Performance evaluation of low GWP large glide temperature zeotropic mixtures applied in air source heat pump for DHW production

This study proposes the low GWP zeotropic mixtures applied in the air source heat pump for the domestic hot water production using the city water of 15 °C. The large glide temperature in zeotropic mixture side was applied to match temperature lift in hot water side in the condenser. Fifteen zeotropic mixtures, composed of the low boiling compositions (R744, R41, and R170) and high boiling point compositions (RE170, R600a, R1234yf, R1234ze(E), and R290), were compared. A new indicator named temperature match degree (TMD) was applied to evaluate the heat exchanging process. Besides, the system performances, including energy efficiency ratio (EER), exergy efficiency (η_ex), volumetric heating capacity (q_v, kJ/m³), are evaluated under different conditions. The results showed that the heat pumps using the zeotropic mixtures show better performance than that of the corresponding pure composition, except for q_v. The maximum EER, η_ex and q_v reaches 4.17, 0.472 and 3702 kJ/m³ with the mole fraction of R744/RE170 of 0.3/0.7.TMD was also improved by the zeotropic mixtures, and the maximum TMD reaches 76 % with the mole fraction of RE170/R600a of 0.6/0.4, which is triple for R600a. The results prove the potential of the heat pumps using the large glide temperature zeotropic mixtures applied in domestic hot water production.