Novel design and performance enhancement of domestic refrigerators with thermal storage

This paper investigates the design and operation of a thermal storage refrigerator. Firstly, compressor performance at a range of typical refrigerator operating conditions was analysed. The model results suggest that larger compressors are more efficient when running, with isentropic efficiency increasing by 50% as the displacement increased from 4 to 8 cm3. The impact of compressor performance on the overall refrigerator efficiency was estimated and the results indicated that an energy reduction of 19.5% can be obtained by replacing a conventionally sized, 4 cm3 compressor by a larger 8 cm3 model. However, using a larger compressor will normally lead to more start/stop events, which reduces overall efficiency. A method is proposed for exploiting the superior performance of large compressors by accumulating their high cooling capacity output in a phase change material (PCM), reducing the number of on/off cycles. Numerical modelling and experimental validation were undertaken using a prototype thermal storage refrigerator, incorporating a PCM, to estimate the PCM charge and discharge rate and the corresponding refrigerator on and off cycle durations at different ambient conditions. The results showed that the integration of a 5 mm PCM slab into the refrigerator allowed for 3-5 h of continuous operation without a power supply. The numerical model was found to be in good agreement with the experimental results, with the error between the simulation and tests below 5% for most experiments.