Energy saving in a heat pump air-conditioning system using liquid desiccant and membrane contactors

ABSTRACT It has been demonstrated in the literature that significant energy savings can be achieved in air-conditioning through the use of so-called hybrid systems, in which a chemical dehumidification system is combined with a vapour-compression heat pump. The advantage of such systems lies in the fact that the heat pump can operate at a higher evaporation temperature than that of a traditional system in which dehumidification is achieved through condensation, thereby achieving higher coefficients of performance. The hybrid system described in the present paper operates as follows: the air supplied to the conditioned ambient is simultaneously cooled and dehumidified in an air-solution membrane contactor. The LiCl solution is cooled by means of a vapour-compression heat pump using the refrigerant KLEA 410A. The solution is regenerated in another membrane contactor by exploiting the exhaust air and the heat rejected by the condenser. A study of the steady-state behaviour of the system in summer climatic conditions was carried out, on varying some significant operating parameters, such as the thermal efficiency of the heat exchangers, the outdoor temperature and the sensible load of the conditioned room. The performances of the hybrid system were compared with those of a traditional direct-expansion air-conditioning plant; the results of the simulations reveal that, in particular operating conditions, energy saving can exceed 50%.