Significant thermal upgrade via cascade high temperature heat pump with low GWP working fluids

High temperature heat pump is a promising solution for efficient high temperature heat supply. However, the poor performance when it operates in large temperature lift hinders it from utilizing low temperature waste heat. To solve this problem, a cascade high temperature heat pump with economized vapor injection was established and a simulation model was developed accordingly. The tests were conducted using R134a/R245fa and R1234ze (E)/HP-1 at heat source temperature from 5 to 30 degrees C and heat sink temperature from 90 to 120 degrees C, with the coefficient of performance (COP) varying in the range of 1.72-2.73 and 1.77-2.75, respectively. The COP about 2.20 was achieved with R1234ze(E)/HP-1 at optimal intermediate temperature and optimal economized vapor injection pressure when the temperature lift is 100 degrees C. In the simulated case study, the heat pump water boiler based on the experimental prototype decreases CO2 emission by 62.8 % compared to electric boiler. Moreover, using low GWP working fluids reduces 1.32 x 104 kg direct CO2 emission in TEWI. Under the current technological, pricing, and operational condition, it takes 16 years for heat pump to have economic benefit over electric boiler, but this duration can be shortened with reduced initial cost, improved COP, and increased operating hours and electricity price. In summary, this work presented a high -efficient, environmentally friendly, and economically viable cascade high temperature heat pump system which has potential to utilize the abundant environmental heat source and deliver high temperature heat, being an alternative to the conventional heat generation equipment such as boilers.