Performance improvement of air-source autocascade high-temperature heat pumps using advanced exergy analysis

Autocascade high-temperature heat pump (AHTHP) have the capacity for significant temperature increases, offering a promising alternative for industrial decarbonization. For a more comprehensive evaluation of the performance improvement potential of an air-source AHTHP, this work proposed a method to select refrigerant blend that has the greatest effect on the performance of an AHTHP by using an advanced exergy analysis. Subsequently, a refrigerant selection for an air-source AHTHP with steam injection technology was performed. The performance enhancement was evaluated under year-round system operating conditions, comparing the selected refrigerant with a refrigerant blend chosen using the conventional thermodynamic method. The results indicate that the refrigerant blend 0.6R245fa/0.4R1234yf, chosen through the advanced exergy analysis, exhibits a more significant capability to enhance heating capacity and output temperature in comparison to the refrigerant 0.5R1233zd(E)/0.5R1234yf, which was chosen through the conventional thermodynamic analysis. When increasing the heating capacity, the average Coefficient of performance (COP) of the refrigerant blend 0.6R245fa/0.4R1234yf at the daily maximum and minimum temperatures increased by 5.60 % and 4.07 %, respectively, while the average power consumption decreased by 6.08 % and 23.81 %, respectively. When increasing the output temperature, the COP difference between the two refrigerant blends is not significant. The average power consumption with 0.6R245fa/0.4R1234yf is 2.19 kW and 2.71 kW at the output temperature is 120 degrees C and 110 degrees C respectively, which is lower than the average power consumption with 0.5R1233zd(E)/ 0.5R1234yf. The results and analysis of this research could provide an effective guidance for enhancing the performance and environmental friendliness of air-source AHTHP.