Thermodynamic analysis of cascade high-temperature heat pump using new natural zeotropic refrigerant mixtures: R744/R600 and R744/R601

Abstract

Many Industrial applications demand clean, high-temperature heating to meet their requirements. High coefficient of performance (COP) and low-pressure ratios are the keys to the development of cascade heat pump systems. The present work investigates the high-temperature heat pump (HTHP) using a two-stage cascade refrigeration system to produce hot water of more than 100 °C and up to 118 °C. MATLAB was used to design and simulate the HTHP model. The results of the simulation were analyzed to explore the production of high-temperature water. The composition of mixed natural zeotropic refrigerants, such as CO2+butane and CO2+pentane mixtures were introduced in the Low-stage (LS) and High-stage (HS) cycle, respectively. Water was used as the secondary fluid and as a heat source with a temperature range of 10–50 °C. The temperature lift, heating capacity, heat sink, hot water delivery temperatures, HS, LS, and total COP, were investigated to identify the performance of the system and expounded in detail. The maximum heating capacity of the system can reach 205 kW. The system's total COP was 4.5, one of the top-notch results in this HTHP research. Overall, the system's use of natural refrigerants, highly efficient performance, and high-temperature water heating abilities make the investigation of high importance. A comparison of the present and published results indicates a substantial improvement of 36% of the total COP. The pressure levels in both LS and HS indicate that the system pressure requirements are in good agreement to operate the system effectively with excellent performance.