Influence of ambient conditions, refrigerant charge and condenser fan speed on thermal performance of an air source heat pump for drying fruits.

Experimental optimization of an air source heat pump for drying fruits was conducted by varying the refrigerant charge, condenser fan speed and the ambient conditions to obtain the optimum operating parameters of the heat pump and the dryer as a single integrated unit. The results showed that, the coefficient of performance (COP) of the overall system and the cycle increased with the increase of condenser fan speed, ambient temperature and refrigerant charge. However, at high refrigerant charge and speed of the condenser fan, the COP of the overall system decreased because of the decreased heating capacity possible due to accumulation of refrigerant in the condenser and increased fan power consumption, respectively. For the developed system, the optimum refrigerant charge was observed to be 1650 grams and 840 rpm of condenser fan speed (60% of the full speed) and the appropriate operating ambient temperature of 20°C. At this point, the COP of the overall system and the heat pump cycle were 3.75 and 5.20, respectively.