Computational analysis of effectiveness of stratified cooling in air-conditioning

Pao Yue-kong Library Electronic Theses Database

Computational analysis of effectiveness of stratified cooling in air-conditioning

 

Author: Chiu, Yat-hon
Title: Computational analysis of effectiveness of stratified cooling in air-conditioning
Year: 2000
Subject: Air conditioning
Cooling
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Dept. of Mechanical Engineering
Pages: xi, 116, [49] leaves : ill. ; 31 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1532171
URI: http://theses.lib.polyu.edu.hk/handle/200/2686
Abstract: This study is to construct a mathematical model that integrates the existing principles in the field of heat transfer and to apply these available theories to predicting the stratified cooling process in air-conditioning. The model treats the air-conditioned enclosure as a coupled air-wall-floor-roof system in which thermal energy is conserved. The steady-state heat convection in the space air is represented by a set of two-dimensional finite difference numerical equations governing the conservation of mass, momentum, and energy. To simulate the stratified cooling effect, this study features the evaluation of boundary conditions by means of empirical correlations and the inclusion of varying air properties with respect to local temperatures. The simulated results are applied to the field measurements done by other academic to demonstrate the validity of the model and program algorithms. Following the same parameters as set up in the field tests, the simulated air temperature gradients are in most cases follow comparatively the patterns of the field measurements. The computer results give a good agreement that the point of transition between the upper and lower zones is determined in the level at which the supply air is introduced. Based on the effect of thermal stratification, the supply air height is then varied to evaluate the cooling load reduction with respect to the supply air level. The computer results show that cooling load reduction of 11% is achieved when the supply air is introduced in the middle level rather than ceiling level based on the conditions of a particular test. However the simulated load calculations are often higher than the field measurements, and a 12% increase in load estimation is resulted. The simulated temperature gradients are in general within the range of up to 4 C deviation when compared to the field measurements.

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