Bottle Cooler, Peak Loading, Phase Change Material, Energy Consumption below 1 kWh/24h
The final results of an analytical and experimental study in reducing the energy consumption of a display bottle cooler using Phase Change Material (PCM) as an active thermal storage are presented. The objective of the study was to design and built a 350 dm3 glass door bottle cooler having an appliance energy consumption reduction of over 75% compared to state of the art bottle coolers (2010 figures). Calculation results show that active thermal storage using PCM can be effectively applied to store and release cold on demand in small cooling appliances subjected to high peak loading. It is shown that by using the thermal storage much smaller cooling systems can be applied, resulting in system operation at reduced temperature lift. A validated control solution, including a sensor which detects the state of the PCM, is presented. It is shown that for a bottle cooler, optimum performance results for a dual forced air evaporator system, with one evaporator embedded in the PCM and the other in direct contact with the air stream. To obtain minimum product cooling times a different refrigerant flow path through the evaporators is required between the main modes of operation (i.e. peak loading or recovery). The optimum position of the PCM embedded evaporator is upstream of the main evaporator with respect to the airflow. A design of a display bottle cooler applying standard heat load reduction measures in combination with PCM as active thermal storage is presented. The design is based on using a 5.19 cm3 R-600a compressor in combination with forced air heat exchangers. The integration of the PCM in the appliance cooling system and the control aspects resulting are discussed in detail. Experimental test results of a demonstrator cabinet at an ambient of 25 °C and 60 %RH show that a 350 dm3 glass door bottle cooler having a total appliance energy consumption (including half reload recovery) of < 1 kWh/24 h can be built while achieving a half reload recovery within 16 h at an ambient of 32 °C and 65 %RH.