Parametric Analysis of Compact Ammonia/Water Absorption Chiller Based on Heat Transfer Performance

Ammonia/water absorption chillers are driven by low grade heat and can cover a wide range of refrigeration temperatures. This paper presents the parametric analysis of a single stage ammonia/water absorption chiller. A numerical model is developed based on the heat exchanger performance. The heat transfer coefficients are calculated as the functions of operating conditions. The model captures variational heat exchanger performances and describes the actual cycle with a varying heat source. Plate heat exchangers are chosen for the desorber, condenser, evaporator, solution heat exchanger and absorber. In ammonia/water cycle, the detrimental effects of refrigerant impurity is analysed quantitatively with the model. To validate the model, the calculated results are compared with experimental data for different boundary conditions. The agreement of the cooling capacity and COP is good. The influence of the operating parameters is analysed for sub-zero refrigeration and above-zero refrigeration, which include the heat source temperatures, the heat sink temperatures and the flow rates and weight concentrations of the rich solutions. The cooling capacity increases with heat source temperatures. There is an optimum heat source temperature around 110 ℃ that maximises the COP. Higher heat source temperatures increase the flow rate of the refrigerant and reduce the weight concentration. For sub-zero refrigeration, when the heat source temperature increases from 100 ℃ to 120 ℃, the refrigerant flow rate becomes more than 60% larger, while the refrigerant weight concentration changes from 0.998 to around 0.97. The weight concentration of the refrigerant has a major influence on heat transfer performance. The refrigerant is not fully evaporated for low weight concentration as the result of temperature glide