Determination of optimum working conditions in heat-pumps using nonazeotropic refrigerant mixtures

The objective of this work is to investigate experimentally the effects of mixture concentrations, source temperature, flow rate of condenser cooling water and air flow rate in the cooling tower on the Coefficient of performance (COP) and eta(ex) (exergetic efficiency) values of vapour compression heat pump systems. The experimental apparatuses consist of a vapour compression heat pump conducting according to the liquid to air principle, refrigerant mixture unit, cooling tower, measuring elements and other auxiliary equipment. Refrigerants R11, R12, R22 and six of their binary mixtures which contain about 25%, 50% and 75% mass fractions of R22 were tested. The experiments were performed in the region of source temperatures from Is to 28 degrees C and flow rates of condenser cooling water from 500 to 1250 kg/h. Four different air flow rates were chosen in those experiments in the cooling tower. To determine the efficiency of the chosen parameters on the system and optimum working conditions, an experimental design method suggested by Genichi Taguchi was used. In this study, it was observed that the COP and eta(ex) increased with the addition of R22 to the system over R11 and R12 pure refrigerants. (C) 1998 Elsevier Science Ltd. All rights reserved.