Journal
APPLIED ENERGY
Volume 88, Issue 12, Pages 4470-4480Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.apenergy.2011.05.047
Keywords
Air source heat pump; Mal-defrost; Heating efficiency; Heating capacity
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Funding
- National Natural Science Foundation of China [50708002]
- Beijing Municipality Key Lab of Heating, Gas Supply, Ventilating and Air Conditioning Engineering [KF201005]
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A study is presented on the characteristics of the air source heat pump (ASHP) under two kinds of typical mal-defrost phenomena. The definition of the Mal-defrost phenomena is put forward, and the possible origins of their occurrence are analyzed. It is concluded that the current defrost strategies may cause mal-defrost phenomena due to the lack of the direct control information, frost thickness. Transient characteristics of the tested ASHP under these mal-defrost phenomena are investigated by field tests. Instant frosting images are captured to record the dynamic frosting process. In the first phenomenon of mal-defrost, the defrost control is carried out over an hour after a critical level of frosting has been reached. It reduces the COP and heating capacity by about 17.4% and 29%, respectively. In the second phenomenon of mal-defrost, three defrost operations occur while almost no frost is observed on the heat exchanger during 6 h testing period. It causes 4.2% decrease for the heating efficiency. (C) 2011 Elsevier Ltd. All rights reserved.
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