(third in a three-part series)
Mike Opitz PE, LEED AP
Certification Manager, LEED for Existing Buildings
U.S. Green Building Council
Recap
The first article of this series summarized what energy Measurement & Verification (M&V) is, and what it can do for building owners and facilities managers. In essence, it’s a standard set of ways to determine how much real savings results from an energy project, which is critical in determining a project’s true impact both to a facility’s bottom line and to the environment.
The second article outlined the main issues you need to consider when deciding how much M&V you need for your energy project. That involves getting a handle on the energy savings risks that limit your actual savings as well as your ability to quantify them. More specifically, M&V will directly reduce one component of energy savings risk: uncertainty risk. All else equal, the more uncertainty you can tolerate in your final savings estimate, the less M&V you need, and the less you’ll need to spend on it.
Once you’ve decided how much savings certainty you’re willing to pay for as an overall goal, you still need to know how to design an M&V process to meet that goal. The mathematical details of computing savings uncertainty are complicated, and are summarized in the resources, but they all depend on how you choose among the standard technical M&V options and then how you implement your choices. This final article will explain these standard options, the key technical planning decisions they encompass, and how these details apply to common energy project examples.
In the end, M&V is about getting better knowledge of the performance of your energy projects, which enables better planning of your future projects. Thus, good M&V helps you to be confident you’ve saved the most energy cost for the smallest initial investment. That’s a concrete competitive advantage all organizations should explore.
Standard M&V Options
Three fundamental industry standard options to determining energy use have been developed by M&V experts, and essentially all assessments of energy projects use one or more of them:
System-Level Measurement—isolating the performance of a single energy-using system or a group of similar systems, such as a bank of light fixtures, a plumbing fixture, or a single chiller, boiler, or air-handler. Requires installation and maintenance of specialized metering equipment tailored to the type of energy consumed, as well as careful data collection and management. Occasionally the metering equipment is built into the system itself (packaged chillers) or available through a separate building Energy Management and Control System. Most suitable when the energy project is targeted at only specific systems, or when high accuracy is desired and the budget allows for the necessary rigor. Good choice if the project is restricted to one type of mechanical system, or if no whole-building utility meters are installed. (NOTE: this option is sometimes split into two separate options, with the second variant allowing some performance parameters to be stipulated using engineering assumptions, e.g., measuring actual lighting usage patterns but not measuring the power draw, instead assuming it corresponds to the manufacturer’s specs.) Generally costs more for all but the simplest of retrofits (e.g., lights or plumbing fixtures).
Whole-Building Measurement—treating the building as a single energy-using system by tracking the flows of all commercial energy sources entering it, including electricity, gas, oil, hot water, and steam. Usually done with consumption data from utility bills, so requires installation of meters on any unbilled energy flows. Provides low accuracy because of noise in utility bill data. Good choice if several energy projects in a building interact, systems don’t need to be isolated, and available technical expertise is limited. Generally costs less if high-quality utility meter data is readily available.
Calibrated Simulation—estimating the energy use with building energy modeling software, at either a system or whole-building level, then comparing those results to some measurement for verification. Requires specialized knowledge and deep experience to get good results, but is the only option when no measured energy baseline is available (e.g., new construction or a retrofit that’s already been done). Also suitable when system-level measurement is too expensive but whole-building measurement isn’t accurate enough.
and Their Implementation Details
You have considerable flexibility in how to implement the three M&V options depending on which measurements you perform and how; which technical information about your equipment or building you collect, and with what detail and completeness; and how you use all this information mathematically to calculate the energy savings. Key technical planning decisions for any of the options include:
- The quality of the surveys of your equipment, both pre- and post-retrofit – this defines how many systems you have, what type they are, and summarizes manufacturer’s performance specs. Good inventories cost more time and money to produce, but provide higher savings accuracy because they give you better, more complete information.
- Instrumentation specs, ease of use, staff training—all instruments introduce error into the readings, depending on their quality and how well they’re calibrated. Even good instruments can produce bad results if misused by inexperienced or poorly trained staff: some are easy to calibrate and deploy, while others require more expertise. Utility meters may have unknown or inappropriate accuracy.
- Data collection & management—data must be reliably recorded and stored and not lost or garbled. System-level measurements may be mismanaged, and utility bill data may be incomplete.
- Sample size and structure—the number of measured mechanical systems or buildings compared to the total number retrofit, and whether that sample is purely random or intentionally weighted. If only some systems are measured, they may not be representative of the whole group, skewing the average. Also, sampling inherently risks that some significant but valid outliers may be missed.
- Measurement duration—whether the measurements are done continuously for the whole project term, on a short-term basis (a few days or weeks to detect a pattern), or only instantaneously to get a single value
- Complexity of the mathematical savings models—all energy savings are calculated using some type of mathematical equation that’s based on a model of the situation. Since all models involve simplifications of reality, they all introduce errors depending on the number of variables used in the equations. Simple equations may not account for all important variables, whereas complex equations may be poorly understood or used incorrectly.
- Assumptions/Stipulations—whether you use engineering assumptions instead of measurements for any parameters in the savings models. Using stipulations simplifies M&V, but may reduce savings accuracy. Even a good model may include questionable assumptions for some of its variables.
All these issues are technical elements of the uncertainty risk discussed in detail in the second article in this series.
As you address these issues you should keep in mind how much technical expertise you have in-house to either perform the M&V work yourself or to monitor the work of consultants. Simple measurements like single-phase spot power readings or short-term run-time checks can be done well by properly trained general technicians, and these activities are readily observed and understood when done by consultants. Other tasks, like continuous logging of 3-phase power, regression analysis of whole-building electric bills, or building energy modeling, require specialized knowledge and experience and close attention to detail to get good results, and are harder to monitor effectively. Having expertise in-house is more important if these tasks are part of your M&V Plan.
Application Examples
As a general rule, a technically more complex project means you’ll have to spend more on M&V to get a given level of savings certainty (or equivalently, you’ll get less certainty for a given amount spent on M&V). An easy way to see this is to compare two common projects that employ the first M&V Option described above: system-level measurement.
A simple lighting fixture retrofit might need only short-term measurements of fixture usage to define a pattern plus spot-measurements of fixture power draw. If accuracy needs aren’t strict or if the budget is tight, you can avoid some measurements by stipulating the power draw using manufacturer’s data. In either case, a simple engineering calculation provides energy use from these quantities, so modeling risk is low. Small sample sizes would provide high savings certainty, and few if any savings adjustments are needed. Plumbing fixture retrofits are similar.
On the other hand, HVAC-related retrofits usually need continuous year-round measurements at either the system level or whole-building level because of large hourly, daily, and seasonal fluctuations in energy use. This high variance means larger sample sizes are needed to get high savings certainty, and savings adjustments are needed for weather at least, and perhaps occupancy hours, temperature setpoints, and other factors as well. Each extra savings adjustment requires its own measurements, which raises M&V costs. Savings models are relatively more complex, resulting in higher modeling risk.
Conclusion
This series has provided only a basic introduction to the complex topic of measuring and verifying energy use and savings. As you can see, you need substantial background knowledge to devise or negotiate a good M&V Plan. Getting an appropriate, technically rigorous result demands that you dig into the issues and make some tough choices, but by the time you’re done you’ll have a good estimate of how much energy and money your project really saved, not just how much the energy bill changed. You’ll also know how confident you should be in that estimate. That puts you in a great position to plan and execute your next energy project even better, which gives you and your organization a real competitive advantage in the marketplace.
Resources
International Performance Measurement and Verification Protocol (www.ipmvp.org)
Offers free downloads of several voluntary M&V standards representing consensus of global experts. Volume I includes an excellent introductory, non-technical overview of M&V concepts.
Federal Energy Management Program’s M&V Resources (www.eere.energy.gov/femp/financing/superespcs_mvresources.cfm)
Free download of the Department of Energy’s FEMP M&V Guidelines for federal government facility managers to use in planning and implementing M&V on energy projects, plus many other M&V planning resources.
American Society of Heating, Refrigeration, and Air Conditioning Engineers (www.ashrae.org)
Publishes ASHRAE Guideline 14: Measurement of Energy and Demand Savings. Highly technical, but a good resource for engineers responsible for executing or overseeing M&V work.
U.S. Green Building Council (www.usgbc.org)
The USGBC’s LEED for Existing Buildings program addresses M&V issues in several of its requirements and credits.
