Thermal performance predictions and tests of a novel type of flat plate solar thermal collectors by integrating with a freeze tolerance solution

A novel design concept of Flat Plate Solar Collectors (FPSCs) is conceived and developed by integrating with a freeze-tolerant (so-called ‘ice immune’) solution using flexible silicone tubing. It is intended to directly run water in the solar thermal systems with the FPSCs instead of using expensive anti-freeze fluids, and to remove secondary heat transfer facilities (e.g. an extra tank with a buried heat exchanger). Successful development of such kind of solar thermal collectors will enable a reduction of installed cost of conventional solar thermal systems without needing secondary heat transfer facilities. In the prophase design, thermal performances of FPSCs with two configurations, i.e. the serpentine tube type and the header riser type, were predicted based on the collector lumped thermal capacitance model alongside CFD (Computational Fluid Dynamics) calculations. Then two prototypes of FPSCs with the ice-immune silicone tubing (one AES serpentine tube type, one modified Chinese micro-heat-pipe-array panel) were made to determine the collector performance and compared to an original AES solar keymark reference panel via experimental tests. The results show that the Chinese micro-heat-pipe-array panel performs better than the AES header riser solar keymark panel in terms of flow rate per m² collector aperture area, while the AES serpentine tube panel with silicone tubing performs somewhat lower than the solar keymark with T_m ^∗≤0.035 and better than the solar keymark when T_m ^∗>0.035. The serpentine tube panel and the Chinese micro-heat-pipe-array panel both integrated with silicone tubing for freeze tolerance are proven to be effective as the modification doesn't compromise the collector thermal performance markedly.