This paper examines two similar studies in Phoenix, Arizona and Houston, Texas that compared the actual energy performance of three classes of homes – ENERGY STAR®, Guaranteed Performance homes and Baseline homes (homes built using standard construction practices and local energy codes at a minimum). In addition to the specific questions of individual residential energy performance, the results illuminate the impact that energy efficiency programs have on the overall building marketplace. The Phoenix study surveyed 7,141 houses, of which 3,336 were Baseline homes, 2,979 were ENERGY STAR homes and 826 were Guaranteed Performance homes. Statistically valid energy data show that ENERGY STAR homes are up to 12% more efficient (kWh/m²) as compared to the typical Baseline homes. The Guaranteed Performance homes were up to 23% more efficient than Baseline homes and 12% more efficient than ENERGY STAR homes. The Houston analysis draws from over 158,698 houses, of which 70,828 were Baseline homes, 81,755 were ENERGY STAR homes and 6,115 were Guaranteed Performance homes. Key findings from this study include:
- Average Baseline homes consumed less energy than the reference homes defined by the modeling program.
- All homes in Houston have become more energy efficient over time - 16% from 2002 to 2007.
- Energy usage differences between the three groups of homes were small.
- Modeling predictions of the energy usage of ENERGY STARhomes are reasonably accurate.
- Regression modeling provided some more detailed results on code influences and construction practices.
An important difference between the Houston study and many others is the robust analysis of real-world data and billing histories rather than models. The data set used here is large enough to have adequate statistical power for high confidence in the results. Finally, evaluating home programs with real-world data allows us to best identify construction techniques and products that deliver truly energy-efficient buildings.