Strategies for bedroom air conditioning in the subtropics

Pao Yue-kong Library Electronic Theses Database

Strategies for bedroom air conditioning in the subtropics

 

Author: Lin, Zhongping
Title: Strategies for bedroom air conditioning in the subtropics
Degree: Ph.D.
Year: 2005
Subject: Hong Kong Polytechnic University -- Dissertations
Air conditioning
Bedrooms -- Air conditioning
Department: Dept. of Building Services Engineering
Pages: xxii, 230 leaves : ill. ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1809942
URI: http://theses.lib.polyu.edu.hk/handle/200/3118
Abstract: In the subtropics, air conditioning serves to maintain an appropriate indoor thermal environment not only in workplaces during daytime, but also at nighttime for sleeping in bedrooms in residences or guestrooms in hotels. However, current practices in air conditioning, as well as the thermal comfort theories on which these practices are based, are primarily concerned with situations in which people are awake in workplaces at daytime. Therefore, these may not be directly applicable to air conditioning for sleeping environments. The thesis reports, first of all, on both a questionnaire survey of the current status of sleeping thermal environments and bedroom air conditioning, and a field monitoring of overnight indoor air temperature and relative humidity in a number of air conditioned bedrooms, in residential buildings in subtropical Hong Kong. This was to gather relevant background information such as the types of air conditioning systems employed in bedrooms, the use of bedding and sleepwear while sleeping and the preferred indoor air temperature settings in bedrooms by occupants, etc. Secondly, a theoretical study on thermal comfort for sleeping environments is presented. A comfort equation applicable to sleeping thermal environments was derived by introducing appropriate modifications to Fanger's comfort equation. In order to solve the comfort equation, the total thermal insulation provided by bedding systems, which is an important parameter included in the comfort equation, must be obtained. Therefore, an experimental study using a thermal manikin on measuring the total insulation values for a wide range of the bedding systems commonly used in the subtropics has been undertaken. A small-scale database of the total insulation values provided by the bedding systems has been developed. Comfort charts have been established, and can be used for determining thermally neutral environmental conditions under a given bedding system. Thirdly, a simulation study to investigate the characteristics of nighttime bedroom cooling load in the subtropics, using a building energy simulation program -EnergyPlus, is presented. The results of the simulation study showed that the characteristics of nighttime bedroom cooling load differed significantly from those at daytime. The total cooling load peaked at the starting time of a nighttime air conditioning process, when the heat stored inside building envelopes and furniture dominated. A method of sizing room air conditioners (RACs) for bedroom was proposed based on the known characteristics of nighttime bedroom cooling load. Finally, the thesis reports on a study on the outdoor air ventilation rate in bedrooms where RACs are employed. Field measurements of both the indoor overnight carbon dioxide (CO2) levels and the outdoor air ventilation rates in bedrooms employing RACs, as well as laboratory experiments on the ventilation characteristics of RACs were carried out. The results of the study suggested that the outdoor ventilation rates in the studied bedrooms equipped with RACs could not meet the ventilation requirement specified in ASHRAE Standard 62-2001 even if there was only one occupant in a bedroom. The ventilation damper currently available in a window-type room air conditioner (WRAC) cannot be expected to provide the ventilation rate as required by a ventilation code and its intended function of controlling ventilation was limited. Therefore, an improved design for a WRAC has been proposed to improve its ventilation control and to save energy. A new ventilation rate of 3.0 L/s per person for sleeping environments has also been proposed.

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