In 2000 the Leadership in Energy and Environmental Design (LEED) rating system for building energy efficiency was launched by the United States Green Building Council (USGBC). LEED grew fast in popularity and soon it became commonly known as the leading “green energy/building” rating system. Perhaps too fast as little performance data has ever being available to confirm this allegation.
To ease the controversy, in 2006 the USGBC hired the New Building Institute (NBI) with support of the U.S. Environmental Protection Agency to generate a report on the LEED certified building energy efficiency performance thus far. The final report was published in March 2008 and concluded that: on average, LEED certifications energy use was 25-30% better than the national average (Frankel & Turner, 2008).
The New Buildings Institute Final Report
To complete the United States Green Building Council’s (USGBC) LEED study request, the New Building Institute asked all LEED-New Constriction version 2.0 certified building’s owners to submit at least a full year measured post-occupancy energy usage data for the entire LEED project. Of the eligible 552 projects only 121 (22%) contributed with their results. With the data collected from the owners, the NBI was able to validate the LEED rating system through the completion of three unrelated studies. The first assessment, and least accurate, assessed the different Energy Use Intensity (EUI) values between LEED and non-LEED buildings. The second study evaluated the Energy Star Rating of LEED buildings vs. Non-LEED. The last strategy compared the post-occupancy measured energy data to the initial modelled energy used expectations. According to the NBI the results show that LEED certified projects “…average substantial energy performance improvement over non-LEED building stock…” (Frankel & Turner, 2008).
1. Energy Use Intensity (EUI) of LEED and national building stock according to building type.
On their first study, the MBI developed a method for paring each LEED building with one of similar characteristics from the 5215 sampled buildings analyzed on the Commercial Building Energy Consumption Survey (CBECS), a quadrennial survey of building energy performance directed by the U.S. Energy Information Administration (Birt, Mancini, & Newsham, 2009).
The New Building Institute report provided a full year of measured post-occupancy energy usage data for each of a 100 LEED certified buildings. For each one the total Energy Use Intensity (EUI) measured in KBtu/ft2/yr was derived from the sum of the total purchased energy of all fuel types (available for only 71 of the buildings). Later on, this was then compared to the initial baseline and design models in LEED submittals (Frankel & Turner, 2008).
Figure 1: EUI (KBtu/ft2) Distribution (Frankel & Turner, 2008).
Figure 1 distributes the results by LEED certification level and displays the Commercial Building’s EUI (KBtu/ft2/yr) for all the 100 LEED-New Construction. The median measured EUI was 69 KBtu/ft2, 24% lower than that of the CBECS national average which was measured at 91 KBtu/ft2. For the most common type: office spaces, LEED averaged a EUI of 33% below CBECS. Additionally, gold and platinum buildings shows a 50% energy saving than that of the CBECS office average. This graph omits the 21 buildings from the study with a median EUI of 238 KBtu/ft2; the NBI chose to eliminate them because these activity types (data centers, supermarkets, and labs) contain a very high energy activity levels driven by constant changing occupancy, and making their analysis more complex (Frankel & Turner, 2008).
2. Energy Star ratings of LEED buildings
The U.S. Environmental Protection Agency’s (EPA) Energy Star program rates building’s energy use in relation to existing national building stock. The pairing is based primarily on building’s activity type, and secondarily on their location’s temperature, schedule, and occupancy respectively. The average Energy Star rating of the national building stock was 50, compared to a median rating of 68 for the LEED buildings. Figure 2 shows that one quarter of LEED certified buildings had ratings below 50, meaning they used more energy than average for comparable existing building stock (Frankel & Turner, 2008).
Figure 2: Energy Star Rating of LEED vs. National Building Stock (Frankel & Turner, 2008).
3. Post-occupancy measurements vs. Initial design modelled energy used expectations.
Measured energy savings for the buildings in this study (Figure 3) average 28% compared to the energy cost budget (ECB) baselines, close to the average 25% savings predicted by energy modeling in the LEED submittals.
Figure 3: Measured versus Proposed EUIs in KBtu/ft2 savings (Frankel & Turner, 2008).
At the extreme, several buildings use more energy than the projected code baseline modeling, as shown in the comparison of measured vs. estimated savings in Figure 5. The NBI justified this degree of scatter by suggesting the need for improvement in the accuracy of energy use prediction on an individual project basis (Frankel & Turner, 2008).
Figure 4: Measured vs. Proposed Savings Percentages (Frankel & Turner, 2008)
Discussion of the Analysis
There is far too many flaws on the NBI’s analysis:
- Biased results by exclusively gathering data from the LEED certified building owners.
- Uneven results due to the comparison of two different metrics of central tendency: the median EUIof the LEED buildings to the mean EUI of all US commercial buildings.
- NBI delivery chose to ignore the data from 21 LEED buildings with the highest EUI such as data centers, labs, and supermarkets by claiming that their analysis required more complexity and therefore only focused on the remaining 100 medium energy use buildings office buildings only.
- Platinum signifies the maximum energy saving point system in the LEED ranking, yet the NBI study only included 2 LEED platinum buildings.
- Failed to create a successful subgroup of non-LEED building with which to compare their LEED certified building data, and therefore failed to accurately match all LEED buildings with CBECS matches.
- Little account between the two datasets regarding climate zone, building size or age.
- Failed to appropriately weight for building size in calculating average LEED energy utilization intensities (EUI).
- Focused on site energy rather than primary or source energy.
In conclusion, all of these factors raise a considerable amount of questions regarding the credibility of the LEED building rating systems. Further work needs to be done to define the authenticity of the LEED certification system.
Frankel, M., Turner, C. (2008). Energy Performance of LEED for New Construction Buildings-Final Report. New Buildings Institute, White Salmon, WA. Retrieved from https://wiki.umn.edu/pub/PA5721_Building_Policy/WebHome/LEEDENERGYSTAR_STUDY.pdf
Leite, F., Stoppel, C. M. (2013). Evaluating building energy model performance of LEED buildings: Identifying potential sources of error through aggregate analysis, Energy and Buildings, 65, 185-196. Retrieved from http://www.sciencedirect.com/science/article/pii/S0378778813002521
Pérez-Lombard, L., Ortiz, J., Pout, C. (2008). A Review on Buildings Energy Consumption Information, Energy and Buildings, 40 (3), 394-398. Retrieved from http://www.sciencedirect.com/science/article/pii/S0378778807001016
Scofield, J. H. (2009). Do LEED-certified buildings save energy? Not really…. Energy and Buildings, 41(12), 1386-1390. Retrieved from http://www.sciencedirect.com/science/article/pii/S037877880900187X