A new paradigm for building codes
Original research by Jennifer Senick, Executive Director of the Center for Green Building at Rutgers University and Alon Abramson, Project Manager at Penn Institute for Urban Research
Performance-based (also known as outcome-based) codes set standards based upon buildings’ actual energy use, rather than on compliance with stipulated technology or design features. For example, a performance-based code would require meeting specified energy use intensity, while a standard, prescriptive code would stipulate a minimum wall insulation level among other specific measures. By holding buildings to a performance target, performance-based codes allow building owners the flexibility to try new (and modify existing) energy conservation measures or, more likely, bundles of conservation measures that are designed to achieve optimal energy performance .
However, prevailing state building codes are not typically performance-based. Rather, they prescribe a uniform set of standards that focus primarily on a building’s physical characteristics. A building design following prescriptive codes must adhere to the current criteria for energy features in its category of building, such as minimum R-values of insulation, maximum U-factors and solar heat gain coefficients of fenestration, maximum lighting power allowance, occupancy sensor requirements for lighting control, and economizer requirements for HVAC systems. Moreover, prescriptive building codes do not mandate post-construction accountability; this creates the possibility that a building will not be operated to the prescribed standard. Since the prescriptive code applies its standards to the constructed energy characteristics, once the building is deemed in compliance, it can be poorly operated and managed without facing any code-based ramifications.
Such prescriptive codes also put unique and historic buildings at a distinct disadvantage as they may prescribe retrofits that diminish the value of a historic building or that fail to recognize certain unconventional strategies that capitalize on a particular building’s inherent strengths. Standardized, prescriptive codes have the potential to leave a substantial amount of energy savings on the table.
n contrast, performance-based codes embrace the fact that the majority of a building’s energy consumption is determined by its use, not only its construction: by how it is operated and by how much energy-saving responsibility the building occupants take upon themselves. Performance-based codes also allow for the combined benefits of deep retrofit solutions: energy savings that come from applying energy conservation measure to multiple building systems simultaneously. When designing to performance-based codes, designers working with existing buildings are thus empowered and incentivized to upgrade operational aspects of a building (such as control system function, maintenance practices, system operation, and local environmental conditions) and to consider elements that modify tenant behavior (such as adjusting plug loads, occupant density, and occupancy schedule and monitoring equipment density and use). These aspects are crucial to energy reduction, with plug loads alone impacting total building energy use by 40% or more, depending on equipment density and use habits . Yet these types of high-yield energy conservation measures are not communicated in standard codes.
Background on National Building Codes
Under the federal Energy Policy Act of 1992 (EPAct 1992), the U.S. Department of Energy mandates that states’ building codes must, at minimum, conform to the current American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) Standard 90.1, “Energy Standard for Buildings Except Low-Rise Residential Buildings,” which is updated every three years. The current version, ASHRAE Standard 90.1-2010, contains an option for performance-based code compliance called the Energy Cost Budget (ECB) method.
Using ECB, a designer has the option to “trade off” compliance by not meeting some prescriptive re¬quirements if the impact on energy cost can be offset by exceeding other prescriptive requirements. Using the ECB approach, a computer simulation of a proposed building design is compared to a reference building design (baseline) that is essentially a duplicate of the proposed design with each building component modeled to meet minimum prescriptive requirements. A building is deemed in compliance when the annual energy cost of the proposed design is no greater than the annual energy cost of the reference building design. Instead of looking at components in isolation, this method allows recognition of the interactions of those components in demonstrating compliance .
ASHRAE puts out many sets of standards and bodies of research, pertaining to an assortment of topics including building systems, energy efficiency, indoor air quality, refrigeration and sustainability. One of those sets is ASHRAE/IES Standard 100, “Energy Efficiency in Existing Buildings,” currently being revised for a proposed 2013 release. Standard 100 is a performance-based code specifically written for existing buildings. States legislate their own building codes, so states will determine whether Standard 100 is an acceptable alternative to the Standard 90.1 ECB compliance path for retrofit designs. Since states are only federally mandated to adhere to Standard 90.1, drafting retrofit codes based on 100 will be optional.
States Lead the Way with Performance-based Codes
California, Washington, and Florida have adopted their own performance-based building codes based on different versions of ASHRAE 90.1. Their challenges and successes serve as case studies for ASHRAE when drafting the scope and requirements of this upcoming version of standards. States may adopt their own codes by evaluating their efficiency requirements against the latest federal building efficiency reference codes, as was the case in California .
California is a pioneer of performance-based codes, having developed the “Title 24” standards in 1978, generally considered to be the most stringent and best enforced energy code in the United States. Title 24 offers flexibility through performance-based specifications, is actively supported through technical assistance, and is commended for its high compliance rates in field verification studies. Coupled with mandates for energy-efficient appliances (a separate program), the Title 24 standards have saved Californians more than $56 billion in electrical and natural gas expenses, according to the California Energy Commission. Although per capita electricity use in the United States has increased by nearly 50% since the mid-1970s, California has essentially maintained its per capita electricity use .
Washington developed a stringent statewide energy code based on ASHRAE 90-1.2004 and the International Energy Conservation Code (IECC) 2006 by updating Chapter 51-11 of the Washington Administrative Code in 2006. Chapter 51-11 includes prescriptive requirements, such as thermal efficiency requirements for HVAC equipment, but also provides a performance-based approach to allow for flexibility and innovation in compliance. The code is a major success for Washington, which also boasts one of the highest rates of compliance in the U.S.
The results in Washington and California contrast with those in Florida, whose voluntary performance-based codes had a poor compliance rate . Given the varying levels of successful compliance with performance-based codes, ASHRAE and other stakeholders want to ensure that the 2013 version of ASHRAE Standard 100 is as informed and implementable as possible.
CBEI Role in Performance-based Code Implementation
In June 2013, CBEI hosted two programs on the subject of performance-based codes: the CBEI/ASHRAE Performance-Based Codes Workshop in Philadelphia, PA, and the CBEI Subject Matter Expert Work Group Session at the ASHRAE Annual Conference in Denver, CO. CBEI researchers also presented their performance-based code work at the ASHRAE NYC conference in January 2013. The heads of nearly every relevant ASHRAE Technical Committee traveled to attend the Philadelphia-based Codes Workshop, which served as a discourse on the limitations of prescriptive codes and the advantages, challenges, and gaps that exist in implementing performance-based codes. The Denver ASHRAE Conference reconvened those experts and others to parse the methods, dilemmas, and possible solutions to the challenges of implementing performance-based codes. The topic and its related challenges was broken into four broad categories: A) general aspects of performance-based codes; B) simulation programs and modelers; C) references and proposed building designs; and D) documentation, verification and approvals.
While the experts at both workshops recognized that new building codes cannot be one-size-fits-all in nature and must encourage innovation and enable individualized building renovation strategies, they also acknowledged that performance-based codes have enforcement and compliance issues that prescriptive codes do not have. When working with performance-based codes, code officials have nothing to measure while the building is still on paper – they must rely on the modeler’s assurance that the model, its inputs and calculations, etc., are correct. And modeling itself has challenges – the three most popular simulation programs have been found to give highly variable results when modeling the same building design. Additionally, compliance with performance-based codes is measured periodically throughout the life of the building (similar to monitoring for compliance with a fire code), which is far more time-intensive, making performance-based codes more expensive to enforce than prescriptive codes. The experts also cited the lack of reliable case studies, formal guidance for engineers and designers, and code official training as making the widespread implementation of these codes into more of a long-term goal than an immediately achievable objective.
Performance-based codes are, in principle, the best and most cost-effective way to achieve ongoing energy efficiency in buildings. Today, states interested in adopting these codes can turn to the existing standards, codes and programs to devise their own performance-based code programs. This material will help states to set their desired performance metrics and to design enforcement mechanisms to drive up compliance. CBEI continues to work with code experts to help with performance-based code development, implementation, and compliance efforts.
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