Performance of Flat-Plate and Compound Parabolic Concentrating Solar Collectors in Underfloor Heating Systems

There is a growing interest in using solar energy in underfloor heating systems. However, the large areas required for the installation of solar thermal collector's array can be discouraging, especially in the apartment buildings where the apartment's roof is a common area. The objective of this study is to investigate the possibility of using compound parabolic concentrating (CPC) solar collectors instead of the commonly used flat-plate collectors (FPCs) in such systems. It is aimed to explore the feasibility of area reduction required by the collectors. Second, the temperature profiles of circulating water loop and the concrete slabs are sought to be examined. The system consists of solar thermal collectors, a storage tank, and circulation of water to transport the heat to four similar floor slabs. The CPC collector outlet fluid's temperature can reach a maximum of 95 °C, compared to 70 °C obtained from the FPCs. The results from the simulations show that a 2 m² CPC collector array can perform satisfactorily to match the job of an 8 m² FPC array, obtaining the same required circulating water's temperature in the slabs.