duct system. The objectives of the duct system are to:

· Supply conditioned air to each room
· Provide proper pressure drop across the air handler’s coil
· Be sealed to provide proper air flow and stop leakage
· Have a balanced supply and return system
· Reduce duct losses and gain from and to surrounding areas

A thorough knowledge of air flow dynamics and duct work design can enable you to easily uncover and resolve what many would consider to be difficult problems.

The actual purpose of HVAC duct work is to deliver air from the system blower to the outlets which distribute the air to the particular room or space. Air moves through the duct work in response to a pressure difference created by the blower. The necessary pressure difference is a function of the way the duct work is laid out and sized. The objective of duct design is to size the duct work so as to minimize the pressure drop through it, while keeping the size (and cost) to a minimum. Proper duct design requires a thorough knowledge of the factors that affect pressure drop and velocity in the duct.

People typically want economical heating and/or cooling systems, and they also want economical duct work systems. All too often, duct design doesn’t get the respect or attention it deserves.

The 3 most important things to understand about duct work designs are:

1. Furnaces and air conditioners require a certain amount of air flow, measured in CFM (Cubic Feet per Minute), to be passed through the equipment (supply and return ducts) in order for the equipment to function properly and efficiently.

2. All structures have unique requirements and construction that pose obstacles when designing the duct work system to accommodate each room or space with proper air flow.

3. The ideal duct work system achieves both goals by providing enough air flow to and from the heating/cooling equipment as well as the structure. For maximum efficiency, this “ideal” system should also be sealed at all seams and should be properly insulated when exposed to unconditioned areas.

The industry-accepted method for residential and/or light-commercial duct design is the Air Conditioning Contractors of America (ACCA) Residential Duct Systems, Manual D.

Various other methods are available that address duct work design and installation for these applications. These methods are readily available for contractors and technicians. However most are based on the fundamentals identified in Manual D. Large commercial duct work systems must utilize design criteria appropriate for those applications which are beyond those methods identified in Manual D.

The typical residential and light commercial air distribution system consists of supply-air and return-air duct work plus the supply-air outlets and return-air inlets, and any other added accessory. The air distribution system is typically designed simultaneously with new structure layout, unless the structure exists already. New construction requires planning for ductwork locations, framing, plumbing and electrical wiring. Existing structures requires determination of modifications to existing duct work to achieve acceptable results.

You must always design the air distribution system and install one based on its performance characteristics, the climate where the structure exists or will be built, the particular structural features, and the heating and cooling loads determined by methods such as ACCA’s Manual J, or MJ8AE. If the size of the HVAC system is incorrect, you will never achieve the proper heat transfer required for the structure, room or space. Always check to assure the system size is correct for the structure as part of your troubleshooting routine. No single type of air distribution system is ideal for every structure, and often two or more types of air distribution systems may be necessary.

Assuming you will utilize Manual D for proper duct work design, the following steps are recommended:

· The length of the longest circulation path and the available static pressure determine the friction rate used for duct work sizing.

· The length of the circulation path includes the straight runs and the equivalent length of the fittings along the path. One fitting can add from 5 feet to more than 60 feet to the length of the path. Always consider the fittings in the air path.

· External static pressure (ESP) is determined from the equipment manufacturer’s blower performance data, preferably for medium-speed operation.

· The available static pressure (ASP) equals the external static pressure (ESP) minus the pressure drop through all the air-side devices in the circulation path. Always refer to blower table footnotes and manufacturer pressure drop data for devices that were not in place when blower performance was laboratory-tested by the equipment manufacturer.

· Accessory or after-market filters (or any device) that produce a substantial increase in system resistance should not be installed if the blower cannot accommodate the increased resistance by speed change. An arbitrary increase in system resistance may cause low air flow to rooms, a high temperature rise across a furnace heat exchanger (if installed), or low suction pressure at the cooling coil.

· The room heat loss and heat gain estimate (Manual J or equivalent) and the heating and cooling factors (Manual D or equivalent) determine the design value for room airflow.

· Duct work size is determined by sectional flow rate and the design friction rate (FR) value calculated from Manual D procedures, not arbitrarily assigned from “rules of thumb.” as frequently done with duct slide rules.

· The duct slide rule should only be used to size the ducts after the Manual D procedures are complete, not to lay out the ductwork using a “standardized” friction rate that can cause ducts to be the incorrect size and result in hot and cold spots.

· The friction chart or duct slide rule used for duct work sizing must always be technically correct for the type of duct material.

· Duct work velocities should not exceed specified design limits.

· Branch (run out) ducts should be equipped with a hand damper (for balancing).

Air flow and air distribution should always be considered when troubleshooting any HVAC system in the field. As discussed in other articles in this blog, checking superheat and sub-cooling on an operating system is dependent on proper air flow.

Even though superheat and sub-cooling determination can identify air flow issues with a system, other faults assume the air flow is already correct, or has been corrected prior to testing the system.

Correct airflow is of crucial importance to the operation of any HVAC system. Part of the heat transfer rate is determined by the air flow across the indoor and outdoor coils. If the air flow is incorrect, then the heat transfer rate is incorrect and can drastically affect the equipment’s performance.

HVAC equipment manufacturers follow the tenants of the Air Conditioning, Heating, and Refrigeration Institute (AHRI) which has a “Test Stand Value” requiring the measured air volume rate, when divided by the measured indoor air-side total capacity, must not exceed 37.5 SCFM per 1,000 Btu/h [this is a maximum of 450 cubic feet per minute (CFM) of airflow across an indoor coil per 12,000 Btu/h of capacity].
Most manufacturers use an acceptable range of 350 to 450 CFM per 12,000 Btu/h of cooling capacity, and over 750 CFM per 12,000 Btu/h of capacity across outdoor coils (most outdoor fans move approximately 1,000 CFM, up to 1,500 CFM, per 12,000 Btu/h of capacity). In the HVAC/R industry, 12,000 Btu/h of capacity is referred to as a “Ton” of refrigeration. Typically, most manufacturers focus on around 400 CFM per “Ton” of cooling capacity when rating their equipment.

There are various methods that help determine the air flow amount across an indoor coil. The indoor coil is typically checked as the air flow must cross this coil to allow the refrigerant to either absorb (cooling) or reject the heat (in the case of air-source heat pump heating) to the appropriate “sink.” In summer (for all cooling systems and air-source heat pump cooling), the “sink” is the outdoors, and during winter (in the case of air-source heat pump heating), the “sink” is indoors.

When furnaces are used, the system air flow during heating must meet the manufacturer’s specifications to achieve acceptable temperature differences across heat exchangers.

For an in-depth and mentored online Air Flow/Air Distribution Course CLICK HERE!

Why Pre-Season Air Conditioning Checkups

2010-05-09T04:17:00.011-05:00

By Roger Desrosiers
HVACRedu.net
About Roger

We all know the value of annual medical checkups because of the possible serious consequences that can develop, especially as we grow older. Finding a possible serious condition can save us a lot of grief. Well, this also applies to the possible consequences of not taking proper action in other aspects of our lives. One of which is the proper maintenance of our home/business air conditioning system.

Spring may not be a time when most of us are thinking about our air conditioning system, but it is the perfect time to schedule an annual check-up to make sure your whole home/ business is ready for summer. A pre-season check of your air conditioning system prior to the summer months can be a real money saver. When your air conditioner is running well it uses less energy to cool your house, and lower energy use means bigger savings for you on your monthly utility bills. Air conditioners at peak efficiency will use up to 20 percent less electricity and last years longer.

Early air conditioner maintenance will reveal most small problems that can lead to major, for more expensive problems if left unattended. Furthermore, if your air conditioner checkup is scheduled for spring, you’ll beat the long waits and higher prices that come with peak season HVAC repair visits. You will also be able to schedule a HVAC professional to come out when it’s most convenient to you for service. Wait until later in the summer, however, and you’ll find all of the pros are booked, and if you need them desperately, it’ll cost you!

Below is a checklist of common maintenance procedures your HVAC contractor should include in their routine maintenance call, and a list of some basic tips that homeowners can do themselves to help maintain their air conditioning systems.

Air Conditioner Maintenance Check List by Contractor.

1. Check for proper refrigerant levels. Low levels indicate a leak that needs to be found and repaired immediately. Low refrigerant levels can burn out your compressor, resulting in the most costly repair when it comes to air conditioners.

2. Check all electrical components and controls to make sure they’re working properly.

3. Clean evaporator and condenser coils. Dirty evaporators and coils reduce the energy efficiency and cooling ability of your unit.

4. Oil motors as needed.

5. Calibrate thermostat to make sure your air conditioner isn’t working overtime.

6. Check the condenser for any possible problems.

7. Check, clean, and/or replace filters.

What the Homeowner can do?

1. Before turning on your unit make sure the condensing unit located outside is not covered up. This unit needs to draw air into the system in order to have something to cool and blow out inside, but the process will be hindered if it cannot pull enough air from the outside.

2. Clean obvious obstructions such as newspaper, leaves, etc. from around the exterior of the unit.

3. A thoroughly cleaned air conditioning unit will operate at top efficiency. Homeowners are strongly discouraged from using a hose and water to try to clean it themselves because of the very serious risk of electrical shock and possible shorting of electrical components. You should contact a licensed HVAC professional.

4. Run your air conditioner for a few minutes now, before you need it. If you wait until the first hot day to discover it isn’t working, you’ll find yourself on a waiting list, sweltering sometimes for days before an air conditioning specialist can come to fix it.

5. Change the filters regularly. Dirty filters restrict airflow, reducing efficiency and worse case, can cause the evaporator to ice up. Disposable fiberglass filters should be replaced. Electrostatic or electronic filters need to be washed regularly.

6. Be sure all access panels are secure, with the screws in place.

7. Be sure the thermostat is set in the cooling mode. Just setting the dial below room temperature will not activate the air conditioning if it is set in the heat mode.

R410-A Refrigerant Charging

2010-05-02T04:42:00.029-05:00

By Phil Rains
HVACRedu.net
About Phil!

An R-410A air conditioner’s ability to operate as designed is dependent upon the amount of refrigerant it contains. U.S. Environmental Protection Agency (EPA) studies suggest that approximately 75 % of installed air conditioners possibly have incorrect refrigerant levels, which can reduce system capacity and efficiency by 20 percent or more.

The level of refrigerant charge is unique to each R-410A air conditioner and is determined by every component, including the outdoor coil and compressor, the indoor coil, and the refrigeration lines that carry the refrigerant between the coils. Correct refrigerant charge and proper refrigerant line sizing protect the compressor from damage, ensure efficiency, and improve performance. You should always verify the refrigerant charge for proper installation of an R - 410A air conditioner.

R-410A air conditioners should be leak-checked during the installation and during each service call. Most R-410A air conditioners are charged with refrigerant at the factory, and are seldom incorrectly charged. R-410A air conditioners that have the correct refrigerant charge and airflow typically perform very close to manufacturers listed cooling efficiencies. Over-charging or under-charging refrigerant however, reduces R-410A air conditioner performance and efficiency.

For satisfactory performance and efficiency, an R-410A air conditioner should be within a few ounces of the correct charge, specified by the manufacturer. You must measure airflow prior to checking refrigerant charge because the refrigerant measurements aren't accurate unless air flow is correct. Several simple methods have been utilized in the field for years by technicians to estimate the Cubic Feet per Minute (CFM) per Ton crossing the evaporator. They include velocity multiplied by area for registers and grilles, and pressure drop across a system or coil. These particular types are useful when you check for airflow across an evaporator during cooling and you should become familiar with these in lieu of simply guessing. Airflow should be between 350 and 450 CFM/Ton per Air-Conditioning, Heating and Refrigeration Institute (AHRI) standards.

When the charge is correct, specific refrigerant temperatures and pressures listed by the manufacturer will match temperatures and pressures measured in the field. Always verify these measurements. If the manufacturer's temperatures and pressures don't match the measured ones, refrigerant should be added or recovered, according to standards specified by the EPA.

R-410A air conditioners charged with refrigerant at the factory are shipped with the refrigerant charge typically noted on the unit nameplate. This charge is for a typical application of between 15 to 25 feet of equivalent line length, depending on the particular manufacturer. Occasionally, you may have to field charge or adjust charge when servicing existing systems. The best method to insure that the R-410A air conditioner is properly charged is by weighing in the amount of refrigerant specified on the outdoor sections nameplate, or per installation and operation manuals. Many contractors and technicians utilize the superheat method (for orifices/pistons), and the sub cooling method (for TXVs) when charging in the field.

R-410A air conditioners installed with more than 25 feet of refrigerant line should be charged following the charging method described in the installation and operation "long-line application" instructions provided by the particular manufacturer, or the superheat method, and/or sub cooling method, as necessary. No additional refrigerant oil charge is usually required for these applications.

Many field variations exist which may affect the operating temperature and pressure readings of an R-410A air conditioner. Some R-410A air conditioners utilize fixed orifice refrigerant control devices prior to the evaporator. The following procedure is for this type of refrigerant control device:

1. Check the condition of coils, blower wheels, and the blower motor speed. Measure airflow. The airflow calculation is very important because it helps you determine evaporator load, and therefore will have a significant effect on system pressures. Correct airflow if necessary prior to performing this check.

2. With both valves fully open, connect a set of manifold gauges to the valves' service ports, being careful to purge the lines.

3. Allow the system to operate at least 10 minutes or until the pressures stabilize.

4. Temporarily install a thermometer on the suction (large) line near the condensing unit's service valve. Make sure that there is good contact.

5. Determine the systems superheat as follows:

a. Read the system's suction pressure on the compound gauge.
b. Using the compound gauge (or a P/T chart) determine the system's saturated
suction temperature.
c. Read the suction line temperature with a temperature measurement device.
d. Superheat = the suction line temperature - the saturated liquid temperature.

6. Adjust the charge as necessary to meet the manufacturer’s requirements by adding refrigerant to lower the superheat, or recovering refrigerant to raise the superheat. Superheat charts are provided by manufacturers.

Most R-410A air conditioners manufactured today are equipped with a TXV prior to the evaporator. You can’t check a unit’s charge by using the previous Superheat Charging Method if this is the case. You must use the Sub-Cooling Charging Method.

TXVs control refrigerant flow by maintaining a constant superheat (for instance, 8ºF to 10ºF). With constant superheat values, the condition of the system charge cannot be determined using superheat. You must look to the condenser and the liquid side to verify proper charge. The following procedure is for this type of refrigerant control device:

1. Check the condition of coils, blower wheels, and the blower motor speed. Measure airflow by using the temperature rise method. Check pressure drop across coils using the manufacturer’s coil specification sheets. Or, use the velocity pressure to calculate airflow. The airflow calculation is very important because it helps you determine evaporator load, and therefore will have a significant effect on system pressures.

2. Check the system operating pressures. Connect the hoses from your manifold gauge set to the pressure taps on the liquid and suction service valves. Measure and record the liquid (discharge) and suction pressures.

3. Measure and record the outdoor ambient temperature.

4. Measure the wet bulb and dry bulb of the air entering the indoor unit in the return duct. This step is very important because it also helps you determine the evaporator load, and therefore will have a significant effect on system pressures.

5. Measure the liquid-line temperature so that sub cooling can be calculated. Use a good thermometer with a probe that can be strapped tightly to the line. Install the probe on the liquid line about 6-in. from the liquid service valve, then measure and record the liquid-line temperature.

6. Measure the high side pressure at the liquid-line service valve pressure tap. Using the discharge gauge (or a P/T chart) convert high side pressure to saturation temperature. Then simply subtract the liquid-line temperature from the saturation temperature of the refrigerant in the condenser to determine the sub cooling value.

Always refer to manufacturer’s data sheets to find the proper operating pressures for the conditions of the air that you’ve measured. Do the same for required sub cooling levels. Some manufacturers have tested their systems in laboratories and developed specific sub cooling requirements. If this has been accomplished, the sub cooling target will typically be visible on the label on the condenser. You should attempt to stay within 3 degrees of the target sub cooling.

If sub cooling is too low, there may be an insufficient amount of refrigerant. Add refrigerant as necessary.

If sub cooling is too high, there may be too much refrigerant in the outdoor coil. Recover refrigerant as necessary.

Zeotropic refrigerants like R-410A must be charged as a liquid from a canister due the possibility of fractionation of the blend of refrigerants it contains. You must consider its temperature glide, which refers to the range of temperatures at which components in a blended refrigerant boil or condense at a given pressures. R-410A’s temperature glide is < .3 º F, making it a near-azeotropic refrigerant mixture. Liquid charging is much faster than vapor due to the density of liquid refrigerant. R-410A must be “liquid charged” into the high side of the system if it is empty, so the components in the blend do not separate. Charging by weight is the preferred method of admitting the liquid charge. If you are “topping off” the charge, it is necessary to charge R-410A refrigerant into the low side of an operating system. You will need to invert most R-410A refrigerant cylinders, as most do not have dip tubes anymore. This will allow liquid refrigerant to flow freely from the cylinder. Connect the service hose to a commercially available throttling device and then to the suction service valve to charge the system. Using the throttling device is recommended, but some technicians have simply “hand throttled” the refrigerant into the system with the low side valve, with very little problem. Either way, you must avoid the possibility of fractionation. Pressures are 50% to 70% higher within an R - 410A air conditioner than what you were used to finding with R-22 refrigerant air conditioners. Always practice safe procedures when working with R-410A refrigerant. For more information about our R-410 online course,
Click Here.

Types of Split System Heat Pumps

2010-04-18T07:53:00.014-05:00

By Roger Desrosiers
HVACRedu.net
About Roger

Two main types of split system air source heat pumps are; "All Electric" and "Add On". If a heat pump is added on to a fossil fuel furnace, the coil is installed in the supply air plenum, which is downstream of the heat exchanger with respect to air flow. It is therefore impossible to run both the heat pump and the backup heat simultaneously.

The mild 105 ºF heat from the indoor coil could certainly not be rejected into a 150 ºF air stream from the heat exchanger of the fossil fuel furnace. Therefore, anytime that supplemental heat is required, the heat pump must shut off and rest while the space is brought up to temperature by the more expensively fueled back up heat. This is why "add on" heat pumps are not as energy efficient as an all electric system.

Since the indoor coil of an "all electric heat pump" can be located upstream of the electric heating elements, there is no problem running the heat pump and the backup heating simultaneously. Note in the diagram how the RA (Return Air) is what enters the indoor coil, not the heated air from the electric elements.

A heat pump is sized to the air conditioning load so that it has a long run cycle, and can properly dehumidify the space. If it is located in a climate where the heating requirements are very much greater than the cooling requirements, there will obviously be a need for additional heat.

This additional heat has several names, but they all mean the same thing; back up heat, auxiliary heat, AUX heat, supplemental heat. Further complicating the situation is the fact that it is harder to extract heat from colder air. (There is less heat content to be extracted). So as heat is required more, it is less available from the heat pump, and there is a greater reliance on back up heat. Whereas, the add on heat pump must shut off every time back up heat is required, the all electric heat pump can continue to provide some portion of the heat at a more energy efficient rate than the fossil fuel system. This layout where electric back up heat is located downstream of the indoor coil is also what is used in packaged heat pump systems.

One might ask, "why not simply locate the indoor coil upstream of a heat exchanger and, then one could have an 'add on heat pump' that could also run back up heat simultaneously with the heat pump"? The reason is a bit illusive. One must look to the cooling mode for the answer. If the indoor coil was upstream of a heat exchanger, then the heat exchanger would become quite chilled by the evaporator outlet air in the air conditioning mode.

Humidity could condense on the heat exchanger, which would promote corrosion and possibly leaks. Leaks are not allowable in fossil fuel heat exchangers, because combustion products contain CO (Carbon Monoxide) which is poisonous. Since the heat exchanger is located in the air stream supplying the conditioned space, codes do not allow such an arrangement.

Heat Pump Controls

A heat pump is a multi-stage heating and cooling system, and therefore multi-stage T-Stats are required to operate them. Manufacturers of commercial package heat pumps sometimes build in latching circuits in their control system design, and those systems therefore require a "standard" multi-stage T-Stat to operate them.

Residential split systems require Heat Pump T-Stats. A Heat Pump T-Stat will allow use of AUX heat simultaneously with 1st stage Heat Pump heat. They are therefore intended for use with "All Electric" Heat Pump applications and not with "Add On" heat pump systems.

An "Add On" heat pump to a fossil fuel furnace requires special controls, because you can not allow simultaneous operation of both heating stages. Years ago the contractor was responsible for designing a control circuit to disable 1st stage heat, and satisfy the load by 2nd stage heat any time 2nd stage called. There are now commercially available controls that provide this function.

The simplest type is called a "Fossil Fuel T-Stat". It disables 1st stage heat any time 2nd stage heat calls. However, no defrost tempering is provided with this type of control system. In other words, any time the heat pump goes into defrost mode, cold air is discharged into the conditioned space for the duration of the defrost causing uncomfortable conditions.

Co-efficient Of Performance is a way of describing a heat pump's efficiency. It is the ratio of heat produced to the amount of energy required to run the system. The COP is calculated by dividing the total heating capacity provided by the heat pump, including circulating fan heat but excluding supplementary resistance heat (Btu's per hour), by the total electrical input (watts) x 3.412. Another rating given to heat pumps is HSPF. Typical COPs for an air source heat pump under optimum conditions are 3 to 1. In other words, for one dollar's worth of energy input you receive 3 dollars worth of energy output. However, conditions are not always optimum.

As outdoor temperatures drop so does the COP. At a COP of 2:1 you would still be receiving twice the heat output compared to straight electric resistance heating elements. If electric elements were rated by a COP, they would rate 1:1. No matter how cold it gets outside the COP of an air source heat pump never gets any worse than 1:1.

However, it is not wise to torture the expensive heat pump under these conditions, when the same output efficiency can be achieved by other means. The annual energy savings attributable to a heat pump are a result of the sum totals of all the individual COPs the system operated under for the entire heating season. Most of the energy savings occur in the milder portions of the heating season, when little or no back up heat is required, and the bulk of the heating requirements are being met primarily by the energy efficient heat pump.

It is possible to relocate heat from the ground or water with a heat pump. Most of the time ground and water temperatures are higher than winter air temperatures, so they are more efficient to use as heat sources. For example, there can be a raging snow storm with air temperatures in the 0ºF range, yet the ground temperature 6 feet down might be 40ºF. However, those mechanical systems are a lot more complicated than air source heat pumps, and although COPs of 4:1 or higher can be achieved, the much greater installation costs, increased maintenance and repair costs should be carefully considered compared to the expected extra energy savings.

It is important that the indoor air handler and duct distribution system are capable of moving an adequate quantity of air to satisfy the air flow requirements of the indoor coil when it is in the condenser mode. A typical rule of thumb for air flow requirements is 400 CFM per Ton (cubic feet per minute) for air conditioning systems, and 450 CFM per ton for heat pump systems. Inadequate condenser air causes high head pressures which lead to compressor failures.

These are some other factors to consider when choosing and installing an air-source heat pump.

Select a heat pump with a demand-defrost control. This will minimize the defrost cycles, thereby reducing supplementary and heat pump energy use.

If you're adding a heat pump to an electric furnace, the heat pump coil should usually be placed on the cold (upstream) side of the furnace for greatest efficiency.

Fans and compressors make noise. Locate the outdoor unit away from windows and adjacent buildings, and select a heat pump with an outdoor sound rating of 7.6 bels or lower. You can also reduce this noise by mounting the unit on a noise-absorbing base.

The location of the outdoor unit may affect its efficiency. Outdoor units should be protected from high winds, which can cause defrosting problems. You can strategically place a bush or a fence upwind of the coils to block the unit from high winds.

Split-system heat pumps, on the other hand, are charged in the field, which can sometimes result in either too much or too little refrigerant. Split-system heat pumps that have the correct refrigerant charge and airflow usually perform very close to manufacturer's listed SEER and HSPF. Too much or too little refrigerant, however, reduces heat-pump performance and efficiency.

For more information on Heat Pumps and other in-depth and comprehensive
HVAC/R Courses, Please visit;
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Residential Load Calculations

2010-04-11T09:04:00.007-05:00

By Phil Rains
HVACRedu.net
About Phil!

A residential load calculation is a way for a contractor (or technician) to determine the envelope loads for a particular residential dwelling.

Every residential structure has these envelope loads which are determined by local weather patterns, features of the structure, and all the building materials and techniques that are or were used in its construction. Other parameters include appliances and the number of occupants in the structure, duct work loads, ventilation loads, and motor heat loads. Effectively, the envelope loads are the total heating and cooling loads for the components that surround the conditioned space (walls, ceilings, roofs, floors, doors, windows, etc.

The residential heating and cooling system must be selected and designed to provide comfort conditions in all occupied spaces regardless of whether is it winter or summer. The installed system must be able to control temperature, humidity, air movement and ventilation simultaneously.

Load calculations procedures produce improved equipment sizing loads for single-family detached homes, small multi-unit structures, condominiums, town houses and manufactured homes. These procedures are also compatible with different types of comfort systems and applications such as:

.Central single-zone systems
.Central multi-zone systems
.Distributed multi-zone systems
.Dwellings with limited exposure or no exposure diversity

The load calculation is the most important step in determining the size and type of cooling and heating equipment required to maintain comfortable indoor air conditions.

The Air Conditioning Contractors of America (ACCA) is a group of air conditioning contractors who work together to improve the HVAC industry, promote good practices, and keep homes and buildings safe, clean and comfortable. As part of their effort, ACCA has developed the HVAC Quality Installation Specifications (QI) from contribution from contractors and other interested parties. These contributors include original equipment manufacturers (OEMs), public, private, and federal electric utilities, and industry associations. Many contractors now follow the concepts and requirements of the QI, either by desire or requirement.

The QI is designed to assist contractors as they go through the process of determining which approach to follow when they design, install and service a system. Also, the QI requires that contractors perform load calculations for new structures and when dealing with existing structures. The QI states the following concerning load calculations:

“The contractor shall provide evidence that for new residential and commercial buildings, or when adding new ducts to an existing structure, room-by-room heat gain/loss load calculations are completed…”

When discussing load calculations, we need to review equipment sizing considerations. Significantly undersized HVAC equipment will typically be unable to maintain the desired set-point temperature when a design load is imposed on the heating and cooling equipment. However, slightly undersized equipment sometimes will often provide acceptable comfort at a lower cost, but never undersized by more than around 10 % of the design loads.

When someone has oversized the HVAC equipment, short-cycles can occur during the cooling mode. This provides only marginal part-load temperature control for the structure, as well as allowing stagnate air pockets to materialize (unless the indoor blower is operating continuously). There will typically be a degradation of humidity control as well, as the system does not run long enough to condense the moisture out of the air. It is only running basically to meet the sensible load controlled by the indoor thermostat. Oversizing requires larger equipment and larger duct systems, increasing the installed cost and results in increased operating costs as well. Utilities also oppose oversing as it results in increased demand on their systems. And finally, oversizing adds unnecessary stress to the HVAC equipment.

The best way to avoid oversizing or undersizing HVAC equipment is to perform a load calculation. Don’t rely on “rule of thumb” methods or on past experience. At best, these can only provide quick design however they are often not precise and can lead to problems.

Also, remember that a well- insulated house is much tighter than an un-insulated house. Always recommend sufficient levels of insulation in lieu of increased system size. But, if the consumer cannot facilitate more insulation, you will have to calculate the system size with the levels present.

As such, a quality installation begins with a load calculation as part of the professional design process, even for a home.

Year-round, comfort is always the goal when performing a load calculation. In the cooling mode the HVAC system not only cools the indoor air (sensible cooling), it also removes moisture (latent cooling). In the winter, your heating system must keep you comfortable without causing high utility bills.

Concepts and fundamentals of HVAC/R equipment sizing is based on heat gain and losses in a dwelling. You will need to remove the amount of heat gain in the summer and add in the amount of heat loss in the winter with the equipment. Heat gain and loss must be equally balanced by heat removal and addition to get the desired comfort.

Many residential load calculation methods are available in the HVAC/R industry. Two of the most recognizable and frequently utilized are ACCA’s Manual J, Eighth Edition (MJ8), and ACCA’s Manual J, Eighth Abridged Edition (MJ8AE). Regardless of the method, a residential load calculation is always a good idea prior to installing or retrofitting any HVAC/R system.

To learn more about HVACReducation.net's online Hvac Load Calculations course,
CLICK HERE

Phillip A. Rains
Copyright © Phil Rains

About the Author: Phil Rains is Master Trainer/Technical Developer for HVACReducation.net. He has over 35 years of HVAC and Refrigeration experience in installation, service, and training. He is NATE-certified in 5 areas, a member of ASHRAE and RSES, and ACCA EPIC-Certified in Residential and Commercial Design. He also holds a Universal Classification in EPA 608.

What Is Wet Bulb Temperature?

2010-04-03T09:13:00.008-05:00

By Phil Rains
HVACRedu.net
About Phil!

“Wet Bulb temperature” is a term used by HVAC technicians when checking cooling operation with a “sling psychrometer”. The result indicates the temperature of air measured using a standard mercury-in-glass thermometer, with the thermometer bulb typically wrapped in gauze or a muslin-type material, with air passing over its surface. The covering is kept wet during testing. The evaporation of water from the thermometer has a cooling effect (Wet Bulb Depression), so the temperature shown is less than the temperature shown on a Dry Bulb thermometer used during the same test.

When compared to the Dry Bulb temperature, the difference indicates to the technician the approximate relative humidity of the occupied space against a known scale, as well as the operating conditions of the system during cooling.

The wet bulb temperature is very dependent on the moisture content of the air. What happens in a wet bulb temperature measurement is that water begins evaporating from the bulb of the thermometer. The evaporation of water causes a cooling effect on the thermometer bulb, and the temperature measured by the thermometer drops. If evaporation occurs easily, as with dry air, there is a temperature drop. However, if there is high humidity conditions, the temperature measured on a wetted thermometer bulb may drop only slightly or not at all, because there is too much moisture in the air. When the wet bulb temperature equals the dry bulb temperature, air is totally saturated with water and no further evaporation can occur. This is called 100% saturation. This is the condition that is met at the surface of the evaporator when air is cooled to its saturation temperature and begins to change state, giving up heat to refrigerant and condensing moisture out to be drained away during cooling. The leaving air is cooled and transferred to the conditioned space in the summer.

Phillip A. Rains
Master Trainer/Technical Developer
copyright(c)2008

OPERATION OF A VARIABLE FREQUENCY DRIVE CIRCUIT

2010-03-27T07:51:00.018-05:00

By Roger Desrosiers
HVACRedu.net
About Roger

By the 1980s, AC motor drive technology became reliable and inexpensive enough to compete with traditional DC motor control. These variable-frequency drives (VFDs) accurately control the speed of standard AC induction or synchronous motors. With VFDs, speed control with full torque is achieved from "0" rpm through the maximum rated speed and, if required, above the rated speed at reduced torque. VFDs manipulate the frequency of their output by rectifying an incoming AC current into DC, and then using voltage pulse-width modulation to recreate an AC current and voltage output waveform. However, this frequency conversion process causes 2% to 3% loss as heat in the VFD — caloric energy that must be dissipated. The process also yields over-voltage spikes and harmonic current distortions.

Figure 1 shows a circuit diagram of a typical variable frequency drive. Notice how the circuit shows three separate sections. The first section shows the rectifier section, where a three-phase diode bridge rectifier changes the three phase AC voltage to pulsating DC voltage. The second section is the filter section where the pulsating DC voltage is smoothed to pure DC voltage. The third section is the transistor switching section which produces the three-phase AC voltage at the desired frequency.

In the first section (rectifier) you can see the six diodes are connected in a bridge circuit to convert the three phase AC voltage to DC voltage. The actual rectifier is mounted on a single module and can be exchanged by removing the three input voltage wires and the two DC bus connectors. Each diode in the module can be tested for front to back resistance ratio with an ohm meter just as if it were an individual diode. The output of the rectifier section is 12 half-wave pulses 60* apart. The output of the bridge rectifier is connected to two large copper conductors that are called DC bus.

The filter section of the circuit consists of several capacitors that are connected in parallel with the DC bus, and a large inductor is connected in series with the DC bus. The capacitors charge and discharge in synchronization with the input voltage. This causes the half wave signal to be converted to pure DC. The capacitors are used to filter the voltage part of the waveform and the inductor is used to filter the current part of the waveform. The transistor section consists of six transistors, two for each output phase. You can see that one transistor of each phase is connected to the positive DC bus and the second transistor is connected to the negative DC bus. Each circuit is controlled by a base firing circuit that is controlled by a micro-processor chip. At the correct time each transistor is turned on in six distinct steps.

Figure 2 shows an example of the wave form that results from turning the transistor on in six steps The Inverters take the voltage from the DC Bus and using Pulse Width Modulation (PWM) sends a signal which appears to the motor as an AC signal.

Pulse Width Modulation

In the diagram above, a close up view of the waveform that goes to the motor shows the switching frequency of the IGBTs. The switching-pattern shown below is known as pulse width modulation or PWM. As the length of time is increased for the IGBT to be ON and then OFF, the motor responds to it as a sinusoidal waveform. The positive IGBT fires first in the diagram followed by its negative counterpart. Only one motor terminal (U) is shown but the same type of activity would appear on V and W, in figure 2.

Typical control for a variable frequency drive is between 0 and 120 % of its rated rpm. In reality the motor is generally adjusted from 60% to 130%of rated rpm, which provides sufficient control for the system being adjusted. It is important to note that the VFD can only rule the motor for a short period of time at RPMs above 100% because the motor will overheat. You can see how important it is to be able to adjust the speed of a very large fan to provide minimal airflow when the temperature conditions are near set point and larger air-flows when the system requires it. The same conditions apply when controlling a refrigeration compressor. A lower heat load requires a lower pumping compressor and a bigger heat load requires an increase in pumping capacity.

How to Charge An Air-Source Heat Pump In Winter

2010-03-21T10:42:00.003-05:00

INDOOR AIR POLLUTION

2010-03-06T07:40:00.020-06:00

By Roger Desrosiers
HVACReducation.net
About Roger

What Causes Indoor Air Problems?

Indoor pollution sources that release gases or particles into the air are the primary cause of indoor air quality problems in homes. Inadequate ventilation can increase indoor pollutant levels by not bringing in enough outdoor air to dilute emissions from indoor sources, and by not carrying indoor air pollutants out of the home. High temperature and humidity levels can also increase concentrations of some pollutants.

Pollutant Sources

There are many sources of indoor air pollution in any home.

These include combustion sources (such as oil, gas, kerosene, coal, wood, and tobacco products), building materials and furnishings (as diverse as deteriorated, asbestos-containing insulation, wet or damp carpet, and cabinetry or furniture made of certain pressed wood products), products for household cleaning and maintenance, personal care, hobbies, central heating and cooling systems and humidification devices, and outdoor sources such as radon, pesticides, and outdoor air pollution.

The relative importance of any single source depends on how much of a given pollutant it emits and how hazardous those emissions are. In some cases, factors such as how old the source is and whether it is properly maintained are significant. For example, an improperly adjusted gas stove can emit significantly more carbon monoxide than one that is properly adjusted.

Amount of Ventilation

Notice the mechanical means of outside ventilation for this home with the air conditioning system.

If too little outdoor air enters a home, pollutants can accumulate to levels that can pose health and comfort problems. Unless they are built with special mechanical means of ventilation, homes that are designed and constructed to minimize the amount of outdoor air that can "leak" into and out of the home may have higher pollutant levels than other homes. However, because some weather conditions can drastically reduce the amount of outdoor air that enters a home, pollutants can build up even in homes that are normally considered "leaky."

How Does Outdoor Air Enter a House?

Outdoor air enters and leaves a house by infiltration, natural ventilation, and mechanical ventilation. In a process known as infiltration, outdoor air flows into the house through openings, joints, and cracks in walls, floors, and ceilings, and around windows and doors. In natural ventilation, air moves through opened windows and doors. Air movement associated with infiltration and natural ventilation is caused by air temperature differences between indoors and outdoors and by wind.

Finally, there are a number of mechanical ventilation devices, from outdoor-vented fans that intermittently remove air from a single room, such as bathrooms and kitchen, to air handling systems that use fans and duct work to continuously remove indoor air and distribute filtered and conditioned outdoor air to strategic points throughout the house. The rate at which outdoor air replaces indoor air is described as the air exchange rate. When there is little infiltration, natural ventilation, or mechanical ventilation, the air exchange rate is low and pollutant levels can increase

Indoor Air and Your Health

IS YOUR HOME OR OFFICE MAKING YOU SICK?

Health effects from indoor air pollutants may be experienced soon after exposure, or possibly years later. Immediate effects may show up after a single exposure, or repeated exposures. These include irritation of the eyes, nose, and throat, headaches, dizziness, and fatigue. Such immediate effects are usually short-term and treatable. Sometimes the treatment is simply eliminating the person's exposure to the source of the pollution, if it can be identified. Symptoms of some diseases, including asthma, hypersensitivity pneumonitis, and humidifier fever, may also show up soon after exposure to some indoor air pollutants.

The likelihood of immediate reactions to indoor air pollutants depends on several factors. Age and preexisting medical conditions are two important influences. In other cases, whether a person reacts to a pollutant depends on individual sensitivity, which varies tremendously from person to person. Some people can become sensitized to biological pollutants after repeated exposures, and it appears that some people can become sensitized to chemical pollutants as well.

Certain immediate effects are similar to those from colds or other viral diseases, making it often difficult to determine if the symptoms are a result of exposure to indoor air pollution. For this reason, it is important to pay attention to the time and place the symptoms occur. If the symptoms fade or go away when a person is away from the home and return when the person returns, an effort should be made to identify indoor air sources that may be possible causes. Some effects may be made worse by an inadequate supply of outdoor air or from the heating, cooling, or humidity conditions prevalent in the home.

Other health effects may show up either years after exposure has occurred or only after long or repeated periods of exposure. These effects, which include some respiratory diseases, heart disease, and cancer, can be severely debilitating or fatal. It is prudent to try to improve the indoor air quality in your home even if symptoms are not noticeable.

While pollutants commonly found in indoor air are responsible for many harmful effects, there is considerable uncertainty about what concentrations or periods of exposure are necessary to produce specific health problems. People also react very differently to exposure to indoor air pollutants. Further research is needed to better understand which health effects occur after exposure to the average pollutant concentrations found in homes, and which occur from the higher concentrations that occur for short periods of time.

Basic Control Strategies

Source Control

Usually the most effective way to improve indoor air quality is to eliminate individual sources of pollution or to reduce their emissions. Some sources, like those that contain asbestos, can be sealed or enclosed. Others, like gas stoves, can be adjusted to decrease the amount of emissions. In many cases, source control is also a more cost-efficient approach to protecting indoor air quality than increasing ventilation because increasing ventilation can increase energy costs.

Ventilation Improvements

Another approach to lowering the concentrations of indoor air pollutants in your home is to increase the amount of outdoor air coming indoors. Most home heating and cooling systems, including forced air heating systems, do not mechanically bring fresh air into the house. Opening windows and doors, operating window or attic fans, when the weather permits, or running a window air conditioner with the vent control open increases the outdoor ventilation rate. Local bathroom or kitchen fans that exhaust outdoors remove contaminants directly from the room where the fan is located and also increase the outdoor air ventilation rate.

It is particularly important to take as many of these steps as possible while you are involved in short-term activities that can generate high levels of pollutants--for example, painting, paint stripping, heating with kerosene heaters, cooking, or engaging in maintenance and hobby activities such as welding, soldering, or sanding. You might also choose to do some of these activities outdoors, if you can and if weather permits.

Conclusion

Advanced designs of new homes are starting to feature mechanical systems that bring outdoor air into the home. Some of these designs include energy-efficient heat recovery ventilators (also known as air-to-air heat exchangers). For most indoor air quality problems in the home, source control is the most effective solution.

HVACReducation.net

PRESS RELEASE

2010-02-21T04:56:00.020-06:00

by Patricia Leiser

Operations Management and
Indoor Air Quality Basics, two new online courses are now available through HVACReducation.net

Heron, Montana/ February 2010/ HVACRedu.net, the leader in online industry education, announces two new online courses for HVACR professionals, Operations Management for Contractors or Managers; and Indoor Air Quality Basics for technicians. We’ve been working to meet the needs expressed in the industry and these courses are just two of our new additions. If you’re a technician or contractor and have been curious about better ways to improve the air quality in your customer’s homes and buildings, you can learn online today. Or if you’re in charge of operations and projects, and need to know how to get things done more efficiently, want to waste less, and improve your profit margin, you can learn the best practices in the industry at your home or office, on your schedule, online. Read the full course descriptions:

221 Indoor Air Quality Basics (18 hours) Foundation
You already know it is your job to provide services related to the comfort of air temperatures inside your client’s buildings. However, temperature management is not the only thing you need to know. This course will help you better understand the various elements of air quality, introduce the science of air quality, and give you some tips on how to identify and address the potential dangers of poor indoor air quality. The course does not address issues of allergies or chemically sensitive clients outside the basics of indoor air quality. You will learn indoor air properties, air flow, ventilation, moisture, and air filtration systems. This course is NATE recognized for 18 hours of continuing education (CEHs) applicable to NATE recertification, and BPI recognized for 9 continuing education units (CEUs). Modules address the following topics:

1. IAQ Basics
2. Properties of Air
3. Air Flow Basics
4. Ventilation
5. Moisture Management
6. Air Filtration

306 Operations Management (18 hours) Advanced
As a contractor or operations manager, there are many challenging elements to overseeing your HVACR work flow. It’s up to you to establish and follow-through on business practices that make your company profitable. This course will help by addressing the best practices in the primary areas of your company’s operations that impact your profit margin. You will learn basic business practices and procedures to help manage the work flow and minimize delays, loss of time, and resources . This course is NATE recognized for 18 hours of continuing education (CEHs) applicable to NATE recertification, and BPI recognized for 9 continuing education units (CEUs). Module topics are:

1. Industry Paperwork and Recordkeeping
2. Personnel Management and Communications Skills
3. Systems Integration: Design
4. Systems Integration: Installation
5. Materials Management
6. Resource Scheduling and Cost Management Awareness

In addition to the two new courses above, HVACRedu.net and GreenCollarEdu.net have a full catalog of online assessments, reviews, short individual module courses, full-length courses, programs, apprenticeship, and customized programs. If you or your organization are considering online learning in the HVACR or related industries, please contact us.

HVACRedu.net, founded in 2000, provides access to complete, comprehensive and growing online education programs, recognized by the leading experts in the HVACR industry as the primary online education resource. Courses are available 24 hours a day, 365 days a year for the convenience of adult learners. Courses are guided by skilled industry professionals who maintain contact with each enrolled student. Quality education, student success, and exceptional customer service are the primary objectives.

GreenCollarEdu.net (a service of HVACRedu.net) is your source for comprehensive education and training programs that support nationally recognized standards from across the green building and green trades industries in areas such as building performance, renewable energy systems, green remodeling, insulation, air sealing, fenestrations, and the HVACR industry.

HVACReducation.net
Introduces new 3-hour online modules just $45.

Introducing 160 new 3-hour online learning modules at just $45 each. Because we listened when you told us how limited and valuable your time is, we’ve rolled out our entire module inventory. Now you can pick and choose the subjects that meet your needs. Visit our Online Campus Store for individual module descriptions and to enroll in the module(s) of your choice. Use your Visa, MasterCard, or PayPal today and begin your learning experience tomorrow.

CONTACT:
Chris Compton, CEO
Web: HVACRedu.net
OR
Web: Greencollaredu.net
Email: ccompton@hvacreducation.net
Phone: (888) 655-4822 x1116
PO Box 77
Heron, MT 59844

By Patricia Leiser
Executive Assistant
HVACRedu.net
GreenCollarEdu.net
About the Author:
Like many of you, I have a passion for education and lifelong learning. I have a Bachelor of Science in Education/Business from the University of Idaho where I transferred after two years at Gonzaga University. I also studied with Berean Bible College and Riverside Community College. I bring to you 35 years of work experience in business and education.
POWER YOUR EDUCATION TO THE NEXT LEVEL!

PROPER TESTING OF HEATING EQUIPMENT

2010-02-13T09:25:00.027-06:00

By Roger Desrosiers
HVACReducation.net

To ensure safe and efficient burner operation, all residential, commercial and industrial space and process heating equipment must be properly tested for:

. Carbon monoxide
. Smoke (Fuel oil only)
. Excess air
. Stack temperature
. Draft
. Possibly NOx, NO, NO2 and/or SO2

Oxygen, Carbon Monoxide and Stack Temperature

The measurement for gases and temperature should be taken at the same point. Typically, this is done by selecting a sample location ‘upstream’ from the draft diverter/hood, barometric control or any other opening, which allows room air to enter and dilute flue gases in the stack. In larger installations it may also be necessary to extract a number of samples from inside the flue to determine the area of greatest flue gas concentration. Another common practice is to take the flue gas sample from the ‘Hot Spot’ or the area with the highest temperature.

Make sure that the sample point is before any draft diverter/hood or barometric damper so that the flue gasses are not diluted and the stack temperature has not been decreased by surrounding air used to balance the draft. The sample point should also be as close to the breach area as possible, again, to obtain an accurate stack temperature. This may also provide a more accurate O2 reading should air be entering the flue gas stream through joints in sheet metal vent connectors.

Oil Burners

Locate the sampling hole at least six inches upstream from the breech side of the barometric control and as close to the boiler breeching as possible. In addition, the sample hole should be located twice the diameter of the pipe away from any elbows.

Gas Burners

Locate the sampling hole on power burner fired boilers at least six inches upstream from the breech side of any double acting barometric control and as close to the boiler breeching as possible. Again, try to stay away from elbows. When testing atmospheric equipment with a draft diverter/hood, the flue gas sample should be taken inside the port(s) where flue gases exhaust the heat exchanger.

Equipment with an economizer, recouperator, or other similar device requires the sampling point be downstream from and as close as possible to the device (assuming they are installed before any draft control) to insure that the net stack temperature will provide an accurate indication of the effectiveness of the entire system.

While combustion analysis is the emphasis here, remember that this is only one important consideration in the overall scope of hvac system efficiency.

Temperature rise, duct static pressures and fuel pressures, for example, all contribute to safe, efficient and reliable heating system operation.

When testing atmospheric, forced air heating equipment with a clamshell or sectional heat exchanger design, test each of the exhaust ports at the top of the heat exchanger. The probe should be inserted back into each of the exhaust ports to obtain a flue gas sample, before any dilution air is mixed in.

Draft tests should be taken from a hole drilled in the stack downstream from the draft hood.

Combustion and draft testing fan assist, furnaces/boilers should be done through a hole drilled in the vent immediately above the inducer fan.

Condensing furnaces/boilers can be tested through a hole drilled in the plastic vent pipe (when allowed by the manufacturer or ‘local authority of jurisdiction) or taken from the exhaust termination.

In order to obtain an accurate Steady State Efficiency reading, an auxiliary thermocouple must be inserted in the combustion air intake so that a true net stack temperature is used in the calculation.

It is important to remember that the vent system on these units operates under a positive pressure. As a result, any holes in the vent need to be sealed.

Domestic hot water heaters with the ‘bell’ shaped draft diverter on top can be accurately tested by attaching a section of copper tubing to the probe or using a flexible probe which is then inserted directly into the top of the fire tube below the diverter.

Another common practice is to insert the probe in the hole drilled for the draft test, direct it down and push it below the level of the draft hood.

When testing boilers with a draft diverter mounted on the back of the equipment, flue gas samples should be taken by passing the probe from one side to the other, again upstream (toward the burner) from the opening into the draft diverter.

Draft tests should be taken from a hole drilled in the vent connector immediately above the diverter.

Boilers, which have a ‘bell’ shaped draft diverter directly on top, should be tested directly below the diverter through a hole drilled in the vent connector.

Should draft tests below the diverter measure insufficient draft levels, an additional test should be performed above the diverter to determine if the reason for insufficient draft is related to a chimney problem or a draft hood problem.

It is also a good idea to test any areas with openings that provide a path for combustion air to be introduced to the flame. These areas provide a path where flue gases can potentially be exhausted.

With forced air systems this area is generally limited to immediately in front of the burners while many styles of boilers allow secondary combustion air to also be drawn in from all around the base of the cabinet.

Gas and oil fired power burners should be tested up stream from the barometric, as close to the breech area as possible.

While stack draft may be an important measurement, fuel oil and gas fired power burners require draft control over the fire to maintain a proper and controlled intake of combustion air.

Comparing stack and overfire O2 can verify that leakage between boiler sections, access door, etc is minimal and the combustion test results are accurate.

Use caution when taking over fire O2 readings. Do not expose thermocouple or sampling assembly to excess temperatures longer than necessary.

When testing (primarily commercial/industrial) equipment with modulating or multiple firing rates, it is critical that tests are performed throughout the entire firing range. Typically, larger burners begin to fire at a reduced firing rate to insure a safe, reliable light off. Once ignition has been proven, air and fuel controls open to the full rated firing capacity of the boiler. Once the call for heat has been satisfied, the firing rate is slowly reduced to a minimum position before the cycle ends and the flame is extinguished.

Failing to test throughout the entire cycle of burner operation may not identify a particular point at which O2 readings are outside the manufacturer’s specifications or excess levels of CO are produced.

Smoke Testing

Complete combustion testing of a fuel oil fired system, #1 - #6, also requires a smoke test.

When dealing with fuel oil fired heating equipment, also perform a smoke test to help identify incomplete combustion. A common misconception is that before an oil-fired appliance will produce CO, it will smoke so badly that it will be immediately evident a problem is occurring.

While it is generally true that a smoky oil flame will produce CO, years of testing experience with electronic instruments has established that the reverse is not always the case.

An oil-fired unit not producing a measurable amount of smoke is very capable of CO production. This is often seen when too much combustion air is introduced into the flame which results in a greater volume of flue gases being produced which acts to dilute the smoke to the point where it may not be picked up by the smoke pump filter paper.

Smoke tests are taken from the same sample location as the combustion tests. A clean piece of filter paper is inserted into the tip of the smoke tester and 10 strokes of the pump are taken. The filter paper is removed and the dot compared to the Smoke Spot Chart.

Generally, modern residential flame retention burners should be set up for a zero smoke with O2 readings within manufacturer’s specifications, while an older conventional style burner may be allowed between a #1 and #2 smoke. A “yellow” dot is an indication of unburned, raw fuel that is escaping the flame pattern and being exhausted with the flue gases.

copyright(c)2009
Roger J. Desrosiers

About the Author: Roger is a contributing faculty member of HVACReducation.net. He has over 40 years experience in Air Conditioning and Refrigeration. He is also a member of R.S.E.S., CM, The Association of Energy Engineers, Certified Energy Manager, ASHRAE, Certified Pipe Fitter United Association and is 608 Universal Certified. More About Roger

PRESS RELEASE

2010-02-09T16:44:00.037-06:00

by Patricia Leiser

Prepare For Industry Certifications ONLINE: Building Analyst Quick Start, Service Core Program, EPA 608 Review, and R-410A Certification Courses
Powered By HVACReducation.net

Heron, Montana/ February 2010/ GreenCollarEdu.net and HVACReducation.net, the leading online industry education providers, deliver the training you need to keep your customer’s homes functioning at the very peak of performance. Now, more than ever, HVACR technicians need certifications. You can study for them in the comfort of your home or office, on your schedule,
ONLINE.

. If you’re interested in working toward BPI’s Building Analyst Certification Exam,
enroll in our Building Analyst Quick Start program.
· If you want to prepare for NATE’s HVAC Core Certification Exam,
enroll in our HVACR Service Core Program.
· If you need to brush up before taking your EPA 608 Exam,
· or earn your R-410A Certification, we have a course for that too
. or you can visit our blog page and view our Free R-410A Webinar.

The Building Analyst Quick Start Program is made up of two comprehensive online courses: Principles of Building Science and Comprehensive Building Assessment. Instruction aligns with ANSI/ACCA Quality Installation & Maintenance Standards. These courses come with an online instructor.

· 107 The Principles of Building Science Course is full of scientific facts, interactive exercises, pictures, videos, graphics, and text. Everything an individual in the building, remodeling, or trade industry needs to know to make buildings perform more efficiently. The PBS course has also been designed to help prepare individuals on the path to various NATE, NARI, BPI, RESNET, and other industry credentials related to green building performance. This course is both BPI and NATE recognized for 28 hours of continuing education.
90 days enrollment.

· 301 Performing the Comprehensive Building Assessment Students will start out learning the systems, tools and techniques commonly encountered during visual observations including evaluation of envelope components, mechanical systems and base loads such as appliances and lighting. They will then step into diagnostic testing learning first how to work safely. Students will learn how to set up and use the blower door for building pressurization/depressurization testing; and how to utilize the data obtained in making decisions. Students will learn combustion safety testing (including worst case depressurization, draft and spillage testing), and how to test various appliances for CO including: furnaces, boilers, water heaters and other combustion appliances. Students will also learn basic duct diagnostic testing. Finally, students will be taught how to use assessment information and diagnostic results to develop a work scope which can then be presented to a customer. This course will refer to the BPI Building Analyst as well as to various industry codes and standards. This course is NATE and BPI recognized for 30 hours of continuing education.
90 days enrollment.

The HVAC Service Core Program is a comprehensive program specifically structured to prepare technicians to successfully pass the initial NATE Core Service Exam. It focuses on learning objectives that have been identified by HVACR industry groups (ARI, NATE, RSES, ACCA, BPI, and PAHRA) and consists of one (1) math review and eight (8) courses students receive a 60 day enrollment for each course. These courses come with an online instructor. Students are registered for one course at a time. For course descriptions, visit our online catalog. The courses making up the Service Core Program are:

R. 050 Applied Math Review
1. HVACR 101 Fundamentals
2. HVACR 102 Safety
3. HVACR 111 Electrical DC Theory Plus
4. HVACR 112 Electrical AC Theory Plus
5. HVACR 113 Electrical Common Components
6. HVACR 114 Electrical Motors
7. HVACR 121 Systems Properties & Measurement
8. HVACR 141 Refrigeration I

EPA 608 Review is a selection of four learning modules designed to provide all the necessary information for a technician to prepare for the EPA 608 Certification exam at the Universal level. Modules are titled: Core, Type I, Type II, and Type III. Although there is no instructor, the course is rich with visuals, animations, and checkpoint tests to enforce your learning experience. Use the modules as an introduction, or a review just before you take the exam.
30 days enrollment.

R-410A Refrigerant Technology for HVACR Technicians course is designed to familiarize the technician with the differences between R - 22 and R - 410A. Background, regulations, impact on the industry, and application requirements will be presented. The course provides the technician with practical knowledge for safe performance of service techniques on systems containing R - 410A. If you understand the parameters of this course and then successfully complete the final examination, you will comply with many equipment manufacturers’ policies requiring safety and service "certification" prior to purchasing equipment containing R - 410A refrigerant. Because this course is a special qualifications course, it does not come with an instructor. However, a complete reference manual is included and is shipped upon enrollment. Instruction aligns with ANSI/ACCA Quality Installation & Maintenance Standards. This course is NATE recognized for 10 hours of continuing education (CEHs) which are applicable to NATE recertification, and BPI recognized for 5 continuing education units (CEUs). This course has been approved by International Comfort Products, LLC. Six Modules cover:

• R - 410A Refrigerant Background
• R - 410A Refrigerant Regulatory Requirements
• R - 410A Refrigerant Basics
• R - 410A Refrigerant Safety, Handling, and Service Considerations
• R - 410A System Components, Retrofitting, and Charging
• R - 410A System Troubleshooting

In addition to the efficiency and performance courses spot lighted above, HVACReducation.net and GreenCollarEdu.net have a full catalog of online assessments, reviews, short module courses, full-length courses, programs, 4 year apprenticeship, and customized employee training programs. If you or your organization are considering online learning in the HVACR or related industries, please contact us. For more information and pricing, visit our online Campus Store.

HVACRedu.net, founded in 2000, provides access to complete, comprehensive and growing online education programs, recognized by the leading experts in the HVACR industry as the primary online education resource. Courses are available 24 hours a day, 365 days a year for the convenience of adult learners. Courses are guided by skilled industry professionals who maintain contact with each enrolled student. Quality education, student success, and exceptional customer service are the primary objectives.

GreenCollarEdu.net (a service of HVACReduc.net) is your source for comprehensive education and training programs that support nationally recognized standards from across the green building and green trades industries in areas such as building performance, renewable energy systems, green remodeling, insulation, air sealing, fenestrations, and the HVACR industry.

CONTACT:
Chris Compton, CEO
Web: http://www.HVACRedu.net
OR
Web: http://www.greencollaredu.net
Email: ccompton@hvacreducation.net
Phone: (888) 655-4822 x1116
PO Box 77
Heron, MT 59844
Blog: http://www.hvacreducationtechtips.blogspot.com/

POWER YOUR EDUCATION TO THE NEXT
By Patricia Leiser
About the Author:
Like many of you, I have a passion for education and lifelong learning. I have a Bachelor of Science in Education/Business from the University of Idaho where I transferred after two years at Gonzaga University. I also studied with Berean Bible College and Riverside Community College. I bring to you 35 years of work experience in business and education. I am honored to work with HVACReducation.net and dedicate myself to providing excellent service to our students, faculty, and staff.

Evaporative Condensers

2010-01-23T10:01:00.027-06:00

By Roger Desrosiers
HVACReducation.net.

Evaporative condensers reject heat from refrigeration and air conditioning systems while using minimum quantities of energy and water. As shown in Figure 5A, water is pumped from the basin section and is distributed over the exterior of the condensing coil by a series of distribution troughs or spray nozzles.

Figure 5A

The flow rate of water need only be enough to thoroughly wet the condensing coil to provide uniform water distribution and prevent accumulation of scale. Therefore, minimum pumping horsepower is required.

A fan system forces air through the falling water and over the coil surface. A small portion of the water is evaporated, removing heat from the refrigerant, and condensing it inside the coil. Therefore, like the cooling tower, all of the heat rejection is by evaporation, thus saving about 95% of the water normally required by a "once-through" system.

The evaporative condenser essentially combines a cooling tower and a refrigerant condenser in one piece of equipment. It eliminates the sensible heat transfer step of the condenser water which is required in the cooling tower/refrigerant condenser system. This permits a condensing temperature substantially closer to design wet-bulb temperature, and consequently, minimum compressor energy input.

The temperatures and water flow rate shown in Figure 5B are typical of an evaporative condenser applied to a refrigeration or air conditioning system at the designated design wet-bulb temperature with either ammonia or a halocarbon refrigerant. These conditions result in an economical evaporative condenser selection. However, a lower condensing temperature and lower compressor energy input could be obtained with a larger condenser at this same wet-bulb temperature. The evaporative condenser offers a number of important advantages over other condensing systems:

Figure 5B

Low system operating costs

Condensing temperatures within 15°F of design wet-bulb are practical and economical, resulting in compressor horsepower savings of 10% or more over cooling tower/condenser systems and more than 30% over air-cooled systems.
Fan horsepower is comparable to cooling tower/condenser systems, and is about one-third that of an equivalent air-cooled unit. Because of the low pumping head and reduced water flow, water pumping horsepower is approximately 25% of that required for the normal cooling tower/condenser installation.

Initial cost savings

The evaporative condenser combines the cooling tower, condenser surface,
water circulating pump and water piping in one assembled piece of equipment. This reduces the cost of handling and installing separate components of the cooling tower/condenser system. Since the evaporative condenser utilizes the efficiency of evaporative cooling, less heat transfer surface, fewer fans, and fewer fan motors are required resulting in an initial material cost savings of 30 to 50% over a comparable air-cooled condenser.

Space saving

The evaporative condenser saves valuable space by combining the condensing coil and cooling tower into one piece of equipment, therefore eliminating the need for large water pumps and piping associated with the cooling tower/condenser system. Evaporative condensers require only about 50% of the plan area of a comparable sized air cooked condenser.

Capacity Control

Most refrigeration and air conditioning systems are subject to wide load variations and substantial changes in ambient temperature conditions. Where refrigerant control requires a reasonably constant condensing pressure, some form of capacity control is required.

Fan Cycling

Fan cycling is the simplest method of capacity control on evaporative condensers. However, this method can result in relatively large fluctuations in condensing pressures. On ammonia systems, most evaporators are fed by high pressure or low pressure float valves, or float switches which are less sensitive to variations in head pressure. On this type of system, fan cycling of the evaporative condenser will usually provide satisfactory capacity control on the high side of the system.

This is particularly true on larger ammonia systems, where the evaporative condenser may have several fan motors which can be cycled in steps. Halocarbon systems generally utilize evaporators controlled by thermal expansion valves. A reasonably constant pressure differential across the thermal expansion valve is required for its proper operation. Therefore, this type of system requires a closer degree of evaporative condenser capacity control than can be obtained with fan cycling.

Variable Frequency Drives

Precise capacity control and energy savings are achieved with the variable frequency drive (VFD) option. VFDs offer a more efficient and durable way to reduce fan speed compared to fan cycling, fan discharge dampers or mechanical speed changers. The inherent ability for VFDs to provide soft starts, stops and smooth accelerations prolongs the mechanical system life (fans, motors, belts, bearings, etc.). Sound levels are also reduced at lower fan speeds, and start-up noise is eliminated with the soft start feature. NOTE: An inverter duty motor is required for all models operating with a variable frequency drive.

Two-Speed Fan Motors

The number of steps of capacity control can be doubled by using two-speed fan motors in conjunction with fan cycling. This is particularly useful on single fan motor units which normally have only one step of capacity control using simple fan cycling.

Normally the two-speed fan motor will be selected so that the low speed is half of the full speed, such as 1800/900 rpm. An evaporative condenser will deliver approximately 58% of its rated capacity at half speed.

An additional benefit of two-speed fan motors is reduced fan horsepower at low speed. Brake horsepower varies as the cube of the fan speed, so the unit will use only about one eighth of the full load brake horsepower when operating at low speed. Maximum load and maximum wet-bulb temperature occur infrequently, so the unit will be operating at half speed and hence sharply reduced brake horsepower much of the time.

Another benefit of two speed motors is that when an evaporative condenser is operating at low speed, it will have substantially lower operating sound levels. The sound pressure levels of both centrifugal and propeller fan evaporative condensers will be reduced by four to ten decibels, depending on the sound frequency.

Modulating Fan Discharge Dampers

Modulating fan dampers, located in the fan discharge of centrifugal fan units, provide an infinite number of capacity control steps. Modulating dampers also affect a reduction in fan motor horsepower which is approximately proportional to the reduction in CFM as the dampers move toward the closed position.

Maintenance

Due to evaporative condensers ability to provide lower condensing temperatures while maintaining low electrical costs, evaporative condensers are effective and a popular means of condensing refrigerant in industrial applications. However, evaporative condensers move a large amount of air and water: approximately 3 gal/min of water is evaporated for every 100 tons of refrigeration. As a result, the condenser's efficiency is tied directly to the effectiveness of evaporation.

Evaporation can be hindered by a number of factors, including condenser water quality, condition of condenser coils and condition of the mechanical equipment. Therefore, it becomes important to system operation that the condenser be in good working order. In fact, maintenance is the single most important factor affecting the life of an evaporative condenser.

By definition, evaporative condensers evaporate water. But, this is not a completely clean process. Just as when water is boiled on a stove, impurities in the water are left behind in the condenser when it evaporates. If left uncontrolled, minerals will build up in the system until they precipitate out, leaving a layer of scale on the coil and sheet metal. To control the buildup of impurities, manufacturers supply condensers with bleed lines to remove a portion of water from the system. Throwing away a small quantity of water (usually equal to the evaporation rate) may seem wasteful, but it is more important to keep scale from building on the coil.

A mere 0.03" of scale will reduce the capacity of an evaporative condenser roughly 30%. Therefore, controlling the mineral level in the water is important. The scale potential for water can be measured in terms of calcium hardness. Calcium hardness is measured in parts per million (ppm), where there are so many calcium carbonate molecules for every million water molecules.

In addition to controlling scale, water chemistry must be maintained to avoid creating a corrosive environment for the evaporative condenser. The vast majority of condensers are built from galvanized steel. While zinc provides good corrosion resistance for its cost, it also is a reactive metal that must be protected.

Monitoring the pH of recirculated water is perhaps the most important aspect of the water chemistry. The pH measures the water's acidity or alkalinity and is a quick indication of corrosives. An extremely low or high pH indicates that the water chemistry is corrosive to galvanized steel. A high pH also may indicate white rust. White rust is the formation of white, porous deposits that are fluffy or waxy. Products of zinc corrosion, white rust forms mostly in new condensers operating at pH's of 8.3 or greater. Maintaining a near neutral pH and moderate levels of hardness and alkalinity will allow a protective barrier of zinc carbonate to form. This protective layer inhibits zinc reaction.

Occasionally, water chemistry cannot be controlled through employing the bleed line on the condenser. In these cases, a reputable water treatment specialist familiar with local conditions should be consulted to control the water's hardness and pH.

Above all, processors should avoid soft water systems. Water always seeks equilibrium with its surroundings. Soft water has been stripped of its mineral content, and when in contact with galvanized steel, it strips zinc from the base metal in an effort to reach equilibrium. Certainly, there are occasions where water must be softened. However, the 50-ppm minimum hardness level must be taken into account. Also, batch feeding of chemicals, especially acid, should be avoided as wild fluctuations in pH typically result in corrosion.

Biological contamination of a condenser can have a dramatic effect on performance. Biological fouling can have the same insulating effect as scale on the condenser's heat rejection capability. Certain strains of algae also can present health risks to employees, so it is important to keep the condenser clean and free from the dirt and debris that act as breeding grounds for bacteria. Biocides often are routine parts of a treatment program and usually are implemented on the system's initial startup.

copyright(c)2009
Roger J. Desrosiers

About the Author: Roger is a contributing faculty member of HVACReducation.net. He has over 40 years experience in Air Conditioning and Refrigeration. He is also a member of R.S.E.S., CM, The Association of Energy Engineers, Certified Energy Manager, ASHRAE, Certified Pipe Fitter United Association and is 608 Universal Certified. More About Roger

What Is A Wet, Atmospheric Cooling Tower?

2010-01-09T07:19:00.025-06:00

by Roger Desrosiers

A cooling tower is a heat rejection device, which extracts waste heat to the atmosphere though the cooling of a water stream to a lower temperature. The type of heat rejection in a cooling tower is termed "evaporative", in that it allows a small portion of the water being cooled to evaporate into a moving air stream to provide significant cooling to the rest of that water stream. The heat from the water stream transferred to the air stream raises the air's temperature and its relative humidity to 100%, and this air is discharged to the atmosphere. Evaporative heat rejection devices such as cooling towers are commonly used to provide significantly lower water temperatures than achievable with "air cooled" or "dry" heat rejection devices (like the radiator in a car), thereby achieving more cost-effective and energy efficient operation of systems in need of cooling. Think of the times you've seen something hot be rapidly cooled by putting water on it (which evaporates, cooling rapidly), such as an overheated car radiator. The cooling potential of a wet surface is much better than a dry one.

Common applications for cooling towers are providing cooled water for air-conditioning, manufacturing and electric power generation. The smallest cooling towers are designed to handle water streams of only a few gallons of water per minute supplied in small pipes like those might see in a residence, while the largest cool hundreds of thousands of gallons per minute supplied in pipes as much as 15 feet (about 5 meters) in diameter on a large power plant.

The generic term "cooling tower" is used to describe both direct (open circuit) and indirect (closed circuit) heat rejection equipment. While most think of a "cooling tower" as an open direct contact heat rejection device, the indirect cooling tower, sometimes referred to as a "closed circuit cooling tower" is nonetheless also a cooling tower.

Figure 1

A direct, or open circuit cooling tower (figure 1) is an enclosed structure with internal means to distribute the warm water fed to it over a labyrinth-like packing or "fill." The fill provides a vastly expanded air-water interface for heating of the air and evaporation to take place. The water is cooled as it descends through the fill by gravity while in direct contact with air that passes over it. The cooled water is then collected in a cold water basin below the fill from which it is pumped back through the process to absorb more heat. The heated and moisture laden air leaving the fill is discharged to the atmosphere at a point remote enough from the air inlets to prevent its being drawn back into the cooling tower.

The fill may consist of multiple, mainly vertical, wetted surfaces upon which a thin film of water spreads (film fill), or several levels of horizontal splash elements which create a cascade of many small droplets that have a large combined surface area (splash fill).

Figure 2

An indirect, or closed circuit cooling tower (figure 2) involves no direct contact of the air and the fluid, usually water or a glycol mixture, being cooled. Unlike the open cooling tower, the indirect cooling tower has two separate fluid circuits. One is an external circuit in which water is recirculated on the outside of the second circuit, (which is tube bundles or closed coils) that are connected to the process for the hot fluid being cooled and returned in a closed circuit. Air is drawn through the recirculating water cascading over the outside of the hot tubes, providing evaporative cooling similar to an open cooling tower. In operation the heat flows from the internal fluid circuit through the tube walls of the coils to the external circuit, and then (by heating of the air and evaporation of some of the water) to the atmosphere. Operation of the indirect cooling tower is therefore very similar to the open cooling tower with one exception. The process fluid being cooled is contained in a "closed" circuit and is not directly exposed to the atmosphere or the recirculated external water.

In a counter-flow cooling tower, air travels upward through the fill or tube bundles, opposite to the downward motion of the water.

In a cross-flow cooling, tower air moves horizontally through the fill as the water moves downward.

Cooling towers are also characterized by the means by which air is moved. Mechanical-draft cooling towers( figure 1) rely on power-driven fans to draw or force the air through the tower. Natural-draft cooling towers use the buoyancy of the exhaust air rising in a tall chimney to provide the draft. A fan-assisted natural-draft cooling tower employs mechanical draft to augment the buoyancy effect. Many early cooling towers relied only on prevailing wind to generate the draft of air.

If cooled water is returned from the cooling tower to be reused, some water must be added to replace or make-up the portion of the flow that evaporates. Because evaporation consists of pure water, the concentration of dissolved minerals and other solids in circulating water will tend to increase unless some means of dissolved-solids control (such as blow-down) is provided. Some water is also lost by droplets being carried out with the exhaust air (drift), but this is typically reduced to a very small amount by installing baffle-like devices called drift eliminators to collect the droplets. The make-up amount must equal the total of the evaporation, blow-down, drift, and other water losses such as wind blowout and leakage, to maintain a steady water level.

Some useful terms, commonly used in the cooling tower industry:

Nominal Cooling Tower Tons– Defined as 3 GPM of water cooled from 95⁰F entering water temperature to an 85⁰F leaving water temperature at a 78⁰F entering wet bulb temperature.

Wet Bulb Temperature– The temperature at which water, by evaporating into air, can bring the air to saturation at the same temperature.

Evaporative Cooling- Cooling accomplished through the exchange of latent heat in the form of evaporation.

Drift- Water droplets that are carried out of the cooling tower with the exhaust air. Drift droplets have the same concentration of impurities as the water entering the tower. The drift rate is typically reduced by employing baffle-like devices, called drift eliminators, through which the air must travel after leaving the fill and spray zones of the tower.

Blow-out- Water droplets blown out of the cooling tower by wind, generally at the air inlet openings. Water may also be lost, in the absence of wind, through splashing or misting. Devices such as wind screens, louvers, splash deflectors and water diverters are used to limit these losses.

Plume- The stream of saturated exhaust air leaving the cooling tower. The plume is visible when water vapor it contains condenses in contact with cooler ambient air, like the saturated air in one's breath fogs on a cold day. Under certain conditions, a cooling tower plume may present fogging or icing hazards to its surroundings. Note that the water evaporated in the cooling process is "pure" water, in contrast to the very small percentage of drift droplets or water blown out of the air inlets.

Blow-down- The portion of the circulating water flow that is removed in order to maintain the amount of dissolved solids and other impurities at an acceptable level.

Leaching- The loss of wood preservative chemicals by the washing action of the water flowing through a wood structure cooling tower.

Noise- Sound energy emitted by a cooling tower and heard (recorded) at a given distance and direction. The sound is generated by the impact of falling water, by the movement of air by fans, the fan blades moving in the structure, and the motors, gearboxes or drive belts. Low sound fans can be ordered by the customer.

copyright(c)2009
Roger J. Desrosiers

About the Author: Roger is a contributing faculty member of HVACReducation.net. He has over 40 years experience in Air Conditioning and Refrigeration. He is also a member of R.S.E.S., CM, The Association of Energy Engineers, Certified Energy Manager, ASHRAE, Certified Pipe Fitter United Association and is 608 Universal Certified. More About Roger

Gas Furnace Troubleshooting Tips

2009-12-25T14:26:00.004-06:00

by Phil Rains

As technicians, during colder months you will be involved with troubleshooting gas furnaces that are not performing as expected or desired. There are several troubleshooting tips that will assist you in assuring the furnace works correctly. We will discuss a few of these in this article. Always follow the furnace installation and operation instructions.

First, you must assure that the furnace is the correct size for the structure heat loss load. This step is often overlooked since the furnace is already installed and not working correctly. But, you should make sure that the furnace is sized to provide 100 percent of the design heating load requirement plus any margin that occurs because of furnace model size capacity increments. Heating load estimates can be made using approved methods available from several sources like the Air Conditioning Contractors of America (Manual J). Most furnaces are of sufficient output capacity to meet most loads if installed by competent technicians, but, always determine if you have enough output capacity with the furnace you are troubleshooting to meet the structure heating needs. Also, excessive oversizing of the furnace could cause the furnace and/or vent to fail prematurely. Never oversize the furnace greater than 140% of the heat loss load.

Always verify several visual aspects of the installation (that are commonly performed during gas furnace start up procedures) such as: type of fuel, power supply, control board connections and fuses, gas supply piping size and installation, and venting size, material and condition. Use the furnace installation and operation instructions as reference for all these checks. Make corrections as necessary.
Check the gas piping system from the gas meter to the furnace connections. All gas piping fittings and connections should be checked by an approved method such as a combustible gas leak detector, soap and water, or an equivalent non-flammable solution. NEVER check for gas leaks with a match or an open flame of any kind. Repair or replace any part(s) of the system that may be found defective.

Check inlet pressure for proper operation. First, make sure that the power is off, turn off the gas supply valve at the furnace and remove the plug from the line inlet pressure tap (usually on the gas valve). Connect a manometer or a “Magnehelic” gauge to the inlet pressure tap, turn on the gas supply and read the pressure on the gauge or manometer (without the furnace operating). The results of this test will be the most accurate when all other gas appliances are operating. Check with the equipment distributor or the installation and operation instructions for the particular furnace you are working on to determine the recommended supply pressures as well as the minimum and the maximum supply pressures for Natural and L.P. gas. Adjustments cannot typically be made to inlet pressure. If modifications are necessary, contact the gas supplier.

Check outlet manifold pressure for proper operation. First, make sure that the power is off, turn off the gas supply valve at the furnace and remove the plug from the gas valve outlet pressure tap (manifold pressure tap). Connect a manometer or a “Magnehelic” gauge to the pressure tap, turn on the gas supply and energize the furnace calling for heat. After the furnace fires read the pressure on the gauge or manometer. The results of this test will be the most accurate when all other gas appliances are operating. Check with the equipment distributor or the installation and operation instructions for the particular furnace you are working on to determine the recommended supply manifold pressure(s) as well as the minimum and the maximum manifold pressures for Natural and L.P. gas. You can typically make adjustments to manifold pressure on the gas valve as necessary by following the installation and operation instructions.

You may have to check and/or change orifice sizes and possibly replace them. Always pay attention to the possibility of electrical shock, fire or explosion possibilities. Failure to properly install orifices could result in death, personal injury and/or property damage. Turn off electrical power (at the disconnect) and the gas supply (at the manual shutoff valve in the gas line) when installing orifices. Changing orifices will require disconnecting the gas line from the gas valve, removing the manifold from the furnace, removing the orifices from the manifold, and replacing them with the properly sized orifices. Then you tighten the new orifices so they are seated and gas tight, and then reinstall the manifold and re-attach the gas line.

Adjust the pilot burner (if so equipped). If the furnace has a pilot flame to light the main burner, the flame should surround 3/8” to1/2”of the flame rod. To adjust remove the cap from the pilot adjusting screw on the gas valve and turn counterclockwise to increase or clockwise to decrease flame (in most applications) as required. Replace the cap after adjusting the screw. Always follow the furnace installation and operation instructions.

Perform a main burner check. Allow the furnace to run approximately 10 minutes then inspect the main burner flames. Check for stable and blue flames. Dust may cause orange tips or wisps of yellow, but the flames must not have solid, yellow tips. Flames should extend directly from the burner into the heat exchanger, and should not touch the sides of the heat exchanger. If any problems with the main burner flames are found, it may be necessary to re-adjust gas pressures, or check for drafts.

When troubleshooting gas furnaces, you will be dealing with three areas of concern that all can have individual problems, and affect each other. These three areas are: air flow, fossil fuel, and electricity. We have discussed simple checks for gas and electrical already.

For air flow, perform a temperature rise check and determine the actual air flow (Cubic Feet per Minute) crossing the heat exchanger during heating operation. Temperature rise can be checked by placing a thermometer in the return air duct within 6 inches of the furnace. Place a second thermometer in the supply duct at least two feet away from the furnace to prevent any false readings caused by radiation from the furnace heat exchanger. Make sure that the filter is clean and that all registers and/or dampers are open.

Operate the furnace for 15 minutes before taking temperature readings. Subtract the return air temperature from the supply air temperature. The result is the temperature rise. Compare the result with the allowable rise listed for the model (size) you are checking in the installation and operation instructions or the unit data plate. The speed is set at the factory but it may sometimes be necessary to adjust the speed selection. The speed taps that the manufacturer sets from the factory are typically based on a nominal 400 CFM per ton cooling and the basic mid range on the temperature rise for heating. If the rise is not within the specified range, it will be necessary to change the heating blower speed. If the rise is too high, it will be necessary to increase the blower speed. If the rise is too low, it will be necessary to reduce the blower speed.

Since the manufacturer cannot establish the static pressure that will be applied to the unit, it is the responsibility of the technician to select the proper speed taps on PSC blower motors for the application when the unit is installed, or when servicing in the field.

In most newer model furnaces if it is necessary to change the blower speed, the adjustments can usually be easily made on the Fan Control Board. Many of today’s furnaces have integrated furnace controls of some kind and this feature will have a position for all blower speeds and you must simply relocate the heating speed wire for the blower motor, or adjust switch positions.

Determine the CFM of the running furnace in the heating mode. Using the thermometers already inserted to check temperature rise, calculate the CFM with the following formula. The most important part of CFM determination is that the temperature rise is within the acceptable range with the CFM moving. If you are unsure, typically an airflow setting that will allow a rise between 40° and 70° will usually be acceptable. Ideally, 3 degrees above mid-point is recommended for optimum performance.

Many furnace manufacturers have modified the ignition systems to achieve higher efficiencies expressed in Annual Fuel Utilization Efficiency (AFUE). New types of ignition systems have and are being developed to meet the following needs: higher efficiency requirements of the government , conservation of fossil fuels, convenience in remote locations, less annoying shut downs, greater electronic control use, and higher safety ratings.

Typical ignition systems now include: standing pilot, spark to pilot, hot surface to pilot, and hot surface ignition.

Upon initial start-up the heat to light the burners (direct ignition) or the pilot (intermittent ignition devices) may be provided by either a spark device or a hot surface device. After lighting the pilot or the burners the heat is provided by the burning of the fuel gas. The fuel used in the furnace may be either Natural Gas or LP gas. Most furnaces are shipped set up for natural gas and must be converted for LP gas operation. The fuel is delivered to the burners through the supply gas piping to a Combination Gas Valve (combination in that it contains the flow regulating feature as well as a pressure regulator), to the burner orifices and then to the burner itself. The oxygen (air) needed for combustion is supplied by the operation of the vent motor assembly (also referred to as the combustion blower motor or exhaust blower). A negative pressure is created in the heat exchanger by the operation of the combustion blower and the positive pressure of the air surrounding the furnace pushes air into the burner box where it is drawn into the burner inlet (primary air) and mixes with the flame at the burner outlet to provide complete combustion (secondary air).

The best way to troubleshoot ignition systems is to determine which type the furnace has and follow the appropriate installation and operation criteria for the furnace you are dealing with. Most will include detailed troubleshooting steps for the ignition system installed. If not available, contact the equipment distributor or the manufacturer for more information. We will discuss troubleshooting some of these systems in future articles.

Phillip A. Rains
Copyright © Phil Rains
About the Author: Phil Rains is Master Trainer/Technical Developer for HVACReducation.net. He has over 35 years of HVAC and Refrigeration experience in installation, service, and training. He is NATE-certified in 5 areas, a member of ASHRAE and RSES, and ACCA EPIC-Certified in Residential and Commercial Design. He also holds a Universal Classification in EPA 608.
More about Phil!

Capacitor Start – Capacitor Run Motor

2009-12-20T08:01:00.021-06:00

by Roger Desrosiers

Capacitor Start-Capacitor Motors or (CSR) are used almost exclusively on Hermetic and Semi-Hermetic motors compressors. Rarely will this motor be used on an open type motor because of the cost of the components necessary to produce it. Most open–type motors do not use a starting relay, but use a centrifugal switch instead. Open type motors are usually built as permanent split-capacitor or capacitor start motors.

Operation

The CSR motor begins operation on a phase displacement between the start winding and the run winding, which allows rotation to begin. The run capacitor adds a small amount of starting torque but its main function is to increase the running efficiency of the motor. The run capacitor is wired in the circuit to provide the most efficient phase angle between the current and voltage when the motor is running. The run capacitor is in the circuit any time the motor is running. Both the start and run capacitors are wired in series with the start winding but are in parallel with each other. Figure 1 shows a schematic diagram of the motor with the starting components.

The microfarad rating of the run capacitor is much lower than that of the start capacitor for any given motor application. The capacitances of the two capacitors in parallel are additive, the same as resistors are in series. If the run capacitor has a capacitance of 10 mfd and the start has a capacitance of 110 mfd their total capacitance is 120 mfd. During startup this combined capacitance in series with the start winding causes a greater phase angle between start and run winding, which gives the motor more starting torque. When the potential relay opens the start capacitor is taken out of the circuit, however the run capacitor and start winding stay in the circuit. The reason the start winding can stay in the circuit is because the run capacitor limits the current going through the start winding. If the run capacitor fails because of an open circuit within the capacitor, the motor may start, but the running amperage might be about 10 % too high and the motor will get too hot if operated at full load. The motor is actually a PSC motor when running. The start capacitor is only used to help start the motor and at 75% of rpm it is disconnected from the start winding.

Troubleshooting

This motor is sometimes difficult to troubleshoot because of the number of components it has. For example, the windings, bearings, potential relay, starting capacitor, and running capacitor must all be checked. The windings of the CSR motor are easily checked with an ohm meter to determine if the windings are shorted, open, or grounded. The windings will be enclosed in a hermetic casing and the terminals will be on the outside of the casing. The technician must know how to determine the correct terminals to check. The bearings of a CSR can be worn so badly that the motor will seize or be very noisy with a knocking sound and the bearings are enclosed, therefore harder to check. A high amp draw can sometimes indicate bad bearings but consideration must be given to other possibilities such as an over charge or a high heat load.

The starting relay can be checked by diagnosing the condition of the contacts and the coil. The contacts can be checked with an ohm meter or be visual inspection. The ohm meter should show zero resistance across the contacts which are normally closed on a potential relay. If you have doubts about the integrity of the relay you can disassemble the relay. Then the condition of the contacts can be determined (sticking, pitting and misalignment). The coil can be checked like the windings of a motor. The starting and running capacitors are easily checked with an ohm meter to determine their condition.

Trouble shooting a CSR motor is done by checking all the components of the motor. These motors must be checked thoroughly to prevent other components from being destroyed. For example, the starting capacitor will be destroyed if the contacts or coil of the start relay are bad.

copyright(c)2009
Roger J. Desrosiers

About the Author: Roger is a contributing faculty member of HVACReducation.net. He has over 40 years experience in Air Conditioning and Refrigeration. He is also a member of R.S.E.S., CM, The Association of Energy Engineers, Certified Energy Manager, ASHRAE, Certified Pipe Fitter United Association and is 608 Universal Certified.

Gas Furnace Start Up Tips

2009-12-13T04:57:00.099-06:00

by Phil Rains

As technicians, during colder months you will be involved with the start up of gas furnaces for proper heating of homes. This will involve both visual inspections and effective start up procedures. We will discuss a few of these in this article.

Prior to the start-up of a gas furnace there are several things that you should verify. These are usually items that can be accomplished by visual inspection.

First, verify the type of fuel being utilized. As simple as this may sound, it is an important item to check. The furnace nameplate will typically detail the type of fuel that should be used. Almost all manufacturers today will produce furnaces that are set-up to use natural gas. These furnaces can easily be converted to LP gas operation by installing the correct LP conversion kit. Part of this kit may be a sticker or a new rating plate that identifies the converted furnace as an LP gas furnace.

Always verify the power supply to the furnace. All electrical connections must conform to the manufacturer’s installation and operation instructions as well as the National Electric Code and any and all local codes.

A HOT wire, a NEUTRAL and a GROUND wire of not less than #14 AWG should typically be run to the furnace from a separate 15 Amp power supply through a disconnect switch. The switch should break the black or hot leg of the 115-volt power supply.

The furnace must be properly grounded as per the National Electrical Code for safety purposes; it also should be grounded to ensure proper operation of any electronic components. The furnace can be grounded to the main panel through the power supply wiring or to a separate ground rod properly installed near the furnace.

The power supply to the furnace connections must be between 104 VAC and 127 VAC during furnace operation for acceptable performance. Field wiring connections must be made inside the furnace connection box. A suitable strain relief should be used at the point the wires exit the furnace casing. Copper conductors must be used. Line voltage wires should conform to temperature limitations of 63°F rise and be sized for the unit maximum amps.

Check and verify proper gas supply piping size. The gas supply must be properly sized to handle the combined appliance load, or run the gas pipe directly from the gas meter or LP gas regulator to the furnace. Inadequately sized gas supply piping could interfere with proper operation of the gas furnace. Additionally, proper gas supply piping installation should always follow local codes and ordinances. In their absence, you should follow the criteria of the National Fuel Gas Code (NFGC). The NFGC is the American National Standard that applies to the installation of fuel gas piping systems and fuel gas utilization equipment that are supplied with natural gas; manufactured gas; liquefied petroleum gas (LPG), in the vapor phase only.

Prior to correctly sizing and properly installing supply gas piping, you should review several considerations. Some of these considerations include, but are not limited to the following: furnace input, pressure drop, length of pipe, pipe fittings, and specific gravity of the fuel.

It is recommended that a manual equipment shutoff valve be installed in the gas supply line outside the furnace. Locate the valve as close to the furnace as possible where it is readily accessible. Also, it is recommended that you always install a drip-leg and a union.

Install a shut-off valve

Install a drip leg

Install a union

In order to ensure proper, safe and efficient operation of a gas furnace, you must pay careful attention to the venting system. You should always review the manufacturer’s installation and operation instructions for the furnace. These instructions will provide the necessary information on the proper venting requirements for the particular furnace.

All gas furnaces are classified by categories. The category of each furnace is shown on the rating plate and this category may determine the type of venting material required for the furnace. The chart below shows the flue gas conditions for each category for use when selecting the vent material.

Most furnaces today are either Category I or Category IV.

Category I furnace vent installations should be in accordance with the National Fuel Gas Code. Category I furnaces are defined as central furnaces that operate a non-positive vent static pressure and with a flue loss not less than 17 percent. These furnaces are approved for common-venting and multi-story venting with other fan-assisted or draft hood equipped appliances in accordance with the NFGC. The venting material should be only Type B or Type L double wall vent pipe.

Category IV appliances include all condensing furnaces. They may be single pipe, direct vent, or dual certified furnaces. Single pipe condensing furnaces require ventilation openings to provide air for proper combustion and ventilation of flue gases. Direct vent condensing furnaces use outside air for combustion ONLY, and must take this air from the same atmospheric pressure zone as the vent pipe.

Dual certified condensing furnaces can be installed as direct vent furnaces using outside air for combustion, or the furnace can use air from inside the structure for combustion. The INLET pipe is optional. If combustion air comes from inside the structure, adequate make up air MUST be provided to compensate for oxygen burned. If combustion air is drawn from outside the structure, it MUST be taken from the same atmospheric pressure zone as the vent pipe.

Category IV furnace vent installations should be usually Schedule 40 PVC unless otherwise specified by the manufacturer. Sizes may range from 2” to 3” and the allowable length will be determined by the manufacturer and is dependent on Btu input and size of the pipe. Always refer to the manufacturer’s data when determining actual size vent required.

Always verify adequate combustion air supply for any furnace. Combustion air is supplied to the furnace to ensure complete combustion of the fuel gas. The combustion process requires a large amount of air.

This air for combustion can be supplied from either inside the structure or from outside. If all air for combustion is supplied from inside the space, it must be determined if that space is a confined space or an unconfined space. A confined space is an area that has less than 50 Cubic Feet of volume for every 1,000 Btu/h Input rating of ALL gas appliances installed in that space.

An unconfined space is an area that has greater than 50 Cubic Feet of volume for every 1,000 Btu/h input rating. Use the previous information in the definitions to determine if the space where the furnace you are starting has an adequate air supply.

On any new installation be sure to check for properly converted furnaces when the furnace is installed in other than the “as shipped” configuration.

Condensate drains are required on all condensing furnaces. This type furnace removes sensible and latent heat from the products of combustion. Removal of the latent heat results in condensation of the water vapor. The condensate is removed from the furnace through the drains in the plastic transition and the vent fitting. The drains connect to the externally mounted (internally on up flow models) condensate drain trap on the side of the furnace. Be sure that the drain is installed correctly and is piped according to the Manufacturer’s requirements and any local codes (drains external to the furnace and drain termination).

Phil Rains
Copyright © Phil Rains

About the Author: Phil Rains is Master Trainer/Technical Developer for HVACReducation.net. He has over 35 years of HVAC and Refrigeration experience in installation, service, and training. He is NATE-certified in 5 areas, a member of ASHRAE and RSES, and ACCA EPIC-Certified in Residential and Commercial Design. He also holds a Universal Classification in EPA 608.
More about Phil!

OIL PRESSURE CONTROL

2009-12-06T05:21:00.022-06:00

by Roger Desrosiers

Many refrigeration compressors serviced today have positive-displacement oil pumps to help lubricate the internal compressor parts. Most compressors that have positive oil pumps also have a control that senses oil pressure and acts as a safety device whenever the oil pressure falls below a certain threshold level.

It is the action of the oil safety control we will discuss in this article.

There are several types of oil safety control devices on the market today. The two basic controls we are most familiar with are the mechanical differential control and the pressure-sensing electronic control.

The mechanical control uses tubing that senses the suction pressure of the compressor and the outlet oil pressure of the pump. The electronic control has a special pressure sensor that mounts in the outlet of the pump and connects only with an electrical cable.

FIG 1

In the mechanical control, such as above, the total pressure from the pump (less the suction pressure) is the actual net oil pressure. The control requires manual reset once it is tripped.

The oil sump is actually the suction pressure of the compressor. This means that the true oil pump pressure is the oil pump discharge pressure less the compressor suction pressure. So the oil pressure control is a pressure differential control which measures a difference in pressure to establish that positive oil pressure is present. A study of the compressor above shows how the net oil pressure is established. A study will show that when the system is using R-22 the crankcase pressure would be about 70 psig when the compressor is running and 125 psig when standing.

Most compressors need at least 30 psig of actual oil pressure for proper lubrication. This means that whatever the suction pressure is, the oil pressure discharge pressure has to be at least 30 lbs. above the oil pump inlet pressure, because oil; pressure inlet pressure is the same as the suction pressure. For example: if the suction pressure is 70 psig, the oil pressure must be 100 psig for the bearings to have a net oil pressure of 30 psig.

The oil pressure control uses a double bellows with one bellows opposing the other to detect the net or actual oil pressure. The pump inlet pressure under one bellows and the pump outlet pressure under the other bellows. The bellows with the most pressure is the oil pump outlet and it overrides the bellows with the least amount of pressure. This override is attached to a linkage that can stop the compressor if the net oil pressure is not established in a predetermined time.

When the compressor starts there is a time delay built into the control to allow the compressor to build up oil pressure in a short time and to prevent un-needed cutouts when oil pressure may vary for only a moment. This time delay is usually about 90 seconds. It is accomplished with a heater circuit and a bi-metal device or electronically.

Oil pressure safety controllers can also incorporate a pressure transducer to sense the combination of oil pump discharge and crankcase pressure.

Oil pressure safety controllers can also incorporate a pressure transducer to sense the combination of oil pump discharge and crankcase pressure. The pressure transducer has two separate ports for sensing suction pressure and oil discharge pressure and the difference between these two pressures is accomplished by the transducer. This pressure transducer is connected to an electronic controller by wires. The transducer is actually mounted directly into the oil pump.

The transducer transforms the pressure signal to an electrical signal for the electronic controller to process. One of the advantages of an electronic controller over a mechanical bellows type controller is that it eliminates capillary tubes, and eliminates the chance of a leak. Also the electronic clock and circuitry are much more accurate and reliable. Net oil pressure varies from compressor to compressor. Net oil pressure usually ranges from 20 to 40 psi. Most oil pressure safety controllers will shut the compressor down if the net oil pressure falls below 10 psi.

The following variables affect the net oil pressure.

· Compressor size

· Oil temperature

· Oil viscosity

· Bearing clearance

· Percent of refrigerant in the oil

Below is a schematic diagram of an oil safety control circuit and three phase motor with internal overload. The oil pressure differential switch is NC and if it’s still closed after say 90 seconds, the “L” and “M” contacts open and takes the compressor off the line.
See FIG 3 also
Fig 4

Other reasons for oil failure:

Inadequate refrigerant in systems which will cause lower velocity and less oil return
If refrigerant charge is low, the expansion valve will not feed the evaporator properly, resulting in high superheat and low gas velocities.
Low head pressure resulting from the cold ambient can affect the thermal expansion valve.
Due to oversized suction line
Blockage in the system usually produces no net oil pressure.

Smaller horsepower compressors can trip an oil failure if the compressor does not start when electrical power is applied to the terminals.
Oil contamination can cause a problem at the pick-up tube in the compressor crankcase.
In older compressors, oil failures can occur because of the pressurization of the crankcase due to blow-by from the pistons or piston rings.

When short cycling occurs, the compressor pumps more oil than normal and can cause the oil control to trip.

copyright(c)2009
Roger J. Desrosiers

About the Author: Roger is a contributing faculty member ofHVACReducation.net. He has over 40 years experience in Air Conditioning and Refrigeration. He is also a member of R.S.E.S., CM, The Association of Energy Engineers, Certified Energy Manager, ASHRAE, Certified Pipe Fitter United Association and is 608 Universal Certified. More About Roger

Troubleshooting a Non-Condensing Gas Furnace Pressure Switch

2009-11-14T17:23:00.041-06:00

by Phil Rains

If you work in the HVACR business, you have probably had the opportunity to troubleshoot non-condensing gas furnaces in the field, whether packaged units, or furnaces combined with air conditioners or heat pumps (split systems). These furnaces are typically rated around 80% AFUE (a measure of efficiency), and are vented to the outside via a metal vent/pipe configuration, or in the case of a packaged system, a side discharge outlet/hood.

On occasion, the non-condensing furnace control board (called various names like integrated ignition control, furnace control board, DSI, etc.) has a diagnostic LED light, especially on modern furnaces. Abnormal heating operation can often be indicated by the diagnostic LED light on the control board if the unit encounters an internal fault.

Occasionally, the furnace will go into a “hard” lockout and turn off the diagnostic LED. If this occurs, check the power supply to unit for proper voltage. Check all fuses, circuit breakers and wiring. Disconnect the electric power for five seconds. If the LED remains off after restoring power, replace the control board.

More often, the furnace will have an “external” lockout which occurs if the control determines that specific faults occur such as, but not limited to, a measurable combustion cannot be established within several consecutive ignition attempts, flame is established but lost during run, the flame rollout protection device opens, a drop in flame signal occurs, the primary limit switch opens, or if flame is detected with the gas valve de-energized. These situations occur sporadically with most gas furnaces.

The other faults that are often more common today concern the pressure switch.

A pressure switch is a safety device to shut down a furnace if proper combustion air flow is not being provided. All pressure switches in a non-condensing gas furnace are placed there for safety purposes. Generally, the single pole type of switch typically used allows electrical current to flow when the pressures are at an acceptable operational level based on the manufacturer design.

A pressure switch problem that often occurs is the pressure switch is closed prior to furnace operation. When the control board senses a call for heat from the thermostat (24VAC on the "W" terminal) one of the first things it does is check to see that the pressure switch is open or non-energized. This is the normal state for most pressure switches on furnaces. If the control board senses that the pressure switch is open it then sends power to the inducer blower and then checks to make sure that the pressure switch closes. If it is then closed after a short time period (based on furnace manufacturer design) the control board proceeds with the ignition sequence.

If the control board senses a closed pressure switch before it has energized the inducer, its program determines that something is wrong and for safety does not continue with the ignition process.

This situation could be caused by something that is causing the switch to stay closed. Blockage in the hose or hoses going to the switch could be the problem. You also could have a defective switch. It is possible (but less likely) that you have a short in the wiring or (even less likely) that you have a defective furnace control board. You can check that the pressure switch opens and closes with an ohmmeter when you blow or suck on the pressure hose. Of course, perform this check with power removed from the furnace.

Another more common pressure switch problem encountered that can arise with furnaces is that the pressure fails to close after the inducer has started to run. This blower is called an "inducer blower." When the furnace gets a call for heat, it starts up the inducer to start blowing air (either sucks it into the burners ahead of the flame or blows it out after the flame—dependent on the manufacturer design). Since the whole point is to create a "draft", the furnace control must determine when this has been accomplished. The pressure switch “tells” the control board that there's sufficient air movement to go ahead and fire up the ignitor and then open the gas valve. In most cases, the pressure switch (normally open when the system is off) will close due to negative pressure created by the inducer running in a short period of time. Different pressure ratings exist for different pressure switches. These ratings often appear on the side of the switch. This is so replacement of a bad switch can be exactly what is there originally.

A pressure switch that is stuck open can be caused by many issues such as a plugged vent, a heat exchanger surface /passage problem due to carbon deposits (usually on LP gas furnace more that natural gas), the inducer slows down due to age, a pressure switch hose is plugged with debris, or simply a bad pressure switch is now in the furnace.

It only takes a small restriction to keep the pressure switch from closing.

One of the first steps in troubleshooting the open switch is to test it to see if it is defective. Remember, electrical devices (switches in this case) typically wear out over time. Using a voltmeter, place one probe on a lead wire going to the pressure switch and "ground" the other probe. To "ground" is to attach the probe to metal that is part of the furnace. The meter, which you should have set to volts AC, should register approximately 24 or more volts (24 to 28 volts is normal). A two wire pressure switch you should be getting 24 or more volts between both leads to ground. If you do not get 24 or more volts with the furnace running then you have a pressure switch problem.

One of the most common problems involves the tubing (typically rubber) where the hose slips onto the draft inducer. It may attach at the top, bottom or center of the draft inducer via a small nipple device. This point will get clogged rather easily. A simple test is to pull the hose off the pressure switch and blow into it. You should be able to blow air into the inducer easily. You can also pull the tube from the pressure switch and listen for air flow when the draft inducer turns on as well.

If you cannot blow air into the inducer, or hear air flow when the inducer is running, take a stiff wire, a piece of coat hanger, or a drill bit to clear the inducer nipple. You simply place the wire, or bit into the nipple on the inducer and tap it gently with a hammer until it breaks free. In extreme cases, you may have to actually drill the debris out with a drill and bit, but not most of the time.

Phil Rains
copyright(c)2009

About the Author: Phil Rains is Master Trainer/Technical Developer for HVACReducation.net. He has over 35 years of HVAC and Refrigeration experience in installation, service, and training. He is NATE-certified in 5 areas, a member of ASHRAE and RSES, and ACCA EPIC-Certified in Residential and Commercial Design. He also holds a Universal Classification in EPA 608.More About Phil

If you are interested in an approved online program addressing the many facets of gas furnace troubleshooting you can contact HVACReducation.net.

HVACReducation.net provides online courses related to furnaces and their proper operation.

Hi Efficiency Heating and Cooling Unit Operating Characteristics

2009-11-14T16:16:00.050-06:00

by Roger Desrosiers

Blower Operation

1. The blower will operate continuously whenever the mode selector of the electronic thermostat is set in the cool mode and the fan selector is set to on.

2. The blower will operate intermittently whenever the mode selector is set to cool and the fan selector is set to auto. A delay is programmed into the microprocessor to allow the blower fan to continue to operate for one minute after the condensing unit has been commanded off by the thermostat.

3. The blower will operate intermittently whenever the mode selector of thermostat is set to heat. The fan is commanded on 35 seconds after the main burner lights and remains on for a predetermined time set by dip switches after the main burner is commanded off.

Heating Cycle

1. When the thermostat is set for heat mode and the room temperature drops one degree below the set point the circuit between the “R” and “W” terminals on the sub base is closed. The microprocessor on the electronic circuit board (ECB) sees a command for heat on the input terminal to the “W” terminal of the thermostat and commands the relay of the induced draft fan to close starting the induced draft fan motor.

2. If the passages through the combustion air piping, vent piping, and heat exchanger passages are unrestricted, the operation of the induced draft fan generates enough air pressure to cause the pressure switch to close within about two seconds. The microprocessor on the ECB reads the input signal from the pressure switch terminals and commands the hot surface igniter relay contacts to close allowing the ignition device to begin heating.

3. After the igniter has been hearing for 15 seconds, the microprocessor on the ECB commands the gas valve relay contacts closed for 7 seconds, opening the valve. As the fuel-air mixture passes across the red hot surface of the igniter, combustion occurs and the entire burner lights.

4. The presence of burner flame allows current to flow (1.7ua) from the tip of the flame sensing rod, through the ionized gases of the flame, and into the grounded surface of the burner. The current can only flow out the top of the rod and into the flame.

5. It cannot flow from the flame into the top of the rod. Consequently, the ac voltage across the flame rod and burner is rectified into a pulsating DC current. As long as a rectified DC current is present at the flame rod terminals, the microprocessor knows that a flame exists and allows the gas valve to remain open.

6. After the flame rod safety circuit has proved that the main burner has been lit for 30 seconds, the ECB microprocessor will command the blower motor relay contacts close, turning on the fan. Since the unit is operating in the heating mode, the fan speed relay coil remains de-energized.

7. When the signal from the “W” terminal of the thermostat opens, indicating that the room is satisfied, the ECB microprocessor will command the gas valve relay contacts open and the gas valve will close.

8. The ECB microprocessor allows the induced draft fan motor to operate for 15 seconds after the main burner is commanded off to purge the combustion gases from the burner box and heat exchangers. The blower motor will remain operating for some set time after the main burner is commanded off.

Cooling Cycle

1. When the thermostat mode is set to cool and the control point rises one degree above the set point, the input signal to the Y terminal on the ECB comes on. The ECB’s microprocessor reads the change in the “Y” terminal’s signal and commands the condensing unit relay contacts to close. This action energizes the condensing unit’s contactor, starting the compressor and condenser fan.

2. The blower fan unit is commanded on when a signal is present on the “G” input terminal from the thermostat. The fan operates for 60 seconds after the signal on the “G” terminal goes open, Indicating the thermostat is satisfied.The condensing unit is commanded off when the signal on the “Y” terminal of the thermostat and the ECB goes open.

The legend for the Electronic Control Board
· HSI = Hot surface igniter
· IDM = Induced draft motor
· GV = Gas valve
· BLM = Blower motor
· EAC = Electronic air cleaner
· ACC = Air conditioning control
· FPE = Flame proving electrode
· FRS = Flame rollout switch
· HLS = High limit switch
· PS = Pressure switch

ELECTRONIC CONTROL BOARD

Humidifier

1. The optional 24V AC humidifier is commanded on by the humidifier control relay whenever the furnace is in the heating mode and its blower motor is commanded on.

2. The humidifier is commanded off 15 seconds after the furnace is commanded off at the end of the post purge cycle.

Safety Strategies

1. During the hearing mode if the flame rod does not detect a flame within the first 7 seconds that the gas valve is commanded open, the ECB microprocessor commands the gas valve closed. A 15 second waiting period occurs before an ignition cycle will be attempted again. The induced draft fan motor remains operating during this period to purge unburned fuel from the heat exchangers.

2. After a flame failure, a second attempt is made to start the furnace. The igniter is started and allowed to operate for 25 seconds before the gas valve is commanded open. If the burner fails to light, another attempt will be made before the ECB microprocessor locks out the ignition cycle. The unit can be reset by a service technician by opening the disconnect switch to the furnace for 60 seconds.

3. If there is a, momentary loss of fuel or flame or a short or an open circuit occurs in the flame rod circuit, the microprocessor will close the gas valve. After 15 seconds the ECB will restart the ignition process. If for some reason the unsafe condition does not clear, the unit will lock out, requiring a manual reset.

copyright(c)2009
Roger J. Desrosiers

About the Author: Roger is a contributing faculty member of HVACReducation.net. He has over 40 years experience in Air Conditioning and Refrigeration. He is also a member of R.S.E.S., CM, The Association of Energy Engineers, Certified Energy Manager, ASHRAE, Certified Pipe Fitter United Association and is 608 Universal Certified.More About Roger

Energy Auditors, One of the New GREEN Jobs, Gain Momentum Across the Country

2009-11-14T15:12:00.056-06:00

by Patricia Leiser

Austin, Texas is one of the first cities in the country to require energy audits on building performance when sold. It is anticipated that most if not all large cities in the country will adopt similar green energy efficiency programs. The Austin City Council approved the Energy Conservation Audit and Disclosure (ECAD) ordinance to improve the energy efficiency of Austin homes and buildings that receive electricity from Austin Energy.

The energy auditor—is listed by the US Department of Labor as one of the new green jobs where growth is anticipated. Energy Auditors, also known as Building Performance Assessors, Home Energy Raters, and perhaps other titles, use equipment such as blower doors and infrared cameras, as well as visual walk through checklists to evaluate a building’s performance levels. As more cities follow Austin’s lead, energy auditors will be in demand.

The research indicates that this line of work is already growing as the interest and urgency in preserving the global environment increases. The International Council for Local Environmental Initiatives (ICLEI-Local Governments for Sustainability) has over 1107 cities, towns, counties, and their associations worldwide that comprise a growing membership. It is an international association of local governments and national and regional local government organizations that have made a commitment to sustainable development. To view a list of their global members, visit:
http://www.iclei.org/index.php?id=772
One of their programs is the Eco-Efficient Cities initiative that helps local governments develop strategies to address air quality, energy efficiency, water resources management, waste stream management, eco-mobility, and others in an integrated manner.

NATIONALLY
Here in the United States we hear a lot about Energy Star. Energy Star is a joint program of the U.S. Environmental Protection Agency and the U.S. Department of Energy helping us all save money and protect the environment through energy efficient products and practices. One concern about home performance is that a home can cause twice the greenhouse gas emissions of a car. Energy Star reports that in 2008 alone, Americans saved enough energy to avoid greenhouse gas emissions equivalent to those from 29 million cars—all while saving $19 million on their utility bills. Their web page

http://www.energystar.gov/index.cfm?c=home_improvement.hm_improvement_index

is devoted to home energy efficiency improvements; they all start with a comprehensive home assessment. If you’re wondering about home energy raters in your area, Energy Star provides an online list of qualified rater/partners by state.

STATES
The state of New Jersey instituted a statewide Clean Energy Program – recognized as a national model—that offers financial incentives, programs and services for New Jersey residents, business owners and local governments to help them save energy, money, and the environment. Their Residential Home Performance Program that offers financial incentives on energy efficient improvements begins with the home energy audit.

New York has been addressing energy efficiency for many years. Their New York State Energy Research and Development Authority (NYSERDA) helps to coordinate the efforts of stakeholders across the state to help utility customers solve their energy and environmental problems while developing new, innovative products and services. The Home Performance with ENERGY STAR® Program begins with a BPI Accredited Home Performance contractor who performs an assessment of the home.

The state of Virginia has implemented the Residential Energy Efficiency Rebate Program that will provide $7 million for energy efficiency improvements and retrofits made by homeowners for replacement of major systems equipment such as: central air conditioning units, heat pumps, furnaces, boilers, water heaters, window replacements, insulation, and programmable thermostats. Homeowners will be eligible to receive up to $250 for the cost of an energy audit conducted by a certified auditor.

The California Public Resources Code Section 25942 directs the energy Commission to adopt a statewide California Home Energy Rating System (HERS) Program for residential dwellings.

Southern California has adopted a Home Performance Program in league with Southern California Edison. This program finds, screens, trains, and mentors qualified HVAC and remodeling contractors to deliver comprehensive home performance improvement packages tailored to the needs of each existing home and its owner. To verify the program’s results they will perform a checklist walkthrough inspection of the reported job scope plus physical tests of each job’s key quantifiable measures, particularly duct sealing, airflow, combustion safety, and envelope leakage reduction.

Missouri passed Senate Bill 1181 into law in 2008. It includes a tax deduction for qualified home energy audits and the recommendations of those audits beginning with the 2009 tax year. For taxpayers to qualify for the deduction, the home energy audit must be performed by an energy auditor certified by the Missouri Department of Natural Resources. Missouri certification includes either the Building Performance Institute (BPI) or Residential Energy Network (RESNET) certification, or a similar alternative program.

Oregon offers home owners a state income tax credit for making their homes more energy efficient and helping preserve Oregon’s environment. Their standards may be more stringent than the federal government’s EnergyStar Program. Oregon Utility companies also offer rebates and incentives for improving home efficiencies. A non-profit organization, Energy Trust of Oregon, helps individuals identify and qualify for all of the energy savings programs that starts with a Home Energy Review.

CITIES AND COUNTIES
At the local government level, momentum is increasing as well. At the end of September, 2009 in Los Angeles, California at the Governors’ Climate Summit 1,000 mayors across the United States signed a pact to reduce greenhouse gas emissions. "We didn't just sign on. I can tell you, we've been working hard to meet those goals," Mayor Antonio Villaraigosa said. Some of the accomplishments already gained by this group of mayors include:
· Seattle was able to reduce its 1990 carbon footprint by 8% in 2005, largely through voluntary emissions reductions by households and businesses.
· Los Angeles reached the 7% Kyoto target in 2008, four years ahead of schedule, in part through an aggressive program in energy efficiency that included light bulb and street light replacements, mandatory green building standards, and a transition to alternative fuel on buses, trash trucks and other city vehicles.
· Boston has increased its solar capacity by 300%.
· Philadelphia has adopted a plan to retrofit 100,000 homes with energy-saving features over the next seven years.
· Cleveland has set a standard of converting to 25% renewable electricity.

Upon looking more closely at a number of cities across the country it is evident that the momentum for energy efficiencies and energy audits is growing.

Montgomery County, Maryland introduced an act to require that a home energy audit be conducted as part of a home inspection completed in connection with the sale of a single family residential building. It goes on to define what a “Qualified home energy performance rater” is: certified by RESNET as a home energy performance rater; or meets other equivalent requirements approved by the Director of the Department of Environmental Protection.

Houston, Texas – the Mayor’s Office of Environmental Programming has developed a home energy audit worksheet. Greenhoustontx.gov states that a home energy audit is often the first step in making your home more efficient. An audit can help assess how much energy your home uses and evaluate what measures you can take to improve efficiency. But remember, audits alone don’t save energy. You need to implement the recommended improvements.

Albuquerque, New Mexico – Executive Order no.20 established green building standards for city projects, including requirements to meet or exceed LEED Silver ratings. In 2007 the Albuquerque Energy Conservation Code – Volumes I and II were signed into legislation. It is the first comprehensive Energy Conservation Code in the State of New Mexico; and it reflects a concerted, combined effort between local government and those in the building, and building-related industries to develop a code acceptable to all. Mayor Martin Chavez states, “The revised building codes support green building targets and are essential to reduce the amount of greenhouse gases generated by buildings. It is estimated that the building industry generates 39% of carbon dioxide (CO2) emissions and 48% of all greenhouse gas (GHG) emissions in the United States.” Also, “. . . states otherwise should not be tied to the latest versions of ASHRAE and IECC standards. Climate change and energy independence are too urgent for localities to wait for Federal consensus on building codes.”

Alexandria, Virginia -- As part of the 2008 Eco-City Charter, the first of its kind in the region, the city adopted a new and progressive green building policy for commercial and residential buildings. The Charter outlines essential environmental sustainability principles and core values. To help them accomplish the goals, the city hired an energy manager. Their efforts have already been recognized as Alexandria just received Platinum Certification in the Virginia Municipal League Go Green Government Challenge, which encourages local governments to reduce energy usage and promote environmental sustainability.

Babylon, Long Island, New York – Mayor Steve Bellone founded The Babylon Project and the Long Island Green Homes project which has completed 120 deep retrofits with another 96 audited in the queue. On average, air infiltration has been decreased by 29%, diminishing CO2by 4.35t per house. The pilot program of 275 homes will be completed by the end of the year. Next year, they will be targeting 1,200 homes and aim to have them retrofitted by the end of 2010, thus reducing Babylon’s carbon footprint by 6, 416t.

Boston, Massachusetts – Because nearly 75% of the city’s green house gas emissions come from the energy demand of the building sector, they’ve developed a comprehensive green building strategy. In addition to the installation of solar power, they are coordinating energy efficiency programs for residents and businesses. Mayor Thomas Menino states, “I expect that the range of energy efficiency measures we are putting in place for existing buildings will be the most important.”

Burnsville, Minnesota -- The city has adopted a Sustainability Guide Plan that includes conducting energy audits on city facilities and retrofitting city facilities with energy efficient technology.

Charleston, South Carolina -- In order to reduce CO2 emissions from buildings, they have a contract with an energy services company. Much of their initial work has involved installing more energy efficient HVAC systems, lighting efficiency retrofits, efficiency control systems retrofits, and low flow water devices. In addition, during 2010 they hope to launch energy efficiency partnerships to bundle energy audits, efficiency upgrades and financing for all residential buildings, small commercial buildings, and many institutions, into a one-stop center. One thousand residential and small business buildings will be targeted for service in the pilot phase.

Denver, Colorado – “We’ve had a lot of success with our Residential Climate Challenge program,” says Mayor John Hickenlooper. They’ve worked with non-profit partners to go door-to-door in Denver’s neighborhoods to provide energy efficiency education and services. “We’re making homes more comfortable and building stronger communities.”

Miami, Florida – Next month, Miami will launch a Home Energy Challenge/ Reduce the Use program in partnership with the local non-profit Dream-in-Green for 50 homes. “We are currently looking for opportunities to scale this project to more homes in the community. This program is critically important because one of the most challenging and important parts of GHG mitigation is including homeowners, apartment dwellers, and small business owners in this effort.” Says Mayor Manuel Diaz

Philadelphia, Pennsylvania -- Released in April, 2009, Greenworks Philadelphia is a comprehensive strategy to lower greenhouse gas emissions and improve the quality of life for all Philadelphians. It includes 169 separate initiatives, of which one of the most important is the ongoing effort to weatherize and install more efficient heating systems in homes. It calls for the weatherization of 100,000 homes over the next seven years.

Pleasanton, California -- Pleasanton has established a collaborative partnership with the local utility to provide energy efficiency audits and a retrofit program; rebates are provided to make this more cost effective. They have established a Green Building Ordinance, and are moving through the steps of creating a special financing district that allows residents and business owners to finance energy efficiency upgrades, including solar, and have it added to their property taxes.

Cape Light of Barnstable, Massachusetts offers a Home Energy Audit for residential customers to see the potential for energy saving measures and to commit to install energy saving improvements with the help of generous program incentives. All audits come with a three-page report summarizing the findings, and a list of recommended mitigation measures.

During the weeks I spent researching and assembling this list of information, new energy efficient activities were emerging every day. The United States is already experiencing a surge in building performance activities that will result in a smaller carbon footprint. One of the keys to almost every residential program is an energy audit that scientifically identifies specific issues of a building’s energy performance, and then makes recommendations to improve any weaknesses. I would encourage you to participate as our country goes green.

Patricia (Patty) Leiser
Executive Assistant,
HVACReducation.net

About the Author:
Like many of you, I have a passion for education and lifelong learning. I have a Bachelor of Science in Education/Business from the University of Idaho where I transferred after two years at Gonzaga University. I also studied with Berean Bible College and Riverside Community College. I bring to you 35 years of work experience in business and education. I have worked as a Classroom Aide, Special Ed Tutor, Preschool Director, Secretary, Office Manager, Assistant for the Dean of Education, Administrative Assistant to Professional-Technical Education, and Human Resources Coordinator for a school district. I believe the future of education is online, and employment opportunities are in the trades. I am honored to work with HVACReducation.net and dedicate myself to providing excellent service to our students, faculty, and staff.

On a personal note, I have a nice little office with a view of the forest from our cabin in the woods. I love the northwest because I can go right outside and enjoy hiking, cross country skiing, biking, canoeing, and camping—my favorite activities. I look forward to working with each of you.

Research and information for this article is taken from:

http://www.austinenergy.com/About%20Us/Environmental%20Initiatives/ordinance/index.htm

http://www.iclei.org/index.php?id=10509

http://www.latimes.com/news/nationworld/nation/la-na-mayors-climate3-2009oct03,0,4137038.story

http://www.njcleanenergy.com/residential/programs/home-performance-energy-star/benefits-and-incentives

http://docs.google.com/gview?a=v&q=cache:MKLwGCRL0ckJ:www.naco.org/cffiles/ggi/green_counties/documents/Montgomery%2520County%2520MD%2520Home%2520Energy%2520Audit%2520Policy.pdf+home+energy+audit+laws&hl=en&gl=us&sig=AFQjCNGtJ--cJUsHbypKgarjFgrhtrY0Cg

http://www.energy.ca.gov/2008publications/CEC-400-2008-011/CEC-400-2008-011-CMF.PDF

http://www.takecareoftexas.org

http://www.greenhoustontx.gov

http://www.getenergysmart.org/SingleFamilyHomes/ExistingBuilding/HomeOwner.aspx

http://www.energytrust.org/

http://www.virginia.gov/eerebates

http://www.capelightcompact.org/home_energy_audit.html

HVAC/R Electronics # 6

2009-11-01T09:17:00.070-06:00

by Roger Desrosiers

Improving air quality is another opportunity for engineers to apply the capabilities of digital systems. Energy conservation strategies require buildings to be airtight to prevent the escape of expensive heated or cooled air. This usually comes at the expense of ventilation. “Sick building syndrome” has become a national concern as researchers continue to uncover the effects of indoor air quality (IAQ) on human health and productivity in the workplace. Concerns over health hazards in the workplace and the spread of airborne contaminants are issues that have reached the forefront of public attention. The control of building ventilation is a problem that is being solved through the application of digital controls. So let’s take a look at a ventilation program.

Ventilating Control Program

Sequence of Operation:

1. Supply fan starts and enables return fan start and system controls.
2. SA smoke detector stops supply fan when smoke detected.
3. RA smoke detector stops supply fan when smoke detected.
4. Controller stops fan when low temperature detected.
5. SA high static pressure control stops fan when unsafe pressure exists.
6. Automatic fan system control subject to commandable on-off-auto software
point.
7. Control program turns supply, return, and exhaust fan on and off dependent
upon optimized time schedule, unoccupied space temperatures, and occupant
override requests.
8. Occupant override switch provides after hours operation when pressed.
9. Duration of operation for override request.
10. Space temperature (perimeter zone) inputs to optimum start-stop, unoccupied
purge, and low limit programs.
11. Set-point at which unoccupied low-limit program executes.
12. OA temperature input to optimum start-stop program.
13. Return fan operation enables exhaust fan control program.
14. Exhaust fan status (operator information).
15. Warm-up mode status (operator information).
16. Supply fan load (VAV type systems-operator information).
17. Return fan load (VAV type systems-operator information).

Air handling system shall be under program control, subject to supply air (SA) and return air (RA) smoke detectors, SA high pressure cut-out, and heating coil leaving air low-temperature limit control; and shall be subject to system software on-off-auto function.

Supply fan shall be started and stopped by an optimum start-stop seven-day time schedule program, an unoccupied low space temperature limit program, or by an occupant via push button request. The push button shall be integral with the space temperature sensor. Any push button request shall provide sixty minutes (operator adjustable) of full system operation. Return fan shall operate anytime the supply fan proves flow (via a current sensing relay). The exhaust fan shall operate during scheduled occupancy periods and during occupant requested after-hour periods anytime the return fan proves flow.

In figure 1 we see a supply air control loop with the sequence of operation.

Sequence of Operation:

The DDC controller uses a temperature sensor mounted in the supply air duct to modulate control valves or mixing dampers to maintain a supply air temperature set-point. In most systems that employ a heating and cooling coil, the hot water valve and the chilled water valve should be modulated in sequence.

When the supply air temperature falls below set-point, the hot water valve begins to modulate open and consequently, the cooling valve begins to modulate closed. If the supply air temperature continues to fall below the set-point, the heating valve will open fully and the cooling valve will close completely.

When the supply air temperature rises above set-point, the hot water valve begins to modulate closed and consequently, the cooling valve begins to modulate open. If the supply air temperature continues to rise above the set-point, the heating valve will fully close and the cooling valve will open completely.

A temperature sensor located in the mixed air stream (between the unit filters and the coils) is used to provide mixed air low limit control. When the temperature sensed by this element falls below the setpoint, the outside air damper fully closes, the return air damper fully opens, the exhaust air damper closes to a minimum position, and the valves on all coils will fully open. This sequence should always be used on systems with wetted coils.

When the unit fan is turned off, the outside air damper fully closes, the return air damper fully opens, the exhaust air damper fully closes, and all control valves return to their “normal” positions.

Design Considerations:

Control Valves:

· Avoid using spring return actuators on control valves for wetted coil
applications.

· When selecting two-way valves for control
of wetted coils:

· For hot water coils, have the valve configured in the “normally” open position.

· For chilled water coils, have the valve configured in the “normally” closed
position.

When selecting three-way valves for control of wetted coils:

· For hot water coils, have the valve piped such that when the valve is in the
“normal” position, the water flows through the coil.

· For chilled water coils, have the valve piped such that when the valve is
in the “normal” position, the water bypasses the coil.It is recommended that
mixing valves be used in all three-way applications unless otherwise
specified.Also be cautious to not pipe globe valves that are designed
for mixing applications for diverting service. The fluid flow will
cause a“hammering”effect and severe noise and damage will follow.

In Electronic #5 I discussed how to program a control loop, following are some of the most common loops that can be controlled that you will find on sophisticated controls.

1. Discharge Air Temperature
2. Mixed Air Temperature
3. Hot Cold Deck Temperature
4. Cold Deck Temperature
5. Humidity or Dew Point Control
6. Indoor Air Quality Control
7. Ventilation Control
8. Supply Fan Static Pressure Control
9. Supply Fan Start/Stop Control
10. Return Fan Start/Stop Control

One of the last steps is to connect the analog inputs and outputs to an 8x computrol controller as shown in figure 1 below.

From this diagram you can see that the DDC is powered with 24 volts supply at the terminal strip in the lower left side. The discrete (on-off) inputs are called binary inputs. They are connected to any terminal that you designate as a binary, because you have the option to designate any of the terminals you like, which is a feature of these controls. Therefore point 1 thru 8 can be an analog input or output or it can be a binary input or output.

One of the main advantages of a DDC system is that it can be connected to a network and be controlled remotely. In some cases the control is setup in a special room, where the HVAC technicians for a large building or campus can monitor the entire system from a single console. Another feature of the network is that its data can be transmitted over dedicated telephone lines or connected through the Internet so that the data are available worldwide. Other features such as energy management, security, fire control and other essential functions can be controlled over these networks.

Conclusion:

This brings me to the end of this series of discussions on the wonderful world of DDC Controls and some of the attributes and marvelous things that can be done with these controls. My intention was not to teach you all about these controls but more of a fundamental introduction. If I aroused your interest into looking further into how these controls work then I will feel that I have done some good for the betterment of this industry. If you are interested in learning more about DDC Controls I urge you to peruse the following web sites:
DDC-Online
Computrols.com

copyright(c)2009
Roger J. Desrosiers

About the Author: Roger is a contributing faculty member of HVACReducation.net He has over 40 years experience in Air Conditioning and Refrigeration. He is also a member of R.S.E.S., CM, The Association of Energy Engineers, Certified Energy Manager, ASHRAE, Certified Pipe Fitter United Association and is 608 Universal Certified.Lean More About Roger!