Thermal analysis of flat evacuated glass enclosure for building integrated solar applications

In this work a flat evacuated glass enclosure is designed and fabricated and its thermal performance characterized for solar thermal applications. To investigate the effect of the thermal insulation provided by the high vacuum pressure in the enclosure, the heat transmission of the enclosure is determined under both atmospheric and vacuum pressures. The flat evacuated enclosure consists of two glass panes hermetically sealed around their periphery to a stainless steel spacer creating a cavity between the glass panes 15mm wide. An array of stainless steel support spacers are set between the glass panes to prevent the panes from collapsing under the influence of atmospheric pressure. A simple solar absorber is integrated into the enclosure and a novel co-centric port is designed for thermal fluid transfer through the edge spacer to the absorber. The assembly is tested under a solar simulator, and using infrared thermography techniques and thermocouples attached to the enclosure its thermal response is analysed. Results show that the greatest heat loss occurs near the support spacers on the glass surface, and near the inlet and outlet ports at the edge spacer.