The study of natural ventilation in residential buildings

Abstract

Modern people spend 90% of their time indoor of which 65% are at home. Residential premises therefore demand a healthy and comfortable indoor environment. Natural ventilation is most preferred by people for cooling and for providing fresh air. However, for a densely populated city of subtropical climate like Hong Kong, air-conditioning is most often used. Energy statistics show that in a typical residential building in Hong Kong, air-conditioning accounts for 25% of the energy consumption. With increasingly crowded indoor environments and continuous growth in residential energy consumption, wider use of natural ventilation in residential premises is receiving greater attention. However, the availability of adequate natural ventilation in dwellings to allow occupants to enjoy a healthy and comfortable environment is not simply by the provision of openable windows. There are other contributing factors including the window types, building orientations, openings configurations, surrounding buildings characteristics, and prevailing wind conditions. They all play very significant role in ensuring adequate natural ventilation in dwellings. Taking all the above factors into account, this thesis presents a study of influence of openings configurations and window types on the natural ventilation performance of a hypothetical residential unit. In the study, CFD simulations and field measurements were used. Varying parameters were carefully determined. Natural ventilation performance of eight openings configurations for the hypothetical residential unit was evaluated. The hypothetical unit was formulated with reference to findings of an extensive survey on the characteristics of dwellings in Hong Kong. The evaluation took into account four building orientations and three prevailing wind conditions. The results indicate that better natural ventilation performance can be achieved by locating two window groups (bedroom windows and living room windows) in opposite directions or in perpendicular to each other. As to the influence of different factors, it is noted that natural ventilation performance is most sensitive to changes in relative windows positions, followed by building orientations and door positions. Based also on the hypothetical residential unit, natural ventilation performance of four commonly used window types was investigated. It was found that when dealing with cross configurations, better natural ventilation performance could be achieved by using full end-slider and side hung windows; while for single-sided configurations, side hung windows performed better than other types of windows to conclude that side hung windows were a better option. The last part of this study is to take into account the complex influence of the surrounding building conditions on the results of the above studies. A large-scale private residential estate was chosen as a representative sample of typical residential environment in Hong Kong for the investigation of wind conditions around buildings. The local wind conditions were used to evaluate natural ventilation performance of different openings configurations and window types. The results indicate that when adding the influence of surroundings buildings, wind speed was reduced and wind direction was changed. Despite wind conditions were affected, the conclusions drawn on the influence of openings configurations and window types on natural ventilation performance were still valid. Given adequate information on the influences of openings configurations, window types and surrounding buildings on natural ventilation performance in dwellings is not available in extant literature, the results of this study are expected to be useful to site planners and architects in Hong Kong while designing residential dwellings for better natural ventilation.