Theoretical and experimental study on a frost-free refrigerated display cabinet
Frosting is a common phenomenon in refrigerated display cabinets (RDCs). As the frost layer thickens, the heat transfer rate and airflow through the evaporator dramatically decline, thus reducing cooling efficiency and increasing energy consumption. Defrosting of RDC evaporators can be achieved using several methods, including off-cycle defrost, electric defrost, hot-gas defrost, and reverse-cycle defrost. However, these methods may lead to several issues such as temperature fluctuations within the cabinets, increased energy consumption, water pooling, and bacterial growth in the drain pan. In this study, a desiccant is applied to eliminate moisture from the air entering the evaporator, thereby preventing frost formation. We propose a frost-free RDC that mainly comprises a compressor, two desiccant-coated heat exchangers (DCHEs), a lowtemperature evaporator and an auxiliary condenser. The return air of the RDC is dehumidified due to one of the DCHEs to prevent the evaporator frosting. Meanwhile, another DCHE works as a condenser, in which the desiccant is regenerated using condensation heat that would otherwise be ejected into the ambient air in conventional RDCs. A theoretical and experimental study is conducted for a forced draft, open-type frost-free RDC, with a cabin volume of 67L and a cabin temperature of 2~8°C. Simulation results show that the required air cooling load of the RDC is 0.43kW and the electric power consumption of the compressor is 0.14kW, respectively. A prototype of the frost-free RDC was made and experiments were conducted. The experimental results show that eliminating defrost cycles in the prototype helps stabilize the internal cabin temperature. Moreover, the proposed frost-free RDC has an energy saving potential of 35.7% compared to commercial RDCs.