The prescriptive-based and performance-based energy codes currently in use in the U.S. have a fatal flaw: neither compliance method measures actual building energy usage and performance over time. Prescriptive compliance is exceedingly complex, relying on a myriad of requirements and calculations and equipment efficiency tables to produce snapshots of "in use" installed power. Performance-based compliance requires computer–simulated energy modeling of anticipated building energy performance. Performance-based compliance is often relegated to large projects due to the expense and need for specialized consultants to provide the energy simulation. Neither approach nor the associated metrics address actual energy usage and performance over any part of the building’s lifecycle.
So how are we supposed to get to zero-net energy (ZNE) buildings if the energy codes that we have in place, and that set maximum limits for energy consumption in buildings, don’t measure actual energy consumption?
The answer is outcome-based energy codes. Outcome-based codes are a new breed of code that incorporates compliance strategies which measure the actual energy usage of a building over a period of time. Right now, the field is open on this type of code compliance and several methodologies are being discussed and proposed. The term "outcome-based" refers to the fact that compliance is tied to the actual energy outcomes for a building and energy usage must be measured after occupancy and commissioning for a period of time, usually one year. Outcome-based compliance could be accomplished by setting energy use intensity (EUI) targets for buildings according to agreed-upon characteristics, putting smart meters on all building circuits to measure energy consumption in real time, and reporting out to an entity that would determine if the number perhaps in kBtu/sf/yr1 is within the limits for the building type and therefore in compliance. Outcome-based codes could also be more comprehensive and include energy allowance packages for safety or emergency building system operation.
Additionally, outcome-based energy code compliance could greatly ease the burden on building officials. Building officials have an important job: make sure buildings are structurally sound and safe for occupants. They inspect all aspects of buildings and building systems, and this includes compliance to energy code requirements, which is often the last and least important item to be checked. It’s no secret that building officials are overworked and that most cities do not employ enough of them. Outcome-based codes could significantly reduce the amount of time a building official would need to spend on energy code compliance if they were simply comparing the reported actual energy consumption of the building to the established threshold for that building type and location.
Another issue that outcome-based strategies address is designers and now even manufacturers are "designing to meet code." Designers must shape together systems that employ multiple control strategies to meet minimum code requirements, limiting creativity and chewing through design fees, while manufacturers must now design product and system functionality to comply with code instead of addressing market needs through innovative solutions. Outcome-based codes could alleviate this issue by reestablishing a singular focus for energy codes: set rigid energy consumption limits for buildings and then directly measuring compliance to these limits for a year after occupancy. Remove requirements from the energy codes that attempt to force energy usage reduction through functional device requirements which have severely limited design creativity, have made the energy codes incredibly complex and difficult to understand and enforce, and have proven to be largely inefficient.
Outcome-based energy codes are a shining new hope for reducing building energy consumption. Will it take a huge effort to change our conventional codes to this new model? Yes. Will it involve parties other than codes and standards developers to get this done? Yes. Is it worth the trouble? Absolutely!
Here’s the most compelling reason to change our thinking and adopt outcome-based compliance strategies: outcome-based codes address the energy being used in buildings that goes completely unaccounted for or is insufficiently regulated. I’m talking about the process loads, the miscellaneous electric loads (MELs), and the plug loads. This energy usage is significant and continues to grow. Process loads2 are currently exempted from the energy codes, while MELs are basically unaddressed. Efforts have been made to address and limit plug-loads through automatic receptacle control requirements with minimal success. The time is now, and the opportunity is outcome-based codes.