A web-based simulation tool on the performance of different roofing systems

The Roof Savings Calculator (www.roofcalc.com) provides the general public with a web-based program for calculating the energy savings of different roofing and attic systems on four different building types (residential, office, retail, and warehouse) in 239 US TMY2 locations. The core simulation engine of the RSC is doe2attic, which couples the AtticSim program developed by Oak Ridge National Laboratory with the DOE-2.1E program originally developed by Lawrence Berkeley National Laboratory in the early 1980's and maintained through the late 1990's. Although simulating heat flows through the roof may seem at first to be easy, modeling the net impact of roofing strategies on building heating and cooling energy use can be challenging. Few simulation programs can model reliably thermal conditions in an attic that has large day-night temperature swings, high ventilation rates, significant radiant exchange between the roof and the attic floor, as well as the complex thermal interactions between the ducts and the attic air and inside surfaces. The doe2attic program has been tested against detailed measurements gathered in two residential buildings in Fresno, California from cooling energy use to air and surface temperatures, and heat fluxes of the roof and attic floor. The focus of this paper is on the doe2attic simulation program, and not the RSC user interface that has been described in other papers.