Air ventilation assessment of typical Hong Kong residential buildings

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Air ventilation assessment of typical Hong Kong residential buildings

 

Author: Hou, Ying
Title: Air ventilation assessment of typical Hong Kong residential buildings
Degree: M.Sc.
Year: 2011
Subject: Dwellings -- Heating and ventilation -- China -- Hong Kong.
Natural ventilation.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Building Services Engineering
Pages: xxiii, 179 leaves : ill. (chiefly col.) ; 30 cm.
InnoPac Record: http://library.polyu.edu.hk/record=b2457875
URI: http://theses.lib.polyu.edu.hk/handle/200/6227
Abstract: Hong Kong is a high density city, and ventilation design is a critical issue. It is necessary to design an available ventilation system through better urban design, planning and building design. This study aims to assess the residential housing ventilation, and to find ways to improve the indoor air ventilation and pedestrian wind environment with examples of public housings. Considering Hong Kong's dense urban conditions, good air ventilation is important and beneficial to improve human health. In this study, research has been conducted to design and plan Hong Kong typical residential buildings for better natural ventilation. Ventilation principles are firstly discussed, and on-site measurements are conducted in the sites of Sau Mau Ping and Lam Tin Estate for collecting characteristics and data of the natural ventilation. Design options for Hong Kong residential buildings are accordingly proposed. An advisory approach is introduced. The measurements data are analysed and assessed. Following the technical guide, related standards and professional suggestions, AVA (air ventilation assessment) is conducted to assess the impacts of building arrangement and building designs on wind environment. The Wind Velocity Ratio (VR) is used as an important wind performance indicator for the AVA system, which also provides an objective basis for evaluating and comparing design options. Generally, the higher wind velocity ratio, the less ventilation problems in Hong Kong. Taking Lam Tin outdoor measurements in summer as examples, the outdoor wind environment is found to be acceptable at most functional areas. For the indoor assessment, generally, the indoor air velocity is larger at higher floors except the ground floors. For ground floor, strong gusts are measured in these blocks due to the reasons, such as outlets, raindrops, and fans installed and so on. The air velocity in the lift lobbies is acceptable and a well-ventilated environment is found. However, the air velocities in the corridors are mostly below 1m/s, which is slightly unsatisfactory in a hot and humid summer. Therefore, it is recommended that fans should be provided and other actions should be taken in the corridors for providing better ventilation.
CFD(Computational Fluid Dynamics) simulation as a deep AVA process is also conducted to assess the air ventilation of the selected public housings and make further adjustments. The simulation results are compared with the measurements data, and conclusions are given accordingly. With the input data from the measurements data, a visual wind environment of the measurements sites can be shown. Simulation has been taken considering of different air directions, floors and, flat types, open/close window or door situation, and so on. The close/open status of windows should depend on the season changing and will affect ventilation difference. In winter, the windows are nearly closed with bad ventilation mentioned above, which causes air quality problems for the leeward side residents. Open window can catch better ventilation than closed one especially in summer. Likewise, the open interior doors can catch better ventilation for bedroom and well-proportioned ventilation in living room. Furthermore, in winter, it is less affected with this factor with nearly no open windows regarding the changes of height. Meanwhile, in summer, it has different air inlet speeds, and better ventilation is found for higher floors. Cases are modeled with different inlet air speeds to show a changing nearby natural wind speed environment. Indoor air movement around 1m/s is considered to be desirable to achieve a healthy and comfortable thermal environment in the summer. In addition, the original layout shows a better average wind environment compared with other design models. In many angles, the current design satisfies the requirements of Air ventilation Assessment.

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