Evaluating Energy Efficiency Using Whole-Building Simulation Tools

September 29, 2007
Publication: Journal of Building Enclosure Design p 10-14

Abstract: Recent trends towards greener building have brought whole-building energy performance into the spotlight. Building and mechanical system designers typically use manufacturer's published R-values and U-factors in their wall and roof assemblies to meet prescriptive building energy code requirements. However, the use of such product properties alone is not indicative of actual performance, since additional heat flow paths are not accounted for in these values (for example, losses or gains due to thermal bridging through steel stud-framed walls or discontinuous insulation at floor slab edges). Similarly, the reported U-factors for window, door and curtain wall systems are based on laboratory performance testing that does not account for the substantial heat loss at the window perimeters that often occurs in typical window installations1. Accurate simulation of window performance is critical, as fenestration heat loss/gain in a building often exceeds that of the opaque (insulated) walls and dominates the envelope loads.|This article examines the differences in calculated envelope loads for a variety of cladding and fenestration systems using both area-weighted manufacturer's insulation values and integrated simulation of connections, such as window-to-wall interfaces. We also examine the effects of relatively minor component changes on the performance of the whole building, including strategic selection of window and glazing types, and varying insulation thickness and placement. Based on our review, we provide strategies for maximizing the effectiveness of whole-building energy simulations.