The use of enhanced heat transfer phase change materials (PCM) to improve the coefficient of performance (COP) of solar powered LiBr/H2O absorption cooling systems

Abstract

The underlying principle employing latent heat storage to store excess solar energy to drive solar powered absorption cooling system and space heating/hot water system has been experimentally investigated. The experimental setup investigated the performance of a 4.5 kW absorption system (COP of 0.66) and a PCM system. Four PCM experiments were conducted using 20 kg each of Erythritol to compare 3 heat transfer enhancement techniques; circular fins, longitudinal fins and multitube systems. The multitube system performed best with shortest complete melt time of 275 min (longitudinal finned – 430 min; circular finned incomplete melting within 8 h). The multitube system however, experienced subcooling during discharge. The longitudinal finned system performed best during discharge and experienced no subcooling. Overall utilization efficiencies achieved for multitube and longitudinal finned systems were 83.2% and 82% respectively. PCM quantities that will be required to meet 4 h of 100% peak cooling load for a semi-detached house (105 m2) were determined to be 242 kg and 238 kg respectively. To ensure overall improved charge and discharge performance, a combination of multitube and longitudinally finned in some configuration would be required. Modified equations for the evaluation of improved COPs of a LiBr/H2O absorption system have been proposed.