I recently caught up with Mark Frankel, Technical Director of the New Buildings Institute (NBI), to discuss the use of prescriptive design criteria as a strategy to increase the energy performance of commercial buildings rather than using project specific energy modeling to do so. NBI’s Core Performance Guide is one of the better-known prescriptive platforms and is receiving increased attention as an energy performance option within the LEED rating system, its use by various utility incentive programs and to inform energy code revisions. (Full disclosure: NEEA, through BetterBricks, is a sponsor of NBI and I am a former member of the Core Performance project team and have worked with NBI to expand the use of Core Performance.)

NBI developed Core Performance using a batched energy modeling approach to analyze the impact of various energy efficiency measures, when applied to three prototype commercial buildings ranging from 10 to 70 thousand square feet, using any of four HVAC systems, in 16 US cities (representing different climate zones). Time after time, a number of measures rose to the top based on the energy benefits provided. These measures have been incorporated into a package of Core Performance requirements that result in modeled building energy performance roughly 20-30 percent better than a prescriptive design using ASHRAE 90.1 2004. (Core Performance requirements cannot be unbundled and still achieve this level of savings.) A group of individual enhanced measures have also been modeled and can be implemented to achieve additional savings.

As we spoke, Frankel suggested that batch modeling applied to the Core Performance strategies consistently produced the same results.  So why ask modelers, project-by-project, to continue modeling the obvious? Experienced designers of high performance buildings already know what strategies should guide high performance buildings.  This begs the question: if and when we should continue to require modeling comparisons to a code baseline when any designer can take a conceptual short cut and start with a proven set of criteria that they can be confident will result in a building that performs better than current codes? According to Frankel, there’s a time and a reason for each approach: “use modeling resources to examine the added benefit of advanced measures,” he said. “Modeling will give you sophisticated answers when you ask sophisticated questions.”

That sentiment is getting a positive response. A Core Performance option will allow LEED Design & Construction projects to meet the Energy and Atmosphere (EA) Prerequisite 2 – Minimum Energy Performance threshold of 10 percent better than ASHRAE 90.1 2007 without requiring energy modeling. Office, School, Retail and Public Assembly projects would meet this prerequisite and earn one additional point for EA Credit One – Optimize Energy Performance. Pursuit of enhanced strategies could earn another two EA Credit One points.

In addition to aligning with LEED, Core Performance has been adopted as the basis for utility efficiency incentive programs in Oregon, Massachusetts and New Brunswick. With funding from The Energy Foundation and the Northwest Energy Efficiency Alliance (NEEA), Core Performance has been converted to International Energy Conservation Code (IECC) language.  And with the support of the US DOE and the AIA, Core Performance has been proposed to become part of the 2012 version of the IECC, resulting in a 30 percent performance increase to the current commercial code—a very significant advancement.

NBI is now applying the same batched modeling approach to perform sensitivity analysis on how building schedule modifications and other occupancy characteristics that we normally assume as fixed when modeling design features, can provide additional energy savings. Frankel says that he will not be surprised to find that these approaches have a bigger impact on energy performance than the design changes that we typically model. If he is right, it will be interesting to see how these findings – resulting from strategies beyond the current reach of codes and prescriptive performance paths – are incorporated into future versions of Core Performance or successor programs.