Parametric study on the effect of using cold thermal storage energy of phase change material on the performance of air-conditioning unit

This paper presents a study on a new technique of using thermal energy storage of phase change material system with conventional air-conditioning unit to increase its cooling performance. The technique is based on integrating plates of phase change material with the condenser of the air-conditioning unit. The phase change material plates use its cold storage energy during the night time to increase the cooling performance of the unit during the daytime. The air is used to transfer the cold storage energy from the phase change material plates to the air-conditioning unit during the daytime. The study is performed during charging the phase change material with cold storage energy at night and discharging this energy to the air-conditioning unit at daytime. A theoretical transient model for the phase change material with air heat exchanger is constructed and a numerical solution of the theoretical model is presented. The numerical solution of the theoretical model is validated with an experimental work. The effect of the phase change material plates configurations and the inlet velocity and temperature of the air inlet to the phase change material plates on the charging and discharging process is carried out. Also, the effect of these parameters on the air-conditioning unit performance is presented. The results show that the longer and thinner phase change material plates configuration has the lower charging and discharging time. The discharging time and the outlet cold air temperature from the phase change material plates are decreased with increasing inlet air velocity and temperature. The charging time is decreased with decreasing inlet air temperature and rising inlet velocity. The maximum increase of the coefficient of performance of the air-conditioning unit with phase change material for the different configurations compared to the conventional one for inlet air temperature 35 °C, is 14%, 13% and 12% for inlet air velocity 0.96 m/s, 1.2 m/s and 1.44 m/s respectively. The discharging and charging time and the outlet cold air temperature from the phase change material plates are decreased with increasing inlet air velocity and temperature respectively. Also, at inlet air temperature 45 °C, and velocity 1.44 m/s, the maximum useful cooling power per kg of the phase change material is 46, 50, 54, 55, and 67 W for the configurations 2, 5, 4, 1 and 3 respectively. The results illustrate that, at air inlet velocity 0.96 m/s, the maximum percentage of the saved power per ton refrigeration for each kg phase change material with respect to conventional AC unit is about 11.6%, 6.7% and 5.4% for inlet air temperature 45 °C, 40 °C and 35 °C respectively.