Technical and economic analysis of wet compression–resorption heat pumps

• Published in: International journal of refrigeration 2020-09, Vol.117, p.140-149
• Main Authors: Gudjonsdottir, V., Infante Ferreira, C.A.
• Format: Article
• Language: English
• Subjects: Ammonia; Analyse technique et économique; Carbon dioxide; Compresseur à double vis; Economic analysis; Electricity pricing; Emissions; Heat exchangers; Heat pumps; Heat sinks; Heat transfer; High temperature; High temperature heat pumps; NH-CO-HO; NH-HO; NH3-H2O; NH3–CO2–H2O; Pompes à chaleur à haute température; Pumps; Technical and economic analysis; Temperature; Thermodynamic models; Twin-screw compressor
• ISSN: 0140-7007; 1879-2081
• DOI: 10.1016/j.ijrefrig.2020.05.010

•It is crucial to account for the price of CO2 emissions when considering heat pumps.•The thermodynamic optimum is, in general, far off the economic one for CRHP.•The payback period for CRHP can be within 3 years for large range of conditions. Heat pumps can efficiently upgrade waste heat from the industry and in that way reduce emissions. One of the main reasons why heat pumps are not applied to a greater extent in industry are large payback periods. Compression–resorption heat pumps (CRHP) enhanced by wet compression are considered a very promising option that can have higher coefficient of performance compared to traditional technologies when the heat source and/or sink have a large temperature glide. In this study the thermodynamic and economic performance of two potential industrial cases are examined for CRHP operating with NH3–H2O and NH3–CO2–H2O. A detailed thermodynamic model of the compressor is used to evaluate the isentropic efficiency for each case. The results are used to calculate the simple payback period, when a boiler is replaced by a CRHP, as a function of the predicted gas and electricity prices in the Netherlands from 2020 to 2035. The results indicate that adding CO2 to the NH3–H2O mixture increases the cycle COP when the temperature glide of the heat sink is 40 K while the opposite occurs when the glide is 80 K. The highest COPs and lowest payback times are obtained when the outlet vapor quality is around 0.50 for both the binary and ternary mixtures. Larger glides require higher outlet qualities. However, it is clear that even for high temperature glides the payback period can be within acceptable limits, especially if the cost of CO2 emissions is taken into account.