The Pacific Northwest National Laboratory (PNNL) analyzed the relationship between the Residential Energy Services Network (RESNET) Home Energy Rating System (HERS) Index and the traditional simulation-based Performance Path used in the International Energy Conservation Code (IECC). The analysis evaluates, for a single-family residence with various characteristics, the ranges of HERS Index values that would imply compliance with the 2012 IECC Performance Path. While this analysis does not attempt to evaluate all the differences between the two approaches, the analysis does show that the variables in certain building characteristics are likely to result in quantifiable differences in the outcomes of the two approaches. What this suggests is that when these characteristics are not accounted for (window-floor ratio, number of stories, etc), two homes that minimally comply with the IECC Performance Path can have HERS Index ratings that differ by as much as 26 points, which ostensibly represents a 26% difference in energy performance.
These findings will be important to be aware of as states and municipalities begin to consider adoption of the 2015 IECC, which includes a HERS-like rating system as an alternative compliance path.
The technical report, “Identification of RESNET HERS Index Values Corresponding to Minimal Compliance with the IECC Performance Path”, can be viewed on the U.S. Department of Energy’s Building Energy Codes website here.