Performance Evaluation of an Evacuated Flat-Plate Collector System for Domestic Hot Water Applications

Abstract

Rapid population growth and increasing energy demand in developing countries are the key drivers behind rising concerns such as energy poverty and environmental degradation. Harnessing solar energy can help the developing countries inch closer to sustainable economic growth. This article presents the performance analysis of a solar water heating system based on an evacuated flat-plate collector (EFPC). EFPCs offer higher optical performance and lower thermal losses in comparison with conventional solar collectors. In this study, a multiparametric analysis provides the guidelines for the design and optimization of a novel low vacuum EFPC system under ambient conditions, for domestic hot water (DHW) applications. A small-scale solar thermal collector system based on a low vacuum (17.5–20 kPa) EFPC of a total area of 4.0 m2 is designed and installed. The system is coupled with a storage tank composed of the helical copper coil configuration inside the tank, which is used as a heat exchanger from a primary loop to a secondary loop. A series of real-time experiments are performed under ambient conditions from December to April. The thermal efficiency of the EFPCs 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 EFPC system provides 100 liters of hot water at 57–69 °C per day for DHW consumption when the average ambient temperature is 24 °C. The overall results highlight the potential of EFPCs for hot water applications. Furthermore, an efficiently optimized EFPC system can also be used for space heating during the winter season.