Specifying for sustainability: performance specifying
One of the cores of LEED v4 or any sustainable design standard is specifying performance. Here's how to do it properly.
Performance specifying is one of the four ways to specify products, systems, or assemblies. (Descriptive, reference standard, and proprietary are the other three types or classes of specifying.) When used properly, performance specifications allow the user to specify complete systems, assemblies, components, products, final performance, and even nonstandard or emerging technologies. It is a great way to specify many—but not all—items as there are limitations, and works best when combined with other types of specifying.
Instead of identifying products or product types, stating compliance with a standard, or naming a manufacturer, performance specifying indicates specific characteristics and performance requirements of the product, system or assembly, and indicates a level of measurable performance of the finished result.
This is a great way to specify a product or system that may not yet be standardized in the industry, something that happened often in earlier versions of LEED and ASHRAE Standard 189.1. This is especially true when dealing with U.S. Green Building Council LEED v4 that awards points for innovation; click here to download a PDF of some of the innovative strategies used in LEED 2009 projects.
Solar carports are a great example: no one standard governing these structures exists, so engineers have to specify minimum electrical and structural characteristics the carports have to meet to justify the cost, energy generated, and structural integrity. This allows multiple carport manufacturers to bid on the project and ensure that all manufacturers meet the performance criteria (to exclude a certain manufacturer, provide a list of approved manufacturers) while allowing for innovation or nonstandard design.
As long as the performance of the solar carport is properly defined, such as output of the solar panels, microinverters, opacity, fittings for luminaires, drainage, etc., the engineer can be assured of a product that meets the owner’s criteria. A performance specification for the carport could range from a very broad description of a carport down to a specific description of the desired operating characteristics.
There are some drawbacks to performance specifying. The first is defining the performance. Performance goals need to measureable or quantitative. Defining these goals, especially for a product that isn’t quite defined, is difficult and it’s easy to make a mistake when determining the desired benchmarks—either setting them too low or too high. The second drawback is that you don’t know exactly what you are going to get. Going back to the carport—you could define all of the performance characteristics, but not the aesthetic characteristics, and end up with a product that doesn’t mesh with the client’s vision. Another challenge is choosing the level of specificity of the performance specification.
Often the level of or nature of the length of the specification will depend on the project delivery type: design-bid-build will have more detailed performance descriptions while a design-build performance description may not have more than watts per square foot (W/sq ft). How the contract is structured, the engineer’s fee, the owner’s requirements, and the level of control the owner has or wants over the project drives the level of description. Going back to the carport, this could be a basic description of a carport, or a carport with exposed structural steel with a specific coating and translucent glass solar panels.
One final point—if you are designing these carports in California, they need to be designed to a seismic standard, which means, that like most specifying, the product was specified using both performance and reference standard specifying methods.
LEED v4 relies on the engineer choosing a level of performance, be it Certified, Silver, Gold, or Platinum, and determining what and how the appropriate reference standards will be met (notice the mix of specification types). Similarly, the International Green Construction Code (IgCC) mandates a certain level of performance. The reference standards, for instance ASHRAE/IESNA 90.1-2010 or a 50% Advanced Energy Design Guide, provide the engineer with a means to set measureable performance goals, whether they be W/sq ft, dimming levels, or number of air changes per hour. Tying these standards into project documents is the engineer’s job and a good justification for earning our fees. Merely naming the reference standard is easy. Translating the standard into performance characteristics and measureable, quantitative levels of acceptable performance—well, that’s what we do. Next up: reference standard specifications.
What are you experiences with specifying for sustainable design projects?
Michael Heinsdorf, PE, LEED AP, CDT is an Engineering Specification Writer at ARCOMMasterSpec. He has more than 10 years' experience in consulting engineering, and is the lead author of MasterSpec Electrical, Communications, and Electronic Safety and Security guide specifications. He holds a BSEE from Drexel University and is currently pursuing a Masters in Engineering Management, also at Drexel University.