What is ENERGY STAR?
You may have seen an ENERGY STAR sticker on a microwave or washing machine, but have you ever noticed an ENERGY STAR plaque on a building? Before a coming series of posts diving into what existing benchmarking data from DC buildings can tell us, it might be useful to quickly look at the primary building energy performance benchmark – the ENERGY STAR score. First of all – yes – when written properly it is all capitalized.
ENERGY STAR is a program administered through the US Environmental Protection Agency (EPA) as a government-backed symbol for energy efficiency. ENERGY STAR covers consumer products as well as residential, commercial and industrial buildings through voluntary self-reporting, although there are programs such as Washington DC’s Building Energy Efficiency Performance Standards (BEPS) that require or incentivize use of ENERGY STAR to report benchmarking data. For this examination we will focus on commercial buildings and how ENERGY STAR specifically applies to programs like DC’s Building Efficiency Performance Standards (BEPS) and other building performance benchmarking.
As discussed in this brief overview of BEPS, a building’s ENERGY STAR score from 1 to 100 is the key metric that DC uses to determine whether a building is subject to BEPS and how much the building performance has improved over the BEPS compliance cycle.
How Does a Building Get an ENERGY STAR Score?
According to the EPA, nearly 25% of all commercial building space in the US is already being benchmarked through Portfolio Manager, the free EPA tool that is used to measure and track energy and water use. Users upload building information and consumption data into Portfolio Manager which then allows users to assess building energy performance, track changes in consumption over time, create reports and share data with outside stakeholders. Portfolio Manager also tracks whether building performance qualifies for ENERGY STAR recognition and encourages users to apply when qualified (an ENERGY STAR score of 75 or above).
Once a building is setup in Portfolio Manager, the key input is utility data from various meters in a building which track energy and water usage. Many utility companies and service providers allow data exchange directly between their platform and Portfolio Manager, minimizing the amount of work needed to track consumption.
To receive an ENERGY STAR score, all energy use for the whole building must be metered and tracked through Portfolio Manager (electricity, gas, oil, onsite renewables, etc) and there must be 12 consecutive months of energy data for all active meters and energy sources. Once these two criteria are met, Portfolio Manager will generate a 1-100 ENERGY STAR score for the building.
What Does an ENERGY STAR Score Mean?
An ENERGY STAR score is a single data point that reflects how efficient a building is at using energy relative to the similar buildings around the country. Specifically, the EPA measures usage of source energy, which includes transmission, delivery and production losses to make a complete assessment of energy efficiency in the building (more on source vs. site energy usage in the future).
An ENERGY STAR score of 50 represents the median score, whereas a 100 is the most efficient building of that type. A score of 75 or higher means the building performs in the top 25% of buildings of that type and qualifies a building as “ENERGY STAR certified”. An ENERGY STAR score condenses dozens or hundreds of data points to assess how a building is performing, while controlling for the type of building, hours of operation, physical characteristics, occupant density, weather and more.
According to the EPA, the objectives of an ENERGY STAR score are to evaluate energy performance for the whole building, reflect actual energy consumption, account for different energy sources, normalize for building activity and provide a peer group comparison.
How Source Energy is Determined
For the purposes of ENERGY STAR scores, the EPA uses a national conversion factor to calculate source energy use intensity (EUI) from site EUI for each energy type (electricity, natural gas, etc). The more technically accurate alternative would be to use the eGrid subregion conversion factors which differ for each area of the country depending on the electricity generation on that subgrid. This is a rather important choice as it more fairly scores buildings independent of their location, and their utility providers.
As an example, Buffalo, NY and New York, NY, while in the same state, have significantly different energy inputs into their electricity grid. 74.1% of the electricity in the NYUP subgrid is generated from nuclear and renewable energy, resulting in the lowest CO2 emissions per MWh of electricity in the country. 400 miles away in the NYCW subgrid, less than 1% of electricity generation is from nuclear and renewables and the resulting electricity generates 3.5x more CO2 per MWh. Identical buildings in Buffalo and New York City receive the same source EUI score due to the EPA’s choice to use a nationally averaged site to source EUI conversion factor.
This is beneficial because the building owner in New York City has no control over the generation mix of their electricity grid, and certain areas of the country would be majorly disadvantaged in ENERGY STAR scoring without this balance. However, it does mask the impact of certain decisions, particularly related to removal of fossil fuels from buildings and electrification. Due to the relative inefficiency of electric heat, transmission and generation losses, and generation mixes, there are areas of the country where switching to all-electric heat generation may actually be less climate friendly than existing on-site fossil fuel-based heating.
Modeling Deep Dive – Feel Free to Skip
Buildings are not just compared to other buildings within Portfolio Manager – the benchmark is a national survey of peer buildings such as the Commercial Building Energy Consumption Survey (CBECS) which is a periodic national survey conducted by the Department of Energy and gathers data on thousands of commercial buildings across the country*. The CBECS data is used to create an equation of building energy use regressed across a number of variables such as size, operating hours, number of occupants per square foot, etc to find the combination of most statistically significant operating characteristics that best explain variance in source EUI. For office buildings the significant variables are size, number of computers, number of workers, weekly operating hours, heating and cooling degree days, % of building that is cooled, and whether the building is a bank branch.
*For some building types industry groups perform their own national surveys to obtain the baseline dataset. For example, Multifamily Residential buildings are benchmarked to a 2012 Fannie Mae industry survey.
With this equation for a typical building, the data entered into Portfolio Manager can be used to calculate the actual source energy use of the building in question and the predicted source energy use from the building model. The predicted source EUI is the mean EUI for a hypothetical population of buildings that share the same values for the key variables mentioned in the paragraph above. The efficiency ratio (actual energy use divided by predicted) of the building can be generated and then compared to the national distribution of efficiency ratios for peer buildings; the percentile of this efficiency ratio becomes the building ENERGY STAR score.
In the figure below for office buildings, an Efficiency Ratio of 0.5 – i.e. the building being scored consumes 50% of the source energy as would be predicted by the regression model – corresponds to a cumulative percentage of 16%. In other words, 16% of office buildings perform better than the examined building, relative to their particular characteristics modeled by the ENERGY STAR equation. This is the 84th percentile of building performance and would result in an ENERGY STAR score of 84.
How Does This Plug into Building Efficiency Programs Like BEPS?
This unified system makes programs like the Clean Energy Omnibus benchmarking requirements and BEPS much simpler to administer and comply with. For government agencies operating programs, ENERGY STAR scores allow for direct comparisons of building performance, whether that is locally or across the country. Local governments do not have to collect data, determine benchmarks, analyze performance or provide the method of grading since the EPA has done that at a national level. For building owners, ENERGY STAR provides a single system that is recognized and accepted nationally, eliminating potential duplication of effort or use of multiple systems and standards in different areas. The EPA provides Portfolio Manager as a free tool that links directly to many utility providers, allowing for automatic data exchange, and easy visualization into a single building or portfolios of buildings.
DC’s Building Energy Performance Standard uses ENERGY STAR scores as both the criteria for which buildings fall into the program, and the metric by which improvement is measured. For BEPS, the DC Department of Energy and Environment (DOEE) determined the median ENERGY STAR score for each building type in the district (for buildings > 25,000 sf) and any building which scored below that median value was subject to the following cycle of enforcement. Due to the standardization of ENERGY STAR scores, program administrators and building owners know that each score is controlled for size, occupancy and other variables, allowing for a direct comparison of building efficiency.
ENERGY STAR is also used on the back end of each cycle of BEPS, as the standard evaluation metric. The simplest way to meet the requirements of BEPS is to raise building performance to that median ENERGY STAR benchmark. Again, the benefits of ENERGY STAR are that the improvements in energy usage are able to be isolated from any building changes over the 6-year BEPS cycle, whether that is an increase or decrease in occupancy, changes in operating hours or weather fluctuations from year to year.
Not Perfection
While ENERGY STAR is a distinctly helpful tool, government agencies and efficiency advocates should remember that the EPA uses a national conversion factor for calculation of source energy use intensity. This may mask the true source EUI associated with buildings in a locality. Specifically, if the energy grid in question is significantly “dirtier” or “cleaner” than the national average, the benefits of reducing site EUI are actually higher or lower than ENERGY STAR would suggest. Additionally, decisions regarding decarbonization of buildings and legislation pushing electrification should consider the specific energy generation mix of the area. In St. Louis, where coal accounts for 51.1% of the electricity generation in the SRWM subgrid, triple the 16.1% national average, a push to electrification may be counterproductive until the emission rates of electricity generation fall.
Also, ENERGY STAR is reliant on national survey data, primarily from the Department of Energy in the form of their Commercial Building Energy Consumption Survey although several building type peer groups are generated from industry surveys. The outputs of ENERGY STAR can only be as good as the inputs, so gaps or non-representative data in the reference data will impact the reliability of the EPA’s building energy consumption models that power ENERGY STAR. In particular, while the CBECS survey is typically updated every 5-7 years, the multifamily residential category is based on a 2012 Fannie Mae industry survey that only collected 350 full observations with energy data for 12 consecutive months. This means that the ENERGY STAR scores for multifamily residential are based upon a model using 14-year-old data on a relatively small subset of buildings. This building category in particular appears to be in need of a reference survey update.
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