Reducing cooling load of semi-stratified air distribution system

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Reducing cooling load of semi-stratified air distribution system


Author: Yang, Fan
Title: Reducing cooling load of semi-stratified air distribution system
Degree: M.Eng.
Year: 2010
Subject: Hong Kong Polytechnic University -- Dissertations
Displacement ventilation
Office buildings -- Air conditioning -- China -- Hong Kong
Cooling load -- Measurement.
Department: Dept. of Building Services Engineering
Pages: [xiv], 91 leaves : ill. ; 31 cm.
InnoPac Record:
Abstract: Compared with traditional mixing ventilation, displacement ventilation (DV) and under-floor air diffusion (UFAD) are both innovative air distribution methods. Although DV system and UFAD system have several advantages over the traditional mixing ventilation system, they are not widely adopted due to lack of fundamental understanding of systems' performance related to cooling load, indoor air quality, thermal comfort and radiant heat. This research aims to investigate the perfonnance of DV system and UFAD system in a typical office located in Hong Kong with changing the supply air velocity and the height of return hoods. In this study, the effects of cooling load, indoor air quality, thermal comfort and radiant heat with different height of return hoods and different number of occupants were analyzed respectively. A stainless steel chamber and two thermal manikins were applied to do the full-scale experiment. Difference of return air temperature and exhaust air temperature have a critical effect on the cooling load calculation. The temperature gradient between return hood (150cm) and exhaust hood (215cm) is not as significant as the temperature gradient of three levels (head level, waist level and ankle level). The cooling load of return air part was almost twice the cooling load of exhaust air. The concentration of contaminant of DV system was lower than that of UFAD system. And the indoor air quality of occupied zone was obviously better than the upper zone in both DV and UFAD system. In this study, high supply velocity cases were able to provide better thermal comfort and at ankle level, although the draft risk was highest than the other two levels. With the aspect of radiant heat, under the condition of low supply air velocity, 72% of radiant heat was distributed in the lower zone. Under the condition of high supply air velocity, up to 76% of radiant heat was distributed in the low zone.

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