New Energy Data Is Changing How We Judge Efficiency-and LEED
Seeking lessons from New York City benchmarking data, researchers question everything we thought we knew about energy metrics.
By Nadav Malin
In the beginning, there was Energy Star.
Supported by the online Portfolio Manager infrastructure and statistical models from the periodic Commercial Buildings Energy Consumption Survey (CBECS), the U.S. Environmental Protection Agency’s Energy Star has been the envy of the energy policy world; no other country has that kind of benchmarking tool. In fact,. (Energy Star for Homes and Energy Star labels for appliances and other equipment are mostly unrelated programs.)
Thanks to a flurry of energy benchmarking mandates (see “”) in the last three years, however, we’re now starting to get unprecedented flows of data about actual energy use in certain cities (just and , so far, but more are on the way). Suddenly, the CBECS database is looking shabby. It’s out of date, thanks to that has , and it’s awfully sparse in comparison to the new datasets.
As a benchmark for energy performance of New York City office buildings, the national CBECS database has relatively few reference points, and they tend to represent smaller buildings, according to Constantine Kontokosta, Ph.D., P.E., deputy director of the Center for Urban Science + Progress at New York University (NYU) and associate professor at the Polytechnic Institute of NYU, who did a lot of the data crunching behind the reports that New York City has put out for the last two years based on the new data.
In the forthcoming paper “From Transparency to Transformation: A Market-Specific Methodology for a Commercial Building Energy Performance Rating System,” Kontokosta has proposed an alternative to Energy Star that draws on the newly available benchmarking data, as well as on additional data sources from CoStar and the Department of City Planning, as a framework for benchmarking the energy performance of urban buildings.
Going beyond Energy Star
LEED project performance is just one aspect of Kontokosta’s analysis, which attempts to isolate the impact of a different variables on building energy use. Using a range of building characteristics from these three datasets and applying regression analysis to correct for factors such as building age, height, and asset class, Kontokosta concludes that the source energy use intensity (EUI) of LEED office buildings as a whole is not different in a statistically significant way from that of other office buildings in the dataset. He also finds that Energy Star-labeled buildings have a 10% lower EUI and that buildings that are both LEED-certified and Energy Star-labeled have a 20% lower EUI.
This analysis is based on a relatively small number of buildings, however. Kontokosta cross-referenced a total of 685 office properties across the three databases, of which 44 are LEED certified. Given that small sample size, “we can’t really look at rating system type,” Kontokosta told EBN, “as it won’t produce statistically significant results.”
The majority of those 44 buildings are certified under LEED for Existing Buildings: Operations & Maintenance (EBOM), and most of the rest under LEED for Core & Shell (CS), both of which have limitations in their ability to affect overall building energy use. LEED-EBOM projects don’t typically entail major system upgrades, and LEED-CS projects have a limited ability to affect tenant energy use. As a result, while this assessment is likely a valid report on the relative energy performance of LEED buildings as a subset of large Manhattan office buildings, it doesn’t tell us anything about how buildings that are designed and built entirely to LEED for New Construction standards actually perform.
Oberlin College physics professor John Scofield, Ph.D., takes a similarly dim view of Energy Star in his analysis of the NYC benchmarking data, published in the December 2013 edition of Energy and Buildings. Rather than coming up with an alternate method like Kontokosta, however, Scofield simply dismisses the high Energy Star scores achieved by the 21 LEED buildings he identifies in the dataset.
Despite the fact that Energy Star at least attempts to factor in occupant density and operating hours, Scofield reverts to basic source EUI numbers to conclude that LEED buildings as a whole are not more efficient than the overall collection of buildings. More specifically, he finds that the most basic LEED Certified-level buildings are actually less efficient, while the Gold-level buildings are more efficient.
The buildings included in this analysis suffer from the same rating system limitations as Kontokosta’s, in that they are exclusively LEED-EBOM and LEED-CS certified. Again in contrast with Kontokosta, who reins in his conclusions, Scofield uses his findings——to argue that LEED fails to deliver energy savings. One of his key assumptions is that each of the LEED buildings has “undergone extensive renovation in the last few years” and therefore should be compared to other recently renovated buildings. LEED-EBOM practitioner Jenny Carney of YR&G disputes that assumption, however. “Most commercial office buildings undergo piecemeal upgrades on a running basis; extensive renovations are more rare and are not often a precursor to a LEED project, in my experience,” she reports.
Energy-efficiency advocates would like us to believe that, as buildings get more efficient and their energy cost goes down, their value increases. That may be the case, but you won’t find any obvious support for that theory here, where the highest-value properties among New York City’s large buildings also tend to use the most energy.
There are a host of possible reasons for this trend: The most valuable properties tend to be tall buildings with high-tech tenants on corner lots. Kontokosta’s regression model reveals that buildings that are freestanding or on corner lots use 9% more energy than those in the middle of a block; that each floor added on a building increases source EUI by 1%; that newer buildings use more energy than old ones; and that a 10% increase in floor area devoted to data centers increases source EUI by 34%.
These confounding factors beg a larger question, suggests the U.S. Green Building Council’s vice president for research, Chris Pyke, Ph.D.: If efficiency is a measure of how much work output we get for our energy input, “what defines efficiency in buildings anyway?” Our conventional metric of energy used per square foot of floor area makes sense if you’re just looking at heating, cooling, and lighting energy, but in many commercial buildings today, other loads dominate the picture.
In search of a more relevant metric, akin to the way the energy efficiency of our economy is measured in Btus per dollar of gross domestic product (GDP), researchers from Buro Happold and Happold Consulting mashed up the New York City energy benchmarking data with the CoStar Tenant Database and classified building tenants according to their likely economic contribution based on their Standard Industry Classification (SIC) code.
In work that they published as part of the, the authors defined the “Building Economic Efficiency Coefficient” for 811 properties as the ratio of source EUI to economic intensity. They found a “loose correlation” between energy consumed and presumed economic contribution.
Applying their economic efficiency coefficient to 28 LEED-NC and LEED-CS-certified buildings in the benchmarking data set, they found a suggestion that LEED buildings have higher economic efficiency than non-LEED buildings and that their efficiency increases with the level of certification (although they note the sample set for this last finding is too small to be statistically relevant).
This work would have been much more compelling if they had actual economic output from the relevant buildings rather than presumed output based on the tenants’ SIC codes. The CoStar database actually contains that level of data in the form of tenant staff costs, but the researchers didn’t have access to those details, according to Pyke.
Many numbers, few conclusions
While more data is streaming in, the unfortunate reality is that we still have little insight into the market-wide impact of green building programs on building energy use. Perhaps more information and analysis will eventually help answer that question, though it’s worth noting that LEED certification addresses much more than energy. There are even aspects of LEED, such as increased ventilation, “that might result in additional energy consumption,” Kontokosta notes. And while recent updates to LEED are likely to drive down energy use in future LEED buildings, it will take a number of years before those impacts are seen in the benchmarking reports.
The LEED conversation aside, the fire hose of new information is starting to help us understand energy-use patterns in urban buildings more generally. Kontokosta is now working on analyzing energy patterns in multifamily buildings, for example, including the affordable housing sector, where residents are especially vulnerable to high energy costs.
More generally, the slight improvement in year-over-year performance in New York (see “”) suggests that the window into energy use could, in itself, have an impact on owner decisions and tenant behavior.