Abstract:
Low to medium-temperature solar thermal collectors have a promising future for harvesting solar energy and acting as an efficient solution towards decarbonizing the domestic hot water applications. In this study, a small-scale solar thermal system based on a low vacuum (17.5 – 20 kPa) Evacuated Flat Plate Collector (EFPC) of a total area of 4.0 m2 is designed and installed. The system is coupled with a storage tank comprising of the helical copper coil configuration inside the tank, which is used as a heat exchanger from primary loop to secondary loop. A series of real-time experiments are performed from December 2020 to April 2021 at NUST, Islamabad (33°38’32.6” N 72°59’03.6” E) under ambient conditions. Thermal efficiency reaches a maximum value of 73.2%, with the glycol-water mixture as a heat transfer fluid at an inlet temperature of 31.2 °C, when the ambient temperature is 15.3 °C, average irradiance is 679.2 Wm-2, and vacuum pressure is 20 kPa. For this duration, the exergy efficiency reaches a peak value of 16%. This evacuated flat plate collector system can provide hot water at 57-69 °C when the average ambient temperature is 24 °C. The hot water is enough for a small residential unit of 2 people with total hot water demand of 100 liters per day under normal ambient conditions.
