Space-cooling load reduction and thermal comfort with stratified air distribution

Pao Yue-kong Library Electronic Theses Database

Space-cooling load reduction and thermal comfort with stratified air distribution


Author: Liu, Peng
Title: Space-cooling load reduction and thermal comfort with stratified air distribution
Degree: M.Eng.
Year: 2012
Subject: Displacement ventilation.
Cooling load -- Measurement.
Office buildings -- Air conditioning.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Building Services Engineering
Pages: 113 leaves : ill. ; 30 cm.
Language: English
InnoPac Record:
Abstract: Compared to the conventional mixing air conditioning system, the stratified air distribution (STRAD) system could reduce energy consumption, improve breathing zone air quality and ensure a high thermal comfort level. In most existing STRAD systems, the return and exhaust share the same group of hoods. Theoretically, more heat will be removed when the exhaust hood is separated from the return grilles due to the temperature stratification in STRAD situation. In other words, split return/exhaust system has further energy saving potential. The potential in an office size chamber was experimentally investigated. Two manikins which were divided into 15 different heat distribution parts were made and located in the chamber , together with two computer. The chamber can provide both displacement ventilation (DV) and under floor air diffusion (UFAD) systems. The height of the return hood was changed to observe its effects on the energy consumption and local thermal comfort with different STRAD system. The temperatures as the main parameter were read and recorded through Midi logger and Hobo Temp/RH boxes. Based on Cheng and Niu's energy analysis equation and Nilsson's local thermal comfort model for STRAD systems, the extra energy saving rate and local thermal comfort condition was determined in the split return/exhaust grilles STRAD systems. Through comparisons, the energy saving rate of STRAD system is around 7% compared with the overhead mixing ventilation for the existence of the thermal stratification. Besides, the additional saving rate (the maximum is about 4%) is not obvious in this configuration compared to the combined return/exhaust STRAD systems when the exhaust hood is separated from the return grilles. Meanwhile, the thermal comfort in the split systems is not considerable due to the excess temperature difference between the head and fee level and uncomfortable opposite temperature gradient although the local thermal comfort is acceptable. Weighting between the effects and the design complexity together with additional investment, it need careful consideration and further research to determine feasibility of employing the split return/exhaust STRAD system in similar configurations as the chamber.

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