Over the last year, I have become the proud owner of an energy efficient home. Designed and built from scratch, based on passive house principles by a team of local building professionals, construction is well underway, and the house will be completed by the end of the year.

Unfamiliar Territory

“What would it be like to build an efficient house? How can it be done? How hard can it be?” I knew there were a vast range and depth of possibilities for clever designs to minimize energy consumption, even if I did not yet know where all the details would land. Most of all, I wanted it to be fun, creative, and provide educational opportunities, for myself and the local building industry, around efficient construction.

The lot before building began

One Size Does Not Fit All

At the heart of the vision for my 1,200 sf house (exterior footprint), were key lessons learned over years of working with energy efficient commercial building design at Cx Associates:

• Conservation first: reduce loads before sizing equipment (passive house)
• Design for part load performance
• Separate ventilation loads from localized space conditioning loads
• Use free energy from the sun
• Reclaim heat energy
• Experiment, measure, and verify

Inclusivity is key. As many renewable sources of energy as possible were incorporated, with no single source expected to ever carry the entire load. Diversity of systems will ensure sufficient capacity during peak load hours, as needed. By designing to passive house standards, loads will be much smaller than for a typical home, with design annual heating loads estimated near $200 annually for a home located in the historically cold climate of Northern Vermont.

Priorities

The first phase of the house would be the performance phase. Solar PV would emphatically not be the first on the chopping block ‘because it could always be done later’. As many renewable sources of energy as possible would be incorporated. Fossil fuels would not be consumed. No compressors allowed. American and/or local materials and equipment preferred.

Architectural Drawing – Cross Section

My house includes the following systems:

• Passive solar design:
  • superinsulation with no leaks
  • generous south facing windows
• Concrete floors
• 90F radiant floor tubing in the bedroom/office and bathroom only, served by indirect solar heated water
• Solar hot water panels
• 0.75 kW grid tied solar PV system with deep discharge batteries
• An energy recovery ventilator with glycol ground loop preheat
• A wood stove
• Operable windows
• Instantaneous hot water heater served by indirect solar preheated water
• Manual dedicated shutoffs for every energy using device
• Manual shutoff for the solar tank heating element
• Temperature and power measurement for all energy using systems

Perhaps not surprisingly, my team was, at times, concerned. I did not want most of the usual things that people want when they build a house, such as internal doors, finished floors, kitchen cabinets, and painted walls. Could they take pride in their finished product? Did I understand what I was asking? Once they accepted that I wasn’t crazy, my building team has been so excited to be working on this project!

The balance sheet below shows the final reckoning of how I afforded my renewables.

Avoided costs and net cost of renewables

In Conclusion

The first year of occupancy will see the measurement and fine tuning of loads and systems for this special house. What will the actual loads be? How much capacity will the renewable systems provide? How many ways can heat be stored, moved, and used, almost for free? Stay tuned…

The house in progress

The post An Energy Efficient Home Informed by Commercial Buildings appeared first on Building Energy Resilience.

One of the first things I became aware of when I joined Cx Associates is that sustainability is a way of thinking. I learned efficiency and judicious use of resources can be approached on many different levels, from choosing a more efficient clothes dryer, to finding alternatives for drying clothes, such as line or rack drying. All efforts toward sustainability are important, and a large impact can often be had for little effort and inconvenience. Multiplied by dozens or even hundreds and thousands of people, a seemingly small change can go a long way.

Culture of Stewardship

Since becoming an employee at Cx, I have definitely reduced my ecological footprint. This blog post is an opportunity to look back and calculate my impact so far in three main areas: electric consumption, emissions and fuel consumption from transportation, and avoided landfill. Some of my efforts in these areas, such as transportation, are directly financially subsidized by the company, however most have come about indirectly via the somewhat intangible, but nonetheless very real, support of our company culture of environmental stewardship.

Electric Consumption

Reduction of my personal electric consumption came by way of what I call ‘Solar for Small Devices’. With a few struggles and a minor learning curve (a topic for a future blog), I have successfully taken all of my personal small devices ‘off the grid’ over the past two years, including:

• 17 inch laptop (personal use)
• Personal tablet
• Music storage/playback devices
• Cell phone (not a smart phone)
• Camera batteries
• GPS locator

for a combined total estimated 5 kWh removed from the grid per year, per person (like unplugging a 60W lightbulb for around 3.5 days, 24 hours per day). If 1,000 people did this, that is 5,000 kWh per year, just for plugging our devices into a different plug. The solar battery has 12V round, and 5V USB outputs. Inverters to transform from 12V to 120V AC are widely and inexpensively available for automotive and marine use.

Since sustainability has little to do with return on investment for one individual person, ROI is not my metric of choice when calculating solar impact. Energy saved does not need to justify the cost of sustainability—it is my responsibility to make the nominal investment.

If the investment in solar power equipment is compared with the cost of the devices themselves, many may agree that the $500 cost of my solar power gear, while not free, is a small cost compared to the devices they power (estimated at $5,000). My solar panels and battery with charge control can be shared with friends and used with all my future new devices as well. When viewed as an environmentally friendly upgrade option to the equipment, I think most people would pay the 10% upgrade cost.

Snowboarder (Photo credit: Sicran)

Many, including myself, could easily spend well over $500 on recreational activities, without ever looking for a payback. I figure, why start looking for payback when it comes to sustainability?

My scorecard so far: 2 years x 5 kWh =

10 kWh reduction in personal power consumption using clean solar PV instead of grid power

This may seem small, but it matters because the source of grid power may not be clean. It is not true that existing power systems are perfectly fine, and that solar systems can only compete if they can prove that they pay for themselves.

English: Crystal River coal power plant, April 2002 (Photo credit: Wikipedia)

Solar panel 3 (Photo credit: Photo Mojo Mike)

Reduction in Emissions and Fuel Consumption for Transportation

I came to Cx with a clean diesel car with a decent track record of 45 MPG average. I was under the impression, as I think many are, that I would need to modify my car to use biodiesel (4.582 lbs CO2/gallon) instead of standard diesel (22.91 lbs CO2/gallon) in my car.

What I found in my research as part of our Green Incentives Working Group is that diesel engines were designed to run on peanut oil, and that if I wanted to, I could go out the next day and fill my tank with B100, maybe even filtered waste vegetable oil. True, I will need to install a heater to use biofuel during the winter, however, between the months of May and October, I am emitting less CO2, and my car clearly likes biodiesel, with an improved average 10 to 15% miles per gallon. Further, my reduction in fossil fuel use by commuting on mass transit using the free bus passes from my company is estimated at 25%.

My three year scorecard so far based on 1,320 less CO2 and 35% less fuel annually:

3,960 lbs CO2 reduction
150 gallons fuel reduction

07-sep-05 (Photo credit: sashafatcat)

Avoided Landfill

Shortly after joining the company, I invested in a portable coffee mug, which I carry with me everywhere. My company also provides them for free, so I did not even need to purchase my own. As an avid coffee drinker, I save approximately one single use disposable cup per day, 365 cups per year, or 91 pounds of CO2 and 340 square feet of natural habitat saved, per person, per year. Combined with choosing to also use my portable cup for fountain drinks at lunchtime, I avoid use of an additional 100 bottles and cans per year—buying bulk when possible instead of buying individual packaging is more sustainable.

Four year score for avoiding single use disposable cups, per person:

364 pounds CO2 avoided
1,360 square feet natural habitat saved

Favorite Mug: MiGo Travel Mug (Photo credit: Mike Rohde)

Summary

In summary, a culture of sustainability in my workplace has positively affected both by own lifestyle, and the environment by providing a powerful incentive. Once I started looking, it was easy to see the ‘low hanging fruit’. The incentive of having an impact, and seeing that my small personal choices do make a difference, is reward enough.

Table 1 – Annual Reductions

⁽¹⁾ The population of Vermont is around 625,000 people.

⁽²⁾ The number of licensed drivers in Vermont is around 500,000 people.

⁽³⁾ Approximately equivalent to the energy use of a typical home in one year.

⁽⁴⁾ Approximately equivalent to planting 33 trees.

⁽⁵⁾ Habitat for one frog.

The post Sustainability and Workplace Culture appeared first on Building Energy Resilience.

This is the third and final post in a series focused on the connection between energy efficiency and sound control. Actually, the choice of sound control is somewhat arbitrary, and the topic could easily have been energy efficiency and temperature control, energy efficiency and lighting design, or energy efficiency and industrial process.

A Design Vacuum

My point is, energy efficient design does not exist in a vacuum. Efficiency is by definition a secondary consideration. As such, an efficient design will achieve its greatest success by association with some primary design requirement or need, such as the need for an appropriate sound environment in buildings, or any number of other design goals.

Zero Impact Not Feasible

Arguably, the only way to truly achieve zero impact on the earth’s resources is to sit still in one place until we die. Any other effort plunges us into the messiness of human existence and resource depletion. Many of us now recognize this messiness can and should be approached with an awareness and respect for the earth and her resources. But even if we apply the mantra of ‘efficient design’ to every aspect of our existence, perhaps instigating a radical change in how we and those around us behave, the intent is not to stop us dead in our tracks. A sustainable design is defined as design based on the capacity to endure in a way that ensures the wellbeing of the earth and resources for future generations. Similarly, if forced to choose between eating and not eating, we must always choose to eat. But how and what we choose to eat can be sustainable or not sustainable.

The Net-Zero, LEED Platinum-certified National Renewable Energy Lab’s Research Support Facility

What the Experts Say

Many experts in the field of designing sustainable buildings have touched on the idea that efficiency and sustainability do not stand separate from, and may even be perceived as of lower importance than, other design elements such as thermal comfort and sound control. John Straube of Building Science Corporation suggested in a presentation at Better Buildings By Design that you should tell people almost anything about the design—it will be quieter, they will be more comfortable—rather than saying it is more efficient!

Joe Becker of Becker Learning, points out that if we consider the benefits of efficient HVAC design (higher customer satisfaction, increased worker productivity), we can quickly convince ourselves, and others, that a more efficient design – which admittedly can sometimes be more complicated and expensive to implement – easily pays for itself. Why? Because it better satisfies a primary goal like building occupant comfort, and does so at a lower lifecycle cost than other alternatives.

Dr. Wolfgang Feist, director of the Passivhaus Institut, was quoted as saying, “We don’t calculate payback times—not on houses and not on solar thermal systems…Instead we look at the annual energy cost and at interest costs.”¹

Payback Can Be Misleading

Simple payback based on energy savings, while convenient and often convincing in a best case scenario, can be misleading, and result in wrong decisions. When it comes to efficient design, for sound control or any other reason, one size does not fit all.

While methods such as ROI may provide a more balanced approach, purely energy-based financial accounting for equipment investments is still in some way separate from the original purpose of the mechanical systems. The special case where two options, one more efficient, and one less efficient, serve the primary purpose identically, is often assumed but may not be true. Other metrics, such as increased productivity and satisfaction², which can also be measured in dollars and cents, paint a substantially more favorable picture for an investment in efficient design.

How Does This Relate to Sound Control?

Two final sound control examples can demonstrate this more holistic view of efficient design.

Example 1: Consider a discharge air duct from one building located directly across from a neighboring residential apartment building bedroom. The discharge air duct is too loud. By retrofitting the duct with a heavy gauge aerodynamic T fitting, the discharge area will more than double, reducing energy losses (yes, even considering the elbow), and will redirect a majority of the sound sideways instead of toward the bedroom.

Figure 1. Directivity of Discharge Duct Sound

The new duct may also reduce the load and energy use of the fan. Whether it pays for itself in energy savings is not relevant, because the primary reason for retrofitting was to reduce noise, not save money on energy costs. That said, we should always consider that a design may exist that will both reduce noise and conserve energy. Any potentially higher costs associated with the initial investment will yield multiple benefits for the life of the equipment, including energy savings, but the energy savings do not need to pay for the cost of the improvement.

HVAC Ducts on Building Exterior with Nearby Telephone Booth (Photo credit: Zach K)

Example 2: Consider the inlet conditions of a fan. In one design, the fan inlet provides turbulent air to the fan; in another, it provides a more streamlined airflow. The design with the more streamlined airflow is the better design, because there is a higher likelihood that the needed amount of ventilation air and comfort cooling will be provided with an appropriately quiet sound level over the life of the system.

It also uses less energy, and is therefore the preferred, most efficient design. The cost of the extra few feet of duct will be far outweighed by a variety of benefits, including reduced maintenance costs. However, if we rely on the calculated energy savings alone to justify the labor and material costs of the better installation, we may wrongly conclude that the improved inlet condition ‘is not really worth it.’.

Conclusion

If we develop tunnel vision on energy efficiency and think only of ROI and payback, the meaning of efficient, sustainable design can become distorted. A good design, whether for sound control, thermal comfort, or lighting, can become a scapegoat to the mistaken view that energy efficiency is the only measure of feasibility. Does that mean the importance of the net impact on the planet is secondary? How can a factor that is arguably a secondary factor also be one of primary importance?

The answer is that how we do things is equally important as what we are doing. If we accept sustainable design as the bar, we should continually strive to refine our design until we reach as close to near zero impact as possible.

In the 21st century, where traditional sources of energy and resources will continue to grow more scarce, and the effects of climate change become increasingly obvious, a design that does not consider sustainability and efficiency holistically is not a good design.

Upgrade and new construction projects already planned for reasons other than saving energy (such as sound control improvements), may represent a tremendous opportunity for the energy efficiency and sustainable design community to make a positive impact on our built environment.

———————-

¹ Energy Design Update Newsletter, May 2004

² BOMA publication “Office Tenant Moves and Changes” by Alton J. Penz and Sandy Beard

Energy Efficiency and Sound Control, Part 1

Energy Efficiency and Sound Control, Part 2

The post Energy Efficiency and Sound Control: Part 3 appeared first on Building Energy Resilience.

This is the second in a series of posts focused on the connection between energy efficiency and sound control. It may seem intuitive that efficient mechanical systems will also be quiet mechanical systems. However, it generally makes sense from cost and performance standpoints to deliberately design with both in mind.

Sound Control Design

It is possible, however undesirable, to apply sound control strategies without actually engineering a solution. For example, if manufacturer’s performance data for a duct silencer is used without understanding the system efficiency impact on of the silencer and project-specific fan sound frequencies, the result will be a design that fails to satisfy your client’s sound targets, and also imposes energy penalties and increased operational costs over the life of the system. A balance can be struck between appropriate background sound level design and equipment efficiency, as the following examples show.

Variable Speed Drives for Indoor Fans

Mechanical sound control recommendations typically assume indoor fans (supply and return) running at 80% flow for a VFD-controlled system. This helps prevent over-design of sound controls. (Passive sound control devices create a ‘pressure drop penalty’ that reduces energy efficiency. The greater the acoustic performance desired, the higher the static pressure drop penalty becomes.)

Space and budget permitting, for sensitive acoustical applications, custom sound traps can be used to target peak fan sounds such as pure tones (irritating fan sounds such as distinctly loud humming and buzzing) while simultaneously reducing static pressure penalties to realize operational cost savings.

Part Load Operation

To understand the acoustic impacts of part load fan operation, the table below shows quantitative and qualitative sound perception impacts for reduced fan speed compared to full speed operation. Based on a typical VAV system load profile with an average fan duty cycle at around 60% flow load ratio, most of the time, the main fan will operate at a speed that is ‘clearly noticeably quieter’ than full speed operation, even before sound controls are applied.

Figure 1. Typical VAV Duty Cycle. Reproduced with data from Energy Engineering, “Profit Improvement with Variable Frequency Drives”, Vol. 86, No. 3 1989

Figure 2. Fan Speed Impact on Sound

Potential first cost savings may be possible by resisting the urge to substantially oversize ducts throughout the building to reduce air velocity (as is sometimes recommended for sound control), and instead treat sound sensitive rooms on a case by case basis. This is possible because as the part load graph above shows, the fan is not running at full speed (the air is slower) most of the time. As shown, 85% of the time the velocity will be below 80% fan speed.

Additionally, right sizing and staging of Dx cooling equipment with respect to part load operation will simultaneously improve efficiency and reduce the potential for irritating sound environments due to compressor short cycling. If a packaged unit is deliberately selected larger to run at a slower quieter fan speed for the same CFM, the standard packaged compressors and motors may very well be over-sized for the application, which could create inefficiencies and acoustical issues. Right sizing of equipment for the load profile, and planning for smart acoustical adjacencies, can overcome both sound and efficiency issues.

While over-sizing the fan diameter for lower tip speed at equivalent CFM could be a good sound control strategy, the motor selection should reflect the intended operating point of the fan to avoid motor efficiency decreases at part load (see graph below).

Figure 3. Motor Part Load Efficiency As a Function of Load, By HP. By John Maxwell, “How to Avoid Overestimating Variable Speed Drive Savings”, 2005

Cooling Tower Fan Control

Over-sizing cooling towers and other capacity control strategies can optimize cooling tower/chiller system efficiency by providing lower temperature condenser supply water to the chiller. For a given design condenser supply water temperature, or for a given capacity control sequence, cooling tower cell design strategies provide ready examples of possible tradeoffs between fan efficiency and sound control.

The table below shows the change in sound perception for operation of multiple fans (such as multiple cooling tower cells) at different design speeds. In the table below, a possible strategy is to use two cells each running at half of the design CFM (9 dB reduction for half flow, plus 3 dB for two fans, for a net 6 dB reduction). This approach should result in clearly quieter sound levels with only a small impact on motor efficiency for motors over 2 HP, and an increased heat transfer efficiency due to the use of multiple cells surface area for heat rejection.

Figure 4. Sound Level Decrease for Multiple Fans Each Running at Part Speed

In this case, an upfront investment in additional cells, or upsizing cells, may help meet both sound and capacity control design goals. Motors should be right sized to operate in their most efficient range. Pony motors (smaller redundant motors which accommodate part load operation) may be an option for optimal motor loading. VFDs may represent environmental sound risk mitigation in addition to capacity control, and VFD efficiency penalties of around 3% may be partially offset by using direct drive fans and avoiding 5 to 8% belt losses.

If fan cycling is used for capacity control of multiple cell cooling towers, the following table shows a simplified view of the impact on sound levels for multiple identical sound sources.

Figure 5. Sound Level Incremental Decrease for Four Equally Loud Full Flow Fans

The length and orientation of the cooling tower assembly are design variables which can be optimized for reduced sound impact. For initial planning purposes, it is useful to consider potential acoustic impacts and benefits of quantity of cells operating. If the fans are single speed (rather than variable speed), the fan and motor can be selected with an optimal motor loading and operating point, and then system efficiency is achieved by turning cells off to match the load when not needed.

Conclusion

Deliberately engineering a system for both low noise and energy efficiency will, and should, result in different equipment selection and system design than would be the case where one or the other is not explicitly considered.

Additional design strategies for efficient sound control, such as improving fan inlet and outlet conditions, and control of exhaust duct discharge area and directionality, will be the topic of my next and final blog post in this series.

In summary, common strategies for reducing mechanical system sound may inadvertently result in higher energy use if part load motor inefficiencies are not avoided during design. A careful design review including sound and efficiency analysis, and specification of balancing for lowest energy use, will help ensure operational cost savings and a successful project.

References:

¹ Energy Engineering, “Profit Improvement with Variable Frequency Drives”, Vol. 86, No. 3 1989

² How to Avoid Overestimating Variable Speed Drive Savings, Jonathan B. Maxwell, 2005.

The post Energy Efficiency and Sound Control: Part 2 appeared first on Building Energy Resilience.

What does sound control have to do with energy efficient design? This blog post is the first in a three part series that will explore the intersection of sound and energy efficiency in existing buildings. My early experience as an applications engineer in mechanical systems noise control made me aware of the connection between the built environment and equipment energy use. System airflow requirements and the impact of total added pressure drop of sound control solutions are primary design variables for a noise control engineer. Full scale HVAC aero-acoustic laboratory testing is an integral component of sound control design.

Importance of Sound

The sound environment in buildings is a comfort condition which significantly affects productivity, occupant satisfaction, and our ability to learn. Any design engineer involved in large-scale building projects has had to consider the impact and control of sound. For a building design to be successful, the built environment, including the background sound level, must be usable for its intended purpose. Since air is widely used for heat exchange and ventilation in HVAC design, and air delivered to a space will convey the sound created by the mechanical equipment and duct system components that it encounters, reduction and control of aerodynamic sound has a reciprocal impact on the design and operation of airside mechanical systems.

Good Design

A good design serves the full range of operational requirements at the lowest possible energy and financial cost over the life of the system. Noise is wasted energy. If a system is noisy, energy is probably being wasted. To give an example of where an improvement in energy efficiency also resulted in mitigation of noise, in a recent pro bono design review by Tom Anderson of Cx Associates for a local church, an oversized air handling unit was eliminated in favor of a smaller energy recovery unit. The result was a smaller, quieter, less expensive system that could be located in the basement away from a noise sensitive sanctuary, easily meeting the stringent NC-20 acoustical design target. Thus a good design was reached through control of energy and noise.

Opportunities in Retrocommissioning (RCx): What to Look For

How can you make low cost modifications to airside distribution systems that will improve occupant comfort and reduce energy costs? From a noise/energy control standpoint, it is generally effective to start at the source, for example, by reducing fan speed, lubricating bearings, and making sure belts are properly tensioned. Even if your building does not currently have variable speed fans or a sophisticated building management system, significant annual savings from improved air distribution design may still be a low cost opportunity.

Reducing unnecessary static pressure losses (such as “system effects”) in an existing constant volume system can improve opportunities for lower fan turndown resulting in quieter sound levels and lower energy use.

Figure 1 – Unnecessary System Pressure Drop Reduces Airflow, Requiring Higher Fan Speed to Reach Design CFM, 2009 ASHRAE Handbook Fundamentals, p21.12

If a system is noisy, it should be on the top of the list for a review of energy efficiency measures, but even if noise is not excessive, there may still be unnecessary losses associated with construction and balancing of your existing systems. Did the balancer add system pressure drop by closing dampers to meet the engineer’s specified operating point, instead of reducing fan speed? If so, the system could be rebalanced for lower fan speed by opening dampers and installing a VFD or resheaving the fan. Did the HVAC contractor install an abrupt transition immediately after the fan? Alternative routing or fan reorientation will mitigate high head losses in blast areas.

Figure 2 – Blast Area High Velocity Profile, High Head Loss, 2009 ASHRAE Handbook Fundamentals, p21.12

In another example, a standard sound attenuator may already be installed, adding 0.25” w.c. static pressure drop to the system, permanently, at all times. If such an attenuator is installed in a non-ideal location due to difficult site conditions, this pressure loss could increase by a factor of two or more due to airflow turbulence interactive ‘system’ effects [1].

Figure 3 – Eliminate Unnecessary System Pressure Drop

It may be possible to replace the sound attenuator for a few hundred dollars with one that adds no pressure drop, or to relocate it to a more favorable location. Potential annual cost savings for eliminating 25% of system pressure drop for an existing mid size constant volume fan may be comparable to average savings for an existing similarly sized VAV supply system with static pressure reset control, assuming an average CFM load of between 75% and 80% design CFM. While 75% to 80% may be on the high side for a typical VAV system, the potential savings for reduced static pressure on a constant volume fan can be in a similar range, 15,000 to 20,000 kWh ($1,500 to $2,000) per year.

Figure 5 – VAV Typical Operating Range A Practical Guide to Noise and Vibration Control for HVAC Systems, M.E. Schaffer, ASHRAE

Make the Most of your RCx Investment

In summary, low cost improvements could result in significant energy and cost savings for a mid size constant volume supply fan, typically paying back in less than five years, even for systems without direct digital control.

An awareness of sound control issues and methods can help your existing building RCx project maximize energy and cost savings and occupant comfort. Even if a system is equipped with automatic controls, a walkthrough of the physical systems and a drawings review including air distribution systems are essential before sitting down with the controls contractor to ‘tweak’ the systems. The danger of relying on controls alone to reduce energy before understanding the actual as-built existing systems is that your RCx effort may only scratch the surface of potential savings.

[1] Application of Manufacturer’s Sound Data, ASHRAE, 1998

The post Energy Efficiency and Sound Control: Part 1 appeared first on Building Energy Resilience.

Anyone involved in the Measurement and Verification (M&V) of building energy savings has encountered Stratified Random Sampling (SRS), a statistical tool used to handle the huge volume of data from the large number of projects and measures in a typical building energy research effort. From calibrated energy modeling to program evaluation and from the field through to the whitepaper, the use of applied statistical principles will simplify and improve the accuracy and defensibility of your M+V work.

Resistance

Now, at first glance, what could go wrong? Engineers are smart and like math, right? However, the reality of seeing a statistical sampling plan through from start to finish can go against the grain for a typical engineer. Here’s a look at why this is an issue in for Measurement and Verification, and what you can do about it.

Why Sampling?

Consider an example project: an efficient lighting retrofit in a school. You are the lead engineer responsible for evaluating the actual energy savings realized in a lighting upgrade. Imagine that this is one of a dozen similar projects that you are responsible for addressing in a relatively short timeframe.

Chances are you will be given a list, by a statistician, with a few dozen different efficiency measures, all with different levels of use to be verified, including new fixtures in the gym, high performance lights in three kinds of classrooms (60 rooms total), the library, office, and auditorium, as well as new LED parking lot fixtures.

It will begin to dawn on even the most intrepid engineer that there may not be enough time and metering equipment available to complete their evaluation in a timely fashion with the level of engineering rigor one might prefer. Enter statistical sampling.

The Sampling Plan

Below is an SRS sample size calculation for a generic school lighting project. For each usage group, the estimated power or energy savings and the quantity of light control switches are used to obtain the number of ‘tests’ required for an acceptable level of statistical accuracy and precision. Note that instead of metering all 180 classroom lighting circuits, sampling allows us to meter only eight and still achieve valid results!

Figure 1 – Sample Size Calculation

The Site Visit

You check in at the front office and successfully complete the field portion of your evaluation, installing the specified number of loggers in the exact random locations shown on the floorplan. The installed equipment is exactly as documented in the project file.

Figure 2 – Installed Logger Documentation

The Analysis

After all the energy loggers have been successfully retrieved two weeks later it is time to hunker down for the analysis. This is where an engineer begins to break faith with the sampling methodology. After all, now that we have The Data, hasn’t sampling reached the end of its useful life? However, for the sampling plan to be effective, it needs to be utilized in the final analysis too.

Figure 3 – Classroom Sample Group Average for 24 Hour

For example, in the Classroom Sample Group graph above, the lights are on 80% of the time between 7 and 8 am, on average. However, since the Classroom 1 energy logger measured that the lights are always on 100% of the time between 7 and 8 am, it can be difficult for an engineer to use the 80% number in their savings calculations for Classroom 1. Yet that is what an SRS approach requires.

In another example, we may have introduced bias on site by choosing ‘the best’ or most convenient metering locations, rather than using random numbers to choose meter locations, as required for SRS. This may result in overestimating, or underestimating, evaluated classroom energy savings.

 Statistics vs. Engineering

The reason following through with an SRS approach can be a challenge is that engineers have learned to rely on their judgment, and in fact have made a career of it. Codes of ethics generally prevent us from expressing a definitive opinion regarding events about which we have no direct knowledge, at least not without a defensible reason. Statistics, on the other hand, has everything to do with drawing precise conclusions about real events, such as lighting usage in a classroom that was not measured, using no judgment or reasoning, using only a random number approach.

If an engineer has been told that ‘no one really uses that room,’ and it was found locked with the lights off, it can take some convincing to persuade them to take measurements in that room. From the statistical point of view though, if the sampling plan was prepared correctly, it does not matter whether a particular room is used all day every day, or only twice every other Sunday. What is important is that the room was randomly chosen without bias, and not out of convenience, since that very randomness is what establishes the validity of the energy savings for the SRS project.

Conclusions

It may be helpful for building energy engineers using SRS for Measurement and Verification to keep three things in mind:

1)     If site conditions are truly inconsistent with the sampling plan, the engineer can and should exercise their engineering judgment by re-sampling the project on site.

2)     Remember that the metering results might surprise you! If you already knew the answer, you wouldn’t need to meter it.

3)     Trust the methodology. Statistics is widely accepted by many as a valid approach. Strike a balance between a healthy level of professional vigilance in the interest of the highest public good, and trusting that your approved sampling plan has captured the primary variables of interest, for the purposes of an energy savings calculation.

In summary, the more we can learn about when, how, and why, buildings use energy, the better we can control it. Using SRS will allow you to stay ahead of the curve, and be the first to predict trends accurately enough to specify optimal energy control solutions, without depleting your time and financial budgets.

The post Measurement & Verification of Building Energy Savings: Work Smart Not Hard appeared first on Building Energy Resilience.

Project-specific energy efficiency baselines, where the starting point for building efficiency is adjusted based on knowledge from our past successes, will become the norm as the energy efficiency market becomes more sophisticated. You read it here first.

I make this prediction based on my onsite measurement and verification experience (M&V) and participation in baseline studies. Let’s examine three examples for a look forward at the efficiency planning landscape in years to come. Project-specific baseline issues apply to existing buildings that have received prior efficiency upgrades and to new buildings subject to increasingly stringent energy standards. Whether efficient systems are installed due to efficiency program incentives or changing attitudes toward responsible energy use, the use of accurate baselines is ultimately essential to successful projects.

Daylight Harvesting Controls in the Baseline for Efficient Lighting Upgrades

Energy efficient lighting savings are often based on ‘always on’ operating hours, however this may not actually be the case. Using an ‘always on’ point of reference can create inflated expectations of cost savings. Whether controlled manually by occupants, by code-required controls, or other automatic controls, when the lights are off, they are not saving energy compared to less efficient fixtures, or compared to a code‑maximum allowed lighting power density (LPD).

It is not unusual to find lighting controls already installed, such as daylight harvesting, occupancy sensors, and multilevel switching.  In fact, automatic lighting control for buildings larger than 5,000 square feet has been required by ASHRAE 90.1 since 1999, and with the adoption of ASHRAE/IES 90.1-2010 automatic lighting controls are even more stringent. In one real world M&V project it was found that the annual energy savings for an efficient lighting project was on the order of 150,000 kWh lower for the actual installed system than for a reference system that was always on. The lower run hours were due to a daylight dimming system that was standard practice for the building owner.

In this example, an ‘always on’ assumption overestimated the impact of the better lights. That said, the efficient fixtures saved a verified 1,630,596 kWh annually, even with the daylighting controls in place. Clearly the efficient fixtures had a substantial impact, however the absolute cost savings reduction over more years due to an incorrect baseline could be significant on a net present value basis. Using project specific baseline hours of operation is therefore essential to avoid possible perceptions of underperforming efficiency investments in the long term.

Productive next steps toward creating a culture of efficient buildings will depend on new benchmarks such as verified success and persistence of efficient measures. In the lighting example above, will the fixtures continue to be replaced with efficient products? It will become increasingly important to shift focus from initial implementation, which can be likened to ‘triage’ for many projects, to a more mature model of responsible energy use. This new model has an emphasis on design review, successful implementation, and ongoing commitment to preserving the energy efficiency infrastructure through real time energy use monitoring systems and continuous commissioning that compares historic use to current, and identifies and attacks upward trends in building energy use.

Variable Flow Fan Systems as Baseline for Outside Air Conservation Measures

In another real world example, fan system sizing in a variable speed integrated lab exhaust system resulted in underestimated fan energy savings by a factor of 200%. Variable speed laboratory exhaust systems are a common option used to satisfy code requirements when the total fume hood exhaust rate is 15,000 cubic feet per minute (cfm). Outside airflow is reduced based on the quantity of hoods in use, saving fan energy in addition to heating and cooling energy. However, the amount of fan energy saved depends on system sizing.

It is not unusual to find installed mechanical systems that are larger than needed, frequently running at part loads less than 50% of the original design due to differences between site conditions and conservative design assumptions. This means that the actual input power of the fan is in a lower range than expected, and fan energy savings are smaller than they would be for a more fully loaded system due to the fan system affinity laws for power and airflow.

‘Right sizing’  in variable speed systems maximizes savings compared with an oversized, partly loaded system. Regardless of whether the savings were smaller or larger than the original estimate, savings calculated based on variable speed baseline systems may be substantially different than expected unless the actual operating point brake horsepower of the baseline system, after balancing, is considered.

VFD in Constant Volume Applications

Savings based on nameplate motor horsepower, even if reduced by a factor to account for motor upsizing, has been shown in our M&V work to overestimate savings when VFDs (Variable Frequency Drives) are installed to permanently reduce the speed of a fan or pump to a lower-than-design constant speed. Future retrocommissioning savings for existing equipment may be significantly less than in the ‘old’ days when constant volume baselines based on the full design brake horsepower provided highly favorable financial justification. Energy savings calculations should be based on the actual operating brake horsepower after balancing of the baseline system.

The Future

Our successes in reducing energy use are paving the way toward a new vision of responsible resource utilization. By championing innovative design and controls implementation, and preserving our hard-won efficient infrastructure, our buildings can advance beyond a collection of efficient products and systems toward a built environment that embodies appropriate use of the Earth’s resources.

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