Control and performance evaluation of a two-evaporator air conditioner

Pao Yue-kong Library Electronic Theses Database

Control and performance evaluation of a two-evaporator air conditioner

 

Author: Jiang, Lingyun
Title: Control and performance evaluation of a two-evaporator air conditioner
Degree: M.Eng.
Year: 2008
Subject: Hong Kong Polytechnic University -- Dissertations.
Air conditioning -- Control -- Evaluation.
Department: Dept. of Building Services Engineering
Pages: xiii, 81 leaves : ill. ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2231983
URI: http://theses.lib.polyu.edu.hk/handle/200/4159
Abstract: A multi-evaporator air conditioner (MEAC) consists of one compressor, one condenser, two or more evaporators and the same number of expansion valve. Because the control strategy used in the MEAC is quite different from that in a single-evaporator air conditioner, the design of the control system for MEAC becomes more challenging. This project aims to evaluate the control and performance of a two-evaporator air conditioner. The methodology adopted was experimental and an experimental rig using on a two-evaporator air conditioner (TEAC) whose brand is DAKIN has been set up. TEAC has one outdoor unit and two indoor units located in two zones respectively. Two experimental studies were conducted in the thesis. The first study focused on the control loop and control mode of TEAC's control system. These experiments were conducted with different setpoints which are 22oC, 24oC and 26oC, respectively. The experimental results reveal that on-off control is designed appropriately. The second experimental study puts emphasis on investigating the performance of TEAC. The experiments were carried out with different setpoints when only one indoor unit performs its operation and the experimental results show that, the temperature of the air-conditioned room can be kept at an acceptable level. When two indoor units operate simultaneously and alternately, the performance is affected by the system deadband significantly and the temperature sewing could cause the occupants feel uncomfortable. The results also indicate that the compressor capacity keeps constant even though the cooling load increases greatly , and the compressor employed by TEAC is a constant speed compressor without using inverters. Because the designed capacity of the compressor is constant and must be the maximum value which should match the total cooling loads of the two zones, the cooling capacity will be inappropriate when only one zone need to be air-conditioned and energy will be wasted. When TEAC provides air-conditioning to the two zones simultaneously, the system deadband will bring about a significant increase of room temperature of the air- conditioned zone and a large range of the temperature swing. Nevertheless, as for the consumer, the regulation of the indoor room temperature and energy efficiency are the major points of concern. TEAC needs further performance improvement, and the further study should be devoted to design (designing) a high-performance controller and appropriate capacity control scheme to improve the energy efficiency and the comfort level.

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