Energy consultants and auditors use energy modeling software for a variety of purposes, including rating the performance of an existing house, calculating the effect of energy retrofit measures, estimating the energy use of a new home, and determining the size of new heating and cooling equipment. According to most experts, the time and expense spent on energy modeling is an excellent investment, because it leads to better decisions than those made by contractors who use rules of thumb.
Yet Michael Blasnik, an energy consultant in Boston, has a surprisingly different take on energy modeling. According to Blasnik, most modeling programs aren’t very accurate, especially for older buildings. Unfortunately, existing models usually aren’t revised or improved, even when utility bills from existing houses reveal systematic errors in the models.
Most energy models require too many inputs, many of which don’t improve the accuracy of the model, and energy modeling often takes up time that would be better spent on more worthwhile activities. Blasnik presented data to support these conclusions on March 8, 2012, at the NESEA-sponsored Building Energy 12 conference in Boston.
Blasnik has worked as a consultant for utilities and energy-efficiency programs all over the country. “I bought one of the first blower doors on the market,” Blasnik said. “I’ve been trying to find out how to save energy in houses for about 30 years. I’ve spent a lot of time looking at energy bills, and comparing bills before and after retrofit work is done. I’ve looked at a lot of data. Retrofit programs are instructive, because they show how the models perform.”
According to Blasnik, most energy models do a poor job of predicting actual energy use, especially for older houses. And since large datasets show that the differences between the models and actual energy use are…