Describes the examination of the thermal performance (U-value) of four complex fenestration systems, using computer simulation tools and guarded hot box testing. The systems include a flat glazed skylight, a domed or bubble skylight, a greenhouse window and a curtain wall. Describes the extra care required in performing simulation and testing of these complex processes. Finds good agreement (within 10%) between test and simulation for two of the four products. The agreement was slightly poorer (maximum difference of 16%) for the two high heat-transfer products - the domed skylight and the greenhouse window. Notes possible causes.

KEYWORDS: Windows, transmittance, calculating, testing, glazing, skylights, windows, curtain walls, greenhouses