Development of a calorimeter for determination of the solar factor of architectural glass and fenestrations

This work presents the development of a calorimeter used to determine the Solar Factor of glazing and windows, including shading devices or not. Solar Factor is an index used around the world for comparing the thermal performance of fenestrations. The development of the calorimeter includes its project, construction, instrumentation particularities and calibration. The calorimeter has two systems of thermal gain measurement: the first one depends on the temperature difference of the fluid used for refrigeration of the main cavity (employed in tests with elements in full-scale); the second system is applied in a secondary cavity, where heat flow transducers are used to measure the solar gain through fenestrations. During the calibration stage, a new formulation for the determination of the Solar Factor was proposed and applied. After this, a reference glass sample (3 mm clear monolithic glass) was tested simultaneously in the two cavities. All tests were conducted under outdoor conditions. The measurement surface was always maintained in vertical position and facing north. The results of Solar Factor measurements were compared to theoretical values determined by ISO 9050. The uncertainty of measurement (absolute) was on average ±0.04 for the secondary cavity, and ranged between ±0.10 and ±0.16 in the main cavity. In general, experimental values showed good agreement with theoretical values. Therefore, the calorimeter can be used for research purposes or as an alternative to determine the Solar Factor of new products, which are not covered by the calculation procedures presented in the existing standardization.