Thermal performance analysis of an air source heat pump drying system operating in a medium to low-temperature environment

Air source heat pump drying (ASHPD) systems are relatively simple in design and have low running costs. However, due to their dependency on weather conditions, the performance of ASHPD systems significantly fluctuates as they are influenced by the change in ambient temperatures. In this study, the thermal performance of an open-loop air source heat pump drying system using R134a refrigerant was investigated experimentally in a controlled ambient temperature environment, and at varied fan speeds. From the results, the COP increased with both the increased fan speed and the ambient temperature. At an ambient temperature of 20 degree C, an overall COP of 3.5, 3.8, and the best overall COP of 3.9 was attained before it decreased to 3.7. The best COP was achieved at a fan speed of 90% and the lowest COP at 60% of fan speed. Moreover, as the ambient temperature decreased, so did the overall COP attaining 10.3%, 28.2%, and 56.8% less COP at 10 0C, 0 0C, and -10 0C respectively at 90% fan speed. This strongly suggests that the energy efficiency of an ASHPD system is lower at low ambient temperatures. Moreover, both the change in fan speed and the ambient temperatures play a significant role in the thermal performance of an open-loop HPD system