Improving system performance of a personal conditioning system integrated with thermal storage

An innovative personal conditioning system called Roving Comforter (RoCo) comprises of a miniature vapor compression cycle (VCC), storing its condenser heat in a phase change material (PCM) thermal storage with helical refrigerant tubes. In the present study, we analyze its system performance with different PCM by using a validated dynamic model in Modelica (R). Mathematical equations and programming decisions for implementation of PCM model in Modelica are discussed. Higher melting temperature of PCM results in higher power consumption during cooling operation, but reduced power consumption during recharge operation (solidification of PCM). Thus, it is necessary to identify the appropriate temperature of PCM that maximizes its coefficient of performance (COP), since RoCo operates with alternating cooling and recharge operations. The PCM melting and solidification from the helical coil geometry is captured with empirical correlations obtained from experiment. Various regimes observed in these asymmetric processes are discussed. An increase of 11% in the COP is observed. The article highlights modeling details and interesting insights of system performance of a vapor compression cycle integrated with PCM, which are increasingly being developed in recent times.