1. Introduction
One of the most important problems facing humans today is that of climate change, driven by anthropogenic greenhouse gas (GHG) emission, which is due in large part to the burning of fossil fuels. U.S. buildings are responsible for 40% of U.S. primary energy consumption and 33% of its energy-related GHG emissions [
1]. In addition to CO
2, the burning of fossil fuels releases other pollutants, including CH
4, N
2O, SO
2, NO
X, and particulate matter, all of which have negative environmental consequences, particularly when released from thousands of buildings in urban centers [
2]. When buildings switch from natural gas or other fossil fuels to electric energy, the accompanying pollutants are shifted to the electric power sector, which may or may not reduce total GHG emission (depending on the details of the electric grid) but does improve air quality by moving emissions sources out of population centers. Moreover, power plants do a better job of reducing pollutants (other than CO
2) than do individual boilers and furnaces.
Energy efficiency is a cornerstone of any strategy for reducing GHG emissions, and green building programs in turn are a major strategy for reducing energy use in buildings [
3]. Founded in 1998, the U.S. Green Building Council’s (USGBC) Leadership in Energy and Environmental Design (LEED) program is the most popular green building certification program in the U.S. [
4]. Many governmental and other types of organizations have mandated that all new buildings and major renovations achieve the LEED Silver standard or better [
5]. As of 1 January 2020, there were 24,500 LEED-certified commercial buildings in the U.S., totaling 380 million m
2 (about 5% of the overall floor area of U.S. commercial buildings) [
6]. These numbers increase to 28,000 buildings with 440 million m
2 when confidential LEED projects are included; we also have not corrected for buildings that have been certified more than once.
A recent study concluded that commercial LEED-certified buildings are projected by their design teams to save 20–40% in energy, depending on their level of certification [
2]. Numerous studies, however, have found a significant gap between the measured energy use of buildings and the energy use projected by their design teams [
7]. In 2013 a review of the literature by the National Academies concluded that “green buildings can result in significant reductions in energy use“ [
8]. We believe that the relevant question is not can, but do green buildings, on average, save energy and reduce GHG emissions? Here we address this question for LEED-certified U.S. offices. Offices represent the largest space-type in the U.S. non-residential building stock [
9].
In 2006 the USGBC contracted with the New Buildings Institute (NBI) to conduct a study that would address this question for LEED-certified buildings. NBI obtained energy data volunteered for 121 LEED buildings (22% of those eligible at the time) and concluded they were, on average saving 25–30% energy [
10]. NBI, however, found limited correlation between the projected and measured energy savings for individual buildings. The NBI study was met with considerable criticism [
11,
12,
13]. Newsham et al. provided an alternate analysis of the NBI data, finding average LEED savings from 18–39% while noting that roughly 1/3 of the LEED buildings used more energy than their conventional counterparts [
14]. Scofield analyzed the NBI data and concluded that LEED buildings were saving only 10–15% in site energy but found no evidence for source energy savings or reduction in GHG emissions [
12,
15].
Since 2009 there have been a number of peer-reviewed studies addressing LEED building energy use [
16,
17,
18,
19,
20,
21,
22,
23,
24]. These studies generally include a small collection (3 ≤
N ≤ 25) of LEED-certified buildings [
16,
21,
23] and typically consider only site energy. In some cases, only electric energy was considered [
16,
22]. We summarized the key features of these studies in [
7]. Due to the small numbers of buildings involved, selection bias, and the variation in methodology, it is difficult to generalize their conclusions. On the whole, they suggest that LEED buildings save energy on site, but the amount and statistical significance is not clear. They also tend to show that LEED buildings use more electric energy than other buildings. Some evidence suggests that the off-site greenhouse gas emission and energy loss associated with increased electric use offset the on-site energy savings so that LEED buildings, on average, demonstrate no primary or source energy savings [
23,
24]. It should be noted, however, that when combined, these studies look at energy use data for only 200–300 of the 25,000 U.S. commercial buildings that have been LEED-certified. Data are typically volunteered and include many different building types, geographical locations, and time frames. The fundamental barrier to answering the question, “Do LEED buildings save energy?” is the inaccessibility of energy consumption data for large numbers of representative LEED-certified buildings.
The USGBC recognized the need for energy performance data and, beginning with version 2009, required all LEED-certified buildings to provide annual energy data for the first five years of operation. Still, a decade and thousands of certifications later, the USGBC has neither made these data public nor published any scientific analysis of these data.
Historically, the Energy Information Administration’s Commercial Building Energy Consumption Survey (CBECS) has provided the best snapshot of the energy usage of U.S. commercial building stock, sampling about 6000 buildings across the U.S. roughly every 4–6 years [
9]. CBECS data provide the basis for most of the U.S. Environmental Protection Agency’s (EPA) Energy Star benchmarking scores.
Municipal energy benchmarking disclosure laws are providing access to energy use data for significantly more buildings on an annual basis. With the assistance of the Institute for Market Transformation (IMT), about 20 major U.S. cities have instituted laws that mandate building owners disclose their annual energy and water use to local city governments [
25]. In many cases, these data are being made public. These data provide the opportunity to compare the energy use of LEED buildings with that of non-LEED buildings for the same geographic region, property type, time frame, and climate, largely avoiding the selection bias associated with voluntary data submission.
We previously used 2011 municipal energy benchmarking data to study the performance of 21 LEED office buildings in New York City (NYC) [
23] and 2015 data to study the performance of 113 LEED offices, multifamily housings, and K–12 Schools in Chicago [
24]. We found no evidence for source energy or GHG savings by LEED buildings in either study.
We obtained 2016 energy data from some 28,500 commercial properties (465 million m2) in 10 major cities spanning the continental U.S. We identified 861 of these properties/buildings as LEED-certified in systems that address whole building energy use.
In this paper, we focus on the subset of buildings that correspond to the office property type. This subset includes 4417 properties, with floor area totaling 110 million m2. Of these, 551 were identified as LEED-certified, totaling 31 million m2. This constitutes the largest study of measured energy performance for LEED-certified buildings ever published.
For each office building in the benchmarking data, we extract five metrics associated with its annual energy consumption: site energy, source energy, electric energy, non-electric energy, and (energy-related) greenhouse gas emission. Each of these metrics, adjusted for building size, are then compared between LEED-certified offices and other offices in the same cities to understand measured savings associated with LEED-certification.
We also obtain, for most of the LEED buildings, the number of points awarded during certification for energy optimization and, from these, we determine the energy savings projected by their respective design teams. We then compare these projected savings with the actual measured savings for each individual LEED building. Finally, we investigate the role of building age and look for differences in energy savings associated with the level of LEED certification.
4. Discussion
We previously reported the LEED office performance for NYC (2011 data) [
23] and Chicago (2015 data) [
24]. The 2016 results reported here for Chicago are consistent with those reported for 2015 for both LEED and non-LEED offices. In Chicago, LEED offices demonstrate 10% savings in site energy (12% in 2015) but no significant savings in source energy or GHG emission (see
Table 3).
NYC offices have lower energy use in 2016 than in 2011, and LEED offices are performing slightly better, relative to non-LEED offices. The reduction for NYC offices from 2011 to 2016 is 11% in site EUI and 16% in source EUI. It is likely that this is partly attributed to NYC’s aggressive programs to benchmark and reduce building energy use. Other factors such as weather and economic activity may also contribute to these differences. In 2011, NYC LEED offices demonstrated neither site nor source energy savings relative to non-LEED offices. For 2016, LEED offices demonstrate 8% savings in site energy but no source energy savings (see
Table 3). This may be related to the evolution of LEED standards, as the vast majority of NYC offices here were certified under LEED version 2009, whereas in 2011 they were mostly LEED v1 and v2.
LEED office energy savings in the eight other cities surpass those found for Chicago and NYC, on average, demonstrating positive savings in both source energy and GHG emissions. In aggregate, savings in both of these metrics is 7%. While well below the projected 25–30% energy savings asserted for LEED buildings [
2,
10] these aggregate savings are nonetheless positive and statistically significant.
To better understand the gap between predicted and measured energy savings for LEED buildings, we looked for a correlation between the two on a building-by-building basis. Our expectation was that LEED offices that earned the most points for energy optimization would be those that actually saved the most energy, either site or source depending on the method for awarding these points. This was not the case. Instead, we found little or no connection between predicted and measured energy savings (see
Figure 4 and
Figure 5). It should be noted that the absence of correlation in
Figure 4 does not depend on whether the site EUI savings are calculated relative to all non-LEED offices or only newer, non-LEED offices. Low correlation between predicted and measured energy savings was first reported by NBI in 2008. Their study focused on LEED-NC v2 [
10]. At that time, there were roughly 600 U.S. LEED-certified buildings, with total floor area of 7.2 million m
2. A decade later with two LEED versions farther along and 40–50 times the number of certified buildings and floor area, this performance gap remains.
For LEED EB systems, the problem is with the Energy Star score, which is the basis for awarding points for energy optimization. One of us has extensively studied the science behind these scores and found it to be highly problematic [
32,
34]. Energy Star scores are half based on measured energy use and half based on adjustments associated with user-supplied operational parameters. The first part is reproducible, but the second part is not, is highly flawed, and is easily gamed by simply adjusting the reported building operating parameters.
It should be noted that our imputed site EUI and source EUI savings based on LEED points awarded for energy optimization (EAc1), while based on reasonable assumptions, are not calculated using methodology identical to that employed by design teams when these points were awarded. We simply do not have access to the predicted baseline site EUI used by the design teams for the NC or CS LEED systems, nor do we have access to the operating parameters used in calculating the Energy Star scores behind EAc1 points for offices certified under EB systems. It is possible that someone with access to this confidential information could use it to demonstrate there is some sense in which these buildings were expected to yield the projected energy savings, but we find there to be little utility in this if it does not result in a significantly lower measured energy use and GHG emission—namely of the kind that is necessary to address climate change and that so many municipalities have pledged to achieve.
Numbers provided in
Table 3 can be readily combined to estimate total savings by LEED offices. For instance, the aggregate reduction in annual GHG emissions for LEED offices is (7%) × (77 kg/m
2) = 5.4 kg/m
2. This savings multiplied by LEED office aggregate floor area yields a total savings for 2016 of 170,000 metric tonne of CO
2, as compared with non-LEED offices of the same floor area in the same cities.
MacNaughton et al. estimated the CO
2 emissions savings for all LEED-certified buildings in the U.S. and five other countries in 2000–2016 to be 33 Mtonne CO
2 [
2]. Their calculation is based on the assumptions that each LEED building annually achieves the energy savings projected by its design team and that these savings occurred uniformly in all fuels. We criticized these assumptions as being inconsistent with the measured energy savings for LEED buildings, and based on our 2015 Chicago data, we offered that these savings are zero or even negative [
7]. Here, our data show that LEED office savings, in aggregate, are greater than those reported for Chicago but significantly lower than projected by design teams. The estimated 33 Mtonne savings above is equivalent to an annual GHGI savings of 22 kg/m
2/year for LEED buildings. This figure is nearly four times the 5.4 kg/m
2/year savings that we report here for U.S. LEED offices in 2016.
Table 3 and
Table 4 show that LEED offices are achieving much higher savings in non-electric energy, i.e., 26% for all LEED, 16% for Silver, 27% for Gold, and 42% for Platinum. It is interesting that these measured savings in non-electric energy roughly track design projections for total energy savings [
2] (
Figure 2). Non-electric energy is responsible for 30% of the energy-related GHG emissions for commercial buildings. This, combined with our observed 26% reduction in aggregate non-electric energy for LEED offices (see
Table 3), implies an 8% reduction in GHG emission, close to the 7% reduction observed for all LEED offices.
It can be argued that it is unfair to compare LEED offices with all other offices in this study. This view is supported by several facts. As noted, LEED offices are, on average, 26 years newer than other offices. It is also the case (see
Table 1 and
Table 2) that LEED offices are, on average, 2–3 times larger than non-LEED offices. (When the total floor area is divided by the number of offices, it can be seen that the average LEED office in this study is 56,000 m
2 while the average non-LEED office is 22,000 m
2.) Others have shown that LEED (and other green-labeled) buildings typically represent more high-end, more desirable commercial space [
22]. These observations suggest that it would be fairer to compare LEED offices with only larger, newer, high-end non-LEED offices. It should be noted, however, that the EPA’s Energy Star office model regression finds that SourceEUI increases with building size, but only up to a floor area of 9300 m
2. For larger buildings, they make no additional adjustment [
35].
While there is merit in the above argument, we find the justification for comparing LEED with all non-LEED to be more compelling. Six of the ten cities in this study (Boston, Minneapolis, NYC, Portland, Seattle, and Washington) are signatories of the Carbon Neutral City Alliance and have pledged to reduce GHG emissions by 80–100% by 2050 [
36]. Chicago has adopted a more aggressive climate action plan in aiming to become 100% carbon neutral by 2040 [
37]. These commitments are to reduce GHG relative to existing levels (i.e., all existing buildings). The comparison of LEED building energy and GHG savings relative to other newer buildings is not relevant to these goals. Fair or not, a successful strategy for addressing climate change will require buildings whose GHG emissions are greatly reduced over those of existing buildings.
The movement to switch from natural gas (and other fossil fuels) to electric energy for buildings is not unique to LEED. This trend is found in our regression on the year built, as seen previously in our 2015 Chicago study [
24], and is evident in CBECS [
9]. Indeed, there are those who advocate the immediate electrification of buildings as the best route to carbon neutrality [
38]. The reasoning is clear: Heating a building with natural gas (or another fossil fuel) locks in the associated GHG emissions for the lifetime of the heating system. Choosing to heat with electricity (typically utilizing heat pumps) instead provides the building a pathway to zero emissions, benefitting entirely from ongoing efforts to make the electric grid 100% carbon-free. However, in the short term, building electrification can and often does result in little or no savings in GHG emission. Moreover, depending on the carbon content of the regional electric grid, building electrification can result in increased (indirect) GHG emission as compared with the alternate employment of efficient natural gas heating. This, for instance, would be the outcome of using resistive electric instead of natural gas heat in most parts of the U.S. Depending on the pace with which the electric power sector lowers its carbon, it is possible for well-intentioned building electrification to result in greater GHG emission over the lifetime of the HVAC system.
Some project a rapid transition to a carbon-free grid [
39]. Indeed, advocates of municipal climate action commitments must implicitly believe a rapid transition to a carbon-free electric grid as the goals of 80–100% carbon reduction by 2040 or 2050 are not possible otherwise. Aspirational legislation, however, does not guarantee scientific outcome.
In 2018, the U.S. electric power sector derived 63% of its primary energy from fossil fuels and was responsible for 70% of the energy-related GHG emissions of U.S. commercial buildings [
40]. The U.S. power sector’s carbon footprint has decreased by 25% over the last 15 years, owing largely to the replacement of old, inefficient coal plants with new, more efficient natural gas plants. Expanded renewables have also lowered GHG emission but have played a minority role. While this replacement of coal with gas is expected to continue, the future benefit will be reduced as natural gas plants also replace retired, carbon-free nuclear plants. Expansion of renewables continues, but absent major advances in storage technology is unlikely to result in a rapid decline of fossil fuel use. In its 2019 report on energy outlook, the Energy Information Administration projects that in 2050 fossil fuels will provide 56% of U.S. grid electricity, despite a projected 230% increase in renewable electricity [
41].
Given the uncertainties in predicting carbon content of future electricity, a sound strategy for new construction and major renovation would be to adopt an HVAC system expected to minimize the integrated GHG emission (both direct and indirect) over the lifetime of this system. This may or may not be an all-electric system, depending on many details including the current and foreseeable fuel mix for the regional electric grid.
Some of the limitations of this study require further comment. The benchmarking data used in this study are assembled using the EPA’s Portfolio Manager. In most cases, energy data are submitted directly by utilities. Building parameters, such as floor area, space type, operating parameters, etc., are submitted by the building owner or their representative. Portfolio Manager incorporates various cross-checking means that prompt the user, should the entered data stand out as anomalous. In New York City, a relatively small number of consultants manage the data entry for a large fraction of the properties, reducing the sources of error. In the case of LEED buildings, we confirmed that floor areas in the benchmarking data are consistent with those recorded in the LEED project database. For Chicago and NYC, we have results from earlier studies, which provide a measure of consistency. Nevertheless, the validity of the data remains an untested assumption.
On average, source energy is a better measure of a building’s energy footprint than site energy is. However, source energy does not account for local or even regional variation in grid efficiency or renewable grid generation. This is particularly concerning for building owners in the Pacific Northwest where hydroelectricity dominates the grid. The disparity, however, is not as large as one might guess, owing to regional electric connectivity and the role of natural gas peaking plants. When the electric load decreases even in a grid dominated by renewable energy, the result is reduced fossil fuel use at an inefficient peaking plant somewhere in the regional grid (see chapter 18 of Ref. [
32]). Still, the usefulness of building source energy is decreasing, with the expanded use of renewable energy in the U.S. electric grid. To remain useful, the definition of source energy must evolve to account for regional differences in the electric grid.
Greenhouse gas figures calculated by the portfolio manager (and used in this study), unlike source energy, do take into account regional variation in the electric grid. They do not, however, reflect local differences within an eGRID region [
27]. Our decision to change the GHG figures for Seattle buildings resulted in significant increases in GHGI for all Seattle buildings but impacted both LEED and non-LEED buildings equally; this had little impact on our conclusion regarding GHGI savings for LEED buildings in Seattle (
Table 3 or
Table 6). In addition, since Seattle contains only 7% of the LEED floor area in this study, this had minimal impact on the aggregate GHGI savings for LEED.
5. Summary and Conclusions
Utilizing 2016 municipal building energy benchmarking data, we compared the energy performance of about 550 LEED-certified office buildings (31 million m2) in 10 U.S. cities with the performance of about 3600 other office buildings (79 million m2) in these same cities for the same time period. This is the largest such study to date with respect to LEED building numbers or floor area. While LEED buildings continue to demonstrate wide variability in energy performance, we nonetheless found that LEED-certified U.S. office buildings, on average, are achieving statistically significant source energy savings and reductions in greenhouse gas emissions. In aggregate, we found that these office buildings save 11% in site energy and 7% in both source energy and GHG emissions, as compared with non-LEED office buildings in their same cities. On average, U.S. LEED office buildings are achieving 26% savings in non-electric fuels (mostly natural gas) while demonstrating no significant savings in electric energy. The total energy savings and reduction in GHG emissions are considerably lower than the 25–30% savings projected for LEED. Broken down by the level of certification, we found that LEED Silver offices achieve no significant savings while Platinum offices show no more savings than do Gold. Only Gold offices demonstrate statistically significant savings.
On average, LEED offices were 26 years newer than non-LEED offices. When compared with newer non-LEED offices, in aggregate LEED the savings were 12%, 10%, 8%, and 21% in site, source, electric, and non-electric energy, respectively, and 10% in GHG emission.
For individual buildings, we compared the projected energy savings (derived from LEED points awarded for energy optimization) with the measured energy savings, and we found little or no correlation between them. The data suggest that energy savings for LEED offices have little connection with LEED-certification points awarded for energy optimization. The total source energy savings for office buildings certified under EB (the vast majority of LEED offices) is less than one fifth the total savings implied by their LEED points earned for energy optimization. Unless corrected, this reward system is unlikely to produce buildings with significant energy savings.
Finally, we showed that LEED offices rely more heavily on electric energy than do other offices. On the one hand, this positions LEED buildings to achieve maximum benefit from future reduction in the carbon content of the U.S. electric grid. On the other hand, as the U.S. electric grid is presently heavily dependent on fossil fuels, LEED offices demonstrate little GHG savings today relative to other offices. Only time will tell whether future savings in GHG emission will justify the choice to rely heavily on electric energy.