Calorimetric determination of the solar heat gain coefficient g with steady-state laboratory measurements

• Accurate g-value measurements are important for complex fenestration systems.
• Test samples can be with or without active solar systems (BIPV or solar thermal).
• We developed our methodology within past 25 years but never published it in detail.
• Comprehensive error analysis for calorimetric g-value testing is part of the paper.
• No standard exists worldwide. Currently ongoing activities in ISO TC163.

The paper describes procedures for the direct calorimetric measurement of the solar heat gain coefficient g in detail. g is also called SHGC, solar factor, g-value or total solar energy transmittance TSET. All these terms are used synonymously in this document although there are some differences in the details of the definitions of these properties (e.g. different reference wind conditions or reference solar spectra). The document aims to summarize more than 25 years of experience in g-value testing at Fraunhofer ISE, Freiburg, Germany, which includes many different transparent and translucent building materials ranging from transparent insulation materials to daylighting and solar control systems and active solar energy harvesting facade components like building-integrated PV systems (BIPV) or building-integrated solar thermal collectors (BIST). The document focuses on methods for the calorimetric measurement of g under steady-state laboratory conditions. Transient outdoor measurements are beyond the scope of this paper. It also describes the corresponding error analysis and methods to correct experimentally determined values gexp to reference conditions, if it is not possible to reproduce the reference boundary conditions exactly in the laboratory.