Updates on revision to ASHRAE Standard 90.2: including roof reflectivity for residential buildings

This paper discusses the results of a simulation effort in support of ASHRAE SSPC 90.2 for inclusion of reflective roofs in the proposed standard. Simulation results include the annual electricity and fuel use for a prototypical single-family one-story house. In order to maintain consistency with the other requirements of the draft standards, we used the 90.2 Envelope Sub-committee DOE-2 prototype building and operating schedules which were supplied to us. The parametric simulations were performed for the following scenarios and combinations thereof: 3 heating systems, 4 duct and duct insulation configurations, 5 levels of ceiling insulation, 4 levels of roof reflectivity, and 4 levels of attic air change rate. The simulations were performed for 32 climate regions. The results are condensed into climate-dependent adjustment factors that give equivalent reductions in roof insulation levels corresponding to increased roof reflectivity. The equivalence is designed such that the net energy use (cooling plus heating) of the building stays constant when compared with energy use of a dark-colored roof. Results indicate that in hot climates, increasing the roof reflectivity from 20% to 60% is worth over half of the roof insulation.