Please use this identifier to cite or link to this item: http://hdl.handle.net/10397/88300
Title: The study of window design to enhance natural ventilation in residential buildings in Hong Kong
Authors: Liu, Tianqi
Degree: Ph.D.
Issue Date: 2020
Abstract: Due to the rapid economic development and urbanisation in the past two decades in Hong Kong, energy consumption in high-rise residential buildings has risen sharply. Energy statistics in Hong Kong show that from 2007 to 2017, the percentage of electricity consumption for air-conditioning (AC) in the residential sector increased from 33% to 38%. The significant increase in cooling energy use is due to the impact of climate change and the higher thermal comfort and indoor air quality requirements. Natural ventilation uses available wind to reduce cooling load, dilute indoor air pollutants and provide thermal comfort in buildings. In favourable climates, residential units with natural ventilation can save 10%-30% of the cooling energy use. Thus, natural ventilation is an effective means to reduce energy consumption for air-conditioning. Wider use of natural ventilation in high-rise residential buildings is, therefore, receiving considerable and increasing attention. Windows are typically provided in residential buildings. Occupants are expected to adjust its opening degree for natural ventilation. However, the continuous increase in energy consumption for air-conditioning in residential sector in Hong Kong indicates that Hong Kong people have not made efficient use of natural ventilation to reduce cooling energy use. Natural ventilation performance of a residential unit is determined by the interactive effects of window type, window opening degree, relative positions of window groups, window orientation and local wind conditions. While window orientation and local wind conditions are often subject to site constraints, other window design options are within the control of building designers. On this basis, it is necessary to investigate the influence of window designs in residential buildings to encourage wider and more efficient use of natural ventilation for reducing cooling energy use and providing thermal comfort. Such information will be useful to users, building designers and policymakers as well as researchers in search of improvement in natural ventilation in Hong Kong and elsewhere in the world. Taking all the considerations given above, this thesis presents a study of the influence of window designs on natural ventilation performance in residential buildings in Hong Kong. In this study, carefully-design and novel methodologies were adopted to achieve the intended research objectives, which include walk-through surveys, site measurements, controlled experiments, computational fluid dynamics simulations, energy simulations, market surveys and statistical analyses. In the statistical analyses, novel approaches including the Central Composite Design method, the Squeeze theorem, the response surface regression method and the artificial neural network were used. Natural ventilation performance of three window types that are commonly used in residential buildings in Hong Kong was evaluated. Their common use were identified by walk-through surveys. The evaluation took into account the interactive influences of four possible window orientations, two relative positions of window groups (cross and single-sided ventilation modes) and nine representative coincident wind data sets. The wind data sets were developed based on a decade's hourly meteorological data in Hong Kong. The results lead to the conclusion that amongst all window types, side hung window is most effective, followed in descending order are top hung window and sliding window. As for the relative positions of window groups, it was found that if window groups can only be located on the same side of a residential unit (single-sided ventilation mode), side hung windows and south-facing top hung windows are preferred.
According to walk-through surveys on window opening habits of Hong Kong residents, it was found that there are limited and inefficient use of natural ventilation in residential buildings in Hong Kong. To encourage wider use of natural ventilation, the optimum window opening degree was investigated. The results show that the optimum window opening degree for Hong Kong, taking into account the seasonal wind conditions and all possible design options, should be in the range of 0.6 to 0.9. Considering that most residential buildings in Hong Kong are permanently limited to locate the window groups on the same side of a wall to become single-sided ventilation, the use of transom window (TW) of different designs to enhance ventilation was thus investigated. Site measurements were conducted at two carefully selected units to determine the influential design characteristics. The results show that indoor air change rate is most sensitive to the presence of TW and the rate is affected the most by the position of TW to the window, followed by wind speed, size of TW, orientation of TW, and wind direction. It was found that depending on the TW's physical characteristics, the improvement in air change per hour (ACH) because of its incorporation ranges from 117 % to 190%, and the average is 153.5%. Based on the improvement in ACH created by TW of the best and the worst designs, whether enhanced ventilation can achieve thermal comfort and further reduce energy usage for cooling are questions that are yet to be answered convincingly. For this purpose, cooling energy usage of a simple air-conditioning system and a hybrid system (using enhanced ventilation created by TW supplemented with air-conditioning) for achieving the same thermal comfort in high-rise residential buildings in Hong Kong were compared. The results found that depending on the TW design, average improvement in ACH ranges from 117 % to 190%, and the associated cooling energy saving from hybrid system ranges from 22.2% to 22.7%. These results confirm the effective use of TW in reducing cooling energy use and providing thermal comfort in high-rise residential buildings in Hong Kong. From the above, the academic contributions of this thesis on the study of window designs in enhancing ventilation in residential buildings in Hong Kong are in four aspects. They include the identification of the most effective window type, the optimum window opening degree, the TW designs to rectify poor ventilation associated with single-sided ventilation that cannot be avoided in most residential buildings in Hong Kong and elsewhere in the world, and the cooling energy savings for the use of TW. It can be seen that the objectives are original. The methodologies adopted are novel. The results are validated and verified and the findings are expected to be useful to the users, building designers and policymakers in Hong Kong as well as researchers for better utilization of natural ventilation to cut cooling energy use and to those living in countries with similar climatic conditions to Hong Kong.
Subjects: Windows -- Design and construction
Natural ventilation
Dwellings -- China -- Hong Kong
Buildings -- Energy conservation
Hong Kong Polytechnic University -- Dissertations
Pages: 165 pages : illustrations
Appears in Collections:Thesis

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