Experimental investigation of indoor thermal environment dynamics during the frosting-defrosting process of air source heat pumps

Wei, Wenzhe, Zhang, Jianfei, Jin, Xinyue, Zhang, Xinyu, Wang, Wei, Luo, Zhiwen ORCID: https://orcid.org/0000-0002-2082-3958, Sun, Yuying, Li, Zhaoyang and Wang, Shiquan 2026. Experimental investigation of indoor thermal environment dynamics during the frosting-defrosting process of air source heat pumps. Energy and Buildings 353 , 116849. 10.1016/j.enbuild.2025.116849

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Abstract

During the defrosting operation of air source heat pumps (ASHPs), heating supply is interrupted. This leads to significant fluctuations in the indoor thermal environment, resulting in thermal discomfort for occupants. However, the dynamic behavior of indoor thermal conditions during the frosting-defrosting cycles remains unclear, which poses a major challenge to improving the heating performance of ASHPs. To solve this problem, two test rigs, one air-water heat pump (AWHP) heating system and one air-air heat pump (AAHP) heating system, were built in an artificial environmental chamber. Space heating experiments were conducted under controlled frosting conditions to investigate the indoor thermal environment during the frosting-defrosting cycles. By doing this work, the indoor thermal environment variation patterns during ASHP frosting-defrosting cycles were revealed for the first time. Results showed that the indoor temperature decreases notably during defrosting for both AWHPs and AAHPs, with greater declines observed for AWHPs. Specifically, the temperature drop ranged from 2.99–4.66 °C for AWHPs and from 1.58–1.79 °C for AAHPs. Furthermore, it was found that for both systems, the lowest indoor temperature does not occur at the end of the defrosting operation, as previously assumed, but rather 4.25–6.00 minutes later for AWHPs and 3.75–4.25 minutes later for AAHPs.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Schools > Architecture
Additional Information:	Rights retention strategy applied
Publisher:	Elsevier
ISSN:	0378-7788
Date of First Compliant Deposit:	10 December 2025
Date of Acceptance:	8 December 2025
Last Modified:	13 Jan 2026 15:45
URI:	https://orca.cardiff.ac.uk/id/eprint/183118

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