Energy transfer procession in an air source heat pump unit during defrosting with melted frost locally drainage in its multi-circuit outdoor coil

• Published in: Energy and buildings Vol. 164; pp. 109 - 120
• Main Authors: Song, Mengjie, Chaobin, Dang, Ning, Mao, Shiming, Deng
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 01.04.2018; Elsevier BV
• Subjects: Air source heat pump; Circuit design; Coiling; Coils; Defrosting; Design optimization; Energy conservation; Energy consumption; Energy efficiency; Energy management; Energy policy; Energy resources; Energy storage; Energy transfer; Energy usage; Frost; Frosting evenness value; Heat exchangers; Heat pumps; Heat transfer; Heating; Indoor environments; Mass transfer; Melted frost locally drainage; Metal energy storage; Metals; Multi-circuit outdoor coil; Reverse cycle defrosting; Thawing; Thermal comfort; Thermal energy; SV; ASHP; COP; MS; Multi-circuit outdoor coil; Melted frost locally drainage; RCD; DEV; DX; A/C; Frosting evenness value; Metal energy storage; FEV; EEV; Air source heat pump; MES; Reverse cycle defrosting
• ISSN: 0378-7788; 1872-6178
• DOI: 10.1016/j.enbuild.2018.01.004

•Energy transfer process in ASHP during defrosting was quantitatively explored.•Effect of the melted frost taken away during defrosting was fully considered.•Metal energy storage effect on defrosting in two-circuit case was calculated at −0.44%.•Defrosting efficiency could be increased by 11.66%, from 47.13% to 58.79%.•The metal energy storage effect on defrosting is calculated at −3.67% for three-circuit case. Air source heat pump (ASHP) units are widely used in recent years, and reverse cycle defrosting becomes the most popular method to solve their undesired frosting problem. During defrosting, a transient and nonlinear heat and mass transfer procession, the metal energy stored in the indoor and outdoor coils are varying as their temperature fluctuations. On the other hand, authors have previously confirmed the effects of melted frost and metal energy storage on system defrosting performance. However, detailed energy transfer procession without melted frost influence is still not identified. This fundamental problem directly affects the development and modification of two coils in a novel ASHP unit or an existing one. Consequently, basing on frost evenly accumulated on each circuit's surface, two cases were thereby designed in this study. Experimental results show that, the heating supply of indoor air thermal energy contributed about 80% of the total energy usage for defrosting, nearly 90% of energy consumed on frost melting and ambient air heating, respectively. After the total area of outdoor coil was enlarged by 50%, the metal energy storage effect was changed from −0.44% to −3.67%. Meanwhile, defrosting efficiency was improved by 11.66%, from 47.13% to 58.79%. Contributions of this study can effectively guide the design optimization of an ASHP unit, improve occupant's thermal comfort and promote the energy saving in buildings and industry.