1. Introduction
Buildings consume a considerable amount of energy and constitute one of the major sources of adverse impacts on the environment. Buildings account for 19% of global greenhouse gas emissions [
1]. In the US, the residential and commercial businesses are responsible for 12% of the total greenhouse gas emissions due to heating and cooking needs, management of waste and wastewater, and leaks from refrigerants in homes and businesses [
2]. It is essential to ensure sufficient energy supply in the future [
3], and it is also necessary to incorporate measures for energy efficiency into the design and construction processes [
4]. A major objective of sustainable design and construction is to minimize the adverse impacts of excessive energy consumption.
Federal, state and local authorities either incentivize or mandate sustainable design and construction in the US [
5]. In addition to such programs, marketing demands and environmental concerns also affect the growing interest in sustainable buildings and systems that certify projects as green buildings. Leadership in Energy and Environmental Design (LEED) has been used as a green building certification system since the 2000s in the US and other parts of the world. According to the United States Green Building Council (USGBC) project directory [
6], 107,383 projects are registered for the certification process across the globe and more than 62,000 of them are located in the US. LEED is a verification system that consists of several categories organized with prerequisites and credits for rating the sustainability performance of buildings. It was launched by USGBC and is flexible enough for use in different type of projects. Building design and construction (LEED BD + C), interior design and construction (LEED ID + C), operating and maintenance (LEED O + M), and neighborhood development (LEED ND) are the rating systems applicable to new construction, existing buildings, schools, healthcare facilities, data centers, warehouses, hospitality facilities, homes, commercial interiors, multifamily midrise and retail buildings [
6].
LEED BD + C: New Construction (NC) is the system applicable to new construction projects. Buildings can achieve four certification levels—certified, silver, gold and platinum—after earning points from credit categories in the system. Since its introduction, the system has been updated many times. The Energy and Atmosphere category accounts for the maximum possible points compared to the contribution of the other categories in LEED for new construction. The credits in this category address energy use reduction, energy-efficient design strategies, and renewable energy sources. In LEED-NC 2009, the Energy and Atmosphere category consists of three prerequisites and six credits. The prerequisites are mandatory conditions to earn points in every credit. The six credits account for 35 of the maximum 110 points. According to Illankoon et al. [
7], energy related credits are the key credit criteria not only in LEED-NC 2009, but among other international green building rating tools. The prerequisites and credits in the Energy and Atmosphere category of LEED-NC 2009 are shown in
Table 1.
The level of achievement in LEED points has been analyzed in past studies by different researchers. The level of achievement in the credits offers insights into projects with LEED certification and provides patterns and trends about green building design and construction. Todd et al. [
8] analyzed the LEED-NC and Existing Building Operations and Management (EBOM) systems to identify patterns, trends and strategies in credit achievement changes at different locations in the world, and found that “EA1—Optimizing energy efficiency” occupied the first rank in the top five highest achieved credits list. Ma and Cheng [
9] used scorecards of 1000 LEED-NC 2009-certified buildings to understand the achievement of individual credits and related credits. Cheng and Ma [
10] analyzed 1381 LEED-certified buildings to explore the interrelationships between credits and to highlight the high-scoring sustainable design strategies. Sullivan and Oates [
11] examined 53 LEED-NC 2.0, 2.1 and 2.2-certified buildings in Arizona to identify credit achievement patterns and found that the percentage of possible credits earned in the Energy and Atmosphere category was 48%. Similarly, Kim and Cheung [
12] examined 43 LEED-NC 2.0-certified buildings and found that the achievement in the Energy and Atmosphere category was 43% on average, but also observed significant differences between projects. Da Silva and Ruwanpura [
13] investigated 42 buildings across Canada certified with earlier versions of LEED for new construction, and found that the greatest percentage of points in the Energy and Atmosphere category was “EA1—Optimizing energy efficiency”. Wu et al. [
14] report that energy-related credits remain difficult to obtain for developers based on their research including LEED 2009-certified projects.
The objective of this study is to analyze quantitatively the information about a building inventory of 1500 silver, gold, and platinum-certified buildings in the US in order to understand energy and atmosphere related practices. The building scorecards used in the research were registered to projects available on the USGBC website. The study highlights designers’ performance in Energy and Atmosphere credits. It identifies and discusses patterns in achieving points relative to certification levels and building ownership; it pinpoints the strategies currently adopted by practitioners to earn points; and it explores the challenges that are encountered in undertaking energy efficient design and construction. After describing the methodology used in the research, the paper presents the findings, and the analysis of the levels of achievement in the different credits in the Energy and Atmosphere category. It also examines variations in achievement levels attributable to certification levels (silver, gold, platinum) and type of ownership. The detailed discussion of the findings is followed by conclusions and recommendations.
4. Discussion of the Findings
The findings of this study are discussed in this section by category (EA1 to EA6), always in the light of the literature relevant to the issues discussed. In other words, the statements about the reasons and/or impacts of the findings are not based on speculation, but on a thorough discussion that draws extensively from past research.
EA1—Optimize Energy Performance
In LEED-NC 2009, the EA1 credit references the ASHRAE 90.1-2007 standard. To reduce environmental and economic impacts, the EA1 credit aims to achieve high levels of energy performance beyond the prerequisite mentioned in the ASHRAE standard. As seen in
Table 1, EA1 consists of minimum energy cost savings, each of which deserves different points. It has the maximum achievable points of 19 for all contributions in the Energy and Atmosphere category in LEED-NC 2009. Therefore, it is important for LEED managers to focus on this credit for earning higher points. There are several strategies adopted by project owners and developers to earn points. For example:
Cedar Rapids Public Library in Iowa targeted platinum certification after being damaged by a major flood. For this purpose, energy and cost-saving features were integrated into the building and roof design [
29]. Setting the Iowa Energy Code standards as a baseline, it was aimed to exceed the baseline by 55%. This was achieved by several strategies such as strategic location of windows, solar light tubes, exterior sunscreens, and use of high-efficiency T5 HE florescent bulbs [
22]. Also, storm water on site was effectively managed. As a result, the maximum achievable 19 points were earned, which contributed a great deal to obtaining platinum certification.
University of Arkansas at Little Rock constructed a new residential student housing with sustainable attributes. Highly efficient HVAC and lighting systems were used to reduce the consumption of energy by 32% [
30]. This implementation provided cost savings through energy efficiency and brought 10 points to the project, which at the end was awarded a gold certificate.
The Sarasota National Guard Armory in Florida earned 14 points out of 19 by implementing a combination of highly efficient lighting and HVAC system designs [
31]. In this project, LED fixtures were selected for all internal and external lighting. The control of lighting was further enhanced by an advanced automation system. The building received silver certification.
Further suggestions for energy efficiency include improving equipment efficiency, such as increased duct size leading to reduced fan power requirements, variable frequency drives for motors, condensing stack boilers, and sophisticated controls [
21]. Projects aiming to achieve higher energy efficiency can benefit not only from the financial and environmental implications, but also can earn more points in this credit. According to
Table 4, all platinum-certified projects earned points in EA1 with 89 of 129 platinum-certified projects earning the maximum 19 points. However, the findings indicate that there are a few buildings that received zero points in EA1 (14 buildings with silver certification, and one building with gold certification). In such cases, the projects tend to compensate with points earned in other credits.
Earning higher points in this category mostly depends on targeted energy efficiency in the project. Therefore, it would be useful for project owners, managers, and LEED consultants to calculate the costs and benefits of implementing different alternatives, and then make a decision about the implementation that promote sustainability goals in the most cost effective way.
Figure 3 shows the achieved percentages of the maximum points in each credit categorized by building ownership. Projects owned by investors and government agencies attain higher percentages than projects owned by other types of owners (
Figure 3). The Bonferroni post-hoc test results presented in
Table 1 show that the differences are consistently and statistically significant at
α = 0.10. This finding can be the result of investors and government agencies generally occupying the constructed facilities themselves rather than immediately selling or renting, and expecting economic benefits in the long run. Buildings under the other types of ownership display achievement rates that are quite similar to each other, that fall around 51%, still not a low performance as it corresponds to cost savings in energy not less than 30%.
EA2—On-Site Renewable Energy
Energy consumption creates one of the most significant environmental impacts during a building’s life cycle [
32]. Use of renewable energy is an option to overcome the adverse impacts. This credit’s objective is to promote the use of energy sources that are not depleted and to avoid the use of sources such as fossil fuels that can be depleted. The LEED system encourages the implementation of strategies that address on-site renewable energy policies that reduce the environmental and economic impacts related to the use of energy generated by fossil fuels. As seen in
Table 1, the maximum number of points that a building can achieve is seven. EA2 specifies the percentage of on-site renewable energy for each point threshold. Several technologies and strategies can be used such as solar, wind, geothermal, low-impact hydro, biomass, and bio-gas [
33]. Using on-site renewable energy in a project that aims to achieve LEED certification enhances the project’s green image and decreases the consumption of grid-purchased electricity [
24]. Different cases exist where efforts were spent to produce on-site renewable energy with varying degrees of success. For example:
The design of Project Vida Community Wellness Center, a platinum-certified building, included a photovoltaic array to produce approximately 40% of the energy necessary to operate the building and earned the maximum seven points in this credit [
34].
The SUNY-ESF College of Environmental Science & Forestry Gateway Center, another LEED platinum building also received the maximum seven points by designing a combined heat and power plant to produce 60% of campus heating needs and 20% of its electricity requirements using natural gas cogeneration, biomass, photovoltaic, and solar thermal systems [
35].
The Bend Broadband Vault project in Oregon, a gold-certified building, installed photovoltaic arrays and all power consumed that was not produced by the photovoltaic system was offset by renewable energy purchased through the Pacific Blue Sky Renewable Energy Program [
36]. The implementation brought one point.
Table 4 shows that out of the 129 platinum-certified buildings, only 8% (10 buildings) received zero, while 67% (86 buildings) scored the maximum seven points. Out of 617 gold-certified buildings, 66% (404 buildings) received zero, while 20% (121 buildings) scored the maximum seven points. If one considers the 747 silver-certified buildings, as many as 86% (640 buildings) received zero and only as few as 5% (39 buildings) earned the maximum seven points. These values show that buildings aiming at higher certification take better advantage of renewable energy sources.
The total investment in renewable energy is reported as
$54.2 billion in 2013 in the US [
37]. Although the US takes place in the list of top countries for total investment of installed renewable electric capacity, the “EA2—On-site renewable energy” credit is underutilized in LEED-certified buildings.
Table 3 shows that the buildings that received zero points in EA2 correspond to 71% of the buildings in the analyzed set, indicating that renewable energy is not a credit that is vigorously pursued by owners, designers, and contractors probably because providers of on-site renewable energy are rare and because acquiring these new technologies is cumbersome and expensive. One of the main reasons for not using renewable energy systems more extensively is that investments require substantial implementation costs followed by a long period of recovering the invested capital through savings in utilities bills [
25]. According to Karystas and Choropanitis [
38], barriers against renewable energy systems can be classified as financial, technical, regulatory, and market related issues, such as lack of qualified personnel to install and promote the systems, limited space for installation and inadequate or unclear financing options.
Active solar energy methods (converting solar energy for heating and cooling), passive solar energy methods that take better advantage of local climate conditions (design of building, windows, walls and floors to keep heat in the winter and reject heat in the summer), and the use of wind and geothermal energy can contribute to lowering energy consumption costs [
39]. However, economic and non-economic barriers such as high initial costs, low cost effectiveness, high technical risks, high market risks, and lack of specialized knowledge negatively affect the adoption of these systems [
25,
40,
41].
Figure 3 shows the percentage of the maximum seven points achieved in EA2, categorized with respect to type of ownership. The highest percentage is recorded for investors. The Bonferroni post-hoc test confirms that the differences between investors and other types of owners are statistically significant.
Figure 3 also shows that educational institutions underperform in this credit, achieving only 14% of the maximum points. It should also be noted that the maximum achievable point in this credit is lowered to three in LEED v4, from 7 in LEED-NC 2009, probably as a response to the generally low percentages observed in
Figure 3.
EA3—Enhanced Commissioning
Commissioning is a verification process that a building undergoes to make sure that the design objectives and the owner’s requirements are in agreement. LEED-NC 2009′s intention is that the commissioning process be initiated early in the design phase and that additional activities be executed after the systems’ performance verification is completed. LEED v4 expands on this intent by further supporting the design, construction, and eventual operation of a building such that the owner’s project requirements for energy, water, indoor environmental quality, and durability are met. Both of these explanations suggest that the project’s energy, water, and indoor air quality systems and the exterior envelope assemblies and systems are designed, installed, and calibrated to perform according to the owner’s requirements, basis of design, and construction documents [
42]. The operation of key systems in the building is checked systematically to close the gap between the design team and subcontractors. An independent commissioning agency is required for better objectivity. The scope of the commissioning process involves verification of heating, cooling, refrigeration, ventilation systems and controls, lighting and day-lighting controls, domestic hot water systems, and renewable energy systems [
43].
The maximum achievable point in EA3 is two points in LEED-NC 2009, but is higher (between two and six points) for new construction in LEED v4. According to the information in
Table 4, 41% of the buildings received zero points in all certification levels combined. This indicates that even though all buildings satisfy the fundamental commissioning prerequisite, not too many seek enhanced commissioning.
The commissioning of systems in buildings depends on the extent and complexity of the systems used in the building [
44]. For example:
Hillsborough Area Regional Transit 21at Avenue received silver certification and earned two out of the six points in this credit. The systems commissioned in the building consisted of an air cooled chiller, chilled water pumps, water handling units, energy recovery units, a chiller with an integral pumping package, air conditioning units in a computer room, exhaust/supply fans, and a water heater [
45].
The Bendbroadband Vault project is a data center building project in Oregon, which received gold certification. The project owner aimed to incorporate the most energy-efficient HVAC system possible due to heavy energy consumption in data centers. Complexities surrounding the mechanical and electrical systems were critical. However, challenging design strategies, such as integration of various control technologies, were implemented in early stages by the commissioning agent and the project received two points in this credit [
36].
Commissioning in the Largo Community Center in Florida, which is a platinum-certified building involved efficient mechanical, plumbing, and fire safety designs [
45].
Fundamental commissioning is a prerequisite and is mandatory for LEED certification. “EA3—Enhanced commissioning” contributes additionally to the energy performance of the building. The possible benefits of enhanced commissioning include improved building system control and performance, improved efficiency and maintainability, early detection of potential problems, and improved occupant comfort and productivity [
44,
46]. On the other hand, commissioning is a costly process [
47]. Owners typically select commissioning agents based on their fee, their qualifications, and their experience [
20]. According to
Figure 3, publicly traded corporations and educational institutions recorded the highest PMP compared to other owners.
Several researchers point out that the perception of additional costs and the lack of experience of project owners and contractors affect the use of commissioning services [
13,
25,
48,
49]. In addition, inadequacy in establishing and distributing a commissioning plan to project participants, and shortcomings in integrating a commissioning plan into the project schedule also constitute barriers to the implementation of this credit [
50]. Continuing the trend in EA1 and EA2, buildings owned by investors seemed to achieve significantly higher points in EA3 also. The results of Bonferroni’s post-hoc test in
Table 7 confirms this finding, which indicates that investors are more informed about commissioning services than other types of owners.
EA4—Enhanced Refrigerant Management
This credit accounts for two points. It intends to reduce ozone depletion, and to support early compliance with the Montreal Protocol while minimizing direct contributions to climate change. The credit basically aims at designing and operating without mechanical cooling and refrigeration systems [
33]. If use of a mechanical system is essential, it suggests utilizing heating, ventilation, air conditinioing, and refrigerating (HVAC&R) systems for the refrigeration cycle, selecting equipment with reduced refrigerant charge and increased equipment life, maintaining equipment to prevent leakage of refrigerant to the atmosphere, and using fire suppression systems that do not contain Hydrochlorofluorocarbons (HCFCs) or halons. A prerequisite is also defined for fundamental refrigerant management in both versions of LEED.
According to the information presented in
Table 4, buildings achieved 1.0, 1.1 and 1.2 points on average in silver, gold and platinum-certified buildings, respectively. These values correspond to 51%, 55%, and 59% of the maximum two points at each level, respectively. Compliance with this credit requires either avoiding refrigerants altogether or using HVAC systems that have low impact on ozone depletion and global warming. Despite the best of intentions, attaining points in this credit can be challenging, since higher efficiency equipment systems generally use larger heat exchangers and require larger refrigerant charges [
51]. For example, the University of Texas at Austin decided to eliminate all CFC refrigerants in chiller systems and started a phase-out plan to convert from dichlorodifluoromethane (CFC-12) to Hydrochlorofluorocarbon-134a (HFC-134a) refrigerant. Also a refrigerant leakage detection and management process was launched to ensure that refrigerant leakage to the atmosphere is kept to a minimum [
52]. Even though the use of complex formulas can act as a barrier to less experienced consultants [
11], it is not difficult to achieve points if manufacturers provide compliant equipment [
21]. According to
Table 3 and
Table 7, investor-owned buildings perform significantly better in EA4, again indicating that investors are more informed about alternative refrigerants than other building owners.
EA5—Measurement and Verification
This credit intends to provide ongoing accountability for building energy consumption over time. The difference between the intended and actual energy consumption should be tracked to evaluate the energy efficiency of the building. The accurate quantification of energy use is measured by installing metering equipment [
33]. According to LEED-NC 2009, the measurement and verification period should cover at least one year of post-construction occupancy. This credit was revamped in LEED v4 and was renamed “advanced energy metering” [
53].
The maximum contribution of this credit is three points (
Table 1). According to
Table 4, 0.8, 1.1 and 2.0 points were achieved on average in silver, gold and platinum-certified buildings, respectively. The number of projects with zero points in all three certification levels add up to 830 corresponding to 56% of the whole building inventory. Only 441 buildings (30%) earned the full three points. Such a finding indicates that in general, this credit is either underperformed or most of the time not performed at all. The cost of advanced meters and the cost of hiring consultants for the measurement and verification process can be the reasons why owners do not fully take advantage of this credit [
54].
In order to earn points, a measurement and verification plan should be introduced to monitor the end uses in the building. Any discrepancies between actual energy use and the original model should be detected. For example:
It was found in a police station that was constructed on the campus of the University of Massachusetts, Amherst that actual electricity use in the first year of occupancy was 70% more than modeled. After identifying HVAC/control issues, the contractor made corrections [
54]. It is argued in this case that if full measurement and verification had been performed, the discrepancy and its causes might have been detected earlier.
In another project at the University of Texas at Austin, building site metering and generation source metering were made available to establish a metric for cooling and combined heat and power systems [
52]. The aim was to quantify and verify the performance of these systems. For example, each building’s chilled water consumption for cooling purposes was digitally metered. Similarly, steam and electricity consumption were also metered for heat and power facilities. These measures were collected and reported monthly to determine total thermal efficiency and electrical generation heat rate to compare actual energy use and the original model.
Table 7 indicates that, the points obtained by publicly traded corporation-owned buildings are significantly different from the points obtained by buildings with different ownership. Publicly traded corporation-owned buildings scored higher points in general, probably because they need to be transparent vis-à-vis their shareholders by putting in place measurement and reporting routines.
EA6—Green Power
This credit aims to encourage the development and use of grid-source, renewable energy technologies on a net zero pollution basis. It requires engagement in at least a two-year renewable energy contract to provide at least 35% of the building’s electricity from renewable sources, as defined by the Center for Resource Solutions’ Green-e Energy product certification requirements [
33]. It corresponds to two points. The intent has been described similarly in LEED-NC 2009 and in LEED v4, but the term of the energy contract has been increased to five years in LEED v4 with the provision of at least 50% (earns one point) or 100% (earns two points) of the project’s energy from green power, carbon offsets, or renewable energy certificates. The newer version increases support for growth in clean energy.
According to the information presented in
Table 4, platinum-certified buildings achieved an average of 1.6 out of the maximum points, whereas gold and silver-certified buildings attained only 1.0 and 0.9 points, respectively. Investors achieved a higher percentage than the other types of owners, a PMP value of 70% (
Figure 3). Governmental buildings significantly underperformed in this credit and achieved lower points (
Figure 3).
This credit encourages the use of off-site renewable energy, which can be administered by several options such as enrolling in the Green Power Program, selecting a Green-e-certified power provider, or purchasing Green-e-certified Renewable Energy Certificates (RECs) [
55]. A REC represents the environmental attributes of the electricity produced from a renewable energy source and is a separate commodity from the electricity [
56]. Each of these options has its own advantages and disadvantages. Enrolling in the Green Power Program is simple and monthly payment of bills is possible, but can be expensive; month-to-month enrollment can often be an option [
24]. Selecting a Green-e-certified power provider may not be the most cost effective alternative and may not be regionally available, which usually results in a lack of communication and support [
24]. Purchasing a REC can be often the least expensive option as it involves simple contracting procedures, but may not be regionally available. Thus, the strategies addressing a solution can change depending on project characteristics and location. Building energy and economic analysis software can be used to model a building’s base line and to support the decision of selecting the applicable option.