Novel design and performance enhancement of domestic refrigerators with thermal storage

• Main Author: Marques, Ana Catarina Almeida
• Published: London South Bank University 2012
• Subjects: 621.5
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.631725

A growing global environmental awareness and the rising costs of energy are driving demand for the development of sustainable cooling technologies. Most governments worldwide have implemented minimum energy performance standards for household refrigerators and innovative new solutions are required to improve the efficiency of these appliances. This thesis investigated the design and operation of a thermal storage refrigerator. The aim was to improve the refrigerator energetic efficiency, temperature stability and extend its offcycle. The research demonstrated that larger displacement compressors are more efficient. The proposed method to exploit the superior performance of large compressors is to accumulate their high cooling capacity in a phase change material (PCM). The combination of thin phase change material with a large displacement compressor is a novel design approach with the potential to enhance the refrigerator efficiency. Theoretical modelling and experimental validation were undertaken to determine the phase change material charge and discharge rate and the corresponding refrigerator on and off cycle durations. The integration of a 5 mm PCM slab into the refrigerator allowed 3 to 5 hours of continuous operation without power supply (compared to 9 minutes without PCM) depending on the ambient temperature. A computational fluid dynamics (CFD) model was used to predict the airflow and temperature distribution within the thermal storage refrigerator. Several design options were investigated by simulation to identify the most effective PCM configuration (horizontal or vertical), the phase change temperature and the design for the refrigerator i.e. conventional door type or top opening drawer appliance. The CFD was used to select the best design options for developing a novel thermal storage refrigerator. A horizontal PCM configuration was found to be more efficient than a vertical PCM. The temperature distribution with a horizontal PCM was tested experimentally and the results were shown to be in close agreement with the CFD predictions. Both the simulation and the experimental results suggested that a eutectic with a phase change temperature below 0°C needs to be employed to maintain the compartment temperature within acceptable limits.