Natural refrigerants versus synthetic refrigerants for steam-generating heat pumps

Industrial heat pumps supplying steam at saturation temperatures up to 200°C are an emerging technology, which can help replacing fossil-fuel driven boilers. For these temperatures, little research is performed on refrigerant selection. In this work, a thermodynamic framework is developed and applied to typical boundary conditions. Five natural refrigerants and five low-GWP synthetic refrigerants are selected and compared in terms of performance and technical aspects. Natural refrigerants showed superior performance. The COP of the best performing natural refrigerant was 38% higher than the best performing synthetic refrigerant in case of high steam temperatures. For low steam temperatures it was 17% higher. Both refrigerant classes experience technical difficulties. The main issues with the investigated natural refrigerants are sub-atmospheric operating pressures, low volumetric heating capacities, high compressor outlet temperatures and high flammability. Isopentane only suffers from flammability issues and is therefore a promising refrigerant. The main issues of the investigated synthetic refrigerants are high compressor discharge pressures and the risk of thermal decomposition at high steam temperatures. Moreover, future use may be restricted due to their potential for trifluoroacetic acid (TFA) depositions