An experimental and numerical study on the thermal environment in an air-conditioned sleeping space

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An experimental and numerical study on the thermal environment in an air-conditioned sleeping space

 

Author: Pan, Dongmei
Title: An experimental and numerical study on the thermal environment in an air-conditioned sleeping space
Degree: Ph.D.
Year: 2012
Subject: Cooling load -- Measurement.
Air conditioning.
Bedrooms -- Air conditioning.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Building Services Engineering
Pages: xxvi, 206 leaves : ill. ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2522711
URI: http://theses.lib.polyu.edu.hk/handle/200/6603
Abstract: A human being spends approximately one-third of his / her life in sleep. Sleep can help people overcome tiredness and is very important to one's memory. The influence of thermal parameters in a sleeping environment on the quality of sleep has been gradually understood. Therefore, air conditioning shall serve to maintain an appropriate indoor thermal environment not only in workplaces during daytime, but also in bedrooms in residences or guestrooms in hotels at nighttime for sleeping. However, the current practices in air conditioning are mainly concerned with the situations in which people are awake in workplaces or other leisure places. These may however not be directly applicable to air conditioning for sleeping environments. Therefore, it becomes highly necessary to study the thermal environment in an air conditioned sleeping space in order to provide people with a thermally comfortable sleeping environment at a low energy consumption. The thesis reports, first of all, two numerical studies on the micro-climate around, and the thermal neutrality of, a sleeping person placed in a space with a displacement ventilation system. A sleeping computational thermal manikin (SCTM) was developed and used to investigate the micro-climate around a naked SCTM, including air temperature and velocity distributions, and heat transfer characteristics. Then, the results of the numerical study on the thermal neutrality for a sleeping person are presented, including the thermal neutrality for a naked sleeping person and the effects of the total insulation value of a bedding system on the thermal neutrality of a sleeping person. The results of the two numerical studies were validated by the experimental data from earlier related studies. The results showed that the thermal resistance of a bedding could significantly affect the thermal neutral temperature of a sleeping person, i.e., the higher the thermal resistance of the bedding, the lower the thermal neutral temperature. It was further suggested that the supply air velocity did not significantly affect the thermal neutral temperature when people were covered with different beddings at 100% percentage coverage of body surface area by bedding and bed. Secondly, a study on developing a four-node thermoregulation model for predicting the thermal physiological responses of a sleeping person is presented. The four-node thermoregulation model for a sleeping person was developed by modifying Gagge's two-node model. The four-node thermoregulation model was validated by comparing the predicted thermal physiological responses, including skin and core temperatures, using the model developed with the experimental data previously obtained by others. The comparison results demonstrated that the four-node thermoregulation model developed could be used to predict the thermoregulatory responses of a sleeping person with an acceptable accuracy. Therefore, the validated four-node thermoregulation model can be used as a useful tool to predict the influences of different indoor thermal parameters, such as air temperature and humidity, in a sleeping environment and different bedding systems on the thermoregulatory responses of a sleeping person.
Thirdly, a study on evaluating the operational and energy saving performance of a novel bed-based task/ambient conditioning (TAC) system is presented. Both experimental and numerical approaches were employed in the study, and are separately reported. In the experimental part, the development of a novel bed-based TAC system placed in an experimental bedroom and the related experimental performance evaluations are presented. The experimental results demonstrated that the use of the novel bed-based TAC system can help achieve energy saving, compared to the use of a full air conditioning (FAC) system. The experimental results also suggested that the operational and energy saving performance of the novel bed-based TAC system would be affected by a number of factors, such as supply air flow rate and temperature, and supply vane angle. Given the limitations of the current experimental bedroom, where simulated space cooling load was only generated indoors, the energy saving potential when using the novel bed-based TAC system in an actual bedroom where there can be space cooling load from outdoors was studied through a theoretical analysis. The results of theoretical analysis demonstrated that the energy saving potential when using the novel bed-based TAC system in an actual bedroom can be significantly larger than that in the experimental bedroom. On the other hand, in the numerical part, a numerical model for the bed-based TAC system placed in the experimental bedroom was established, and validated using the experimental data obtained. The validated numerical model was further used to analyze the performances of the bed-based TAC system developed at the operating conditions other than the experimental conditions. The numerical results showed that the supply air flow rate of 75 L/s might be regarded as an optimum one for the novel bed-based TAC system because of the largest energy saving potential without the risk of cold draft inside the occupied zone. At a supply vane angle of +60°, the predicted value of EUC was even smaller than 1. When the supply vane angle was set at +30°, the predicted EUC value was larger than 1. The predicted EUC values increased when the supply vane angle was altered from -30° to 0°, and then to -60°. Therefore, it was shown that by suitably controlling its supply air flow velocity and temperature, supply vane angles, the bed-based TAC system can be operated to maintain an acceptable level of thermal comfort without cold draft in an occupied zone at a low energy consumption.

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