Angular divergence of solar simulators and its impact on the measured Solar Heat Gain Coefficient of fenestration systems

The solar protection feature of shading devices is characterized by the Solar Heat Gain Coefficient (SHGC) or g-value. Given their complex light-scattering properties, it is advisable to test innovative shading devices calorimetrically in a laboratory. In the case of an indoor calorimetric facility, a solar simulator is required as the light source. The light beam radiated by commercial solar simulators is not parallel and in general more divergent than direct sunlight. This study analyses the impact of the angular divergence of radiation from solar simulators on the experimental determination of the SHGC of fenestration systems. It is shown that this effect is not negligible in many cases. Two methods are proposed for this purpose: (1) an experimental one based on measurements with a luminance camera, and (2) a numerical one based on a digital model of a calorimetric facility. Both methods build on the calculation of contribution coefficients from different regions of the field of view of the sample. The methods can be used to correct the effect of angular divergence on SHGC measurements in the future.