Please use this identifier to cite or link to this item: http://hdl.handle.net/10397/7503
Title: A study on thermal environmental control, indoor air quality and energy efficiency using task\ambient air conditioning (TAC) systems in sleeping environments in the subtropics
Authors: Mao, Ning
Keywords: Bedrooms -- Air conditioning
Bedrooms -- Heating and ventilation.
Air conditioning.
Indoor air pollution.
Hong Kong Polytechnic University -- Dissertations
Issue Date: 2015
Publisher: The Hong Kong Polytechnic University
Abstract: A human being spends approximately one-third of his / her life in sleep. Sleep is not simply a state of rest, but has its own specific functions to help people overcome tiredness. Recently, the influence of indoor thermal environment and air quality in a bedroom on the quality of sleep has been gradually understood. On the other hand, the use of air conditioning in bedrooms significantly contributes to the increased energy use in buildings. Therefore, it becomes highly necessary to study the air conditioning systems applied to sleeping environments where an appropriate indoor thermal environment and suitable air quality should be maintained at a low energy use. A programed research work on applying task\ambient air conditioning (TAC) to a sleeping environment has been therefore carried out and is presented in this thesis. The first part of the programmed research work reported in this thesis is an experimental study on the thermal, ventilation and energy saving performances of using a ductless bed-based TAC system in an experimental bedroom, as compared to that of using a full volume air conditioning (FAC) system. The experimental results demonstrated that using the ductless bed-based TAC system could lead to better ventilation effectiveness and energy saving performance, but a poor thermal performance in terms of a higher draft risk, than using the FAC system. To reduce the draft risk, while still maintaining an acceptable energy saving performance, it was possible to select a proper supply air temperature and air flow rate as well as a proper supply vane angle. In the second part of the programmed research work, an experimental and numerical study on the influence of return air inlet locations on the performance of the TAC system was carried out. In this study, two settings for the TAC system were designed. For Setting 1, the same TAC system as that in the first part of research work was used. For Setting 2, the TAC system was modified by adding a return air plenum with an inlet placed under the bed. The operating performances of the bed-based TAC system at the above two settings in terms of thermal environmental control and energy saving were experimentally evaluated. A computational fluid dynamics (CFD) method for evaluating air flow and temperature fields in the experimental bedroom was then developed and validated using the experimental results. Using the validated CFD method, the air flow and temperature fields were obtained, which helped explain the differences in the operating performances of the bed-based TAC system at the two settings. Both the experimental and numerical study results suggested that the bed-based TAC system at Setting 2 performed better in controlling thermal environment in an occupied zone but with a relatively poorer energy saving performance, as compared to that at Setting 1.
Considering that the position of a supply outlet in an air conditioning (A/C) system would significantly influence its operating performances in terms of thermal control, ventilation effectiveness and energy saving, in the third part of the programmed research work, a study on performance evaluations of an A/C system installed in the experimental bedroom with its supply outlet positioned at five different heights was carried out. The study included a numerical simulation using a CFD method and performance evaluation based on the CFD simulation results. The detailed distributions of air flow, temperature and CO2 concentration inside the bedroom were simulated using the CFD method when the A/C system was operated at different supply air temperatures, supply air flow rates and fresh air flow rates, with its supply outlet placed at 5 different heights (5 height settings). Based on the simulation results, the operating performances in the three aspects of ventilation effectiveness, thermal control and energy saving for the A/C system operated at different conditions, were then obtained and analyzed. In view of the inadequacy of using separately each of the three performance evaluating indexes, an evaluating tool called TOPSIS (Technique for Order Preference by Similarity to an Ideal Solution) was employed to evaluate the overall performance of the A/C system at various operating conditions, through integrating the indexes for ventilation effectiveness, thermal control and energy saving. The study results indicated that the best overall performance was achieved at a supply air temperature of 23 °C, a supply air flow rate of 50 l/s and a fresh air flow rate of 13 l/s when the supply outlet was placed at 1.1 m above floor level (H1100 setting). Among the five height settings, the A/C system performed the best at H800 setting. In the last part of the programmed research work, an optimization study for the operating parameters (supply air temperature, supply air flow rate and supply air humidity) of the ductless bed-based TAC system installed in the experimental bedroom was carried out, in order to obtain a thermally neutral sleeping environment at minimum energy use, taking into account the total insulation values of beddings and bed. A CFD method was firstly applied to calculating the PMV (Predicted Mean Valve) and EUC (energy utilization coefficient) values for 16 simulation cases. Based on the simulation results, the DOE (design of experiment) method was applied to identifying operating parameters, individually or combined, which would significantly affect thermal neutrality and energy use, and linear regression models for PMV and EUC using the identified parameters were respectively established. Thereafter, the linear regression models were used to obtain the optimum operating parameters of the bed-based TAC system, so that a thermally neutral sleeping environment can be maintained at a minimum energy use.
Description: xxviii, 248 leaves : illustrations (chiefly color) ; 30 cm
PolyU Library Call No.: [THS] LG51 .H577P BSE 2015 Mao
URI: http://hdl.handle.net/10397/7503
Rights: All rights reserved.
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