Abstract: Recovering waste heat is essential for primary energy savings and carbon emission reduction. To provide direct and reliable suggestions for factories to recover waste heat, energetic, economic and exergoeconomic comparison between direct heat exchange (DHE) and open-cycle mechanical heat pump (MHP) under various operating conditions is carried out in this work. The price ratios R_ES (electricity to steam) and R_HS (hot water to steam) are introduced to quantify regional impacts and conduct quantitative analysis. A semi-empirical formula is obtained to explore the exergoeconomic performance of the two systems. For waste heat within 373.15-423.15 K, the exergy efficiency of the DHE with a temperature difference of 10-90 K is always lower than that of the MHP with a temperature lift of 10-50 K. The economic performance of the two systems has a break-even point, depending on the operating parameters and relative prices of electricity, steam, and hot water. Under the average R_ES (3.8) in China, if R_HS is higher than 0.748, the annual revenue of the DHE is always higher, whereas the MHP is more economical when R_HS is lower than 0.110. In regions where R_ES is higher than 4.353, the annual revenue of the MHP will be negative in some cases.

Key words: Mechanical heat pump, Direct heat exchange, Exergy efficiency, Annual revenue, Exergy price

摘要： Recovering waste heat is essential for primary energy savings and carbon emission reduction. To provide direct and reliable suggestions for factories to recover waste heat, energetic, economic and exergoeconomic comparison between direct heat exchange (DHE) and open-cycle mechanical heat pump (MHP) under various operating conditions is carried out in this work. The price ratios R_ES (electricity to steam) and R_HS (hot water to steam) are introduced to quantify regional impacts and conduct quantitative analysis. A semi-empirical formula is obtained to explore the exergoeconomic performance of the two systems. For waste heat within 373.15-423.15 K, the exergy efficiency of the DHE with a temperature difference of 10-90 K is always lower than that of the MHP with a temperature lift of 10-50 K. The economic performance of the two systems has a break-even point, depending on the operating parameters and relative prices of electricity, steam, and hot water. Under the average R_ES (3.8) in China, if R_HS is higher than 0.748, the annual revenue of the DHE is always higher, whereas the MHP is more economical when R_HS is lower than 0.110. In regions where R_ES is higher than 4.353, the annual revenue of the MHP will be negative in some cases.

关键词: Mechanical heat pump, Direct heat exchange, Exergy efficiency, Annual revenue, Exergy price