Evaluating energy codes on a scale

ASHRAE Standard 189.1 and IgCC are leading the way to high-performance green buildings. Learn how these two “maps to net zero” handle the enigma of “percent better than code,” with the outright goal being to have updates to energy codes be evaluated on a scale.
By Josh Greenfield, PE, CEM, BEMP, LEED AP BD+C, O+M, Primera Engineers, Chicago November 12, 2014

This article has been peer-reviewed.Since the launch of various energy codes, energy engineers have compared their proposed energy model to a baseline energy model via a “percent better than code” metric. Whether this metric is a percent energy savings or percent energy cost savings output, what significance does this value have outside of the realm of the specific code or standard under which the model was analyzed? What adjustments must be made to correlate a project’s energy model percent savings to determine how close the project is to a long-term target of net zero, or even compare against that of an alternative project’s performance? 

The newly constructed Northeastern Illinois University El Centro building incorporates: a highly efficient curtainwall system, vertical exterior fins for reduced direct solar gain through windows, interior daylight harvesting, and a soon-to-be-installed 80 kW dc roof-mounted photovoltaic array. The building’s modeled design site and source Energy Use Intensity (EUI) metrics are 54.6 kBtu/sq ft/yr and 127.6 kBtu/sq ft/yr, respectively, which correlates to a Zero Energy Performance Index (zEPI) value of 48.6. Courtesy: JGMAASHRAE Standard 189.1 and the International Code Council’s (ICC) International Green Construction Code (IgCC) are leading the way to high-performance green buildings, and this article will dig deep into how these two “maps to net-zero” handle the enigma of percent better than code, with the outright goal being to have updates to energy codes be evaluated on a scale, as opposed to having code updates redefine the scale by way of evolving the use of “percent from zero.”

ASHRAE 189.1-2011

Standard 189.1 was created through a collaborative effort involving ASHRAE, the U.S. Green Building Council (USGBC), and the Illuminating Engineering Society (IES). The 2011 version of the standard is written in code-intended (mandatory and enforceable) language so that it may be readily referenced or adopted by enforcement authorities to provide the minimum acceptable level of design criteria specifically for high-performance green buildings within their jurisdiction. Prior to Standard 189.1’s release in 2010, it was anticipated that it would be in direct competition to the IgCC, as both were in development concurrently. 

Instead, rather than competing with Standard 189.1, when the IgCC was debuted in 2012, it included Standard 189.1 as an alternate compliance path as a first step to greater integration, connecting it to ICC’s code network that reaches all 50 states and 22,000 local jurisdictions. This alleviated a major concern that was brewing in the industry—that inconsistency in codes from one community to another complicates the work of designers and contractors, and competing options might have bogged down the entire code adoption process. 

Figure 1: Typical confusion is seen when using “percent better than code.” Courtesy: Primera Engineers

Standard 189.1 addresses site sustainability, water use efficiency, energy use efficiency, indoor environmental quality (IEQ), and the building’s impact on the atmosphere, materials, and resources. The standard devotes a section to each of these subject areas, as well as a separate section related to plans for construction and high-performance operation. With respect to the energy efficiency section, an available path for compliance is the performance option (in lieu of the prescription option), which adheres to the ASHRAE Standard 90.1 Appendix G modeling guidelines, commonly known as the performance rating method (PRM). In addition to the standard PRM modeling parameters, Standard 189.1 alters the modeling guidelines to create an enhanced baseline model or, one might say, a baseline model on steroids. Specific changes from a typical ASHRAE 90.1 PRM baseline model include:

  • 10% reduction of calculated fan power values
  • Above-grade exterior wall shading
  • ASHRAE Standard 55: Thermal Environmental Conditions for Human Occupancy
  • ASHRAE Standard 62.1: Ventilation for Acceptable Indoor Air Quality
  • Economizer minimum capacities stringency increase
  • Economizers for systems that include gas-phase air cleaning
  • Energy Star rated appliances/electronics
  • Exhaust air energy recovery requirement stringency increase
  • Inclusion of on-site renewable energy
  • Increased daylighting by side-lighting
  • Increased daylighting by top-lighting
  • Increase in fan motor electrical efficiencies
  • Increased use of automatic lighting controls
  • Low-flow plumbing fixtures
  • MERV filtration requirements
  • Minimum roof reflectance requirements
  • Permanent exterior shading projections
  • Supermarket condenser heat rejection recovery (if applicable)
  • Variable speed fan control for commercial cooking hoods.

Inclusion of on-site renewable energy is a significant change to the baseline model requirements per Section 7 of Standard 189.1. The proposed building design must generate as much, or more, renewable energy than what is required in the baseline model to not be penalized in the PRM results. Much like the PRM output of a Standard 90.1 energy model analysis, the output of a Standard 189.1 energy model is a percent better than code value, in either percent energy savings or percent energy cost savings. 

To date, efforts to compare the energy efficiency of buildings have almost always pointed back to our nation’s energy codes and standards. But therein lies the problem: Since 2000, there have been anywhere from six to eight major commercial energy codes or standards under current adoption at any given time in the United States. Comparing the energy efficiency of buildings by referencing their “percent better than code” can often create more confusion than clarity. Which code? What year? ASHRAE 90.1-2004, 2007, 2010, IECC 2006, 2009, 2012, Title 24 2008, 2013 . . . and the list grows with the addition of an ASHRAE 189.1 modeling guideline. (Note: A draft of ASHRAE 90.1-2013 Addendum bm recently was released that would begin to combat this specific industry confusion if approved. The draft addendum is currently under its third public review.)

Standard 189.1 does, without a doubt, provide a clear path to a high-performance building, as it mandates the implementation of numerous load reduction and efficiency-increasing strategies to assure maximum energy conservation, but it’s also a continuation of the move away from outcome-based codes. 

Outcome-based codes 

Outcome-based codes are such that the metric by which building performance is judged is the actual energy use. This approach focuses on real and measurable energy performance improvement rather than on the relationship of the buildings’ energy characteristics compared to a theoretical building built to a code baseline. The Architectural Energy Corp. recommended in a 2009 study titled “Rethinking Percent Savings” that percent savings past code minimum be abandoned as the basis for green building rating systems and energy labels. Architectural Energy Corp. notes that the code-based baseline moves every 3 years or even more frequently as codes are updated, making the concept confusing and ambiguous. Percent savings has served its purpose, but as goals are set for zero net energy, as codes become more stringent, and as nonregulated energy use becomes larger than regulated energy use, it is time to move on to a stable scale.

ICC 2012 IgCC

After a multi-year development process, the ICC released the IgCC in partnership with the American Institute of Architects (AIA) and ASTM International on March 28, 2012. Gone was the dreaded competition, replaced with the collaboration of the ICC/AIA/ASTM and ASHRAE/USGBC/IES teams, due to the inclusion of ASHRAE Standard 189.1 as an alternate compliance path of the IgCC. 

The IgCC addresses natural resources, material, and water and energy conservation, as well as IEQ and comfort, building commissioning, operations and maintenance for new and existing buildings, building sites and building materials, components, equipment, and systems. With respect to the energy conservation and efficiency section, an available path for compliance is the performance option, similar to the path options for Standard 189.1. However, despite the IgCC being part of the ICC family of codes (International Building Code [IBC], International Plumbing Code [IPC], International Energy Conservation Code [IECC], etc.), the IgCC does not use the energy modeling guidelines from that of the IECC. 

Continuing the collaborative effort, the IgCC adheres to the ASHRAE 90.1 Appendix G modeling guidelines, the PRM, again similar to Standard 189.1. A major difference is that while Standard 189.1 beefs up the baseline model parameters, the IgCC maintains the business-as-usual 90.1 Appendix G baseline model parameters, and provides only a handful of mandatory energy compliance requirements to be combined with additional energy conservation features the design team sees fit to meet overall performance compliance. 

Figure 2: Zero Energy Performance Index (zEPI ) is a scalar representing the ratio of energy performance of the proposed design compared to the average energy performance of buildings relative to a benchmark year. Courtesy: Southern California EdisonSpecific compliance requirements for the proposed model that the IgCC mandates include:

  • Automatic plug load control
  • Commercial food service equipment efficiency increase
  • Conveyor system energy conservation
  • Elevator energy conservation
  • Escalator energy conservation
  • Inclusion of on-site renewable energy
  • Moving walkway energy conservation.

Similar to Standard 189.1, one or more on-site renewable energy systems (solar photovoltaics, wind, or solar thermal) are mandated in the proposed design, per Section 610 of the IgCC. While a Standard 90.1 energy model analysis output would be a percent better than code metric, the IgCC lays the groundwork for an industry sea change, and states that the performance rating shall be based on source energy instead of site energy. 

  • Site energy = the sum of the energy delivered to a facility (or site), excluding that used to produce or transmit the energy to the facility (i.e., the energy directly consumed at a facility typically measured with utility meters)
  • Source energy = the sum of the energy consumed at a facility (or site), and the energy required to extract, convert, and transmit that energy to the facility

By taking “all” energy use into account via the use of source energy in lieu of site energy, the relative efficiencies of buildings with varying proportions of primary energy (raw fuel that is burned on-site to create heat and electricity) and secondary energy (the energy product [heat or electricity] created from a raw fuel, such as electricity purchased from the grid or heat received from a district steam system) can be identified and effectively compared. The proposed model source energy and baseline model source energy outputs from the IgCC modeling procedure are then used to calculate the zEPI, the Zero Energy Performance Index, considered to be the future of scalar energy performance comparisons.

zEPI

The zEPI is defined as a scalar representing the ratio of energy performance of the proposed design compared to the average energy performance of buildings relative to a benchmark year. The Architectural Energy Corp., in collaboration with Southern California Edison (SCE), developed the zEPI to clarify how commercial building efficiency levels are measured and compared. The basis for zEPI can be traced back to a scale presented in the previously mentioned paper written by Charles Eley (Architectural Energy Corp.) and co-written by Randall Higa (SCE) and Devin Rauss (SCE), called “Rethinking Percent Savings.” Eley makes the persuasive case for the adoption of a more stable, absolute scale that would be used to benchmark buildings as opposed to the percent better than code baselines (ASHRAE 90.1 2004, 2007, etc.), which are continuously shifting as more stringent codes are developed and adopted. The scale establishes zero net-energy as the absolute goal. The only metric that matters is how far a building deviates from zero net-energy, that is, the percent from zero.

The scale goes from 0 to 100 following the less-is-good-more-is-bad concept, with 100 (more is bad) representing the average energy consumption based on 2003 Commercial Buildings Energy Consumption Survey (CBECS) data. A modeled building with net-zero energy use receives a score of 0 (less is good). The zEPI scale extends in a linear fashion between, above, and below those two points. Therefore, a building that uses twice as much energy as an average 2003 CBECS building receives a score of 200. A building that uses half as much energy as an average 2003 CBECS building receives a score of 50. 

The zEPI scale can also measure buildings that go beyond net-zero and produce more energy than they consume; these buildings receive negative scores. The simple relationship between zEPI scores can be readily understood by code makers, architects, and engineers, as well as nontechnical building owners and tenants. The built-in comparison-friendly attributes of the zEPI metric eliminate any need to stipulate an energy code or standard of reference when documenting the zEPI, as the percent from zero value scale of the zEPI is adaptable to all buildings.

zEPI integration into the IgCC

Section 602.1.1 of the IgCC provides the compliance equation to determine the zEPI value of the proposed building design (Equation 6-1), and stipulates that “Performance-based designs shall demonstrate a zEPI of not more than 51 as determined in accordance with Equation 6-1 for energy use reduction…”. Equation 6-1 states that the “zEPI = 57 x (EUIp/EUI).”  Further explained, the fixed value of 57 is multiplied times the ratio of “EUIp” (proposed source energy use 

index [kBtu/sq ft/yr]) to “EUI” (baseline source energy use index [kBtu/sq ft/yr units]). If the proposed model was designed to match the specific requirements of the ASHRAE 90.1-2010 Appendix G PRM, “EUIp” would equal “EUI” in this equation, and thus the ratio would be 1.0, resulting in a zEPI of 57 when multiplied by the fixed value of 57 per Equation 6.1. This fixed value of 57 is a pre-analyzed number provided by the ICC to be integrated into the zEPI equation, which represents the zEPI of an average baseline building design that complies with the 2012 IECC/ASHRAE 90.1-2010 when scaled to the performance of the 2003 CBECS zEPI value of 100. 

The IgCC performance compliance section requires that the proposed design shall demonstrate a zEPI of not more than 51. The addition of the IgCC mandated energy conservation design requirements will aid in achieving a zEPI of 51, while additional design-team chosen energy efficiency strategies/measures will push the zEPI below and beyond the 51 threshold.

Future, and more stringent, editions of the IgCC will possibly include updated fixed values in the zEPI equation that are lower than 57 to accurately reflect the average baseline building design performance of that particular code/standard edition (i.e., 2015 IECC/ASHRAE 90.1-2013, etc.). In addition, a variety of past energy codes and standards have been analyzed to determine their zEPI equation multipliers, and thus the zEPI can be calculated for previously completed projects already part of the existing building stock. This allows comparison of past and present buildings, regardless of the design energy code/standard, a significant feature that the “percent better than code” metric never mastered in a simple manner.

Percent better than code expiration

Highly regarded organizations in the building industry, including Architectural Energy Corp., AIA, Building Owners and Managers Association (BOMA), and New Buildings Institute (NBI), have become big proponents of zEPI because it sets a constant goal (zero) and shifts the conversation from percent better than code to percent from zero. High-performance green building codes and standards, such as ASHRAE 189.1 and the IgCC, are defining a clear path for the building industry to net-zero energy buildings (NZEB). Buildings represent approximately 40% of total world energy consumption, and with limited world energy supply and resources, the necessity for net-zero buildings is inarguable. 

While the use of a metric, such as the zEPI, does not save energy alone, it is an identifier. The zEPI identifies the building industry’s progress in creating an energy conservation culture. The zEPI identifies where we still need to go, and how far (or close) we actually are. The zEPI identifies buildings that should be recognized for their superior design, as well as the ones that should be recognized for their energy shortcomings and/or the potential energy reduction opportunities they offer. While the percent better than code metric is a convenient tool to use, it is bound and limited to beneficial use within a small subset of building projects, those which share the same energy code/standard. The percent better than code was an identifier in that it identified that updates to energy codes should be evaluated on a scale (the zEPI), as opposed to having code updates redefine the scale, by way of evolving the use of “percent from zero.”


Josh Greenfield is VP, energy services manager at Primera Engineers. He has 12 years of experience highlighted by energy grant acquisition, extensive energy consulting, and sustainable design experience both as the project LEED consultant as well as serving as the mechanical engineer on several LEED design projects.  


The references in this article are based on published versions of ASHRAE 189.1-2011 and the 2012 IgCC. Any provided commentary as to when/if the codes/standards will adapt to the use of the zEPI are solely the opinions of the author. Future adoption of the zEPI metric will be determined by the code/standard development committees during the development cycle of a particular code or standard. Specific to the IgCC, the use of zEPI in future editions is dependent on the proposals received from the building industry for possible approval and incorporation into the 2015 IgCC.