Compression-resorption heat pumps (CRHP) utilizing wet compression are a very promising option to upgrade waste heat from industry. CRHPs have the potential to have higher coefficient of performance (COP) than the traditionally used vapour-compression heat pumps (VCHP). However, commercial solutions utilizing wet compression are not available yet. Also, wet compression is a feasible option only if the efficiency of the compressor is sufficiently high, 0.7 or higher, as identified by several authors. In this study, we develop and validate a model of a twin screw compressor that is suitable for wet compression. The model is adapted to calculate the entropy production generation in order to identify where the major irreversibilities are located in the compressor. The effects of clearance size, rotational speed, ammonia concentrations, compressor inlet vapor quality as well as under- and over compression are analysed. The results show that the clearance size and the rotational speed have the largest effects on the entropy production. Additionally, increased ammonia concentration and decreased vapor quality lead to decreased losses. The results indicate that it should be feasible to reach the targeted performance if the clearances size is limited to 50 μm, the rotational speed maintained above 10,000 rpm, the ammonia concentration kept in the range of 30–40 wt.%, and the inlet vapor quality in the range 0.5–0.7.

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Compression-resorption heat pumps (CRHP) enhanced by wet compression are considered a very promising option to upgrade low grade waste heat from the industry. This is especially true for applications where the heat source and/or sink have a large temperature glide. But commercial solutions using wet compression are not yet available on the market. Compared to the classically used vapor compression heat pumps (VCHP), CRHP can provide much better performance but only if the efficiency of the compressor exceeds 0.7. In this respect, a twin screw compressor has been identified as a potential solution to reach this efficiency goal. This study makes use of the entropy production minimization to identify where the major irreversibilites are located in a CRHP system operated with an ammonia-water mixture. A detailed model of the wet compressor and the resorber are coupled with simplified models of other components of the HP cycle to analyze where potential improvements can be made. The results show that significant benefits can be obtained using CRHP.@en