Investigation of the performance of a high-temperature heat pump using parallel cycles with serial heating on the water side

High-temperature heat pumps can be widely utilized for industrial heating as an energy-saving method due to their high condensing temperatures. This paper describes a cycle analysis and experimental study on the performance of a high-temperature heat pump (HTHP) system. The performance comparisons are conducted using performance calculations among the parallel cycles with serial heating on the water side, a two-stage compression cycle and a single-stage cycle. The results show that the performance of the heat pump using parallel cycles with serial heating is the best when the condensing temperature exceeds 75 °C. Based on the cycle analysis, a prototype HTHP using parallel cycles with serial heating on the water side with a heating capacity of 700 kW was built in this study. Also, a screw compressor was modified due to the high-temperature conditions. The measured performance shows that the HTHP can stably provide an outlet water temperature of up to 85 °C with a high coefficient of performance (COP). The experimental results indicate that the average heating capacity and coefficient of performance of the HTHP could be improved significantly in high-temperature conditions due to the parallel cycles with serial heating on the water side and the modified compressor. All the results indicate that the HTHP using parallel cycles and modified compressor with serial heating on the water side is very competitive in industrial heating applications.