A study of thermal comfort in sleeping conditions

Pao Yue-kong Library Electronic Theses Database

A study of thermal comfort in sleeping conditions


Author: Chau, Chun-wa
Title: A study of thermal comfort in sleeping conditions
Degree: M.Eng.
Year: 2010
Subject: Hong Kong Polytechnic University -- Dissertations
Dwellings -- Air conditioning
Air conditioning -- Computer-aided design
Department: Dept. of Building Services Engineering
Pages: ix, 119 leaves : ill. ; 31 cm.
InnoPac Record: http://library.polyu.edu.hk/record=b2356321
URI: http://theses.lib.polyu.edu.hk/handle/200/5783
Abstract: Hong Kong is situated in subtropical region; air conditioner is an essential for every family. The major function is to maintain an acceptable indoor thermal comfort conditions. It is not only in workplaces during daytime, but also in dwelling rooms at night. However, current codes and standards do not provide rigid guidelines nor standards in sleeping conditions and general thermal comfort standards might not be applicable to sleeping environments. Therefore, investigation of thermal comfort in sleeping conditions is essential to providing a better understanding on this neglected topic. This study employed computational fluid dynamics (CFD) software to evaluate the sensible heat loss, mean radiant temperature and air velocity in sleeping condition. The mathematical investigation is carried out with PMV-PPD models. The comfort equation developed by Fanger was applied to estimate the thermal conditions in sleeping condition. In the results, it was shown that the thermoneutral temperature and inlet air temperature to maintain thermal comfort are 28.8°C and 23.2°C, respectively. The results also demonstrated that high mean radiant temperature can be compensated by increasing inflow air velocity to achieve thermal comfort, meanwhile, low mean radiant temperature can be compensated by lowering inflow air velocity. From the data obtained from simulation, adaptive model with mean radiant temperature against inflow air velocity bas been established. The room mean radiant temperature and air inflow velocity should be set within the thermal comfort area in adaptive model to maintain thermal comfort.
Secondly, a questionnaire survey of current status of sleeping thermal environments was conducted. The respondents would like to have relatively low temperature of 24°C or below for thermal comfort in sleeping environments. Moreover, the survey shows that more than 85% of respondents would like or cover a quilt or blanket while they were sleeping in air conditioned bedroom. In order to know the relationship between real situation and the results from survey, field monitoring of overnight indoor air temperature and relative humidity in air conditioned bedrooms were carried out. The results showed that the actual temperature in all bedrooms were slightly higher than set point 1°C to 4°C when compared with the set points of air conditioner. From the statement of nearly 85% respondents would like to have 24°C or below, with the adjustment of 2°C between actual radiant temperature, the statement becomes "Majority of respondents would like to have 26°C or below to maintain thennal comfort in sleeping condition" which it was closer to the optimum radiant temperature obtained from CFD simulation. The difference of thermal comfort temperature between CFD simulation (28.8°C) and survey (below 24°C) may be due to sleeping habits of occupants, such as covering with thick quilt and blanket, sleepwear and bedding system. In order to maintain thermal comfort in sleeping condition and use energy efficiently, the occupants should increase the set point of the air conditioner by 1 -4°C with wear less sleepwear and using thin blanket in bedrooms.

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