A New Method for Predicting the Solar Heat Gain of Complex Fenestration Systems

TitleA New Method for Predicting the Solar Heat Gain of Complex Fenestration Systems
Publication TypeConference Paper
Year of Publication1992
AuthorsJoseph H Klems, Jeffrey L Warner
Conference NameThermal Performance of the Exterior Envelope of Buildings V Conference Proceedings
Date Published12/1992
Conference LocationClearwater Beach, FL
Call NumberLBL-32198

A new method of predicting the solar heat gain through complex fenestration systems involving nonspecular layers such as shades or blinds has been examined in a project jointly sponsored by ASHRAE and DOE. In this method, a scanning radiometer is used to measure the bi-directional radiative transmittance and reflectance of each layer of a fenestration system. The properties of systems containing these layers are then built up computationally from the measured layer properties using a transmission/multiple-reflection calculation. The calculation produces the total directional-hemispherical transmittance of the fenestration system and the layer-by-layer absorptances. These properties are in turn combined with layer-specific measurements of the inward-flowing fractions of absorbed solar energy to produce the overall solar heat gain coefficient.The method has been applied to one of the most optically complex systems in common use, a venetian blind in combination with multiple glazings. A comparison between the scanner-based calculation method and direct system calorimetric measurements made on the LBL MoWiTT facility showed good agreement, and is a significant validation of the method accuracy and feasibility.

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