Energy code equivalence is assessed based on a quantitative analysis of the energy use of a state base code and amendments through DOE's energy modeling framework to determine the overall state energy index. This provides a greater level of accuracy and replaces the previous approach, which was comprised of a simpler qualitative review of state code titles and provisions.
State Code Adoption Tracking Analysis
The U.S. Department of Energy (DOE) Building Energy Codes Program tracks adoption of energy codes for residential and commercial buildings. State adoptions are reviewed based on the national model energy codes–the International Energy Conservation Code (IECC) for residential buildings and Standard 90.1 for commercial buildings (42 USC 6833). DOE analyzes state energy codes to assess the energy and economic impacts associated with code amendments.
State Analysis
A quantitative analysis is performed to assess the energy impacts within a given state, resulting in an energy index. For residential, the Energy Index represents the ratio between the whole-building site energy intensity of a state code and that of the 2006 IECC. The underlying energy use intensities (kBtu/ft2-yr) are derived from per-dwelling unit intensities (kBtu/unit-yr) which are aggregated across building types, foundation types, system types, and climate zones using weighting factors based on new-housing permits. For commercial, the Energy Index represents the ratio between the whole-building site energy intensity of a code and that of 90.1-2004. The underlying energy use intensities (kBtu/ft2-yr) are derived from per-building intensities (kBtu/building-yr) which are aggregated across building types and climate zones using weighting factors based on new-building permit data.
This comparison allows for a categorization of each state, with categories based on recent editions of the model codes. Any code for which the Energy Index is not more than 1% higher than that of an IECC or Standard 90.1 edition is considered equivalent to that code edition. For states whose codes fundamentally differ from the national model codes, PNNL may consider analysis conducted by others as a basis for its categorization.
The Energy Index relative to the 2006 IECC is used instead of direct EUI for two primary reasons. First, the Index value is easier to interpret because it directly shows relative performance (i.e., as a fraction or percentage of the 2006 baseline). Second, the EUI values tend to change a bit from year to year (or quarter to quarter) due to improvements in the EnergyPlus simulation tool, bug fixes in DOE's simulation infrastructure, updated site-source conversion factors, differences in construction weighting factors, etc. Index ratios between a given code and the 2006 IECC tend to change much less in such situations, so they avoid the appearance of a state code's performance changing when the state didn't change its code.