Dual-pressure condensation high temperature heat pump system for waste heat recovery: Energetic and exergetic assessment

High temperature heat pump (HTHP) is an energy-saving solution to recover the industrial waste heat. Five configurations of dual-pressure condensation HTHP are proposed and studied to improve thermal matching in the heat sink. The energy and exergy models are established, and the performance of dual-pressure condensation HTHP systems is assessed and compared with that of traditional single-stage, two-stage and cascade HTHP systems in detail. The results show that the dual-pressure condensation HTHP system is superior to traditional HTHP system from the perspective of energy efficiency and exergetic performance. A maximum COP is obtained at the optimum intermediate water temperature. The COP of dual-pressure condensation water-cooled saturated system (DWSAS) is the highest of 4.16, and 3.37-9.34% higher than the traditional HTHPs. R1234ze(Z) shows much higher energy efficiency over the other refrigerants for the applications of HTHP, and the COP is 2.62-4.47% larger than using R600a at the outlet temperature of heat source of 15-35 degrees C. The exergy destruction is also significantly reduced by using dual-pressure condensation HTHPs due to the improvement of thermal matching in the condensers. DWSAS shows the lowest exergy destruction, which is 4.28-19.35% lower than traditional HTHPs. DWSAS by using R1234ze(Z) is recommended due to its outstanding energetic and exergetic performance.