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Utilities across the U.S. are investing in smart meter infrastructure to give them more flexible tools to manage the electric grid. These tools will help them address challenges and capitalize on opportunities presented by distributed and renewable energy generation, and the use of energy efficiency as a resource to offset new generation needs. Although smart meters are already in much of the U.S., their potential for data is just beginning to be explored.
One area of interest is in quantifying the impact of energy efficiency programs, projects, and measures. The use of smart meter data to determine net-metered energy savings is not new. It’s been around for years under the moniker “whole-building” savings verification, Option C under the oft-cited International Performance Measurement and Verification Protocol. Before smart meters, this option for measurement and verification gained a reputation for having limited applicability and being slow and expensive compared to other methods. With only monthly billing data available, whole-building savings typically required at least a year of baseline and post data, and savings on the order of 10% or more of the building’s energy use.
Smart meter data, often available in 15-minute intervals and stored in electronic databases, has expanded the possibilities of using meter data to verify savings. The shorter data interval increases the sample size and reduces unexplained variability, allowing whole-building techniques to work on projects with smaller savings and shorter monitoring periods. The vast amount of data allows for approaches that can quantify savings at the program or population level.
This increase in the granularity and availability of big data made possible by smart meters is beginning to show itself in policy. In California, Assembly Bill 802 calls for the authorization of programs to “increase the energy efficiency of existing buildings… taking into consideration the overall reduction in normalized metered energy consumption as a measure of energy savings.” The implementation of this bill has so far resulted in several new programs designed around meter-based energy savings. Additionally, meter-based savings have the potential to form the underpinnings of a new energy economy, validating savings to pay for financed investments in energy-efficient technologies and buildings.
Predicting Savings at the Meter
As meter-based savings become more applicable to a variety of programs and more economical to deploy, a program’s ability to generate real savings at the meter will be tested. In the past, utilities have relied on deemed or custom savings estimates to predict the performance of programs, projects, and measures. Upfront prediction of savings is necessary to estimate economic benefits and inform incentive calculations at the time customers are considering an investment in energy efficiency. Accurate predictions are also necessary for utilities, implementers, and financial backers to effectively run programs and invest confidently in building upgrades.
Deemed savings inherently ignore measure-to-measure and project-to-project variability, attempting to estimate the typical savings that will be produced. This works fairly well for simple programs offering simple measures like light bulb replacements, but for more complex measures and programs, deemed savings have a terribly inaccurate and variable track record in terms of ability to predict actual energy savings. This is evident in a sample of California HVAC program EM&V results over the past decade or so, where verified savings average only 41% of savings claims, and the correlation between deemed and actual savings is extremely weak.
Meanwhile, custom savings have traditionally been accompanied by troublesome requirements for eligibility pre-qualification, project data, and documentation requirements. This puts custom claims out of reach economically for mass-market programs targeted at the residential and small commercial markets that represent most building energy consumption and savings potential. Additionally, most custom savings claims fail to account for variations in actual installed system performance relative to rated equipment performance, relying on ratings themselves or assumptions rather than measurements to establish baseline and proposed efficiency values.
With meter-based savings verification becoming the yardstick for measuring program success, the shortcomings of both deemed and custom savings estimation approaches will become even more apparent. For programs, projects, and measures that involve more complex systems like HVAC, the industry will need to come up with approaches that balance data and documentation requirements with the need for improved savings estimates that accurately predict energy savings at the meter.
Performance-Based Savings
Energy savings estimates and claims that incorporate field-measured system performance and key building operation attributes are one potential solution. The National Comfort Institute recently completed a study for a major electric utility showing the measured performance of HVAC systems could be used to reliably predict metered energy savings for duct system renovation and equipment restoration improvements. Renovation work was completed on 31 systems serving seven commercial buildings. The performance-based savings predictions aligned quite well with the actual savings measured.
Interestingly, these results do not account for variability in building operation, and the project sites included both fast-food restaurants with nearly around-the-clock operation and small offices with typical weekday operation. The correlation is purely dependent on the measured pre- and post-capacity and efficiency of the HVAC systems serving each site.
In addition to informing accurate energy savings estimates, measuring system performance in the field provides HVAC contractors with valuable diagnostic tools to allow them to develop a targeted scope of work to improve system performance. Scores representing system capacity and efficiency, in addition to the savings estimates, are effective sales tools for contractors to use in explaining opportunities and benefits to customers.
Predicting Metered-Savings
Meter-based savings verification holds great potential for improving the transparency and accuracy of energy savings claims, potentially spurring new energy efficiency financing models and investment opportunities. However, accurate up-front savings estimates are required to provide customers, utilities, investors, and other stakeholders the confidence they need to provide the required up-front capital. The traditional deemed and custom savings approaches fail to provide accurate savings estimates that can cost-effectively be applied to HVAC efficiency improvements in the residential and light commercial building sectors. Deemed savings were never intended to capture variability between individual buildings and the systems serving them. Custom savings are typically accompanied by onerous data collection requirements, yet still do not typically account for variability in system performance relative to manufacturer ratings.
Ben Lipscomb is a professional engineer in Whitefish, Montana. He serves as National Comfort Institute’s engineering manager, where he draws on experience in HVAC lab testing, field research, and utility energy efficiency program design to provide technical leadership for the company and consulting services for clients.
