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.


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.

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