CFD simulation of displacement ventilation to reduce space cooling load

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CFD simulation of displacement ventilation to reduce space cooling load

 

Author: Lee, Wai-yee
Title: CFD simulation of displacement ventilation to reduce space cooling load
Degree: M.Eng.
Year: 2009
Subject: Hong Kong Polytechnic University -- Dissertations.
Displacement ventilation.
Energy conservation.
Energy consumption.
Indoor air quality.
Fluid dynamics -- Computer simulation.
Department: Dept. of Building Services Engineering
Pages: 78 leaves : ill. (some col.) ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2303470
URI: http://theses.lib.polyu.edu.hk/handle/200/4439
Abstract: Air conditioning systems are the major energy consumers in buildings. Energy consumption can be reduced by enhancing systems' efficiency. Displacement ventilation is an innovative air distribution system, which supplies fresh and cool air at the floor level and returns at the ceiling level. The system has been proved to be able to provide better indoor air quality and consume less energy than a traditional mixing ventilation system. The cooling load of a displacement ventilation is dependent on the heat sources distribution as well as the room geometry. Researchers have carried out a number of studies to analyze the effects of various factors on the cooling load of displacement ventilation system. However, most of the studies have only focused on small office rooms. Only a few have studied the system performance in atrium and there is a lack of investigation for cases of middle sized premises. This research aims to investigate the displacement ventilation system performance in a lecture theatre with changing ceiling height. In the study, the effects of distribution ratio of radiant heat from heat sources, interaction between the heat sources as well as the required air handling unit's capacity were analyzed. Computation fluid dynamics (CFD) simulation has been used to examine the thermal condition in the displacement ventilated room. Radiant heat distribution ratios of heat sources have a critical effect on the accurate cooling load estimation of displacement ventilation. Two sets of radiant heat distribution ratio produced a 6% variation in heat gain in the occupied zone. Accurate distribution ratio is required for accurate displacement ventilation cooling load estimation. Moreover, the 3% difference between the cooling load with integrated heat sources and the sum of individual heat sources shows the interaction effects between the heat sources. The actual value of required air handling unit capacity is higher than the theoretical value. This difference is the corollary of the uneven distribution of enthalpy on the horizontal plane of return air. In the study, the uneven distribution is caused by the changed ceiling height. Further study is required to analyze the effect of location of return air grill. For the lecture theatre in the study, application of displacement ventilation provides 13.5% reduction in cooling load. Some assumptions are made in the current study, such as distribution ratio of radiant heat and heat source interaction. More accurate estimation requires further study on the radiant heat distribution ratio, the heat sources interaction and the location of return air grill.

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