Evaluation of Home Energy Rating Systems

The objective of this project was to evaluate the technical and administrative characteristics of Home Energy Rating Systems (HERS) and assess their treatment of gas-fired appliances, space conditioning equipment and related distribution systems.  Three HERS tools in wide use at the time were evaluated: Energy Rated Homes of America (ERHA), REM/Rate, and California Home Energy Efficiency Rating System (CHEERS).  The first two are widely used while CHEERS can only be used in California.  In general, a HERS consists of two parts, the rating tool and the rating method.  The rating tool is the means by which a prediction of energy consumption is made.  In every case, the rating tool is a computer based energy simulation or estimation program which uses methodologies ranging from simple degree-day type calculations up through complex hour-by-hour simulation programs.  The rating method is the means by which a predicted energy consumption is converted to a rating.  The algorithm used can be a simple equation, or it can be more complex, involving comparisons between the rated house and hypothetical baseline houses.  None of the HERS evaluated appeared to be fully adequate for nationwide use.  Conversion of energy consumption to a rating value depends heavily on the objectives of the HERS and the audience for which it is intended.  The rating tools evaluated focus on weatherization type energy conservation measures.  Treatment of adding insulation or improving window R-value is handled reasonably well.  None of the tools were well suited however for investigating the effects of equipment changes (other than straight-forward efficiency improvement) or more complex energy conservation approaches such as infiltration reduction, solar energy systems, thermal distribution system efficiency improvements, or even the addition of basement wall insulation.