Theoretical and experimental analysis of heat storage material integration in household refrigerators

In recent years, the application of heat storage materials (HSMs), particularly phase change materials (PCMs), in heat exchangers and/or refrigerated compartments of household refrigerators has increased substantially. This growth has been primarily driven by the implementation of stringent energy efficiency enhancement policies. The present study first provides a theoretical analysis of the impact of integrating HSMs into refrigerated compartments and heat exchangers of a refrigerator. Specifically, it elucidates the mechanism by which an HSM decreases the difference between condensing and evaporating temperatures and examines the behavior of this attenuation as a function of the compressor run-time ratio and the heat transfer coefficients involved. Subsequently, the study experimentally investigates the effects of incorporating HSMs into natural-draft condensers of household refrigerators. Four distinct types of HSMs were attached to a natural-draft wire-and-tube condenser of an A++ European single-compartment refrigerator. The performance of the refrigerator, with and without HSMs, was assessed through standardized energy consumption tests conducted under varying system operating conditions. Energy savings of up to 7.4 % were achieved by attaching 700 g of a copolymer compound to the condenser. The findings reveal that optimal system performance is associated with specific compressor on-time and off-time periods, which are influenced by the condenser size, HSM attachment method, and material thermal capacity. Furthermore, energy savings were observed to be more pronounced at lower compressor run-time ratios and shorter compressor on-time intervals. These observations suggest that the application of HSMs in natural-draft condensers is not recommended for systems equipped with variable-speed compressors.