A modular approach to study the performance of a two-stage heat pump system for drying

The performance of a two-stage evaporator heat pump drying system with chlorodifluoromethane (HCFC22) as the working refrigerant was experimentally studied. The system employed low- and high-pressure internal evaporators for cooling and dehumidification of the drying air. On the condenser side, two subcoolers were used for additional sensible heating. The system further incorporated a passive evaporator-economiser for pre-cooling of the air before the evaporators and pre-heating before the condenser. The system performance was evaluated in terms of the amount of heat recovered at the evaporators, the system COP and SMER. It was demonstrated in this paper that more heat, up to 35% more, could be recovered via the two-stage evaporator system in comparison to a single evaporator system. By varying the pressure level of the high-pressure evaporator, greater amount of heat recovered could be realised when the ratio of latent to total load at the two-stage evaporator was improved.