Using energy modeling can help provide insight and identify energy saving opportunities in the building design process. However, not all energy models are created equal. It is very important to identify the objectives of the energy model and understand its limitations.
For better or worse, the most prevalent energy modeling appears to be compliance modeling. Compliance modeling is typically done in support of an incentive program, a green building certification, or to demonstrate compliance with building code requirements. The results are usually a comparison of the proposed design against a reference or baseline building.
One of the issues facing the energy modeling industry is the confusion over the various baseline references used in compliance modeling. ASHRAE 90.1 is a common reference; however that standard is often revised and frequently updated. While the current version of ASHRAE 90.1 is 2010, there are still plenty of LEED-NC v1.0 projects that may certify using an ASHRAE 90.1-1999 baseline or ASHRAE 90.1-2004 baseline. Further, ASHRAE 90.1-2004 and later versions also include an Energy Cost Budget Method (ECB – Section 11), and a Performance Rating Method (PRM – Appendix G). The ECB is used to document code compliance, while the PRM is used to document an energy efficiency rating.
Another frequently cited issue that can cause confusion when discussing compliance modeling results is the use of cost savings as a metric. The primary issue here is that as energy cost fluctuate so do the energy modeling results. Despite this shortcoming, several incentive programs and green building certification systems look at cost savings as the primary indicator of performance.
Finally, compliance modeling often occurs too late in the design process, when all the major decisions have already been made. While these models can validate that the project teams have met the design goals, this brings low value to the design team.
The greater value in energy modeling comes from using the model early in the design process as a tool to test potential design options and rank their impacts. In this scenario, the focus is on the relative impacts of each measure, and the interactions that the measures will have on energy end use. Using energy modeling in this manner can bring high value to the design team. The main difference is the early involvement of an experience energy modeler. Once the design has been finalized, the design model may still be used as a compliance model.