chiller maintenance and control

advanced absorption chillers party2

2022-06-03T22:06:00.000+03:00

ADANCED ABSORPTION CHILLERS

PARTY 2

For Utilization of Exhaust Gas from MGT

CH-KE series can use exhaust gas from MGT directly. The exhaust gas

thermal energy retrieved by exhaust heat exchanger and exhaust heat retriever to

achieve high efficiency operation. Exhaust gas operation takes priority whenever

there is sufficient exhaust heat available in respect of the cooling or heating load.

When exhaust gas mode as a function of electrical demand is not sufficient to satisfy

cooling or heating requirement, dual fuel mode, exhaust gas and natural gas, will

automatically commence. 100% direct gas fired mode will cater heating demand when there is little or no heat available from the for cooling or heating demand when there is littre or heat available from the micro gas turbin

For Utilization Renewable Energy

In July 1974, Yazaki Experimental Solar House was completed, realizing a

solar energy system earlier than any other project in the world. The success of

development solar energy system is based on Hot-water Fired Chiller (WFC)

technology. The WFC series has been installed 3,851 projects in Japanese market

Biomass Energy – Wood Pellet

Fig 8 indicates the Pellet Fired Absorption Chiller, which is energized by wood

pellets. The Wood pellet Fired Absorption Chiller-Heater is under development and it

2007.will launch to Japanese market in

Figure 8. System of Pellet Fired Absorption Chiller-Heater

Using wood pellet as fuel is considered as “Carbon-neutral”. Since tree

planted to replace the wood burned as fuel can absorb carbon dioxide, this resource

has attracted interest as a carbon-neutral fuel, that is, one which does not increase

the amount of carbon dioxide in the atmosphere

The model business, which is indicated Fig 9, in local recycling of wood

biomass involves collecting thinned wood from forestry maintenance operations

wood cut-off from sawmills, and other remnant material and recycling them into

pellets for local use as fuel. By doing so, the scheme aims to promote the principle of

local production for local consumption in timber and energy supply through efficient

use of forestry resources. The Yazaki Group is working in the framework of publicprivate

partnership with the aim is to stimulate the forestry industry and at same time

to maintain and preserve forests and reduce atmospheric carbon dioxide

Fig 10 is one of “Renewable Energy Utilization Cooling System” which is

consisted by solar cooling system and wood pellet cooling system. During daytime

if sunlight is enough to sufficient cooling requirement, solar cooling suffices cooling

requirement without wood pellet absorption chiller operation. If there is less sunlight

the wood pellet can cover insufficient cooling capacity of solar cooling during

morning and evening time or cloudy day

Kandi younes

ADVANCED ABSORPTION CHILLERS PART 1

2022-06-02T13:31:00.001+03:00

ADVANCED ABSORPTION CHILLERS

Summary

One of significant feature of absorption cooling technology is that various

thermal energies can be used for air-conditioning by the technology. The main types

of thermal energy are hot water, steam, and exhaust gas. In this document, Yazaki’s

advanced absorption chillers and systems are introduced for effective usages not

.only waste thermal energies but also renewable energies

Utilization of Various Waste Thermal Energies

By an onsite electrical generator and manufacturing process of factory

various types of thermal energy are discharged, such as hot water, steam, and

exhaust gas. Absorption chiller can use not only fossil fuel but also the waste

thermal energies for cooling. In combination with an electrical generator and an

absorption chiller, the combined system can improve overall efficiency rate by using

the waste thermal energy for cooling. For effective utilization of energy, Yazaki

provides absorption chillers for each type of thermal energy

For Utilization of Hot Water

Hot water Fired Chiller (WFC) is the first type of chiller forutilizing waste head

The WFC absorption cycle is energized by hot water and the lower side operational

temperature range of hot water is expanded to 70 degree C for effective utilizthe thermal energy

In general, if the hot water temperature is not enough to operate the WFC,

additional boiler is installed into the system to produce an increase in temperature.

WFC-SCB and WFC SHB series are the packaged type of auxiliary boiler. By

optimal control of auxiliary boiler and WFC, waste energy of hot water can be used

effectively

For Utilization of Steam

CH-KGST can use wasted steam for cooling. In the case of high-pressure

steam, the CH-KGST operates double effect cooling cycle. If the steam pressure

decreases, the CH-KGST cooling cycle switch to single effect cooling cycle. By the

cycle switching control, CH-KGST series can operate continuously under steam

pressure fluctuation from 98 kPa to 686 kPa and realizes effective use of lowpressure

kandi younes

Water Chillers and Maintenance parti 4 Extended (long-term) maintenance checks

2015-12-19T00:08:00.001+03:00

Water Chillers and Maintenance

parti 4

Extended (long-term) maintenance checks

Extended (long-term) maintenance checks

Extended (long-term) maintenance checks:

1. Every 5 years (or more frequently as the chiller ages), perform eddy current

(electromagnetic) testing of heat exchanger tubes. [This testing will

typically detect tube pits, cracks, and tube wear (thinning).] If only 1–5

tubes are found defective, plug tubes. If more than 5 are found defective,

replace tubes. (Any tube that is replaced as a result of this testing should

be examined and cross-sections cut so the cause of the defects can be

evaluated.)

2. Other components must be serviced, inspected, and/or replaced at the

intervals recommended by the chiller manufacturer.

Recommended maintenance procedures for water-cooled electric-drive rotary

compressor water chillers are as follows:

Daily monitoring/visual inspection: The majority of chiller operating problems

and maintenance needs are discovered by visual inspection and

frequent monitoring of equipment operating parameters.

Monthly, quarterly, and annual preventative maintenance:

1. Clean the evaporator tubes every 2–4 years (annually for chillers serving

air washers or other “open” cooling loads).

2. Clean the condenser tubes every year.

3. Quarterly, calibrate pressure, temperature, and flow controls.

4. Annually, inspect starter wiring connections, contacts, and action. Tighten

and adjust as required. Perform thermographic survey every 5 years.

5. Annually, test the operation of safety interlocks devices, such as flow

switches, pump starter auxiliary contracts, phase-loss protection, and so

on. Repair or replace as required.

6. Annually, perform dielectric motor testing to identify failures in motor

winding insulation. For large chillers (100 tons or larger), additional

annual motor tests are required to test for the imbalance of electrical

resistance among windings, imbalance of total inductance with phase

inductances, power factor, capacitance imbalance, and running amperage

versus nameplate amperage.

7. Annually, check the tightness of the hot-gas valve (as applicable). If the

valve does not provide tight shutoff, replace it.

8. Annually, replace lubricant (oil) filter and drier.

9. Laboratory analysis of the lubricant should be performed annually during

the first 10 years of chiller life and every 6 months thereafter. Analysis

must address oil moisture content, acidity, and chiller wear as follows:

a. Maximum moisture content of 50 ppm. Higher levels may indicate

air leaks in low-pressure chillers or heat exchanger tube leaks.

b. Maximum acidity of 1 ppm is normal for a new or reclaimed refrigerant.

Higher levels may be caused by oxidation of oil during aging

and/or degradation of refrigerant. If higher levels are found, contact

the chiller manufacturer.

c.Trace amounts of metals could be metal oxides formed from moisture

in the oil or may indicate excess wear conditions. Due to variations

in metals used by different chiller manufacturers, there are no

standard limits. However, if metal content increases from year to

year, one or more of the following excess wear conditions may be

responsible:

Aluminum: impellor or bearing wear

Chromium: wear on rechromed shafts

Copper: corrosion

Iron: corrosion and/or gear wear

Tin: bearing wear

Silicon: leakage of silica gel from dehydrator cartridge or dirt

in system

Zinc: zinc left over from the manufacturing process or loss

of galvanizing from some parts

10. Valve and bearing inspection in accordance with manufacturer’s

recommendation.

11. Relief valves (both refrigerant and water) should be checked annually.

Disconnect the vent piping at the valve outlet and visually inspect the

valve body and mechanism for corrosion, dirt, or leakage. If there are

problems, replace the valve; do not attempt to clean or repair it.

12. Annually, inspect gearbox for wear and repair or replace it as needed.

13. Perform chemical testing of system water at least quarterly. Treat as

needed to ensure proper water chemistry.

Extended (long-term) maintenance checks:

1. Every 5 years (or more frequently as the chiller ages), perform eddy current

(electromagnetic) testing of heat exchanger tubes. [This testing will

typically detect tube pits, cracks, and tube wear (thinning).] If only a

limited number of tubes are found defective, plug tubes. If more than few

are found defective, replace tubes. (Any tube that is replaced as a result

of this testing should be examined and cross-sections should be cut so

that the cause of the defects can be evaluated.)

2. Every 3–5 years, perform vibration test and analysis to evaluate motor

and rotor balance, bearing and gear alignment, and bearing and gear

wear. Use accelerometer-type sensors for gears and bearings (high frequency)

and piezoelectric velocity sensors for compressor motors, rotors,

and bearings (low velocity).

3. Every 5 years, perform an acoustic emission test to identify potential

stress cracks in pressure vessels, tubes, and tube sheets.

4. Other components must be serviced, inspected, and/or replaced at the

intervals recommended by the chiller manufacturer.

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Water Chillers and Maintenance part 3 Chiller data logging form

2015-12-18T23:45:00.000+03:00

Water Chillers and Maintenance

part 3
Chiller data logging form

annual preventative maintenance

Monthly, quarterly, and annual preventative maintenance:

1. Clean evaporator every 2–4 years (annually for chillers serving air

washers or other “open” cooling loads).

2. Quarterly, calibrate pressure, temperature, and flow controls.

FIGURE 7.1 Chiller data logging form.

3. Annually, inspect starter wiring connections, contacts, and action.

Tighten and adjust as required. Perform thermographic survey every 5

years.

4. Annually, test the operation of safety interlocks devices, such as flow

switches, pump starter auxiliary contracts, phase-loss protection, and so

on. Repair or replace as required.

5. Annually, perform dielectric motor testing to identify failures in motor

winding insulation. For large chillers (100 tons or larger), additional

annual motor tests are required to test for imbalance of electrical

resistance

among windings, imbalance of total inductance with phase

inductances, power factor, capacitance imbalance, and running amperage

versus nameplate amperage.

6. Annually, check the tightness of the hot gas valve (as applicable). If the

valve does not provide tight shutoff, replace it.

7. Annually, change the lubricant (oil) filter and the drier.

8. Laboratory analysis of the lubricant should be performed annually

during the first 10 years of chiller life and every 6 months thereafter.

[This oil analysis will define the moisture content (not to exceed

50 ppm), oil acidity (maximum 1 ppm) that may indicate oil oxidation

and/or refrigerant degradation due to high temperatures, and metals

or metal oxides that indicate chiller component wear and/or moisture

in the oil.]

9. Valve and bearing inspection in accordance with manufacturer’s

recommendation.

10. Relief valves (both refrigerant and water) should be checked annually.

Disconnect the vent piping at the valve outlet and visually

inspect the valve body and mechanism for corrosion, dirt, or leakage.

If there are problems, replace the valve; do not attempt to clean or

repair it.

11. Every 6 months, inspect and clean air-cooled condensers as follows:

a. Check unit casing and clear any leaf litter or organic matter in

contact

with the casing. Remove leaves, sticks, and so on, on or in

the unit casing. Check for condition of paint, metal, and so on and

repair as necessary.

b. Check outdoor fans for proper rotation and that the fans do not run

backward when off. Clean and, if needed, balance the fan blades.

c. Lubrication: Typically, fan motors have sealed bearings and require

no lubrication.

d. Inspect condenser coils and clean, if necessary.

12. Perform chemical testing of chilled water at least quarterly. Treat as

needed to ensure proper water chemistry.

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Water Chillers and Maintenance part 2 Electric-Drive Chillers

2015-12-18T23:18:00.001+03:00

Water Chillers and Maintenance

part 2
Electric-Drive Chillers

Water Chillers and Maintenance

Electric-Drive Chillers:

1. Determine that the chiller full load amperes (FLA) is within 5% of design.

2. Test volts, phase-to-phase.

3. Compute voltage imbalance and determine that the maximum variation

between phases is less than 2%.

Absorption Chillers:

1. Determine that the high generator temperature is within the design range.

2. Test high/low generator solution level.

3. Determine that supply steam pressure is within 5% of design.

4. Test automatic overconcentration, dilution cycles, and dilution on

shutdown.

Water-Cooled Chillers:

1. Confirm that the cooling tower has been commissioned (see the section

“Tower Commissioning” in Chapter 15).

2. Determine the entering CDW temperature and confirm that it is within

1°F of setpoint.

3. Determine leaving CDW temperature and compare to design.

4. Determine CDW temperature range and compare to design.

Air-Cooled Chillers:

1. Determine ambient air temperature.

2. Determine chiller head pressure and compare to rated value.

Operations and Control:

1. Confirm that the chiller appears to meet load.

2. Confirm that the chiller operates without alarm conditions or safety

shutdowns.

3. Confirm that the chiller start sequence operates properly.

4. Confirm that multichiller staging sequence operates properly.

CHILLER MAINTENANCE:

When establishing a maintenance program for chillers, maintenance managers

have three options:

1. Implement the program fully in-house.

2. Outsource the entire program.

3. Use a combination of in-house and outsourced functions.

One of the most important benefits of a program that uses in-house personnel

is the institutional knowledge of those systems. Maintenance personnel who have

been working with those chiller systems for years are most likely to know what

many of the existing maintenance problems are.

Another benefit of using in-house personnel is long-term quality. Maintenance

managers and in-house personnel are better able to focus their attention and

efforts on both short- and long-term requirements, up to the expected life of the

equipment. Outsourced programs tend to have a much shorter focus, that is, the

period of the maintenance contract.

However, the cost of establishing a complete in-house program can be very

high. Managers have to arrange for the training of maintenance personnel on the

specifics of maintaining the chiller(s) installed in the facility, provide specialized

training for infrequent testing and servicing, and purchase specialized test

equipment

for many of the inspection and maintenance activities that must be

performed.

Combination of in-house and outsourced programs typically assign the routine

and preventive maintenance tasks to in-house personnel, while contracting is utilized

for specialized activities that require a higher level of expertise than is available

in-house. This approach maintains in-house personnel being actively involved

in the maintenance, while outside experts assist them by performing the more

complex and infrequent tasks. This arrangement helps preserve the institutional

knowledge and typically is the most cost-effective approach.

No matter which maintenance scheme is utilized, a preventative maintenance

program to ensure that the chiller operates reliably over its design life is required.

The majority of chiller operating problems and maintenance needs are discovered

by visual inspection and the monitoring of equipment operating parameters.

Figure 7.1 is a form that can be used to guide chiller visual inspection and to collect

operating data every 2 h during the day. These data will give a complete

“snapshot” of the running conditions of the chiller, and variations in data between

observations can be a prime indicator of operating problems.

Over the long term, these data can be used to predict maintenance requirements.

These data, along with the data collected during periodic checks and routine

maintenance

procedures, can be plotted against time so that a trend or change

in conditions can be identified. A decision on maintenance can then be made from

the trend.

Recommended preventative maintenance procedures for air-cooled electricdrive

water chillers are as follows:

Daily monitoring/visual inspection: The majority of chiller operating problems

and maintenance needs are discovered by visual inspection and

frequent monitoring of equipment operating parameters.

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Water Chillers and Maintenance part 1 Installation Checklist for Absorption Chillers

2015-12-18T23:01:00.000+03:00

Water Chillers

and Maintenance

part 1
Installation Checklist for Absorption Chillers

Installation Checklist for Absorption Chillers

CHILLER COMMISSIONING:

Every chilled water system can be operated on the basis of meeting two goals:

Goal 1: Satisfy imposed cooling loads

• Maintain proper chilled water supply temperature to offset imposed sensible

and latent cooling loads.

• Maintain proper supply water flow in variable flow systems to minimize

pumping energy consumption.

Goal 2: Minimize the cost of cooling

• Maintain chilled water temperature as high as possible, but still low

enough to satisfy both sensible and latent cooling loads.

• Maintain condenser water supply temperature as low as feasible. Most

chillers operate satisfactorily with entering condenser water temperature

as low as 70°F. And, at least one chiller manufacturer rates its machines

for operation with an entering condenser water temperature of 55°F.

• Operate each chiller, to the maximum possible extent, in the 40–80%

load range.

To ensure that this type of operation is attainable, the chilled water system

must be properly installed and placed into service and its operation verified by

test, a process called commissioning.

The first step in this process is to verify that the chiller installation is correct

and in accordance with both the design and the manufacturer’s recommendations.

The design engineer should be retained to review the installation process and

perform a final inspection to ensure compliance with the design requirements.

Before the chiller can be started for the first time, the chilled water pump(s)

must be placed in operation and the chilled water flow “balanced” to within ±5%

of design rates. The basic steps required to place the chilled water pump in service

include the following:

1. Check pump installation, including mountings, vibration isolators, and

connectors,

and piping specialties (valves, strainer, pressure gauges,

thermometers, etc.).

2. Check pump shaft and coupling alignment.

3. Lubricate pump shaft bearings as required by the manufacturer.

4. Lubricate motor shaft bearings as required by the manufacturer.

5. Turn shaft by hand to make sure the pump and motor turn freely.

6. “Bump” the motor on and check for proper rotation direction.

The air-cooled condenser or condenser water system must be placed into operation

(see the section “Tower Commissioning” in Chapter 15). System controls

must be tested and their proper operation must be confirmed. Chillers should be

initially placed into service only by the manufacturer’s service technicians, a process

often called factory start-up.

The following checklist may be used for verifying both chiller installation and

functional performance upon start-up:

General Installation Checklist

1. Test and balance completed (chilled water (CHW) and condenser water

(CDW) flows with –5% to +10% of design).

2. Observe no visible water or oil leaks.

3. Observe no unusual noise or vibration.

4. Chilled water piping insulation in good condition.

5. Pressure gauges, thermometers installed and operable.

6. Confirm that O & M manuals are onsite.

7. Confirm that training was provided for operating staff.

Additional Installation Checklist for Absorption Chillers

1. Confirm that the steam control valve is installed and operating for an
indirect-fired chiller.
2. Confirm that the chiller has been leak tested according to manufacturer’s
instruction.
3. Confirm that unit was evacuated properly before charging with refrigerant
and solution.
4. Confirm that distilled water was used for refrigerant charge and proper
amount of inhibitor added.
5. Confirm that the proper amount of lithium bromide was installed.
6. Confirm that the proper amount of octyl alcohol was installed.
7. Test electrical service to each pump for
8. Test operating amps for each pump.
<
Functional Performance Checklist

1. Confirm that the factory start-up and tests were completed and the chiller
is ready to be placed into service.
2. Determine entering CHW temperature and compare to design.
3. Determine leaving CHW temperature is within 1°F of setpoint.
4. Compute CHW range and compare to design.

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HVAC Water Chillers Chiller Configurations Pump Parallel Configuration parti 1

2015-12-13T01:44:00.003+03:00

HVAC Water Chillers

Chiller Configurations Pump Parallel Configuration

parti 1

Multiple-Pump chiller

One-Pump Parallel Configuration:

The one-pump parallel chiller configuration is shown in Figure 2.3 and the overall system performance and temperature conditions are summarized in Table 2.2.

With this configuration, there is an inherent problem. If both machines were operated for the full-load range (15–100% of peak capacity), by the time the total system load drops to 30% of full load, each individual chiller would be operating very inefficiently. Thus, most designers utilize controls to shut off one chiller

when the total system load, as evidenced by the return chilled water temperature, falls below 40% of full load.

One-pump parallel chiller configuration.

One-pump parallel chiller configuration with isolation valves.

However, with this piping arrangement, if one chiller is not in operation, chilled water from the operating chiller will mix (blend) with the return water passing through the nonoperating chiller, effectively raising the system’s chilled water supply temperature. In many cases, this may not be a problem. But, generally the interior spaces of large buildings still require more or less full cooling even when the perimeter spaces require no cooling at all and an elevated chilled water supply temperature may not satisfy these interior load conditions. In hot, humid climates, an elevated chilled water supply temperature may result in loss of humidity control. To attempt to eliminate the blended supply water problem with the one-pump

configuration, some designers have used chiller flow isolation valves, as shown in Figure 2.4. With this configuration, flow through the nonoperating chiller is closed off when the chiller is not in operation. This arrangement results in increased flow through the operating chiller, but does reduce the blending problem, as illustrated in Table 2.3.

Multiple-Pump Parallel Configuration:

To ensure that the blended water condition does not occur, the multiple-pump parallel chiller configuration shown in Figure 2.5 is widely used.

One-Pump Parallel Configuration

Multiple-pump parallel chiller configuration.

With this configuration, each chiller has an individual chilled water pump. Thus, when one chiller is not operating, one pump is off, flow through the nonoperating chiller is zero, and no blending results.

Table 2.4 summarizes the performance and temperature conditions for this configuration at various load conditions.

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HVAC Water Chillers Chiller Configurations Pump Parallel Configuration parti 2

2015-12-13T01:44:00.001+03:00

HVAC Water Chillers

Chiller Configurations Pump Parallel Configuration

parti 2

Multiple-Pump Parallel

Primary–Secondary Parallel Configuration:

Each of the configurations discussed above is essentially a constant flow system that utilizes three-way control valves at the cooling coils. Constant flow systems circulate the same amount of chilled water, no matter what the imposed cooling load, and, consequently, impose high pumping energy requirements.

To reduce these costs, the primary–secondary variable flow piping arrangement illustrated in Figure 2.6 is very commonly applied. Here, the production loop through the two chillers is hydraulically isolated from the distribution loop by a piping bridge. The bridge is a short section of piping shared by both loops

and designed to have little or no pressure drop. Thus, the flow in one loop is not affected by flow in the other.On the primary or production loop side, the system acts as multiple-pump parallel chiller installation, as described in the section “Multiple-Pump Parallel

Multiple-Pump Parallel Configuration

Primary–secondary parallel chiller configuration.

Configuration.” Flow in this loop varies in “steps” as the chillers are staged on or off and their respective pumps are started and stopped. However, in the secondary or distribution loop, the cooling coils utilize two-way control valves and the distribution pump(s) utilize a variable frequency drive(s) so that the

chilled water flow rate is modulated from 0% to 100% of peak design flow as a function of the imposed cooling load. Thus, this loop has fully variable flow, but maintains a constant temperature range. At any load condition, the supply water temperature is the same as the water temperature leaving the chiller(s),as long as the production loop flow rate equals or exceeds the distribution loop flow rate. Table 2.5 summarizes the performance and temperature conditions for this configuration at various load conditions.

Primary–Secondary Configuration Flows and Temperatures

Variable flow primary parallel chiller configuration

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HVAC Water Chillers Chiller Configurations CHILLER SYSTEM

2015-12-13T00:13:00.002+03:00

HVAC Water Chillers

Chiller Configurations CHILLER SYSTEM

MULTI CHILLER SYSTEMS

THE SINGLE-CHILLER SYSTEM:

The basic chilled water piping configuration for a single chiller is shown in Figure 2.1. Here, a single chiller provides chilled water to the cooling coils utilizing a single chilled water pump.

For small systems, this configuration has the advantage of lower initial cost, but does have some basic disadvantages:

1. With the single-compressor system, failure of any component (compressor, pump, or condenser) will result in no cooling being available. For most facilities, this is unacceptable and the use of multiple chillers allows at least some cooling (50% or more) be provided even if one chiller fails. In cases where cooling is critical to the facility (computer centers, hospital, laboratories, pharmaceutical or textile manufacturing, etc.), multiple chillers with at least one redundant chiller are often used. In this case, even if one chiller fails, 100% of the design cooling load can still be met.

2. As discussed in Chapter 1, once the cooling load imposed on a rotary compressor chiller falls to below about 30% of the chiller capacity, theefficiency of the chiller begins to decline. Thus, the use of multiple chillers allows a better overall capacity-to-load ratio and improved operating efficiency.

MULTI CHILLER SYSTEMS:

For multiple chiller systems, there are two basic configurations that can be utilized,series or parallel flow.

In a series configuration with two chillers, as shown in Figure 2.2, each chiller is selected to produce half of the required cooling at the full system flow rate.Thus, half of the total design range is produced by each chiller. Load ratios other than 50/50 are possible, but this is by far the most common condition because of

control problems with chillers at very small temperature differences.

Table 2.1 summarizes the temperatures at various load conditions for the configuration shown in Figure 2.2.

Series chiller systems are rarely utilized in present times because this configuration requires a constant chilled water flow rate at all times, resulting in high pumping costs. But, if a relatively large temperature difference is required or if there is a very steady base cooling load, the series configuration may offer some advantages.

Constant flow, single chiller configuration.

The parallel chiller configuration is far more common. In a two-chiller configuration, each chiller is typically selected to operate with the same design range, but with only a half of the total system flow requirement. This again results in a 50/50 load split, but other load ratios may be selected if dictated by operational requirements. And, there is no real limitation on the number of parallel chillers that can be utilized in one system.

Series chiller configuration.

Series Configuration Temperatures

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ABSORPTION CHILLERS Determining the Chilled Water Supply Temperature

2015-12-12T23:36:00.000+03:00

ABSORPTION CHILLERS

Determining the Chilled Water Supply Temperature

Determining the Chilled Water Supply Temperature

Determining the Chilled Water Supply Temperature:

The first step in designing or evaluating a chilled water system is to determine the required chilled water supply temperature.

For any HVAC system to provide satisfactory control of both space temperature and space humidity, the supply air temperature must be low enough to simultaneously satisfy both the sensible and latent cooling loads imposed in that space. Sensible cooling is the term used to describe the process of decreasing the

temperature of air without changing the moisture content of the air. However, if moisture is added to the room by the occupants, infiltrated outdoor air, internal

processes, and so on, the supply air must be cooled below its dew point to remove this excess moisture by condensation. The amount of heat removed with the

change in moisture content is called latent cooling. The sum of the two represents the total cooling load imposed by a building space on the chilled water cooling coil.

The required temperature of the supply air is dictated by two factors:

1. The desired space temperature and humidity setpoint

2. The sensible heat ratio (SHR) defined by dividing the sensible cooling

load by the total cooling load On a psychrometric chart, the desired space conditions represent one endpoint of a line connecting the cooling coil supply air conditions and the space conditions.

The slope of this line is defined by the SHR. An SHR of 1.0 indicates that the line has no slope since there is no latent cooling. The typical SHR in comfort HVAC applications will range from about 0.85 in spaces with a large number of people to ~0.95 for the typical office.

The intersection between this “room” line and the saturation line on the psychrometricchart represents the required apparatus dew point (ADP) temperature for the cooling coil. However, since no cooling coil is 100% efficient, the air leaving the coil will not be at a saturated condition, but will have a discharge dry

bulb temperature of about 1–2°F above the ADP temperature.

While coil efficiencies as high as 98% can be obtained, the economical approach is to select a coil for about 95% efficiency, which typically results in the supply air wet bulb temperature being about 1°F lower than the supply air dry bulb temperature.

Based on these typical coil conditions, the required supply air temperature can be determined by plotting the room conditions point and a line having a slope equal to the SHR passing through the room point, determining the ADP temperatureintersection point, and then selecting a supply air condition on this line based on a 95% coil efficiency. Table 1.6 summarizes the results of this analysis for

several different typical HVAC room design conditions and SHRs. For a chilled water cooling coil, approach is defined as the temperature difference between the entering chilled water and the leaving (supply) air. While this approach can range as low as 3°F to as high as 10°F, a cost-effective value for HVAC applications is ~7°F. Therefore, to define the required chilled water supply temperature, it is only necessary to subtract 7°F from the supply air dry bulb temperature determined from Table 1.6.

Refrigeration Machines:

Typical Supply Air Temperature

Establishing the Temperature Range:

Once the required chilled water supply temperature is determined, the desired temperature range must be established. The required chilled water flow rate is dictated by the imposed cooling load and the selected temperature range. The larger the range, the lower the flow rate and, thus, the less energy consumed for transport of chilled water through the system. However, if the range is too large, chilled water coils and other heat exchangers in the system require increased heat transfer surface and, in some cases, the ability to satisfy latent cooling loads is reduced.

Historically, a 10°F range has been used for chilled water systems, resulting in a required flow rate of 2.4 gpm/ton of imposed cooling load. For smaller systems with relatively short piping runs, this range and flow rate is acceptable. However,

as systems get larger and piping runs get longer, the use of higher ranges will reduce pumping energy requirements. Also, lower flow rates can also result in economies in piping installation costs since smaller-sized piping may be used. At a 12°F range, the flow rate is reduced to 2.0 gpm/ton and, at a 14°F range,

to 1.7 gpm/ton. For very large campus systems, a range as large as 16°F (1.5 gpm/ ton) may be used (though low flow rates may introduce problems in selecting cooling coils).

kandi younes

ABSORPTION CHILLERS Lithium Bromide Absorption Chillers

2015-11-20T02:28:00.001+03:00

ABSORPTION CHILLERS
Lithium Bromide Absorption Chillers

Lithium Bromide Absorption Chillers

ABSORPTION CHILLERS:
Lithium Bromide Absorption Chillers:
The vast majority of water chiller systems utilized for HVAC applications in the
United States are vapor compression cycle systems. However, in some applications,
principally in large cities and at large universities and hospital complexes,
steam distribution systems are available. In the past years, the cost of steam was
often cheaper than the cost of electricity and was used to provide cooling, utilizing
the absorption refrigeration cycle. This is generally no longer the case and
little or no new absorption cooling is utilized except where a waste heat source is
available, such as with cogeneration or some industrial processes, or where the
use of absorption cooling during peak cooling load periods may allow a reduction
in seasonal electric demand charges (see the section “System Peak Cooling Load
and Load Profile” in Chapter 2).

Absorption chillers using lithium bromide are defined as indirect-fired or
direct-fired and may be single stage or two stage, as follows:

1. The indirect-fired single-stage machine uses low- to medium-pressure
steam (5–40 psig) to provide the heat for the absorption process. This
type of chiller requires ~18,500 Btu/h per ton of cooling effect, resulting
in a chiller COP of about 0.67.
2. The indirect-fired two-stage chiller utilizes high-pressure steam (at least
100 psig) or high-temperature hot water (400°F or higher) and requires
~12,000 Btu/h per ton of cooling effect, resulting in a chiller COP of 1.0.
3. The direct-fired chiller, as its name implies, does not use steam but utilizes
a natural gas and/or fuel oil burner system to provide heat. These chillers
are two-stage machines resulting overall COP of 1.0–1.1.
For the indirect-fired units, the overall COP must be reduced to account for the
losses in the steam production in the boilers. With a typical boiler firing efficiency
of 80–85%, this reduces the overall COP for the single-stage system to ~0.54 and
to ~0.80 for the two-stage system.
As absorption cooling has a COP of only 0.54–1.1, it competes poorly with
electric-drive rotary compressor chillers, as shown in Table 1.5. (A two-stage,
direct-fired absorption chiller will cost ~$0.107/ton-hour of cooling to operate,
almost twice the cost of an equivalent electric-drive chiller.)
Other factors that must be considered for absorption chillers include the
following:

1. Absorption chillers require ~50% more floor area than the equivalent
electric-drive (vapor compression cycle) chiller. Additionally, due to their height, mechanical equipment rooms must be 6–10 ft taller than the
rooms housing electric-drive chillers. Finally, because the liquid solution
is contained in long, shallow trays within an absorption chiller, the
floor must be closer to an absolute level.
2. Absorption chillers will weigh at least twice as much the equivalent
electric-drive chiller.
3. Due to their size, absorption chillers are sometimes shipped in several
sections, requiring field welding for final assembly.
4. While most electric chillers are shipped from the factory with their
refrigerant charge installed, the refrigerant and absorbent (including
additives) must be field installed in absorption chillers.
5. While noise and vibration are real concerns for electric-drive chillers
(see the section “Noise and Vibration” in Chapter 6), absorption chillers
(unless direct-fired) are quiet and essentially vibration free.
6. Due to the potential for crystallization of the lithium bromide in the
chiller if it becomes too cool, the condenser water temperature must be
kept above 75–80°F.
7. An emergency power source may be required if lengthy power outages
are common. Without power and heat input, the chiller begins to
cool and the lithium bromide solution may crystallize. However,
because an absorption chiller has a very small electrical load requirement
(usually less than 10 kW), a dedicated backup generator is not a
major element.

8. The heat rejection rate from the condenser is 20–50% greater than for
the equivalent electric-drive chiller, requiring higher condenser water
flow rates and larger cooling towers and condenser water pumps.
9. Finally, an indirect-fired absorption chiller will be at least 50% more
expensive to purchase than the equivalent electric-drive chiller. Directfired
absorption chillers will cost almost twice as much as an electric
machine, and have the added costs associated with providing combustion
air and venting (stack).

Direct-fired absorption cycle chillers should be carefully evaluated as an alterative
anytime an engine-drive vapor compression cycle chiller is being considered.
Even though the energy costs for the absorption chiller may be higher, the
increased maintenance costs associated with engine-drive systems may make the
absorption chiller more cost effective.

Ammonia Absorption Chillers:

Small-capacity (3–5 tons) ammonia absorption chillers and heat pumps are
marketed
for commercial and industrial applications. These units are direct-fired
(typically natural gas) air-cooled chillers and generally have a COP of
about 0.5.

CHILLED WATER FOR HVAC APPLICATIONS:

<
Typical applications for chilled water systems include large buildings (offices,
laboratories, hospitals, universities, etc.) or any multibuilding campuses where it
is desirable to provide cooling from a central facility.
As shown in Figure 1.8, the typical water-cooled HVAC system has three heat
transfer loops:
Loop 1. Cold air is distributed by one or more air-handling units to the
spaces within the building. Sensible heat gains, including heat from
temperature-driven transmission through the building envelope; direct
solar radiation through windows; infiltration; and internal heat from
people, lights, and equipment, are “absorbed” by the cold air, raising its
temperature. Latent heat gains, moisture added to the space by air infiltration,
people, and equipment are also absorbed by the cold air, raising
its specific humidity. The resulting space temperature and humidity
condition is an exact balance between the sensible and latent heat
gains and capability of the entering cold air to absorb those heat gains.
The distributed air is returned to the air handling unit, mixed with the
required quantity of outdoor air for ventilation, and then directed over
the cooling coil where chilled water is used to extract heat from the air,
reducing both its temperature and moisture content so that it can be distributed
once again to the space.
As the chilled water passes through the cooling coil in counterflow to
the air, the heat extraction process results in increased water temperature.
The chilled water temperature leaving the cooling coil (chilled
water return) will be 8–16°F warmer than the entering water temperature
(chilled water supply) at design load. This temperature difference (range)
establishes the flow requirement via the following relationship:

where
Fchw = chilled water flow rate (gpm)
Q = total cooling system load (Btu/h)
Range = chilled water temperature rise (°F)
500 = conversion factor (Btu min/gal °F h) (1 Btu/lb °F × 8.34 lb/
gal × 60 min/h)

Loop 2. The warmer-returned chilled water enters the water chiller where it
is cooled to the desired chilled water supply temperature by transferring
the heat extracted from the building spaces to a primary refrigerant. This
process, obviously, is not “free” since the compressor must do work on
the refrigerant for cooling to occur and, thus, must consume energy in
the process. Since most chillers are refrigerant-cooled, the compressor

Water-cooled HVAC system schematic.

energy, in the form of heat, is added to the building heat and both must
be rejected through the condenser.
Loop 3. The amount of heat that is added by the compressor depends on the
efficiency of the compressor. This heat of compression must then be
added to the heat load on the chilled water loop to establish the amount
of heat that must be rejected by the condenser to a heat sink, typically the
outdoor air

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Water Chillers: HVAC Water Chillers and Cooling Towers Electric-Drive Chillers

2015-11-20T01:22:00.001+03:00

Water Chillers:

HVAC Water Chillers and Cooling Towers

Electric-Drive Chillers

Electric-Drive Chillers

Electric-Drive Chillers:

Electric-drive chillers may be configured as hermetic or open-drive machines. With
open-drive chillers, the compressor and motor are separated, with their shafts being
connected via a flexible coupling. The advantage of this concept is that in the event
of motor failure, it does not contaminate the refrigerant and the motor can be readily
replaced. The disadvantage is that the chiller motor is cooled by ambient air and
these large motors may impose a high heat gain in the mechanical equipment room.
The alternative, and by far more popular design, contains both the motor and
the compressor within a common, sealed enclosure. In this configuration, the
compressor is rigidly connected directly to the motor shaft, eliminating the need
for a flexible coupling. The motor is cooled by the refrigerant flow and thus
imposes no heat gains that must be separately addressed. The only disadvantage
is that in the event of motor failure, the refrigerant system is often contaminated,
requiring a difficult and expensive cleaning in addition to replacing the motor.
The energy consumption by a rotary compressor chiller decreases as the
imposed cooling load is reduced, as shown in Figure 1.7. These chillers operate
efficiently at between ~30% and 100% load and most efficiently between 40% and
80% load. Within this capacity range, the refrigerant gas flow rate is reduced, yet
the full heat exchange surface of the cooler and the condenser is still available,
resulting in higher heat transfer efficiency.
Below about 30% load, the refrigerant gas flow rate is reduced to the point
where heat pickup from the motor and mechanical inefficiencies have stabilized
input energy requirements.

Typical rotary compressor part load performance.

The vast majority of electric-drive rotary compressor water chillers utilize
a single compressor. However, if the imposed cooling load profile indicates that
there will be significant chiller usage at or below 30% of peak load, it may be
advantageous to use a dual-compressor chiller or multiple single-compressor
chillers.
The dual-compressor chiller typically uses two compressors, each sized for
50% of the peak load. At 50–100% of design load, both compressors operate. But,
if the imposed load drops below 50% of the design value, one compressor is
stopped and the remaining compressor is used to satisfy the imposed load. This
configuration has the advantage of reducing the inefficient operating point to 15%
of full load (50% of 30%), reducing significantly the operating energy penalties
that would result from a single-compressor operation.
Negative-pressure chillers are typically somewhat more efficient than positivepressure
chillers. A peak load rating of 0.5 kW/ton or less is available for
negative-
pressure chillers, while positive-pressure chiller ratings below 0.55 kW/
ton are difficult to obtain.
Positive-pressure chillers tend to be smaller and lighter than negative-pressure
chillers, which can result in smaller chiller rooms and lighter structures. Negativepressure
chillers generally have a higher first cost than positive-pressure
machines.
Driven by the evermore stringent requirements of each new edition of
ASHRAE Standard 90.1, manufacturers are constantly trying to improve the
efficiency of electric-drive rotary compressor water chillers. In the past few
years, a magnetic bearing compressor has been offered that reduces compressor/
motor friction losses, thus reducing power input requirements, by eliminating
bearings. In this design, a magnetic field holds the compressor/motor shaft
in alignment.

This technology was developed by Daiken Corporation of Japan and this
manufacturer
is currently the sole supplier of magnetic bearing motors that are
used with centrifugal compressors. Daiken (and Donfoss, under license) sells the
magnetic centrifugal compressor/motor for retrofit applications in the range of
70–270 tons.
McQuay/Daiken and JCI/York offer water chillers using magnetic bearing
compressors. McQuay offers a dual-compressor machine in the capacities of
140–
550 tons, while JCI/York offers their dual-compressor chiller in the range of
210–400 tons.
Packaged electric-drive chiller “modules” are available from several manufacturers
(Multistack, Tandem, etc.) in 20-, 30-, 50-, and 70-ton packages, each with
dual independent scroll compressors utilizing R-410A. Each chiller module is
designed to be mix–matched to form water-cooled chillers featured by a total
capacity of 20 to 600 tons.
Each chiller module is constructed with compressors, an evaporator, a condenser,
and a control cabinet mounted on a common frame with a very small
footprint, typically about 28″ wide and 48″ deep, allowing each module to pass
through a normal 30″ doorway for installation. Chilled water and condenser water
piping headers are included with quick-connect couplings for piping modules

together. Modules are wired to provide for single-point electrical connection to
serve each chiller configured from multiple modules.
The advantages of modular chillers over more typical factory-fabricated chillers
are flexibility, especially in retrofit installations where space and accessibility
are
limited, and ease of future expansion. Their disadvantages include higher maintenance
cost and lower energy efficiency (0.65 kW/ton or higher).

Engine-Drive Chillers:

>
In an open-drive configuration, natural gas- and propane-fueled spark ignition
engines have been applied to rotary compressor systems. The full-load cooling
COPs for engine-drive chillers are ~1.3–1.9 for helical screw compressors and 1.9
for centrifugal compressors. These low COPs can be improved if the engine water
jacket heat and exhaust heat can be recovered to heat service hot water or for other
uses.
Engine-drive chillers have been around for many years, but their application,
most typically utilizing natural gas for fuel, has been limited by a number of
factors:
1. Higher first cost
2. Air quality regulations
3. Much higher maintenance requirements
4. Short engine life
5. Noise
6. Larger physical size
7. Lack of integration between engine and refrigeration subsystems

Since the mid-1980s, manufacturers have worked very hard to reduce these
negatives with more compact designs, emissions control systems, noise abatement
measures, basic engine improvements, and development of overall systems controls
using microprocessors.
However, the maintenance requirements for engine-drive chillers remain
high, adding about $0.03–$0.04/ton-hour to the chiller operating cost.
Currently, the engines used for chillers are either spark ignition engines based
on automotive blocks, heads, and moving components (below about 400 tons
capacity) or spark ignition engines using diesel blocks and moving components
(for larger chillers). While the automotive-derivative engines are advertised
to have a 20,000 h useful life, the real life may be much shorter, requiring an
engine replacement every 2 years or so. The diesel-derivative engines require an
overhaul every 10–12,000 h (equivalent to a diesel truck traveling 500,000 miles
at 50 mph).
Newer engines use lean burn technology to improve combustion and reduce
CO and NOx emissions. By adding catalytic converters to the exhaust and additional
emissions controls, natural gas-fired engine-drive chillers can meet stringent
California air quality regulations.

Gas engine-drive chillers remain more expensive than electric-drive units, and
including maintenance costs, have higher overall operating costs (see Table 1.5).
However, engine-drive chillers may be used during peak cooling load periods to
reduce seasonal peak electrical demand charges (see the section “System Peak
Cooling Load and Load Profile” in Chapter 2).

Condensing Medium:

>
The heat collected by the water chiller, along with the excess compressor heat,
must be rejected to a heat sink. Directly or indirectly, ambient atmospheric air is
typically used as this heat sink.
For air-cooled chillers, the condenser consists of a refrigerant-to-air coil and
one or more fans to circulate outdoor air over the coil. The performance of the
condenser is dependent on the airflow rate and the air’s dry bulb temperature.
Air-cooled condenser airflow rates range from 600 to 1200 cfm/ton with a
10–30°F approach between the ambient dry bulb temperature and the refrigerant
condensing temperature. For typical HVAC applications, the condensing temperature
is about 105–120°F. Thus, the ambient air temperature must be no greater
than 95°F with a loss of efficiency. As the ambient air temperature increases, the
condensing temperature increases and net cooling capacity decreases by about
2% for each 5°F increase in condensing temperature.
Water-cooled chillers typically use a cooling tower (or some large water source
like a river, lake, or ocean) to reject condenser heat to the atmosphere and Chapters
9 through 17 of this book address this topic in detail. At the chiller, with 85°F (or
lower) condenser water temperature supplied from the cooling tower, condensing
temperatures are reduced to 94–98°F, reducing the “lift” required of the compressor
and significantly improving the chiller COP when compared with air-cooled
machines.

Chiller Efficiency and Estimated Energy Cost

Table 1.5 illustrates the relative efficiency and operating cost for the various
types of chillers with both air- and water-cooled condensing.

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Water Chillers: Fundamentals Application, and Operation VAPOR COMPRESSION CYCLE WATER CHILLERS

2015-11-20T01:05:00.004+03:00

Water Chillers: Fundamentals
Application, and Operation
VAPOR COMPRESSION CYCLE WATER CHILLERS

VAPOR COMPRESSION CYCLE WATER CHILLERS

VAPOR COMPRESSION CYCLE WATER CHILLERS:

As introduced in the section “Vapor Compression Refrigeration,” a secondary
refrigerant is a substance that does not change phase as it absorbs heat. The most
common secondary refrigerant is water and chilled water is used extensively in
larger commercial,
institutional, and industrial facilities to make cooling available
over a large area without introducing a plethora of individual compressor
systems. Chilled water has the advantage that fully modulating control can be
applied and, thus, closer temperature tolerances can be maintained under almost
any load condition.
For very low-temperature applications, such as ice rinks, an antifreeze component,
most often ethylene glycol or propylene glycol, is mixed with the water and
the term brine (left over from the days when salt was used as antifreeze) is used
to describe the secondary refrigerant.
In the HVAC industry, a chiller using the vapor compression cycle consists of
one or more compressor(s), evaporator(s), and condenser(s), all packaged as a
single unit. Where multiple compressors are used, it is typical to provide multiple,
separate refrigeration circuits so that the failure of one compressor will not impact
on the operation of the remaining compressors. The condensing medium may be
water or outdoor air.
The evaporator, often called the cooler, consists of a shell-and-tube heat
exchanger with refrigerant in the shell and water in the tubes. Coolers are designed
for 3–11 fps water velocities when the chilled water flow rate is selected for a
range of 10–20°F.
For air-cooled chillers, the condenser consists of an air-to-refrigerant heat
exchanger and fans to provide the proper flow rate of outdoor air to transfer the
heat rejected by the refrigerant.
For water-cooled chillers, the condenser is a second shell-and-tube heat
exchanger with refrigerant in the shell and condenser water in the tubes.
Condenser water is typically supplied at 70–85°F and the flow rate is selected for

a range of 10–15°F. A cooling tower is typically utilized to provide condenser
water cooling,
but other cool water sources, such as wells, ponds, and so on, can
also be used.

Scr oll Compressors:

Scroll compressors are positive-displacement orbital motion compressors that use
two spiral-shaped scroll members, one that is fixed and the other that rotates, to
compress refrigerant gas.
Scroll members are typically a geometrically identical pair, assembled 180°
out of phase. Each scroll member is open on one end and bound by a base plate on

the other. The two are fitted to form pockets between their respective base plates
and various lines of contact between their walls. The flanks of the scrolls remain
in contact, but the contact point moves progressively inward, compressing the
refrigerant gas, as one scroll moves. Compression occurs by sealing gas in pockets
of a given volume at the other periphery of the scrolls and progressively reducing
the size of the pockets as the scroll relative motion moves them inward toward
the discharge port.
Two different capacity control mechanisms are available. The most common
approach to capacity control is variable-speed control, utilizing a variable
frequency
drive to control the rotational speed of the moving scroll. The cooling
capacity, then, varies directly as a function of its speed. Another control
method is called variable displacement, which incorporates “porting” holes in
the fixed scroll. Capacity control is provided by disconnecting or connecting
compression chambers on the suction side by closing or opening these porting
holes.
Scroll compressors are available in capacities from 1.5 tons to about 40 tons
and are applied in both single and multiple compressor configurations. The maximum
chiller size typically applied is 80–160 tons, using a multiple compressor
and usually with air-cooled condensing.

Rotary Scr ew and Centrifugal Compressors:

For larger chillers (150 tons to over 10,000 tons), rotary compressor water chillers
are utilized. There are two types of rotary compressors applied: positive-displacement
rotary screw compressors and centrifugal compressors.
Figure 1.5 illustrates the rotary screw compressor operation. Screw compressors
utilize double-mating helically grooved rotors with “male” lobes and “female”
flutes or gullies within a stationary housing. Compression is obtained by direct
volume reduction through rotary motion. As the rotors begin to unmesh, a void is
created on both the male and the female sides, allowing refrigerant gas to flow into
the compressor. Further rotation starts the meshing of another male lobe with a
female flute, reducing the occupied volume, and compressing the trapped gas. At a
point determined by the design volume ratio, the discharge port is uncovered
and
the gas is released to the condenser.
Capacity control of screw compressors is typically accomplished by opening
and closing a slide valve on the compressor suction to throttle the flow rate of
refrigerant gas into the compressor. Variable-speed control can also be used to
control the compressor capacity.

The design of a centrifugal compressor for refrigeration duty originated with
Dr. Willis Carrier just after World War I. The centrifugal compressor raises the
pressure of the gas by increasing its kinetic energy. This kinetic energy is then
converted into static pressure when the refrigerant gas leaves the compressor and
expands into the condenser. Figure 1.6 illustrates a typical centrifugal water
chiller configuration. The compressor and motor are sealed within a single casing
and a refrigerant gas is utilized to cool the motor windings during operation.

Cutaway of a typical centrifugal water chiller.

Low-
pressure gas flows from the cooler to the compressor. The gas flow rate is
controlled by a set of preswirl inlet vanes and/or a variable frequency speed
controller
that regulates the refrigerant gas flow rate to the compressor in response
to the cooling load imposed on the chiller.
Normally, the output of the chiller is fully variable within the range 15–100%
of full-load capacity. The high-pressure gas is released into the condenser, where
water absorbs the heat and the gas changes phase to liquid. The liquid, in turn,
flows into the cooler, where it is evaporated, thus cooling the chilled water.
Centrifugal compressor chillers using R-134a are referred to as positive-pressure
machines, while those using R-123 are considered to be negative-pressure
machines, as defined by the evaporator pressure condition. At standard
Air-
Conditioning and Refrigeration Institute (ARI) rating conditions and using
R-134a, the evaporator pressure is 36.6 psig and the condenser pressure is
118.3 psig, yielding a total pressure
increase or lift provided by the compressor of
81.7 psig. However, for R-123, these pressure conditions are −5.81 psig in the
evaporator and 6.10 psig in the condenser, yielding a total lift of 11.91 psig.
Mass flow rates for refrigerants in both positive- and negative-pressure chillers
are essentially the same at ~3 lb/min ton. However, due to the significantly higher
density of R-134a, its volumetric flow rate (cfm/ton), which defines impeller size,
is over five times smaller than R-123 volumetric flow rate.

\Rotary screw compressor operation.

Early compressors using R-123 typically used large-diameter impellers (~40″
diameter) and direct-coupled motors that (at 60 Hz) turn at 3600 rpm. These large
wheel diameters required by R-123 put a design constraint on the compressor and,
to reduce the diameter, current designs typically utilize two or three impellers in
series or stages to produce an equivalent pressure increase. In practice, the flow
paths from the outlet of one stage to the inlet of the next introduce pressure losses
that reduce efficiency to some degree.
Compressors using R-134a typically use much smaller impellers (about 5″
diameter) that are coupled to the motor through a gearbox or speed increaser and
can operate at speeds approaching 30,000 rpm.
Since the evaporator in positive-pressure chillers is maintained at a pressure
well above atmospheric, any leaks in the refrigeration system will result in a loss
of refrigerant and the effect of any leaks is quickly evidenced by low refrigerant
levels in the chiller. However, any leaks associated with a negative-pressure
machine result in the introduction of atmospheric air (composed of noncondensable
gases and water vapor) into the chiller.

Noncondensable gases create two problems:

1. The compressor does work when compressing the noncondensable
gases, but they offer no refrigerating effect.
2. Noncondensable gases can “blanket” evaporator and condenser tubes,
lowering heat exchanger effectiveness.
Noncondensable gases can lower the efficiency of the chiller by as much as
14% at full load.
Moisture introduced with atmospheric air is a contaminant that can allow the
formation of acids within the chiller that can cause serious damage to motor
windings (of hermetic motors) and bearings.
To remove potential noncondensable gases and moisture from negative-pressure
chillers, these chillers are furnished with purge units. While purge units
are very efficient at separating and venting noncondensable gases and moisture
from the refrigerant, it is not 100% efficient and some refrigerant is vented to the
atmosphere each time the purge unit operates. Additionally, to reduce the potential
for leaks when chillers are off, the evaporator should be provided with an
external heater to raise the refrigerant pressure to above atmospheric.
The energy requirement for a water-cooled rotary compressor chiller at peak
load is a function of (1) the required leaving chilled water temperature, and (2) the
temperature of the available condenser water. As the leaving chilled water temperature
is reduced, the energy requirement to the compressor increases, as summarized
in Table 1.4. Similarly, as the condenser water temperature increases, the
compressor requires more energy (see Chapter 10). Thus, the designer and owner
can minimize the cooling energy input by utilizing a rotary compressor chiller


Rotary Chiller Input Power Change as a Function of Chilled Water Supply Temperature

kandi younes

Section A Water Chillers: Fundamentals Application, and Operation PART 2 C hiller Fundamentals

2015-11-20T00:39:00.000+03:00

Section A

Water Chillers: Fundamentals
Application, and Operation
PART 2

C hiller Fundamentals

Water Chillers

Refrigeration Machines:

However, a new class of refrigerants called hydrofluoro olefins (HFOs) is now
becoming available. The first of these refrigerants is Dupont’s R-1234yf, designed
to be a direct replacement for R-134a. While all research to date has focused on
applying R-1234yf to automobile compressors, Dupont anticipates that this refrigerant,
or blends of this refrigerant with R-744 (carbon dioxide), can reduce GWP
by 50% over R-134a. Already, retrofits of existing R-134a compressors with
R-1234yf have been implemented and the results are promising, with no oil problems
or capacity loss and even small efficiency improvements.
ASHRAE Standard 34-2010 classifies refrigerants according to their toxicity
(A = nontoxic and B = evidence of toxicity identified) and flammability (1 = no
flame propagation, 2 = low flammability, and 3 = high flammability). Thus, all
refrigerants fall within one of the “safety groups,” A1, A2, A2L, A3, B1, B2, B2L,
or B3. The “L” designation indicates that a refrigerant has lower flammability
than the range established for the “2” rating, but is not a “1.”
Table 1.3 lists the safety group classifications for common refrigerants.

Implementation of HCFC Refrigerant Phaseout in the United States

ABSORPTION REFRIGERATION:

>
Absorption Refrigeration Cycle:

The absorption refrigeration cycle is a relatively old technology. The concept
dates back to the late 1700s and the first absorption refrigeration machine was
built in the 1850s. However, by World War I, the technology and use of reciprocating
compressors had advanced to the point where interest in and development of


HVAC Refrigerant Safety Groups

absorption cooling essentially stagnated until the 1950s. During this period, the
two-stage, indirect-fired absorption refrigeration machine was developed in the
United States, while the direct-fired, two-stage concept was perfected in Japan
and other Pacific-rim countries. The direct-fired option was developed primarily
in response to government energy policies around the Pacific rim.
The fundamental “single-stage” absorption cycle is represented in Figure 1.4.
The absorption chiller has no compressor; heat, directly or indirectly, provides
the motive force for refrigerant phase change. The evaporator consists of a heat
exchanger, held at low pressure, with a separate refrigerant (typically, water)
pump. The pump sprays the refrigerant over the tubes containing the chilled
water, absorbs heat from the water, and evaporates as a low-pressure gas. The lowpressure
gas flows to the absorber, due to the pressure differential. The absorber
is at a pressure lower than the evaporator because the concentrated absorbent
solution exerts a molecular attraction for the refrigerant. The absorbent solution is
sprayed into contact with the refrigerant vapor. Condensing of the refrigerant

Refrigeration Machines:

Single-stage steam absorption chiller schematic.

occurs because the heat is absorbed by the absorbent. The absorbent, then, is
cooled by condenser water.
The absorbent now consists of a dilute solution, due to its having absorbed
water vapor refrigerant. The dilute solution is pumped to the concentrator, where
heat is applied to reevaporate the refrigerant. The concentrated solution of the
absorbent is then returned to the absorber. The refrigerant vapor goes to the condenser,
where it is condensed by the condenser water. To improve efficiency, a
heat exchanger is used to preheat the dilute solution, with the heat contained in the
concentrated solution of the absorbent.
Leaks allow air to enter the refrigerant system, introducing noncondensable
gases. These gases must be removed, or purged, to prevent pressure in the absorber
increasing to the point where refrigerant flow from the evaporator will stop. The
solution in the bottom of the absorber is relatively quiet and these gases tend to get
collected at this point. They can be removed through the use of a vacuum pump,
typically called a purge pump.

Refrigerants:

>
Today, there are two basic refrigerants used in absorption refrigeration chillers:
water/lithium bromide and water/ammonia. Larger absorption units utilize water/
lithium bromide solutions, while small units more commonly utilize water/
ammonia solutions.
Lithium bromide is a corrosive, inorganic compound that has a very high
absorption rate for water (hydroscopic). Thus, it makes an ideal “carrier” for the
water refrigerant in absorption cycle chillers. However, the corrosion issues make
lithium bromide solutions, especially at the higher temperatures associated with
direct-fired chillers, which are difficult to address.

Since the water/lithium bromide solution in an absorption chiller is a corrosive
salt solution, the primary potential for corrosion in these chillers is the
ferrous
metals
used in them. The generator (or “concentrator”) is the most critical
location for potential ferrous corrosion since the highest salt concentration
and highest temperatures
are present in this heat exchanger, along with the
potential impact of erosion corrosion as the refrigerant vapor is driven off by
surface boiling.
Basic ferrous corrosion occurs when iron reacts with water to produce an iron
oxide called magnetite and hydrogen. Under acidic conditions, this reaction is
greatly accelerated. Also, in an absorption chiller, hydrogen is a “noncondensable”
gas, that is, it does not act as a refrigerant, and the performance of the chiller
is negatively impacted on.
There are basically two approaches to corrosion protection: (1) choose a metal
compatible with the chemical environment in which it has to survive, or (2) modify
the chemical environment so that it is less corrosive to carbon steel. The first
approach, which requires the use of high-quality stainless steel for heat exchanger
components, can add significantly to the cost of an absorption chiller and most
manufacturers and owners have been unwilling to pay the premium involved.
Since chemical modification is much cheaper, this is the approach most commonly
taken by chiller manufacturers.
Two types of chemical modifications are generally made:

1. To reduce the acidity of the water/lithium bromide solution, a compatible
alkaline, lithium hydroxide, is added. To reduce ferrous corrosion, it is
desirable to maintain the solution as alkaline. But, since copper corrodes
readily at higher alkaline levels, it is necessary to maintain the level high
enough to help protect the steel, without being too high and accelerating
copper corrosion.
2. To additionally protect the steel in a corrosive environment, a compatible
corrosion inhibitor is added. In this case, this inhibitor is lithium
chromate. Lithium chromate “passivates” the iron with which it comes
into contact (i.e., makes it less reactive) by forming a protective molecular
film on the surface. Lithium chromate has the advantage of working
well at low-alkalinity levels, allowing the solution to be maintained at
levels more suitable to the copper in the chiller.
This chemistry balance is complex and requires routine adjustments to maintain
correctly. If the alkalinity is not adjusted properly, the solution will become
acidic and accelerate ferrous metal corrosion. If alkalinity is too high, the copper
in the chiller will corrode. If the lithium chromate level is too low, it offers poor
protection to the ferrous metals in the chiller. But, if the level is too high, it can
initiate pitting in the ferrous metals due to scaling and the resulting localized
corrosion,
while also increasing copper corrosion rates.
Water/ammonia solutions have much lower corrosion issues, but suffer from the
safety concerns associated with the use of ammonia. Thus, the use of ammonia as

Refrigeration Machines 15
the refrigerant in absorption cooling systems is typically limited to industrial
applications.

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Section A Water Chillers: Fundamentals Application, and Operation PART I C hiller Fundamentals

2015-11-20T00:15:00.002+03:00

Section A

Water Chillers: Fundamentals
Application, and Operation
PART I

C hiller Fundamentals

Water Chillers: Fundamentals

1-Refrigeration Machines:

Heat flows from hot regions to cold regions, driven by temperature differencand nature’s desire to “level” energy differences (the Third Law of Thermodynamics).e To reverse this process in a system and move heat from a lower-temperature region to a higher-temperature region requires that “work” be done on the system. Thus, we use refrigeration machines to provide work to move heat from a cooled area and reject it to a hot area. The performance of these machines is usually characterized by a quantity known as the coefficient of performance
(COP), defined as

Therefore, COP is a dimensionless ratio of how much heat is transferred out of the cooled space to the amount of work that is used to accomplish this task. Unlike typical definitions of “efficiency,” the COP can be larger than unity. Higher values are better, indicating that more heat is removed for a given amount of work. COP is usually dependent on operating conditions, such as the temperatures of the cooled space and the hot space to which heat is to be rejected, and the type of refrigeration cycle utilized. All refrigeration cycles hinge on one common physical characteristic: if a chemical compound (which we can call a refrigerant) changes phase from a liquid to a gas, which is called evaporation, the compound must absorb heat to do so. Likewise, if the refrigerant changes phase back from a gas to a liquid, which is
called condensation, the absorbed heat must be rejected. Thus, all refrigeration cycles depend on circulating a refrigerant between a heat “source” (with heat to be
removed, thus resulting in cooling) and a heat “sink” (where the collected heat can be rejected).Overall, there are two basic refrigeration cycles in common use: the vapor compression cycle and the absorption cycle. Each of these cycles can be used to cool a secondary refrigerant, usually water, which is then used to cool the spaces in a building. The refrigeration machine utilized in this application is typically called a water chiller or simply a chiller.

VAPOR COMPRESSION REFRIGERATION:
Refrigeration Cycle
The vapor compression cycle, wherein a chemical substance alternately changesfrom liquid to gas and from gas to liquid, actually consists of four distinct steps:

1. Compression. Low-pressure refrigerant gas is compressed, thus raising its pressure by expending mechanical energy. There is a corresponding increase in temperature along with the increased pressure.

2. Condensation. The high-pressure, high-temperature gas is cooled by outdoor air or water that serves as a “heat sink” and condenses to a liquid form at high pressure.

3. Expansion. The high-pressure liquid flows through an orifice in the expansion valve, thus reducing the pressure. A small portion of the liquid “flashes” to gas due to the pressure reduction.

4. Evaporation. The low-pressure liquid absorbs heat from indoor air or water and evaporates to a gas or vapor form. The low-pressure vapor flows to the compressor and the process repeats. As shown in Figure 1.1, the vapor compression refrigeration system consists of four components that perform the four steps of the refrigeration cycle. The compressor raises the pressure of the initially low-pressure refrigerant gas. The

FIGURE 1.1 Basic components of the vapor compression refrigeration system. Condition
point numbers correspond to points on pressure–enthalpy chart (Figure 1.3).

Refrigeration Machines :

condenser is a heat exchanger that cools the high-pressure gas so that it changes

phase to liquid. The expansion valve controls the pressure ratio, and thus flow

rate, between the high- and low-pressure regions of the system. The evaporator is

a heat exchanger that heats the low-pressure liquid, causing it to change phase

from liquid to vapor (gas).

Thermodynamically, the most common representation of the basic refrigeration

cycle is made utilizing a pressure–enthalpy chart, as shown in Figure 1.2.

For each refrigerant, the phase-change line represents the conditions of pressure

and total heat content (enthalpy) at which it changes from liquid to gas and vice

versa. Thus, each of the steps of the vapor compression cycle can easily be plotted

to demonstrate the actual thermodynamic processes at work, as shown in

Figure 1.3.

Point 1 represents the conditions entering the compressor. Compression of the

gas raises its pressure from P1 to P2. Thus, the “work” that is done by the compressor

adds heat to the refrigerant, raising its temperature and slightly increasing

its heat content. Thus, point 2 represents the condition of the refrigerant leaving

the compressor and entering the condenser. In the condenser, the gas is cooled,

reducing its enthalpy from h2 to h3.

The portion between points 3 and 4 represents the pressure reduction that

occurs in the expansion process. Due to a small percentage of the liquid evaporating

as a result of the pressure reduction, the temperature and enthalpy of the

remaining liquid are also reduced slightly. Point 4 then represents the condition

entering the evaporator. The portion between points 4 and 1 represents the heat

gain by the liquid, increasing its enthalpy from h4 to h1, completed by the phase

change from liquid to gas at point 1.

Basic refrigerant pressure–enthalpy relationship.

HVAC Water Chillers and Cooling Towers:

Ideal refrigeration cycle imposed over a pressure–enthalpy chart.

For any refrigerant whose properties are known, a pressure–enthalpy chart can
be constructed and the performance of a vapor compression cycle analyzed by
establishing the high and low pressures for the system. (Note that Figure 1.3
represents
an “ideal” cycle and in actual practice there are various departures
dictated by second-law inefficiencies.)

Refrigerants:

Any substance that absorbs heat may be termed as a refrigerant. Secondary
refrigerants, such as water or brine, absorb heat but do not undergo a phase change
in the process. Primary refrigerants, then, are those substances that possess the
chemical, physical, and thermodynamic properties that permit their efficient use
in the typical vapor compression cycle.
In the vapor compression cycle, a refrigerant must satisfy several (sometimes
conflicting) requirements:
1. The refrigerant must be chemically stable in both the liquid and vapor
states.
2. Refrigerants must be nonflammable and have low toxicity.
3. The thermodynamic properties of the refrigerant must meet the temperature
and pressure ranges required for the application.

Refrigeration Machines:

Early refrigerants, developed in the 1920s and 1930s, used in HVAC
applications
were predominately chemical compounds made up of chlorofluorocarbons
(CFCs) such as R-11, R-12, and R-503. While stable and efficient in
the range of temperatures and pressures required within contained HVAC cooling
systems, these CFC refrigerants were also used as aerosol propellants and cleaning
agents in a wide range of industrial and commercial products. Once released into
the air, these refrigerants had significantly adverse effects on the atmosphere.
CFC refrigerant gas was found to be long lived in the atmosphere. In the lower
atmosphere, the CFC molecules absorb infrared radiation and, thus, contribute to
atmospheric warming. Then, once it is in the upper atmosphere, the CFC molecule
breaks down to release chlorine that destroys ozone and, consequently, damages
the atmospheric ozone layer that protects the earth from excess UV radiation.
These, and all other refrigerants, are now assigned an Ozone Depletion Potential
(ODP) and/or Global Warming Potential (GWP), defined as follows:

• ODP of a chemical compound is the relative amount of degradation it
can cause to the ozone layer.

• GWP is a measure of how much a given mass of a gas contributes to
global warming. GWP is a relative scale that compares the greenhouse
gas to carbon dioxide with a GWP, by definition, of 1.
Table 1.1 summarizes the ODP and GWP for a number of refrigerants commonly
used in HVAC chiller systems.
The manufacture of CFC refrigerants in the United States and most other
industrialized nations was eliminated by international agreement in 1996. While
refrigeration equipment that utilizes CFC refrigerants is still in use, no new equipment
using these refrigerants is now available in the United States or Europe.
Earlier on, to replace CFCs, researchers found that by modifying the chemical
compound of CFCs by substituting a hydrogen atom for one or more of the chlorine
or fluorine atoms resulted in a significant reduction in the life of the molecule
and, thus, almost eliminated ODP and significantly reduced GWP. Some of these
compounds, called hydrochlorofluorocarbons (HCFCs), are currently used in
HVAC water chillers, especially R-22 and R-123.
While HCFCs have reduced the potential environmental damage from refrigerants
released into the atmosphere, the potential for damage has not been totally
eliminated. Again, under international agreement, this class of refrigerants is
slated for phaseout for new equipment installations in 2010–2020, with total halt
to manufacturing and importing into the United States mandated by 2030, as
summarized in Table 1.2.
>
To replace HCFCs, a third class of refrigerants, called hydrofluorocarbons
(HFCs), has been developed since about 1990, including R-134a, R-410A, and
R-407C, all of which are commonly applied in HVAC equipment, although the
latter two are primarily used only in smaller-packaged DX systems. This class
of refrigerants has essentially no ODP and GWP levels that are 50–70% lower
than CFCs.

ODP and CWP for Common Refrigerants

R-134a is utilized in positive-pressure rotary compressor water chillers offered
by the vast majority of manufacturers. However, at least one manufacturer continues
to offer negative-pressure centrifugal compressor water chillers using R-123
(an HCFC), creating a design dilemma for engineers and owners. At this time,
R-123 chiller has only 8–9 years of guaranteed refrigerant supply and new installations
of chillers using this refrigerant should be avoided.
Unfortunately, HFCs still have fairly high GWPs. Already, in Europe, there is
legislation requiring that these refrigerants be eliminated. The European Union
has issued a directive to phase out refrigerants with a GWP greater (ultimately)
than 150 in autos beginning in 2011. This limitation is expected to be applied to
HVAC systems beginning in 2015.
While no GWP-limiting legislation exists for the United States, there is a search
underway for new low-GWP refrigerants to replace HFCs worldwide. This search is
currently centering around older refrigerants such as R-245a (propane), especially in
Europe, and R-717 (ammonia). Both refrigerants are highly flammable and ammonia
has specific safety concerns and requirements that limit its potential application.

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ABSORPTION CHILLER FOR THE CHENA HOT SPRINGS AURORA ICE MUSEUM

2015-10-21T22:34:00.003+03:00

ABSORPTION CHILLER FOR THE CHENA

HOT SPRINGS AURORA ICE MUSEUM

Absorption Chiller prior to installation.

INTRODUCTION:

Absorption chilling uses a refrigeration cycle that requires little or no electric input, because it does not employ a mechanical compressor. Instead, the refrigeration effect is produced through heating and cooling a circulating absorbent liquid. When a moderate temperature heat source is available and/or local electric costs are high, absorption refrigeration can be quite economical. The type of absorption chiller most familiar to the general public is the ‘propane refrigerator’, which is found in RV’s or at remote homesteads. In fact, absorption chilling is not a new concept. The first simple ammonia/water absorption chiller was built by Ferdinand Carre in 1846 and marketed as an ice-making machine. Moderate temperature geothermal resources have long been recognized as promising heat sources to drive an absorption cycle, but the 230ºF minimum temperature classically considered necessary to make an air-cooled system cost effective encroached on temperature ranges which could
similarly be used for power generation. For this reason, and because of increased maintenance issues when working with unique systems, no absorption chillers were in operation on geothermal sites between 1989 and 2004. Prior to 1989, the Oregon Institute of Technology used a lithium bromide/waterabsorption chiller for air conditioning buildings on campus.

Interior view of the Aurora Ice Museum.

THE AURORA ICE MUSEUM:
In 2003, Chena Hot Springs Resort built the first Ice Museum in the United States. Chena is located 60 miles (100km) northeast of Fairbanks, Alaska, which is the traditional world capital of ice art. The Aurora Ice Museum was from its inception intended to be a year-round structure, something which had never before been attempted. Unfortunately, due to a number of reasons, the initial version of the Museum did not survive an unseasonably warm spring in 2004. One of the primary problems was immediately identified as the cost of refrigeration for the structure. A standard 200- ton (700kW) Trane air-conditioning unit reprogrammed to circulate 300 gpm (19 l/s) of glycol was originally planned, but the cost of operating the unit was quickly deemed too high. Chena Hot Springs is located 30 miles (50km) from the nearest utility grid. Prior to the installation of a geothermal power plant in 2006, the cost of power generated onsite
from a 200kW diesel generator was calculated to be 30¢ per kWh. The onsite generator was not large enough to power the 200-ton (700kW) Trane unit, and so a separate 500kW generator needed to be installed to start and operate it. The fuel cost alone for operating the Trane unit was over $500 per day.

ENERGY CONCEPTS COMPANY:
Once the first Aurora Ice Museum melted, it was clear that in order to justify rebuilding the structure an alternative refrigeration system would be needed. The geothermal resource at Chena Hot Springs is 165ºF (74ºC), substantially lower than the minimum threshold generally considered for absorption systems. Fortunately, the owners of Chena were familiar with an absorption chiller operating in Kotzebue on the northwestern coast of Alaska, to make ice for the local fishing fleet. The Kotzebue chiller was powered by 165ºF
(74ºC) jacket water from a diesel generator (coincidentally the identical temperature as the Chena geothermal resource).
The system uses a three pressure ammonia/water absorption cycle, and had been in operation for 10 years. Chena contacted Energy Concepts Company, the manufacturer of the Kotzebue system, in late 2004, to order a similar unit for the Aurora Ice Museum. The order was placed in early January 2005, and installation was required by the end of March. This meant that there was no time for a shop test of the unit before shipping. It also meant that the unit had to be air
shipped to meet the schedule, and hence compactness was at a premium.

Absorption Chiller prior to installation

CHENA ABSORPTION CHILLER:
Chena Hot Springs required significantly more refrigeration capacity than Kotzebue, and so Energy Concepts designed a unique three pressure system for the Ice Museum,using an ammonia-water absorption cycle. One significant advantage Chena had over other sites was a supply of readily available cold river water to cool the absorbers and condenser.Special heat exchangers are used throughout the system to give high performance in a very compact package. The components which contact external fluids (hot spring water, river water, chilled brine) are constructed of stainless steel. Other internal cycle components are carbon steel. The chilled brine which transfers heat out of the Ice Museum is a CaCl2 solution, concentrated to allow temperatures as low as -50ºF (-46ºC) (typical for winter temperatures at Chena). The brine circulates behind the Ice Museum and through an air handler,which cools an annular space in the Ice Museum between a thin inner wall and the external insulated wall. With 165ºF (74ºC) hot spring water (85 gpm (5.4 l/s)), and 40ºF (4ºC) (80 gpm (5.0 l/s)) river water, the brine is delivered at -20ºF (-29ºC) (55 gpm (3.5 l/s)) and the temperature in the ice hotel is maintained at a constant 24ºF (-4ºC). An additional system component is a 2000 gallon (7.56m3) brine storage tank, which acts as a giant ‘fly wheel’ in the system. If the brine in the tank is kept below freezing, it can
continue to provide cooling to the Ice Museum for one hour during shutdown of the absorption chiller for any reason. Additionally, defrost of the air handlers has not been perfected and is accomplished using hot water sprayed onto the
coils. This heat can unbalance the absorption chiller, and therefore the tank allows the brine to circulate freely while allowing the air handlers to be cut out of the loop.

other

Springs Absorption Refrigeration System.

SYSTEM ECONOMICS:

While the absorption chiller uses only two 1/2hp (0.37kW ) pumps to circulate the ammonia-water mixture, an additional 20hp (15kW) are required to operate the cold and geothermal supply pumps, 3hp (2kW) are required for the CaCl2 brine circulating pump, and 20hp (15kW) are required for the air handler. In total, the absorption system requires 44hp
(33kW), while the backup vapor compression system requires 148hp (110kW) to operate. This results in fuel cost savings alone of $400 per day, or more than $12,000 per month at current diesel fuel prices ($2.47 per gallon ($0.65/ liter) for bulk diesel). The Chena absorption chiller plant (“Thermochiller”) has now operated through two warm seasons, keeping the Aurora Ice Museum frozen year-round. It demonstrates that absorption refrigeration is possible with very low driving
temperatures, and in very compact packages. The Chena Thermochiller displaces both the conventional mechanical compressor chiller plant, and also 100 hp (75 kW) of other
wise required power plant capacity. The capital cost of the Thermochiller is substantially less than the capital cost of those two displaced components. Therefore, even with the installation of the 2 x 200kW geothermal power plant at Chena, the absorption chiller will remain in operation as the most economical cooling option for the Ice Museum because the upfront installation costs have already been covered.

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ADVANCED ABSORPTION CHILLERS UTILIZATION OF VARIOUS HEAT ENERGIES FOR AIRCONDITIONING parti 2

2015-10-21T21:45:00.001+03:00

ADVANCED ABSORPTION CHILLERS
UTILIZATION OF VARIOUS HEAT ENERGIES FOR AIRCONDITIONING

parti 2

Renewable Energy Utilization Cooling System

5. For Utilization Renewable Energy:

5.1 Solar Thermal Energy:

In July 1974, Yazaki Experimental Solar House was completed, realizing a solar energy system earlier than any other project in the world. The success of development solar energy system is based on Hot-water Fired Chiller (WFC) technology. The WFC series has been installed 3,851 projects in Japanese market.
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CH-KE System with MGT

Yazaki Experimental Solar House

Utilizing Renewable Energy

5. 2 Biomass Energy – Wood Pellet:

Fig 8 indicates the Pellet Fired Absorption Chiller, which is energized by wood pellets. The Wood pellet Fired Absorption Chiller-Heater is under development and it will launch to Japanese market in 2007.

System of Pellet Fired Absorption Chiller-Heater

Using wood pellet as fuel is considered as “Carbon-neutral”. Since tree planted to replace the wood burned as fuel can absorb carbon dioxide, this resource has attracted interest as a carbon-neutral fuel, that is, one which does not increase the amount of carbon dioxide in the atmosphere. The model business, which is indicated Fig 9, in local recycling of wood biomass involves collecting thinned wood from forestry maintenance operations, wood cut-off from sawmills, and other remnant material and recycling them into pellets for local use as fuel. By doing so, the scheme aims to promote the principle of local production for local consumption in timber and energy supply through efficient use of forestry resources. The Yazaki Group is working in the framework of publicprivate partnership with the aim is to stimulate the forestry industry and at same time to maintain and preserve forests and reduce atmospheric carbon dioxide.

Wood Biomass Local Recycling System

Fig 10 is one of “Renewable Energy Utilization Cooling System” which is consisted by solar cooling system and wood pellet cooling system. During daytime, if sunlight is enough to sufficient cooling requirement, solar cooling suffices cooling requirement without wood pellet absorption chiller operation. If there is less sunlight, the wood pellet can cover insufficient cooling capacity of solar cooling during morning and evening time or cloudy day.
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Renewable Energy Utilization Cooling System

younes kandi

ADVANCED ABSORPTION CHILLERS UTILIZATION OF VARIOUS HEAT ENERGIES FOR AIRCONDITIONING parti 1

2015-10-21T00:29:00.001+03:00

ADVANCED ABSORPTION CHILLERS

UTILIZATION OF VARIOUS HEAT ENERGIES FOR AIRCONDITIONING

parti 1

Steam Fired Absorption Chiller-Heater – CH-KGST series

Summary:

One of significant feature of absorption cooling technology is that variousthermal energies can be used for air-conditioning by the technology. The main types of thermal energy are hot water, steam, and exhaust gas. In this document, Yazaki’s advanced absorption chillers and systems are introduced for effective usages not only waste thermal energies but also renewable energies.
>
1. Utilization of Various Waste Thermal Energies:

By an onsite electrical generator and manufacturing process of factory, various types of thermal energy are discharged, such as hot water, steam, and exhaust gas. Absorption chiller can use not only fossil fuel but also the wastethermal energies for cooling. In combination with an electrical generator and an absorption chiller, the combined system can improve overall efficiency rate by using the waste thermal energy for cooling. For effective utilization of energy, Yazaki provides absorption chillers for each type of thermal energy.

Type of Waste Heat and Absorption Chillers

2. For Utilization of Hot Water:

Hot water Fired Chiller (WFC) is the first type of chiller for utilizing waste heat.The WFC absorption cycle is energized by hot water and the lower side operational temperature range of hot water is expanded to 70 degree C for effective utilization of the thermal energy.

Co-generation System with WFC-SCB or WFC-SHB

In general, if the hot water temperature is not enough to operate the WFC, additional boiler is installed into the system to produce an increase in temperature. WFC-SCB and WFC SHB series are the packaged type of auxiliary boiler. By optimal control of auxiliary boiler and WFC, waste energy of hot water can be used effectively.

3. For Utilization of Steam:

CH-KGST can use wasted steam for cooling. In the case of high-pressure steam, the CH-KGST operates double effect cooling cycle. If the steam pressure decreases, the CH-KGST cooling cycle switch to single effect cooling cycle. By the cycle switching control, CH-KGST series can operate continuously under steam pressure fluctuation from 98 kPa to 686 kPa and realizes effective use of lowpressure steam.

Steam Fired Absorption Chiller-Heater – CH-KGST series

4. For Utilization of Exhaust Gas from MGT:

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CH-KE series can use exhaust gas from MGT directly. The exhaust gas thermal energy retrieved by exhaust heat exchanger and exhaust heat retriever to achieve high efficiency operation. Exhaust gas operation takes priority whenever there is sufficient exhaust heat available in respect of the cooling or heating load. When exhaust gas mode as a function of electrical demand is not sufficient to satisfy cooling or heating requirement, dual fuel mode, exhaust gas and natural gas, will automatically commence. 100% direct gas fired mode will cater for cooling or heating demand when there is little or no heat available from the micro gas turbine.

Reference Image of Exhaust gas Operation Priority

kandi younes

what is it Absorption Chiller

2015-10-20T23:46:00.000+03:00

what is it Absorption Chiller

what is it Absorption Chiller

Outline:

Steam-fired absorption is a good application where there is a low cost of steam such as a cogen or waste energy plant. Direct-fired natural gas units are used in hybrid and high-cost electricity Outline areas. Absorption chillers do NOT use a CFC or HCFC refrigerant; therefore, some users purchase absorption chillers for this environmental advantage.

Principle and Mechanism:

Principle It seems unreasonable to burn a flame to produce cooling, but that is what happens inside an absorption & chiller. The refrigerant used is actually water, as that is the working medium that experiences a phase Mechanism change that causes the cooling affect. The second fluid that drives the process is a salt, generally lithium bromide. Heat is used to separate the two fluids; when they are brought back together in a near vacuumenvironment, the water experiences a phase change to remix with the salt at a very low temperature (at normal atmosphere pressure, water vaporizes at 212F; in an absorber, water vaporizes cold enough
to produce 46F chilled water).

Description Structure explanation, shapes, and/or System diagram:

Absorption chillers cost more to operate than electric chillers. They also cost about twice as much to purchase. Therefore, a reason other than average electric cost is needed to justify a
base-loaded absorption system. Economics are more favorable for hybrid systems. Hybrid systems combine absorption chillers for use during on-peak electric hours and electric chillers for base load operation.

Energy Saving effect :

is expected to be 50 percent more efficient than conventional chillers.

fecteffect effect

Economics equipmen Cost:

The cost of the equipment selection depending upon several factors including:
Equitment building type, equipment, climate, utility rate, and scalar ratio. Remark:

Absorbers have a Coefficient of Performance (COP) that is about 1.0, compared to engine driven
compressors about 1.5 and electric at about 3.0.

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Trane Horizon™ Absorption Series Two-Stage Steam-Fired Absorption Water Chillers, 380 to 1650 Tons parti 2

2015-10-20T23:14:00.000+03:00

Trane Horizon™ Absorption Series
Two-Stage Steam-Fired Absorption
Water Chillers, 380 to 1650 Tons

parti 2

Trane Horizon™ Absorption

Increased System Efficiency:

The Horizon absorption chiller can optimize the total system efficiency and lower initial equipment costs. Designed around 3.6 gpm/ton cooling tower water flow, the two-stage design is lower than ARI’s 4.0 gpm/ton standard for absorption chillers. Lower gpm’s through the condenser and absorber section gives the design engineer the opportunity to downsize the cooling tower and cooling tower pumps. This means lower equipment costs and reduced chiller plant electrical usage.

Efficient Pump Drives:

In the Horizon machine, absorption solution flow is controlled byadjustable frequency drives on the pump motors. The drives allow the chiller to react to changing conditions up to ten times faster than other absorbers. The UCP2 control system maintains efficient pump operation during chiller start up, operation and shutdown phases. This increases unit reliability and reduces maintenance expense.

Designed for Easier Installation Start-up and Service:

The many user-friendly features designed into the Horizon absorption chiller are a collection of ideas and comments from absorption chiller owners and operators over the past 35 years. Second to reliability, ease of installation and maintenance are also important to Trane customers. All Horizon chillers ship fully assembled for fast installation. However, the new modular design allows the chiller to be disassembled at the job site for applications with limited access. To make annual tube cleaning easier and less costly, all Horizon chillers include marine-style waterboxes on the cooling water circuit. The boxes serve as a leak tight, removable cover for easy accessibility into the chiller shells.

Standard Specification:

• 1.2 COP at ARI standard rating conditions
• Victaulic™ water connections
• Industrial-grade tubes unmatched in the industry

— First stage generator - 409 stainless steel

— Second stage generator - .028” wall 95/5 CuNi

— Evaporator - .028” wall copper

— Absorber - .022” wall 95/5 CuNi

— Condenser - 0.28” wall copper

• Factory mounted and tested microprocessor controls

• 150 psig waterboxes marine style on the condenser and absorber sections

• Cooling water crossover pipe factory installed between the absorber and condenser

• Connections and valves are provided as standard for lithium bromide filter

• Industrial duty factory mounted energyvalve Optional Specification

• 150 psig raised face flanges for the evaporator, condenser, and absorber water connections

• Dissassembled unit — providing foreasy disassembly and reassembly of major components at the jobsite.

• Lithium bromide filter

• Factory installed cold insulation

• Field installed hot insulation

TWO-STAGE STEAM-FIRED ABSORPTION UNIT

Serviceability:

• All tubes individually replaceable
• Removable absorber, evaporator and generator spray tree systems
• Marine style waterboxes on absorber and condenser allowing tube cleaning without removing water connections
• Training of owner’s operating personnel
• Quality post-warranty service from trained technicians
• Parts readily available
• Local trained service personnel that are backed by headquarters experts
• Customizable extended warranty plans Controls
• Improved reliability and performance
• Factory installed and commissioned
• Proportional integral derivative (PID) control. Adaptive Control™ strategies for stable, efficient, reliable, and optimal chilled water temperature control
• Easy-to-use operator interface
— Two line 40 character backlit LCD display in clear language
— English or SI units
— Standard and custom reports
— Over 200 diagnostics including time and date stamping

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Trane Horizon Absorption Series Two-Stage Steam-Fired Absorption Water Chillers, 380 to 1650 Tons parti 1

2015-10-20T22:34:00.001+03:00

Trane Horizon Absorption Series
Two-Stage Steam-Fired Absorption
Water Chillers, 380 to 1650 Tons

parti 1

Water Chillers Absorption

Made in the USA:

Trane has been manufacturing absorption chillers for more than three decades. The newest line, the Trane Horizon™ two-stage steam fired absorption water chiller is the only line of two-stage absorption products designed, built and supported in the USA.

A Good Environmental Choice:

The Trane Horizon absorption chiller is a wise choice for owners concerned about the environment. Water being the base refrigerant means fewer concerns about refrigerant management and availability. Absorption technology reduces the requirement for electric energy. The steam-fired design allows the machine to be fueled by waste heat or available
steam. This contributes to the conservation of the world’s fuel resources and makes economic sense.

Trane Horizon Absorption

Quality:

Trane uses the highest quality materials available to resist corrosion and extend the chiller’s operating life. Additionally, the absorption chiller manufacturing facilities in La Crosse are ISO 9001 certified to help deliver high quality in design, development, production and product records.

Efficient Operation:

Trane’s unique absorption Reverse Series Cycle can be as much as 5-15 percent more efficient, at full load conditions, than other absorption cycles. In addition, the microprocessor
based control (UCP2), along with variable speed pumps, optimizes the machines performance to provide significant operating cost savings at partload operation. The Purifier™ purge, provided as standard on all Horizon absorption chillers is fully automatic and maintains efficient chiller operation. The Purifier purge removes air and other noncondensibles that have
filtered into the system. And since Purifier purge communicates with the UCP controller, the chiller controls can take appropriate action to protect the machine when air is present.

Automatic Crystallization Protection:

Maintenance Considerations of Water Chillers chiller trane party 2

2015-09-17T23:19:00.000+03:00

Maintenance Considerations
of Water Chillers chiller trane
party 2

Maintenance Water Chillers chiller trane

Other design-specific requirements:

Other design-specific requirements

◆    Change oil when oil analysis dictates
◆    Replace oil filter periodically
◆    Replace filter drier periodically
◆    Clean oil strainers annually
◆    Check shaft alignment annually
◆    Check coupling annually
◆    Replace shaft seal every 2 to 4 years
◆    Compressor teardown inspection every 5 to 10 years

Some helical-rotary compressor designs do require periodic maintenance of mechanical system components. This includes oil and refrigerant filter changes, oil strainer changes, and a compressor rotor inspection.
Open-motor compressor designs require shaft alignment, coupling inspection, bearing lubrication, and cleaning of the motor windings, rotor ends, and fan blades on a quarterly or annual basis.
In all cases, strictly follow the manufacturer’s published maintenance requirements and recommendations.

Recommended maintenance:

Recommended maintenance

◆    Use a qualified water treatment specialist
◆    Clean condenser tubes as needed (water-cooled)
◆    Clean water-side strainers
◆    Test tubes every 3 years
◆    Clean condenser coils as needed (air-cooled)
Optimum performance of heat transfer components depends on keeping the heat transfer surfaces free from scale and sludge. Even a very thin deposit of scale can substantially reduce heat transfer capacity. Owners of water-cooled chillers should engage the services of a qualified water treatment specialist to determine the level of water treatment required to remove contaminants from the cooling tower water.
Scale deposits are best removed by chemical means. The water-cooled condenser is commonly isolated from the rest of the cooling tower water circuit by valves, and a pump circulates cleaning solution through the condenser tubes.
Sludge is removed mechanically. This involves removing the water boxes from the condenser and loosening the deposits with a stiff-bristled brush. The loosened material is then flushed from the tubes with clear water. As part of this procedure, the strainers on both the chilled water and cooling tower water circuits should be cleaned every year.
Every 3 years, or more frequently for process or critical applications, it is recommended that a qualified service organization perform non-destructive tube inspections on both the evaporator and condenser tubes. The eddy- current tube test is a common method.
Rarely, problems may arise that cause refrigerant or water leaks. These must be repaired immediately.
For air-cooled chillers, the condenser coils should be cleaned at least annually in order to maintain proper efficiencies and operating conditions. Follow the manufacturer’s instructions to avoid damage to the coils.

Fluid Analysis:

~~\Fluid Analysis~~

▲ Oil analysis
◆    Conduct annual analysis to verify system integrity
◆    Measure oil pressure drop to determine if filter needs changing
◆    Measure charge
▲ Refrigerant charge
◆    Measure charge and trim as necessary
◆    Measure superheat and subcooling

Probably the most important annual maintenance task required for helical- rotary water chillers is an oil analysis. It may be conducted more frequently for chillers that run continuously or more often than normal. This test, performed by a qualified laboratory, verifies the integrity of the refrigeration system by testing the moisture, acidity, and metal concentration levels. This analysis can determine where problems exist or could potentially develop. By taking oil samples on a regular basis, normal operating trends for the compressor and bearing metals can be analyzed. As opposed to changing the oil once a year whether it needs it or not, regular oil analyses can be used to determine proper oil change intervals as well as predict major problems before they occur.
Refrigerant analysis measures contamination levels and determines suitability for continued use. It can also determine the acceptability of recycled refrigerant for reuse. Refrigerant analysis helps extend the life of the existing charge and ensures that the chiller is operating at peak efficiency.
Logging the oil and refrigerant charges, and examining the trends of this data, can help identify potential problems before they occur.

Fluid Analysis:

Fluid Analysis2

▲ Why perform regular oil analyses?
◆    Helps reduce maintenance costs
◆    Detects problems without compressor disassembly
◆    Extends service life of oil charge
◆    Reduces environmental problems related to oil disposal
◆    Helps maintain compressor efficiency and reliability
◆    Helps lower refrigerant emissions

An oil analysis is a key preventive maintenance measure and should be conducted at least annually. It will help the compressor last longer while improving chiller efficiency and reducing refrigerant emissions. A certified chemical laboratory has years of experience in analyzing oil and refrigerant from all types of compressors.
Often the chiller manufacturer can provide this service.

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Maintenance Considerations of Water Chillers chiller trane party 1

2015-09-17T22:24:00.003+03:00

Maintenance Considerations

of Water Chillers chiller trane

party 1

Maintenance Considerations

Maintenance Considerations:

This period discusses general maintenance requirements of helical-rotary water chillers. Although some of the information applies specifically to the design presented in this clinic, requirements for other helical-rotary chiller designs are also included.

Maintenance Considerations

Once a helical-rotary chiller is installed and put into operation, it usually continues to function without a full-time attendant. In many cases, the machine starts and stops on a schedule controlled by the building automation system or a simple time clock. The only daily maintenance requirement is to check the operating log.
Water chillers are designed for maximum reliability with a minimum amount of maintenance. Like all large mechanical systems, however, certain routine maintenance procedures are either required or recommended.

Operating log:

Operating log

▲ Chilled water inlet and outlet temperatures and pressures
▲ Chilled water flow
▲ Evaporator refrigerant temperature and pressures
▲ Evaporator approach temperature
▲ Condenser water inlet and outlet temperatures and pressures
▲ Condenser water flow
▲ Condenser refrigerant temperature and pressures
▲ Condenser approach temperature
▲ Compressor refrigerant suction and discharge temperatures
▲ Refrigerant level
▲ Oil pressures, temperature, and levels
▲ Addition of refrigerant
▲ Addition of oil
▲ Vibration levels

The American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) has published Guideline 3 titled Reducing Emission of Halogenated Refrigerants in Refrigeration and Air Conditioning Equipment and Systems.
This guideline includes a recommended list of data points to be logged daily for each chiller. Much of this data may be available through the chiller’s control panel.
Special attention should be given to the following:
■    Review the operating log and trends
■    Measure the oil pressure drop to determine if the oil filter needs to be replaced
■    Measure refrigerant superheat and subcooling
■    Measure both the refrigerant and oil charges

Mechanical Components:

Mechanical Components

▲ Required maintenance
◆    Compressor and motor: no maintenance required
◆    Controls: no maintenance or calibration required
▲ Recommended maintenance
◆    Visually inspect overall unit
◆    Inspect safety controls and electrical components
◆    Tighten electrical connections
◆    Check for leaks
◆    Test vent piping
Direct-drive, semi-hermetic compressor designs require no periodic maintenance on the compressor/motor assembly. The compressor contains only 3 main moving parts: the male and female rotors and the slide valve. The semi-hermetic motor eliminates the need for external shaft seals associated with open motors. These seals are a prime source of oil and refrigerant leaks. It also eliminates annual coupling and seal inspections, alignment, and shaft seal replacement.
With the advent of microprocessor-based controls, the control panel and auxiliary controllers require no recalibration or maintenance. Remote-mounted electronic sensors send information to the unit controller, which can be connected to a building automation system in order to communicate information and allow for system-level optimization. These systems can notify the operator with an alarm or diagnostic message when a problem occurs.
Like any mechanical equipment, a daily visual inspection of the chiller is recommended to look for oil leaks, condensation, loosened electrical or control wiring, or signs of corrosion. Special attention should be given to the safety controls and electrical components.
It is recommended that a qualified service technician check the chiller annually for leaks. In the normal service of any air conditioning system, the Unites States EPA mandates that whenever a refrigeration circuit is opened, recovery of the refrigerant is required.
Finally, the vent piping of all pressure relief valves should be leak-tested annually for the presence of refrigerant to detect improperly sealed valves. Leaking relief valves should be replaced.

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Compressor Capacity Control Water Chillers trane

2015-09-17T21:47:00.001+03:00

Compressor Capacity Control

Water Chillers trane

Compressor Capacity Control chille trane

Compressor Capacity Control:

The capacity of the helical-rotary compressor presented in this clinic is controlled by a slide valve that is an integral part of the compressor housing.
Other helical-rotary compressor designs may use a variety of methods to vary capacity. Some of these methods are similar in function to the slide valve presented in this period. One major difference is whether the compressor is designed to unload in steps, like a reciprocating compressor, or if it has variable unloading.

slide valve :

slide valve

The position of the slide valve along the rotors controls the volume of refrigerant vapor being delivered by the compressor, by varying the amount of rotor length actually being used for compression.
Note that the compressor discharge has 2 components. First, a port within the slide valve provides a radial discharge path. Second, a port within the end- plate of the compressor housing provides an axial discharge path.

slide valve position Full Load:

slide valve position Full Load

At full load, the slide valve is closed. The compressor pumps its maximum volume of refrigerant, discharging it through both the radial and axial ports.

slide valve position Part Load

slide valve position Part Load

At part load, the slide valve modulates toward the open position. The opening created by the valve movement allows refrigerant vapor to bypass from the rotor pockets back to the suction side of the compressor. This reduces the volume of vapor available for the compression process. It also reduces the amount of rotor length available for compression. In this manner, the volume of refrigerant that is pumped by the compressor is varied, unloading it to balance the existing chiller load.

compressor capacity control Unloading:

compressor capacity control Unloading

As the slide valve continues to open, further unloading the compressor, its radial discharge port eventually travels past the opening in the compressor housing. Once this occurs, all of the refrigerant vapor being pumped by the compressor is discharged through the axial port in the compressor’s end-plate.
The compressor discharge ports and slide valve are designed to allow the compressor to operate efficiently over a wide range of conditions.

Slide Valve Operation:

Slide Valve Operation

The slide valve is operated by a piston and cylinder assembly. Extension and retraction of the operator shaft positions the slide valve along the compressor rotors.
High-pressure refrigerant vapor, controlled by 2 solenoid valves, is fed to or bled from this assembly in order to position the valve. To close the slide valve and load the compressor, the load valve is opened and the unload valve is closed. This allows high-pressure refrigerant vapor to enter the cylinder from the discharge of the compressor, extending the operator shaft and moving the slide valve so that it covers more of the rotor length.
Conversely, to open the slide valve and unload the compressor, the load valve is closed and the unload valve is opened. This allows the high-pressure refrigerant vapor to bleed out of the cylinder into the low-pressure area within the compressor housing. A spring helps return the piston, retracting the operator shaft and moving the slide valve such that the rotors are more uncovered. This reduces the effective length of the rotors, which are compressing vapor.
On shutdown the unload solenoid valve is energized and the spring drives the slide valve to the fully-unloaded position. This ensures that the compressor always starts fully unloaded.
When both solenoid valves are closed, the operator shaft holds the slide valve at its current position.

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helical-rotary water chiller Refrigeration Cycle

2015-08-24T00:56:00.001+03:00

helical-rotary water chiller
Refrigeration Cycle

Refrigeration Cycle:

A pressure-enthalpy (p-h) chart illustrates the refrigeration cycle of the helical- rotary water chiller.

Refrigeration Cycle chiller

But first, lets review the components of the helical-rotary chiller’s refrigeration cycle...
Refrigerant vapor leaves the evaporator and flows to the compressor where it is compressed to a higher pressure and temperature. Oil is removed from refrigerant vapor in the oil separator and the refrigerant travels to the condenser while the oil is recirculated back to the compressor.

In the condenser, the refrigerant vapor rejects heat to water or air and leaves as a sub-cooled liquid. The pressure drop created by the expansion device causes a portion of the liquid refrigerant to evaporate and the resulting mixture of liquid and vapor refrigerant enters the liquid/vapor separator. Here the vapor is separated from the mixture and routed directly to the suction side of the compressor and the remaining liquid refrigerant enters the evaporator.
In the evaporator, the liquid refrigerant boils as it absorbs heat from water. The resulting vapor is drawn back to the compressor to repeat the cycle.

Pressure–Enthalpy (p-h) Chart

Pressure–Enthalpy (p-h) Chart:

The pressure-enthalpy chart is simply a plot of the saturated properties of a refrigerant. It plots refrigerant pressure (vertical axis) versus enthalpy (horizontal axis). Enthalpy is a measurement of the heat content, both sensible and latent, per pound [kg] of refrigerant.
For example, A represents the heat content of saturated liquid HFC-134a refrigerant at 147.5 psia [1.02 MPa] and 104°F [40°C]. B represents the heat content of saturated vapor HFC-134a refrigerant at the same pressure and temperature. The difference in heat content, or enthalpy, between A and B— that is, 70.2 Btu/pound [163.2 kJ/kg]—is the amount of heat required to
transform 1 pound [1 kg] of saturated liquid refrigerant to saturated refrigerant vapor at the same pressure and temperature.
If the heat content of the refrigerant at any pressure falls to the right of the curve, the vapor is superheated. Similarly, if the heat content of the refrigerant

Refrigeration Cycle

Refrigeration Cycle:

The theoretical vapor-compression refrigeration cycle for a helical-rotary water chiller can be plotted on a pressure-enthalpy chart.
The refrigerant leaves the evaporator as saturated vapor ➀ and flows to the suction end of the compressor where it enters the compartment for the suction- gas-cooled motor. Here the refrigerant flows across and cools the motor, then
enters the compression chamber. The refrigerant vapor is compressed in the compressor to a high pressure and temperature ➁. Energy input to the motor and compressor is imparted to the refrigerant as superheat. Superheated
refrigerant vapor leaves the compressor and enters the condenser.
Water or air flowing through the condenser absorbs heat from the hot, high- pressure refrigerant. This reduction in the heat content of the refrigerant vapor causes it to desuperheat ➂, condense into liquid ➃, and further sub-cool ➄ before leaving the condenser to travel to the expansion device.
The pressure drop created by the expansion process causes a portion of the liquid refrigerant to evaporate. The evaporating refrigerant absorbs heat from the remaining liquid refrigerant. The resulting mixture of cold liquid and vapor
refrigerant enters the liquid/vapor separator ➅. Here the vapor is separated
from the mixture and routed directly to the suction side of the compressor ➀
and the remaining liquid refrigerant enters the evaporator ➆.
The cool low-pressure liquid refrigerant enters the distribution system in the evaporator shell and is distributed over the tubes in the evaporator tube bundle, absorbing heat from water that flows through the tubes. This transfer
of heat boils the film of liquid refrigerant on the tube surfaces and the resulting vapor is drawn back to the compressor ➀ to repeat the cycle.

Refrigerants

Refrigerants:

Manufacturers are continuously improving their designs of helical-rotary water chillers. New chillers need to be designed around the characteristics of the refrigerant. Today there are 5 strong candidates for use with positive- displacement, helical-rotary chillers. They are HCFC-22, HFC-134a, HFC-404a, HFC-407c and HFC-410a.

refrigerants Thermodynamic Characteristics

refrigerants Thermodynamic Characteristics:

Today the most commonly used refrigerant in helical-rotary chillers is HCFC-22. Due to the scheduled phaseout of HCFC-22, most helical-rotary chillers will be redesigned using HFC refrigerants. Many challenges are encountered when redesigning a chiller to use a refrigerant with different thermodynamic characteristics. This is due to the different efficiency, capacity, and operating pressure characteristics of each of the refrigerants.
Take a closer look at each of these issues by examining the effects of using different refrigerants in the same helical-rotary chiller designed for use with HCFC-22.
■    Efficiency – In order to meet today’s high standards of energy efficiency, chillers using refrigerants with a lower thermal efficiency, such as HFC-404a and HFC-410a, will require larger heat exchangers and more efficient compressors. These changes add to the product cost and increase the physical size of the chiller.
■    Capacity – HFC-134a has a lower capacity compared to HCFC-22, which means more refrigerant needs to be pumped through the chiller to achieve the same capacity. This can be accomplished by using a larger compressor or increasing the speed of the compressor. Both tend to increase product cost and design complexity. On the other hand, HFC-410a has a higher capacity compared to HCFC-22, which means less refrigerant needs to be pumped through the chiller to achieve the same capacity. The advantage is that smaller, less expensive compressors can be used.
■    Operating Pressure – A refrigerant that operates at a higher pressure requires heat exchangers and pressure vessels to be designed for the higher pressure. This adds cost. Conversely, higher pressure refrigerants have a greater density. As density increases, the required amount of refrigerant decreases, meaning that smaller or slower-speed compressors can be used. Lower pressure refrigerants, such as HFC-134a, will require larger or higher- speed compressors in order to achieve the same capacity as a similar chiller using HCFC-22.

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