Performance of a cascade high-temperature heat pump steam system based on intermediate optimization of operating conditions

doi:10.19799/j.cnki.2095-4239.2025.0293

Abstract

Abstract:

A steam-generation system integrating a cascade high-temperature heat pump with a vapor-compression machine is presented in this study. The system utilizes R134a, R245fa, and R718 refrigerants as working fluids for the low-temperature, high-temperature, and steam stages, respectively. Based on the dynamic optimization of intermediate conditions, the thermodynamic performance of the system is investigated at environmental temperatures ranging from -15 ℃ to 40 ℃ and steam-outlet temperatures from 140 ℃ to 170 ℃. Thereafter, an experimental platform is constructed to validate the simulation data. The results, based on the dynamic optimization model, reveal that as the intermediate-steam temperature increases, the spray rate decreases, and the optimal low-temperature-stage condensation temperature increases. At a steam-outlet temperature of 170 ℃, the system coefficient of performance (COP) increases from 1.183 to 1.914 as the environmental temperature rises from -15 ℃ to 40 ℃. At an environmental temperature of 20 ℃, as the steam-outlet temperature increases from 140 ℃ to 170 ℃, the system COP decreases from 1.945 to 1.657, whereas the steam output increases from 0.856 to 1.170 t/h. The experimental results reveal that at a steam outlet temperature of 170 ℃ and environmental temperatures between 23 ℃ and 27 ℃, the system COP and total power are 3%—5% and 8%—12% lower than the theoretical values, respectively. Error analysis of the simulation and experimental performance indicators reveals that the largest errors are concentrated in the cascade heat pump power (13.29%) and total power (10.01%).

Key words: high-temperature heat pump steam system, optimization of intermediate operating conditions, start-up process, performance studies, error analysis

CLC Number:

TK 14

Zhihui HU, Zhipeng JIANG, Shuaiqi LI, Wenye LIN, Wenji SONG, Ziping FENG. Performance of a cascade high-temperature heat pump steam system based on intermediate optimization of operating conditions[J]. Energy Storage Science and Technology, 2025, 14(10): 3774-3784.

Figures/Tables 11

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工质	R134a	R245fa	R718
单位摩尔质量/(g/mol)	102	134	18
临界温度/℃	101.06	154	373.9
临界压力/MPa	4.06	3.65	22.06
GWP (全球变暖潜能值)	1300	858	0
ODP (臭氧层消耗潜能值)	0	0	0
ASHARE安全等级	A1	B1	A1
常压下沸点/℃	-26.07	14.9	100

变量名	范围/℃	精度/℃	限定工况
环境温度T_e	-15~40	1	T_s=170 ℃
蒸汽出口温度T_s	140~170	1	T_e=20 ℃
中间蒸汽温度T_gas	100~130	0.1	T_s=170 ℃，T_e=20 ℃
低温级冷凝温度T_mid	(T_e+T_gas)/4-5~(T_e+T_gas)/4+35	0.1	T_s=170 ℃，T_e=20 ℃