Alternative formats to achieve more efficient energy codes for commercial buildings.
Codes and standards govern the manner in which buildings are designed, constructed, commissioned, and in some instances operated. They cover a wide range of topics focused on health, life safety, and welfare, and can present requirements in many different formats. In general, a performance-based code format establishes a desired outcome without indicating how that outcome is to be achieved. Conversely, a prescriptive code format provides specifics to individually govern all items in a building that would affect the outcome.
The first known code was that of Hammurabi (circa 1772 BCE), who established a performance-based code with strict penalties for noncompliance (Harper 1904). According to Hammurabi's code, if a builder builds a house for someone and does not construct it properly, and the house which he built falls in and kills its owner, then that builder shall be put to death. If it kills the son of the owner, the son of that builder shall be put to death. If it kills a slave of the owner, then the builder shall pay, slave for slave, to the owner of the house. That first code did not specify how the building was to be constructed or the materials to be used, but instead very clearly established a desired outcome and incorporated with it a very effective compliance verification process. Unlike buildings today, there were likely no plan reviews or inspections, nor would they have been needed considering the desired outcome and penalty were sufficient to drive an interest in compliance.
As will be discussed there are different forms of performance-based codes. Some address simulated performance and verify compliance before construction, while others focus on actual outcomes after the building is occupied. While performance based, Hammurabi's code focused on outcomes after occupancy.
The scope of what is covered by and in codes and standards has increased over the years, as has the format for presenting the requirements and the means of ensuring compliance with those requirements. Today, the scope of codes and standards includes energy efficiency, and the format for the presentation of requirements is generally considered prescriptive in nature. Compliance verification is generally conducted through a review of building plans and specifications, and then an inspection of the building during construction to validate conformance with the approved plans and specifications. Upon completion of construction, an occupancy permit is issued. No other validation or verification actions are taken with respect to energy codes and standards, unless an addition or major renovation is made to the building. In those situations, depending on the nature of the addition or renovation, all or part of the energy code or standard in effect at the time of the work would apply and compliance would be verified in the same manner as the original building.
This means of compliance verification (e.g., enforcement) pre-dates the inclusion of energy efficiency within the scope of codes and standards. Generally speaking, because compliance verification has focused on the review of plans and specifications and inspection of construction, the format for codes and standards has tended to be prescriptive in nature. When energy efficiency was added to the scope of codes and standards in the mid-1970s (ASHRAE 1975) the format and presentation of the requirements was based on how and when compliance would be verified and enforced. Initially the provisions were a mixture of prescriptive and performance formats. For example, providing minimum insulation levels on air distribution systems is prescriptive, while a desired thermal performance level (overall U-factor) for building envelope assemblies is a performance format, because it does not prescribe how to achieve the required performance.
Over the past 40 years, the provisions in codes and standards covering energy efficiency in buildings have become increasingly prescriptive. For instance, requirements associated with building envelope assemblies have evolved from a single overall average U-factor to specific requirements for each product or material used in each building envelope component. This movement to very specific and prescriptive provisions has resulted in challenges to find additional energy efficiency because of diminishing returns associated with increasing the stringency of what is prescribed. Paralleling this evolution toward more prescriptive criteria and increased stringency in those criteria, the historical infrastructure to ensure compliance through enforcement has become increasingly strained. As energy codes included more specific and increasingly stringent provisions that demand increasing compliance verification resources, the resources available to enforce compliance were diminished. The desire to increase commercial building energy efficiency in the face of the challenges to develop more stringent prescriptive requirements and ensure compliance with those requirements suggests consideration of new formats for energy codes and standards that are tied to innovative compliance verification and enforcement mechanisms.
This paper explores how the format of energy codes and standards can impact the ability to secure increased energy efficiency in new commercial buildings (1) and through that generate an increased interest in considering different formats to present energy codes and standards criteria that take their lead from new and innovative ways to verify compliance. Five formats are considered: prescriptive, performance based (including the variations of performance equivalency and performance targets), capacity constrained, and outcome based.
There are many different ways to present energy codes and standards criteria applicable to commercial buildings. They range from telling the designer exactly what to do to expressing a desired outcome without detailing how to achieve the outcome. The former presumes that if the prescriptions are followed, a specific outcome will be achieved. The latter simply states the desired outcome without detailing how it is to be achieved. An example would be listing out all the things that have to be done to seal an air distribution system compared to simply stating a maximum allowable leakage rate at a specified pressure. The former provides a detailed listing of things to do (and check) that if followed are assumed to yield an acceptable leakage rate. The latter simply establishes an acceptable leakage rate and testing method without detailing how to reduce ductwork leakage.
As discussed later, format is integrally tied to the means of compliance verification. In this case, securing compliance with the prescriptive criteria is somewhat subjective, time intensive, and not easily verified throughout construction compared to a simple pressure test and maximum allowed leakage. The latter requires a singular test and verification of compliance based on the test result, which is certainly less subjective and time intensive than the former. In addition, if compliance is not achieved the system must then be modified until it does pass, which is an incentive for latter systems to be sealed effectively from the start.
Prescriptive formats establish minimum criteria for energy-related characteristics of individual building components such as minimum required R-values of insulation, maximum U-factors and solar heat gain coefficients (SHGC) of fenestration, occupancy sensors for lighting control, or a specific way to provide daylighting through lighting system controls and fenestration area, shading, and orientation. Energy codes and standards have primarily been prescriptive in nature, although the exact nature of the prescriptions in terms of scope and stringency has changed over time. Of particular relevance, the minimum prescription for each component is typically developed individually with little or no consideration of how it interacts with other regulated components of the building. A prescriptive code may contain other compliance paths and elements, but they are usually a function of the prescriptive requirements. This results in energy performance that is driven by the prescriptive requirements rather than the other way around. As such the realization of a specific outcome in terms of energy use of a building is not as easily estimated and guaranteed.
A variant of the prescriptive formats is component performance (not to be confused with performance based discussed below). Component performance provides some level of performance within a particular building component such as an opaque wall or roof/ceiling that is intended to achieve the same energy efficiency as that resulting from the application of the prescriptive provisions. An example is the presentation of the provisions for a commercial building wall in terms of an overall U-factor for the opaque portions of the wall or for the entire wall. The former does not specify a particular framing material or spacing, nor does it require the application and use of a particular sheathing material. The latter goes beyond that and includes the relative areas and thermal properties of the fenestration as a function of the entire wall. A further extension of this approach is a limit on the overall U-factor for the entire building thermal envelope and beyond that a limitation on peak heat loss or gain of a building as a function of floor area or other metric. Unlike a capacity-constrained approach, this approach limits the load heating, ventilating, and air-conditioning (HVAC) equipment would "see" as opposed to limiting the energy use being input to not only HVAC equipment but all building energy services.
Performance based refers to code compliance formats that are based on predicted building performance using energy simulation, but not actual energy consumption. There are two main variations of performance-based codes considered here: performance equivalency and performance targets. The differences in those approaches are described in the following paragraphs, but they have one important characteristic in common. The predicted performance of a proposed building must be better than some agreed upon metric. The performance metric can be established by a comparison to a prescriptive-equivalent building simulation that changes with the building design as is the case now with ASHRAE Standard 90.1 Energy Cost Budget Method (ANSI/ASHRAE/IES 2010), or to a static predetermined level of performance based on the building type and location such as was the case with Building Energy Performance Standards (BEPS) proposed by the U.S. Department of Energy, pursuant to the Energy Conservation and Production Act of 1976 (Pub.L. 94-385).
The performance metric might be expressed in terms of site energy, source energy, or energy cost. The metric might be an annual value or it could be expressed in terms of a longer period over the expected life of the building. The metric might be normalized by building size (e.g., Btu/f[t.sup.2] of conditioned floor area), number of occupants, operating hours, etc., or might be an absolute consumption value. The latter would make compliance easier for smaller buildings and compliance more difficult for larger buildings. The metric might include only the end uses within the scope of the code (e.g., heating, cooling, water heating, lighting) or might refer to whole-building energy use (including major appliances and miscellaneous plug loads and other energy using equipment). The following two code formats are variations of the performance approach.
Performance Equivalency. Performance equivalency refers to a compliance path that evaluates a proposed building design through energy analysis software simulation against a standard reference building that is essentially a clone of the proposed building but changed to exactly satisfy the minimum prescriptive requirements. Note that in this case, "performance" is judged as to whether a particular design is energy (or energy cost) equivalent to a building meeting the prescriptive minimums, not against a specific and pre-established performance metric. A variation on this format is a requirement that a building as designed have an expected energy use that is a certain percentage less than if it just satisfied the prescriptive provisions of an energy code or standard. Some refer to this approach as Prescriptive Plus or Performance Plus.
Performance Targets. Performance targets refer to a code format that specifies its fundamental requirements in terms of an absolute design energy consumption, energy cost, or some other metric, which is estimated using energy simulation software. For example, the code might be simply "not more than XX Btu/f[t.sup.2]-year," or "not more than xx $/f[t.sup.2]-year." The key is that the requirement is an absolute performance level rather than a relative comparison to a code minimum prescriptive-equivalent building, or a list of component prescriptions. In its purest form, a performance-based code would have no component prescriptions at all. Compliance with this approach requires only one simulation - that of the proposed building as designed and specified.
Capacity constraint refers to a code or standard that expresses its requirements in terms of limits on one or more service capacities (e.g., a limit on the capacity of the electric service panel (amps) and/or natural gas service). In its purest form, such restrictions would be the only limitations established in the energy code or standard. For many years energy codes and standards have taken the first step down the path of capacity constraints in one particular area--lighting--in the form of maximum lighting power densities as a function of building type or space use. Increasing the scope to all energy uses in the building would also bring plug and process loads into the scope of an energy code or standard--something that in the past has been a challenge to address due to limitations associated with current compliance verification processes that only have jurisdiction up to occupancy and not beyond. This is in contrast to a performance approach or outcome-based approach as discussed below in that instead of being based on an amount of energy use over time with no specific limit on peak use, it addresses a limit on peak use without a specific limit on the timeframe over which that use occurs.
Outcome based is similar to the concept covered above under performance targets but instead of being evaluated in the design and construction stage it goes beyond simulation and anticipated energy use in design to verify actual building performance by monitoring a building's energy consumption for a specified period of time after occupancy. An outcome-based code has been in place in Sweden since 2006 (Wahlstrom 2010). Implicit in this type of approach is the assumption that the code is expressed in terms that can be verified by billing data (or other metered data). Interestingly, unlike any of the other formats discussed, an outcome-based approach readily embraces existing building energy use and allows such an energy code or standard to be readily applied to all buildings, not just new buildings. The approach also gives credit for proper operation of energy using systems. Challenges to implementing this approach include post-occupancy evaluations, uncertainties related to occupants and their habits, and the potential requirement for corrective post-occupancy reconstructions.
There are advantages and disadvantages to each of the formats previously discussed, each of which must be considered from a particular point of view. Clearly a designer will have a different point of view than a code official or a product manufacturer. Regardless of the point of view, the desired result is increased energy efficiency in commercial buildings, and the bottom line associated with achieving that result is compliance. Clearly though, as discussed above, the format and presentation of criteria has a lot to do with the level of energy efficiency and whether it is presumed or actually achieved.
Favoring the prescriptive format, the requirements are simple, easy to understand, and relatively consistent from building to building. Because prescriptive requirements are fixed, they are relatively easy for designers, builders, and code officials to remember and apply. Existing enforcement infrastructures are accustomed to this format, which is aligned with other construction codes (e.g., structural, electrical, plumbing). Training materials and compliance aids are easier to develop and deploy as well. This format helps transform markets because the prescriptions tend to drive what is available in a given area from manufacturers and distributors.
With those things said, it is impossible to make a direct connection to actual building energy use. The relationship between prescriptions and energy use is indirect and variable, depending on which prescriptive options are included. This approach is inflexible and generally requires that one or more alternative prescriptive as well as equivalent performance paths be added, complicating the code. It is also difficult to establish equitable requirements across various alternative construction types (e.g., wood-frame walls, steel-frame walls, concrete walls, metal building walls). A focus on the most common construction types (e.g., steel-frame walls with fiberglass batt insulation) may disadvantage alternative types (e.g., steel-frame walls with sprayed cellulose insulation). Prescriptions can be used by manufacturers of predominant materials and equipment to disadvantage manufacturers of alternative materials. Simplicity and inflexibility may also hinder achieving the most cost-effective designs. It is also difficult to design and maintain a prescriptive format as stringency increases. Achieving a specified increase in energy efficiency as a percentage over a specific code or standard may be relatively easy for a particular building for which size, shape, number of stories, orientation, and other factors are known, but designing a simple prescription that will achieve that same percentage improvement for all buildings (or all buildings on average) is much more difficult and impractical because it does a very poor job of accounting for the complex interactions between building systems. Prescriptive formats do not, and are not likely to ever, regulate issues such as building geometry, passive solar, etc. because they are difficult to prescribe. This results in buildings of the same type in the same location both meeting minimum prescriptive requirements having a difference in anticipated annual energy use of 200% or more.
Compared to a prescriptive format, this approach provides flexibility in achieving the energy goal as represented by the prescriptive criteria and rewards designs that account for the interactions between various building components (integrated design). It also retains the fundamental format of the existing codes, making existing enforcement infrastructures, training materials, etc. useful with modest changes. In addition, it allows the code to support limited market transformation while retaining flexibility in achieving full energy compliance.
Compared to the performance targets approach, the main benefit to the two-model reference building approach used in the performance equivalency format is that it normalizes parameters that could affect the energy use of the building, but are not regulated by the code. For example, the simulation tool, modeler preferences, weather, building schedules, unregulated loads, outdoor air ventilation, etc. are all held constant between the two comparison models. This provides a powerful level of simulation quality control that cannot occur with the single model methodology used in the performance targets format.
Compared to prescriptive approaches, the required performance calculations can increase enforcement complexities for the code official unless the code official is inclined to accept the calculations at face when provided by a registered design professional. One way to mitigate this complexity is to develop compliance tools to avoid "cheating" because it is a calculation that is being regulated not actual consumption. Another downside is that the trade-offs generated by this approach are not necessarily equitable, since they have differing lives (example; envelope improvements verses lighting controls). Most importantly, the performance is only compared to a minimum prescriptive code building and as such the inequalities associated with the prescriptive approach are carried forward.
Target energy use indices or other design budgets provide maximum flexibility in achieving the energy goal and eliminate virtually all market manipulations by special interest groups. Unlike performance equivalency, there is a direct specification of the desired performance level as opposed to "building" one on a prescriptive basis. Like performance equivalency, this format rewards integrated designs that account for the interactions between various building components, but also more effectively considers the impacts such as design geometry, passive features, etc., as these are not zeroed out by the reference building.
On the down side, performance targets do a poor job accounting for individual building differences such as schedules, occupant and equipment density, ventilation and temperature requirements, etc. These differences can cause a building that does a very poor job on building infrastructure (e.g., envelope, lighting, HVAC), to look good because transient or assumed building usage or equipment can cause modeled energy use to be low. The opposite is also true. A building with good infrastructure can have high energy use if it is used intensively. For example, a university building that has a full set of night classes could look much worse than the same building holding classes from 9 a.m. to 5 p.m. It is possible for a code using this format to dictate mandatory assumptions for schedules or other sensitive parameters, thus taking them out of the compliance equation.
Quality control is extremely difficult with each one of the thousands of inputs in a single simulation needing to be verified, as they can affect the outcome as compared to the parallel model approach, where mostly the inputs that differ between the two models impact the result. Most importantly is the challenge in establishing meaningful target values.
A limit on capacity to use energy is extremely simple and easy to understand. After a value is established, it requires an absolute minimum of labor to enforce yet can easily guarantee virtually 100% compliance. Interestingly, the loads associated with commercial buildings are already needed for compliance verification with electrical, gas, and other codes, so a key component associated with this approach already exists. This approach also places very real incentives on the designer to "get it right." Beyond simply achieving compliance, designers and contractors have direct incentive to care about all the details, including for instance insulation levels as well as quality of installation, glazing SHGC as well as shading, orientation, efficiency of pre-installed appliances, solar access, balancing of duct systems, air sealing, etc. It is unknown whether such a simple code format can really work in complex commercial buildings because the relationship between capacities and energy consumption is indirect, and the method fails to consider efficiency at part load, which is where building energy systems operate during the majority of the time. This approach does place a very large and new burden on designers and contractors to effectively design and construct buildings that work because if the building cannot perform its intended function as a result of flawed design or construction, it can be difficult and costly to find and correct the problems given the limitation on connected load.
This format is the only approach that directly addresses actual building energy use. It is easily adaptable to existing buildings and eliminates or minimizes many of the cons associated with the other approaches. It also easily fits into the marketplace to attract energy efficiency as opposed to mandating it. Designers and contractors have the freedom to innovate, and code officials need only focus on ensuring the building is constructed in accordance with the plans and specifications. In reality, because the designer and contractor will be held accountable post-occupancy via an assessment of actual energy use, they will have a greater interest in ensuring the construction complies with the plans and specifications. The downside is this high risk for owners and designers and the need for a post-occupancy compliance infrastructure that does not exist on a widespread basis for energy. There is also the prospect for liability issues and consequent legal expenses should a building fail to meet the required outcome.
Energy codes and standards have been traditionally adopted as law by state or local government and enforced through the building regulatory process. When developing a process for verifying code compliance, a jurisdiction must consider both the methods that will be used and the time at which verification is determined. The methods for verifying compliance consist of many separate and parallel activities that address the conformity assessment of all the items (e.g., products, materials, equipment, appliances, components, devices) that comprise the building and its systems. Compliance verification also involves assessing the assembly of those items to ensure that they conform to codes and standards, and that the assembled system as a whole complies with the adopted requirements. Verification that a building complies with an energy code or standard is traditionally addressed during design and construction, although recent efforts at building labeling may move that into the lease or purchase market.
The building designer is required to document that what they propose to build meets the adopted requirements. Then those responsible for building the building must do so in compliance with the approved construction documents. When a building occupancy permit is granted, it is an indication that the building as designed and constructed meets the adopted requirements. However, an occupancy permit can be taken away in some instances such as failure to maintain means of egress or fire alarm systems in the building or a change in use of the building that would make it unsafe. While an occupancy permit could be rescinded because work on an existing building caused a noncompliance with an energy code or standard, it is not likely.
As previously discussed, all except the outcome-based compliance verification approach use the traditional code compliance model of plan review, construction inspection, and issuance of a certificate of occupancy. Some approaches are easier to apply in evaluating compliance than others. If increased energy efficiency is desired while continuing to rely on strained state and local government resources then approaches that consider all building energy uses, are easily checked as to compliance, and provide a foundation for relief in other venues such as the courts may be more desirable in the future. This suggests an energy target and/or capacity limitation. Both would rely on a registered design professional, create incentives for designers and contractors to ensure compliance, and address the downside of prescriptive criteria that challenge increased energy efficiency and do not consider commercial buildings as a whole. With that said, the identification of a failure would continue to be a challenge and there would not be any connection to actual energy use, although a capacity limitation would logically have some impact on actual energy use. Where incentives and other mechanisms could be put in place to reward good performance and penalize poor performance an outcome-based approach, if combined with an energy target and/or capacity limitation approach, could provide for actual delivery of energy efficiency and lead to a better understand the sources contributing to higher energy usage.
The popularity of energy code and standard formats is directly related to historical methods of compliance verification. The manner in which codes and standards for buildings have been historically enforced through plan review and construction inspection has had a significant impact on the format of energy codes and standards tending to move them towards a prescriptive basis. Any limitations associated with energy codes and standards, such as increasing challenges to securing greater energy efficiency through more rigorous criteria and/or increasing the scope of the provisions, are integrally tied to the manner in which compliance is verified. As additional energy efficiency in commercial buildings is desired, consideration should first be given to adjustments in the manner in which compliance is verified and then the provisions of the energy code or standard presented and formatted to fit with the chosen compliance verification mechanism. An outcome-based approach considers the building as a whole, allows total design freedom to achieve a desired end, and measures and validates compliance as occupied and used. The challenge with this approach is not compliance verification: that is simply measuring and expressing building energy use. The challenge is in providing the incentives for compliance, the penalties for noncompliance, and the mechanisms within which those incentives and penalties would function. This could be augmented to further the probability of compliance through the application of energy targets and/or capacity constraints imposed in the design and construction process and which are more easily assessed with respect to compliance.
As ever-increasing levels of energy efficiency and rates of compliance are being sought in energy codes, it is becoming apparent that the current approach of relying mainly on prescriptive requirements and the existing building code enforcement infrastructure is not an effective long-term solution. Future codes and standards will need to consider alternative formats if those goals are to be achieved.
HVAC = heating, ventilating, and air conditioning
SHGC = solar heat gain coefficient
(1) For the purposes of this paper, commercial buildings are all buildings other than one- and two-family dwellings, townhouses, and multifamily residential buildings (e.g., condos and apartments) not over three stories in height above grade as defined in ANSI/ASHRAE/IES Standard 90.1-2010. New is intended to include not only new buildings, but also additions and/or renovations to existing buildings.
ASHRAE. 1975. ASHRAE Standard 90-75, Energy Conservation in New Building Design. American Society of Heating, Refrigerating and Air-Conditioning Engineers.
ANSI/ASHRAE/IES. 2010. ANSI/ASHRAE/IESNA 90.1-2010, Energy Standard for Buildings Except Low-Rise Residential Buildings. American Society of Heating, Refrigerating and Air-Conditioning Engineers.
Conover, D., Makela, E., Stacey, J., Sullivan, R. 2011. Compliance Verification Paths for Residential and Commercial Energy Codes. PNNL-20822, Pacific Northwest National Laboratory.
Energy Conservation and Production Act of 1976. (P.L. 94-385, 15 USC 790).
Harper, Robert Francis. 1904. The Code of Hammurabi King of Babylon. Chicago: University of Chicago Press. Rosenberg, M., 2011. Advantages and Disadvantage of Alternative Energy Code Formats to Achieve 50% Improvement over Standard 90.1-2004. PNNL-SA-86510
Wahlstrom, Asa. 2010. "Trade Introduction of a New Building Code with Requirements for Energy Performance." Proceedings of the 2010 American Council for An Energy-Efficient Economy Summer Study on Energy Efficiency in Buildings.
David Conover is a senior technical advisor at Pacific Northwest National Laboratory in Washington, D.C. Michael Rosenberg is a senior research scientist at Pacific Northwest National Laboratory Richland Washington. Mark Halverson is a senior research engineer at Pacific Northwest National Laboratory Richland, Washington. Zachary Taylor is a senior development engineer at Pacific Northwest National Laboratory Richland, Washington. Eric Makela is a partner at Britt/Makela Group Inc. Richland, Washington.
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|Author:||Conover, David; Rosenberg, Michael; Halverson, Mark; Taylor, Zachary; Makela, Eric|
|Date:||Jan 1, 2013|
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