Analysis of a Solar Assisted Ejector Cooling Cycle for Air Conditioning in a Mediterranean Climate

Using low grade thermal energy instead of electricity to operate a refrigerator can have important environmental benefits, especially when it is powered by a renewable energy source (e.g. solar thermal). Ejector refrigeration is one of the most promising technologies because of its relative simplicity and low initial cost. In this work, a theoretical study has been carried out to asses system and refrigeration efficiencies of a solar assisted ejector cycle using water as the operating fluid. The model was based on a 1D ejector approach, including both the refrigeration and solar collector cycles. In the development of the mathematical model, several assumptions were made e.g. steady state, negligible thermal losses during transport, constant ejector efficiencies. Ejector performance was evaluated for different operating conditions. The results indicated that in order to achieve an acceptable COP, generator temperatures should not fall below 90ºC. Evaporator temperatures below 10ºC and condenser temperatures over 35ºC resulted in a significant drop of system efficiency, and therefore these conditions can be identified as minimal (reference) design values. The required solar collector area to provide 5 kW of cooling power was calculated for different operating conditions. Ejector dimensions were also calculated using the constant pressure mixing ejector theory.