Optimal utilisation of low-grade solar-air source for heat pump water heating using a dual-source evaporator with forced convection

This research utilises a Direct Expansion Modified Solar-Air dual-source Heat Pump (SAHP-MDX) for water heating applications. Unlike conventional dual-source heat pumps, which rely solely on natural convection for extracting ambient thermal sources during partial sunshine and dusky hours, the SAHP-MDX incorporates a dual-source evaporator adapted with forced convection, effectively removing the dual-source energy throughout the day. The system operates in three distinct modes: Solar-Air source Natural Mode (SANM), Solar-Air source Forced Mode (SAFM), and Air-source Forced Mode (AFM). This study investigates the performance of the SAHP-MDX under various ambient (solar radiation and ambient temperature) and operational conditions (water tank temperature). The average daily Coefficient of Performance (COP) of SAHP-MDX is approximately 3.22, with average COP values of 3.51, 3.16, and 2.99 in SANM, SAFM, and AFM, respectively. The average heating times of SAHP-MDX in SANM, SAFM, and AFM cycles are 163, 177, and 197 min, respectively. Furthermore, the daily power consumption analysis reveals that the SANM, SAFM, and AFM heating cycles contribute 45.89%, 20.57%, and 33.54%, respectively. Considering these findings, the proposed SAHP-MDX system demonstrates the promising potential for water heating applications throughout the day, particularly in regions characterised by diverse ambient and operational conditions.