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Review Article

# A Perspective of Energy Codes and Regulations for the Buildings of the FutureOPEN ACCESS

[+] Author and Article Information
Michael Rosenberg

Pacific Northwest National Laboratory,
2032 Todd Street,
Eugene, OR 97405
e-mail: michael.rosenberg@pnnl.gov

Duane Jonlin

Seattle Department of
Construction and Inspections,
P.O. Box 34019,
Seattle, WA 98124
e-mail: duane.jonlin@seattle.gov

American Council for an
Energy-Efficient Economy,
529 14th Street NW #600,
Washington, DC 20045

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING: INCLUDING WIND ENERGY AND BUILDING ENERGY CONSERVATION. Manuscript received May 2, 2016; final manuscript received September 23, 2016; published online October 13, 2016. Assoc. Editor: Patrick E. Phelan. The United States Government retains, and by accepting the article for publication, the publisher acknowledges that the United States Government retains, a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for United States government purposes.

J. Sol. Energy Eng 139(1), 010801 (Oct 13, 2016) (6 pages) Paper No: SOL-16-1202; doi: 10.1115/1.4034825 History: Received May 02, 2016; Revised September 23, 2016

## Abstract

Today's building energy codes focus on prescriptive requirements for features of buildings that are directly controlled by design and construction teams and verifiable by municipal inspectors. Although these code requirements have had a significant impact, they fail to influence a large slice of the building energy use pie—including not only miscellaneous plug loads, cooking equipment, and commercial/industrial processes but the maintenance and optimization of the code-mandated systems as well. Currently, code compliance is verified only through the end of construction, and there are no limits or consequences for the actual energy used in a building after it is occupied. In the future, our suite of energy regulations will likely expand to include building efficiency, energy use, or carbon emission budgets over their full life cycle. Intelligent building systems, extensive renewable energy, and a transition from fossil fuel to electric heating systems will likely be required to meet ultralow-energy targets. This paper considers short and long-term trends in the building industry, lays out the authors' perspectives on how buildings may evolve over the course of the 21st century, and discusses the roles that codes and regulations will play in shaping those buildings of the future.

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## Background—Where Are Building Energy Codes Today?

Building energy codes in the U.S. have been in existence since 1975 when the first national building energy code—American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Standard 90 was published [1]. Figure 1 shows the relative improvement of each new addition of the model residential and nonresidential energy codes since the inception of Standard 90 as tracked by the U.S. Department of Energy.1 Although energy codes have evolved since that time and been separated into separate residential and nonresidential versions, a number of central tenets have remained consistent throughout the 41 years of code evolution.

###### Focus on Prescriptive Requirements.

Building energy codes have traditionally been developed around prescriptive requirements under which the quality or efficiency of specific components are regulated individually, typically constrained by considerations of cost effectiveness. This applies to provisions such as the allowed wattage of lighting, the R-value of wall or roof insulation, and the efficiency of heating or cooling equipment. In addition to the prescriptive path, most energy codes also include what is referred to as a performance path, but what could be better described as a predictive performance path based on modeled projections of energy use. The required performance varies with the individual components selected for the design. For example, if a designer chooses to heat a building with a heat pump, the code requires a minimum efficiency for the heat pump, whereas if the designer chooses to heat the same building with a natural gas furnace, the code requires a minimum efficiency for the furnace. Both the heat pump and the furnace may just meet the minimum requirements of the code, but they result in a different usage of energy. That means that two otherwise identical buildings with the same building program can be designed to meet the code but result in very different energy performance.

To study this, Pacific Northwest National Laboratory (PNNL) quantified the variation in predicted energy cost for a prototype office building in Chicago, IL by simulating different code compliant options from within the prescriptive path of ASHRAE Standard 90.1-2013 [2,3]. Five building design parameters including Heating, Ventilating, and Air Conditioning (HVAC) system type, HVAC system size, roof, wall, and window construction material, and window-to-wall ratio were varied, while efficiency of these components was held at code compliant levels. That analysis showed that varying just these five design parameters resulted in an energy cost index (ECI) range of from $0.883 to$1.04/ft2 yr (18% variation). If more parameters were varied such as orientation, building aspect ratio, floor-to-ceiling height, and service water heating system type, the range could be much larger.

Another drawback to the prescriptive approach is that there are limits to the savings that can be achieved by strengthening individual prescriptive requirements, leading to diminished returns for each incremental improvement. For example, adding R-11 insulation to an uninsulated wall decreases heat loss by about 75%, while adding an additional R-11 only results in 11% more reduction. For some systems such as certain classes of HVAC equipment, efficiency improvements are reaching practical and theoretical limits. For example, increasing air-conditioner or chiller efficiency may require larger heat exchangers with a diminishing return similar to adding insulation, and the cost of materials needed for the heat exchanger continues to escalate [4]. Figure 2 shows the same improvement in the nonresidential energy code since 1975 shown in Fig. 1, but adds individual component improvement based on changes in prescriptive efficiency requirements. The dashed line shows the projected improvement through 2030, assuming the rate of improvement from the period of 2004 to 2013 is maintained. If the same rate of change in component efficiency is maintained, it is unlikely that the goal of zero-net-energy (ZNE) new construction by 2030, an established goal of several stakeholders in the building industry will be met [5,6].

Energy codes have traditionally regulated only those building systems that are the responsibility of the building design professional, including the building envelope, HVAC, lighting, and service water heating systems. Other energy-using components such as receptacle loads, cooking equipment, and process loads are largely unregulated. As the regulated loads are reduced through codes, the unregulated portion becomes a larger proportion of overall building energy use, and further reductions of regulated loads are more difficult to achieve. Figure 3 shows the portion energy cost due to unregulated loads increasing from 21% to 29% from 2004 to 2013 [7]. If ultralow-energy (ULE) and ZNE goals are to be met, those currently unregulated loads cannot be ignored.

###### Actual Energy Use Not Considered.

Energy codes have until now only regulated building design and construction and not energy use. Code compliance is determined by a building official whose association with the project ends once a certificate of occupancy (CO) is granted. Because of this, actual building energy use never comes into play when determining energy code compliance. Tenant behavior and operational characteristics such as thermostat setpoints, hours of operations, maintenance of equipment, raising and lowering of window shades, and opening and closing of windows—while all extremely impactful from an energy perspective—are simply not under the purview of the code. A recent study by the New Buildings Institute (NBI) determined the operations of a building can be at least as important in determining a building's energy use as the designed efficiency qualities of building energy-using systems [8].

###### Energy Codes Impact a Small Portion of the Building Stock in Any Given Year.

Energy codes only apply to new construction and new systems or components added to existing buildings. For the majority of buildings, this means that the energy code only impacts them significantly once when they are built and possibly once again if they undergo a major renovation. According to the recently released Commercial Building Energy Consumption Survey (CBECS), as of 2012, approximately 80% of existing commercial buildings were built before the year 2000, 65% before 1990, and 45% before the first energy code was introduced in 1975 [9]. Less than 2.5% of the existing commercial building stock is retrofitted each year [10]. This means that a relatively large portion of the existing building stock was constructed to older energy efficiency standards and almost half to no energy standard at all.

## What the Future Will Hold—How Will Buildings and Energy Codes Evolve in the Future?

Our abilities to predict the future are confounded both by our anticipation that current trends will evolve further and faster than they typically do, and by severely underestimating how soon revolutionary and disruptive changes will take place. The remainder of this paper discusses the authors' predictions of how energy codes will progress in the future and what advances in buildings and building technologies will support those more stringent codes.

###### The Evolution of Buildings—Strategies Contributing to Significant Reductions in Future Building Energy Use.

As buildings and building codes continue to evolve, a variety of opportunities for reducing energy use and greenhouse gas emissions present themselves. This section discusses a number of opportunities that may become key strategies for meeting the next generation of energy code requirements.

###### Intelligent Efficiency and the Sophistication and Miniaturization of Sensors and Controls.

Intelligent efficiency refers to the use of sensor, control, and communication technologies to gather, manage, interpret, communicate, and act upon disparate and often large volumes of data to improve device, process, facility, or organization performance and achieve energy savings and higher levels of energy efficiency. Intelligent efficiency can be applied in homes, commercial buildings, manufacturing, and transportation—sometimes separately labeled smart homes, smart buildings, smart manufacturing, and smart transportation. In commercial buildings, intelligent efficiency often involves a sophisticated building or facility energy management system and extensive sensors and software algorithms to better optimize performance. For example, a 2013 study identified 13% average energy savings from these strategies in three large buildings that were already considered efficient—qualified or nearly qualified for Energy Star designation [11]. And in the long-term, Rogers et al. have identified opportunities for energy use reductions of 35–50% for major commercial building end-uses such as lighting, HVAC, and office equipment [12].

A large proportion of energy use in buildings is wasted, with the lighting, air conditioning, computers, and other equipment continuing to run, while no occupants are present to make use of them. Often such energy-consuming systems are both fundamentally inefficient to begin with and have drifted away from their optimal efficiency settings. If our long-term intention is to stretch the limited supply of renewably generated electricity to accommodate all of the essential functions of society, the first step is to cut such energy waste out of our buildings. That would require not only the use of highly efficient equipment but also responsive controls that energize it only to the extent that it is needed and then turn it completely off the remainder of the time. This evolution is already well underway and will provide exceptional efficiency benefits as it enters the industry mainstream.

There are numerous examples of potential technical solutions. Light-emitting diode fixtures are already available with onboard daylight and occupancy sensors, so that they supplement daylight to just the lighting level that is actually desired, and only when occupants are actually present in the space. Advanced controls can even be set to modulate the HVAC system, so that the ventilation turns down and the heating or cooling sets back as people filter out to lunch, and then they ramp back up again when they return. As another example: building occupants often complain paradoxically of feeling too cold indoors on warm summer days. One research team has achieved significant HVAC energy savings and user comfort reports using prototype wearable control devices [13]. What we now just think of as simple windows might soon be required to selectively optimize heat and light transmission through the glass based on exterior conditions and the needs of the people inside (dynamic glazing). It is reasonable to assume that such developments will continue to occur and that new and heretofore unheard-of technologies will enter the design and construction mainstream.

In a related trend, some new building control systems are configured to optimize themselves as they learn occupant and weather trends over time, providing self-diagnostics and self-correction while providing specific maintenance advice to guide work priorities down to the individual thermostat or light fixture [14]. As it is now however, building operators can be overwhelmed with hundreds of alarms and meter readings, while major malfunctions can go unnoticed for years.

###### Zero-Net-Energy and Ultralow-Energy Buildings.

There is a growing interest in advancing building energy codes to ZNE levels of performance, meaning that on an annual basis a building would be required to produce as much energy—usually via renewable energy systems—as it uses. Several efforts are targeting ZNE codes by 2030; for example, such targets are envisioned by the state of California and ASHRAE [5,15]. Related to ZNE are ultralow-energy (ULE) buildings. By reducing energy use, ULE construction makes ZNE much more feasible and is sometimes labeled “ZNE-ready.” The New Buildings Institute has documented approximately 300 ZNE commercial buildings in the U.S. as of December, 2015 [16]. The Zero Energy Coalition has identified more than 3000 ZNE homes in the U.S. [17].

However, much work needs to occur before we can go from a few thousand ZNE projects to on the order of a million projects a year that would be involved if most new homes and commercial buildings were built to ZNE codes. Amann discusses obstacles to ULE and ZNE codes and suggests a combination of research and development (R&D), implementation, and building code strategies for reaching this goal [18]. For example, R&D would include development of workable system performance metrics to determine how much energy buildings would use once occupied. Implementation strategies could include building rating and labeling; public sector leadership; stretch codes, green codes, and beyond-code guidelines and incentives; as well as valuing efficiency in financial transactions. Building code strategies include mandatory inclusion of demand response capability and renewable energy systems when cost effective and “renewable ready” requirements when they are not.

###### Deep Retrofits.

Even in 2040, the majority of homes and buildings will be ones that already exist today [19]. Thus, retrofitting existing homes and buildings will need to be an important part of strategies to reduce overall energy use and greenhouse gas emissions. There is growing interest in deep retrofit strategies, typically defined as achieving energy use reductions of about 50%. Dozens of such projects have been documented in the residential and commercial sectors [20,21].

Building codes primarily impact existing buildings when they undergo substantial renovations. This only affects a small portion of buildings each year, and thus conventional building codes cannot be the only path to deep energy retrofits. Other options may need to be considered such as retrofit energy codes. For example, France recently passed a law requiring existing homes to meet steadily more stringent energy efficiency requirements, with the targets set many years in advance. In Europe, many buildings are rated on an A–G scale, with A the most energy efficient. Under the French law, all F and G rated homes must be retrofitted to at least the E level by 2025 before they can be sold or rented. In this way, building owners have many years of lead-time to determine when and how to upgrade their buildings [22]. There is also a longer-term goal of requiring a D or better rating by 2030, C or better by 2040, and B or better by 2050. Implementing regulations for the early tiers still need to be developed, and the latter goals do not yet have the force of law. Here, in the U.S., New York City has a regulation in place mandating that lighting systems in existing buildings be upgraded by 2025 [23].

###### Embodied Carbon of Materials and Construction.

The “embodied energy” in the materials that are used to construct a building, while not insignificant, is typically a small fraction of the energy that will be consumed within the building over its lifetime. However, by definition, a zero-net-energy building consumes no net energy at all during its operation, so reducing the embodied carbon of construction materials may present itself as another big frontier. The extraction and processing of steel, cement, glass, aluminum, and other construction materials is highly energy-intensive, but some changes are appearing on the horizon. For instance, the use of cross-laminated timber for the structural members and floor “slabs” in high-rise buildings could become a reality within the next decade, and research on low-carbon substitutes for Portland cement is underway in several places around the world. It is not hard to imagine a future energy code that imposes limitations on embodied energy or carbon, or one that requires additional renewable energy production to offset that embodied energy over time.

###### Reducing Energy Beyond the Individual Building.

Most of the preceding discussion has centered on reducing energy use, focused on individual buildings. It is clear that there are opportunities for significant reductions in energy use if that framework is expanded to include surrounding building and communities.

###### Communities and density.

Overall energy use per capita can often be reduced with higher density development. For example, multifamily dwellings use less energy per person than single-family homes, and denser development makes public transportation more viable. To illustrate, in 2009, the average U.S. single-family residence used 37.7 kBtu (11.0 kWh) of energy per household member, while the average multifamily residence used 27.2 kBtu (8.0 kWh) per household member [24]. The density of development is primarily determined by zoning laws and market forces, but potentially building codes could play a role, such as by tightening code requirements for less dense developments or placing caps on home energy use no matter how large the home. For example, the Energy Star New Home Specification currently requires homes larger than a specified benchmark home to be more efficient than those smaller than the benchmark home [25].

###### Communities connected by district energy networks.

Perpetuating the current isolated buildings strategy is one possible energy future, but another future might feature an energy exchange market where the local pizza restaurant transfers its excess oven heat (what we currently refer to as “waste heat”) to the nearest hotel, while a data center sells its excess heat to the hospital down the street, all through some district thermal energy distribution system. The implication for codes might be that we need to develop networks of buildings now that are capable of connecting together into thermal exchanges in the future. Vancouver, BC has designated districts where new buildings are required to utilize hydronic heating so that they can eventually tap into emerging district energy systems, and Denmark has already connected tens of thousands of buildings to such systems [26]. The city of Klamath Falls, OR has had a downtown district heating system in place for 35 years that is served by the extensive geothermal resource in that area [27].

A thermal district energy system can make good use of low-grade heat energy, but getting that system up and running would require some extremely expensive and disruptive infrastructure construction. Although a few major North American universities have successfully installed new campus-wide hot water systems over the past several years, doing this for a large sector of an existing city would be a daunting prospect. This is complicated by the extensive use of electric resistance heating in our existing building stock, which provides no pathway for distributing thermal energy within those buildings. Still, the prospect of a system that can recapture excess heat from sewer lines, industrial processes, data centers, refrigeration condensate, and other sources is not only tempting but also may eventually prove to be a necessary step in achieving zero-carbon cities. This concept can even be extended to ground source heat pump systems for storage of excess summer heat in the deep thermal mass of the earth, which can then be withdrawn using heat pumps when needed in winter.

###### Fuel choice and electricity sharing.

Another emerging issue is the question of fuel choice. Traditionally, the choice of fuel for a home or building is left to the designers, builders, and developers. But several recent studies have suggested that in order to limit greenhouse gas emissions it may be advantageous to electrify space and water heating, provided the electricity comes from low-carbon generation [2830]. Potentially building codes could also require or encourage certain fuel choices. Such steps should be based on localized analyses. For example, a recent study by Nadel finds that in the U.S., use of electric heat pumps relative to gas furnaces makes more sense in some parts of the country based on current average energy use and costs and current equipment efficiencies [31].

Electricity has the advantage that it can be economically transferred long distances over a grid that already exists, but the disadvantage that it is still quite expensive to store at a utility scale. Most low-rise buildings will eventually be able to generate enough power for all their electricity needs using their own rooftop photovoltaic (PV), and perhaps they will have battery storage systems to continue running overnight. Where this renewable electricity is used for heating, heat pump systems can currently get three times the heat energy from each unit of electricity than is provided by electric resistance and the theoretical limit for heat pump efficiency is considerably higher than that. Some low-rise buildings, such as schools and warehouses, will produce more than they need, and those could sell their excess electricity for use in vehicle batteries, taller buildings, or process loads, using the electric utility as a broker. This is already occurring to some extent with the implementation of net-metering electric tariffs. We will still need energy sources to carry us through the winter and extended periods of cloudy weather. Wind (and perhaps tidal) power will fill some of that gap, as can ground source heat pumps, while hydropower and perhaps biomass or biogas generators would be critical components for maintaining dependable power during periods when neither sun nor wind is available. It has even been suggested that millions of vehicle batteries plugged into charging stations could have agreements in place that would allow power to flow back out to the grid whenever the power purchase price is right.

###### The Need for Building Energy Codes to Evolve.

Where left to market forces, the changes to standard construction practices discussed above tend to occur at a snail's pace. This is partly because the benefits of energy efficiency flow to the tenants and long-term owners, not the people who shoulder the burdens of designing, constructing, and financing the buildings. Thus, one fundamental requirement for accelerating change is a highly effective and broadly enforced energy code for new construction and alterations, ensuring that buildings are at least capable of operating at very high efficiency. This should be combined with retrocommissioning or building tune-up policies that ensure optimal functioning of the systems over time, as are already in place in New York City and Seattle. There are numerous precedents for such regulations; many regions require periodic vehicle smog checks as a condition of license plate renewal, and the annual recertification of elevators, boilers, and fire alarm systems is almost universal.

###### The Move to Performance-Based Codes.

For building energy codes to continue to progress as they have over the last 40 years, the next generation of building codes will need to provide a path that is led by energy performance, impacts the entire building stock, and ensures a measurable trajectory toward net zero energy buildings and beyond.

###### Predicted performance.

As building energy codes continue to evolve, changes will be needed in the basic structure and approaches used. Standard 90.1-2013 is 270 pages long. At some point in the future, all building energy codes will be much simpler than they are today and will be led by whole building energy performance. The current prescriptive approach of basing requirements on cost effective efficiency of individual components will become obsolete. Instead, efficient and cost effective solutions integrating all aspects of a building's design will be used to set design budgets for predictive energy use for different building types and locations. Those budgets could be defined in the form of energy cost, source energy, or greenhouse gas emissions. Table 1 shows predicted energy use for prototype buildings compliant with 90.1-2013 for several climate zones [32]. A table like this could become the heart of a future commercial building energy code. We are already starting to see the budget approach being used in the green codes like the International Green Construction Code (IgCC) and rating programs like ASHRAE's Building Energy Quotient (BEQ) [33,34]. Building energy modeling (BEM) tools to support this approach will become sophisticated enough to provide consistent predictions of energy use (with assumed operational conditions). We are even beginning to see the advent of BEM tools that can provide real-time energy feedback as design alternatives are considered [35].

###### Maintaining efficiency in existing buildings.

To address the issues of both unregulated loads and the impact of operations and maintenance on building energy use, a number of recent writers have pursued the idea of an “outcome-based code” that would change the required compliance path from prescriptive compliance or predictive modeling to limiting the actual energy use of the building once it is occupied [2,36]. Variations on this concept are currently available as optional compliance paths in a few U.S. cities, but have been rarely used due primarily to the additional risk and uncertainty for the owner and project team [37,38].

One alternative approach would be to create a separate code or ordinance that would govern energy use of all buildings after occupancy. Energy use targets could be set using a standardized table of values, or perhaps by using the design phase energy modeling for the building. The deep retrofits and intelligent efficiency discussed previously, while not explicitly required by outcome-based codes, will become strategies necessary to reach aggressive performance goals.

There are number of challenges that must be addressed if energy codes based on actual energy performance are to be implemented. Those include setting fair and reasonable energy use targets for the enormous variation in building types, sizes, functions, and locations around the country, as well as setting fair and reasonable consequences for buildings that did not meet those energy targets. The operating hours, occupant density, tenants, equipment, and other factors continually change and evolve in buildings, in addition to remodeling and system upgrades, so a mechanism would have to be in place to adjust targets as required [39]. Such a system would involve considerable municipal staff time and effort. An outcome-based code might potentially drive a building owner to hold the design and construction teams responsible for the energy use of the building after construction, even though they have no control over the maintenance and operation of the building.

Another approach would be to require auditing and correction of the building energy-using systems on a periodic or continuous basis, ensuring that those systems operate as efficiently as possible. This type of program could be somewhat simpler to administer. Such an approach has recently been enacted in New York City for buildings over 50,000 ft2 (4645 m2) [40].

Any of the above approaches could potentially be combined with a set of future targets to mandate upgrades of the energy-using systems in existing buildings over time, while giving building owners years of advance notice to enable planning.

## Conclusions

How will the energy codes of the future take shape? The correct answer is of course that we do not know. However, a range of plausible pathways and outcomes presents itself, still subject to constraints imposed by advances in technology and the political or economic climate. Based on observed trends and advances in codes and building related technologies as discussed above, the authors provide the following predictions.

Building energy codes will transition from an emphasis on meeting prescriptive design requirements to meeting requirements for energy performance, both as predicted during design and as experienced throughout the lives of buildings as indicated by their true operational energy use. Thus, both existing buildings and new construction will be required to meet energy use targets, encouraging efficient operations, energy benchmarking, improved maintenance, deep retrofits, and retrocommissioning. An enormous challenge will be the setting of fair and reasonable targets which are likely to be customized by building type, function, and climate.

To ensure that new buildings are optimized for low or no energy use, design tools that provide real-time feedback on the energy impact of design decisions will become standard practice among the design community.

To facilitate the low-energy operation of existing buildings, smarter buildings with advanced controls, sensors, communications technology, and self-diagnostics will gather, manage, interpret, communicate, and act upon disparate and often large volumes of data.

The interaction between onsite, community based, and utility scale renewable energy combined with energy storage and other means of load shifting will be optimized to take full advantage of renewable energy resources. Energy codes have typically permitted the use of any fuel source, but if net zero energy use or carbon neutral operation is the ultimate objective, fossil fuel use must eventually give way to a combination of efficiency and renewably generated electricity, perhaps combined with district thermal energy sharing. As coal-fired plants are retired over time, and renewable energy sources continue to proliferate, the nation's electrical grid will become cleaner overall and electric heat pumps will provide a lower-carbon alternative to onsite fuel combustion.

Building energy codes will evolve to include other energy impacts of buildings besides those from purchased utilities. This could potentially include consideration of embodied energy in construction materials and urban planning that maximizes housing density and minimizes the need for fossil fuel-based transportation systems.

While energy codes and building designs evolve to ensure that society's aggressive energy and greenhouse gas emission reduction goals are achieved, regulations developed by policy makers must consider the need for buildings to remain healthy, functional, comfortable, and desirable places for human beings to live and work.

## Acknowledgements

Michael Rosenberg's participation is funded by the U.S. Department of Energy's Building Energy Codes Program.

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## Figures

Fig. 1

Improvement in the residential and nonresidential energy codes since 1975

Fig. 2

Improvements in nonresidential energy codes with projections to 2030

Fig. 3

Nationally weighted end use cost breakdown for new construction

## Tables

Table 1 Energy use in kBtu/ft2 yr (kWh/m2 yr) for prototype buildings compliant with ASHRAE Standard 90.1-2013a
aEnergy use indices are based on simulation and are shown as examples only.

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