Investigation on the defrosting characteristics of an air-to-air heat pump under different operation conditions

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Investigation on the defrosting characteristics of an air-to-air heat pump under different operation conditions

 

Author: Yao, Ting
Title: Investigation on the defrosting characteristics of an air-to-air heat pump under different operation conditions
Degree: M.Eng.
Year: 2010
Subject: Hong Kong Polytechnic University -- Dissertations
Heat pumps -- Evaluation.
Thawing
Department: Dept. of Building Services Engineering
Pages: x, 77 leaves : ill. ; 31 cm.
InnoPac Record: http://library.polyu.edu.hk/record=b2356387
URI: http://theses.lib.polyu.edu.hk/handle/200/5759
Abstract: Frosting is a common phenomenon for air-to-air heat pumps working in winter. It affects the efficiency and capacity of the air-to-air heat pump significantly. Although previous research focused on the performance and characteristics of air-source system during defrosting process, few studies were concerned with the effects caused by compressor operation and EEV regulation. In this study, the influence caused by difference in operation of compressor and EEV regulation is considered. Experiments were carried out with three operating conditions: 1) Normal defrosting condition: the speed of compressor was 3000r/min, and the EEV was fully open throughout the defrosting process without degree of superheat regulated. 2) Condition with different speed of compressor: the speed of compressor was set to 2700r/min, 2400r/min and 2100r/min during defrosting process. 3) EEV regulation according to the degree ofsuperheat condition: at the initial of defrosting process, degree of superheat was set to be 5℃, and then the opening of EEV was regulated accordingly. The performances of system with different operation conditions were analyzed and the experimental results of the three conditions were compared. The experimental results indicated that decreasing the speed of compressor could help to system avoid melted frost vaporized. EEV regulation according to degree of superheat could short defrosting time and improve defrosting efficiency. Both these measures can be adopted by operators for efficient air source system defrosting.

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