Methods of Preliminary Estimation of Total Solar Energy Transmittance (TSET) on a Sun Protected Window with Climatic Chamber and Hot Box Apparatus

The total solar energy transmittance (TSET, g - value) is a parameter of transparent system, which can significantly affect the heat demand for cooling of buildings in the summer. A wide range of progressive transparent and shading systems have been developed and applied to a large number of buildings. Their energy performance and efficiency can be determined using simulation tools or measurements. The methodology for accurate g - value determination is described in ISO 19467: 2017. The aim of the study was to derive and verify an alternative methodology for estimating the total solar energy transmittance of selected specimens of transparent systems in case when the standardized equipment is not available or the aim is not to know the exact TSET value. Window specimens were tested under laboratory conditions, which were retrofitted with elements that improve their original properties in terms of heat transfer coefficient and protection against overheating. In total, three methodologies were designed and described, based on A) monitoring of heat fluxes through glazing, B) monitoring of temperature rise in the hotbox and simulation, and C) determination of the difference in heat fluxes of an irradiated specimen and in the absence of radiation. A solar simulator and a heated hotbox were used for the measurements according to the needs of the chosen methodology. The results from the different approaches for determining g - values differ only slightly but are informative. The conclusion from all measurements is the fact that the tested specimens representing type of windows applicable in building retrofitting showed high potential in terms of reducing heat gains from the sun.