Energy saving mechanism analysis of the absorption–compression hybrid refrigeration cycle

Focusing on the effective use of low-grade solar heat as heat source to provide refrigeration for residential and commercial space cooling, an absorption-compression hybrid refrigeration cycle has been studied on the basis of available data of working pair 1,1,1,2-tetrafluoroethane (R134a) and dimethylformamide (DMF). In order to investigate their performance, the energy saving mechanism of the hybrid cycle was analyzed, by means of thermodynamic diagrams of log p–T, log p–h and T–s. The results show that the hybrid refrigeration cycle has a relatively high thermodynamic perfectibility and can use low-grade heat to replace parts of mechanical work for obtaining lower temperature refrigeration effect owing to its energy complement and cascade refrigerating configuration between the internal sub-cycles. Moreover, on the basis of two new criteria, the heat powered coefficient of performance and the electricity saving rate, the competition behavior between the sub-cycles of the hybrid cycle, i.e. the trade-off effects of compressor pressure on the low-grade heat utilization performance were also investigated. It was found that the sub-cycles compete in their contribution to the hybrid refrigeration system and the cycle preferences depend on the dominance which one achieves. In other words, there is an optimum compressor outlet pressure region under specified working conditions, where the hybrid refrigeration cycle has the maximum heat powered coefficient of performance and electricity saving rate.