In natural ventilation systems fresh air is often provided through opening of windows. However, the knowledge of the performance of windows is rather limited. Computation of natural ventilation air flow through windows is most commonly made using discharge coefficients, that are regarded as being constant. The reported results show that the discharge coefficient for a window opening cannot be regarded as a constant and that it varies considerably with the size of the opening area, the window type and the temperature difference.
For natural ventilation of rooms there is a wide range of possibilities with regard to the selection of window type, size and location. A bottom hung window mounted near the ceiling is often used as it has proved to work well with regard to draught risk and thermal comfort in the room. However, there is a need for more detailed information on the performance of this and other types of windows to make it possible to use improved design methods for natural ventilation systems.
Natural ventilation systems for industrial buildings have traditionally been designed using empirical engineering models, which often require the designer to 'over-engineer' the design to achieve a 'guaranteed' level of ventilation performance. This paper describes an application of computational fluid dynamics (CFD) and multi-zone thermal and airflow modelling to analyse the effectiveness of natural ventilation in removing moisture from a red mud filtration building used in the alumina industry in Australia.
The "step-down" tracer gas technique was used to evaluate experimentally in a mechanically ventilated test room the effect of varying thermal boundary conditions, inlet flow rates, and inlet - exhaust grids position on the Air Change Efficiency (ACE) values. The paper shows that the measured global ACE values are strongly correlated to the Archimedes number (Ar).
Natural ventilation driven by a solar chimney attached to a single-room building is investigated experimentally with a small-scale model using a recently developed fine bubble technique. Parameters studied in the experiments are the cavity width of the solar chimney, the solar radiation intensity, the height of the solar chimney, the room inlet area and the solar chimney inlet area. Results showed that for given building geometry and inlet areas, there is an optimum cavity width at which a maximum ventilation flow rate can be achieved.
A number of new techniques have been developed in recent years, by various researchers, to assist in the sizing and positioning of natural ventilation openings. These may be of considerable assistance in the natural ventilation design process, while still allowing architectural freedom. This paper reviews some of the available techniques. The complexity of the configurations accounted for by the procedures ranges from two openings with the indoor air at a uniform temperature to a technique that allows for multiple openings throughout a multi-zone structure.
As the climate in the Nordic countries is cold for several months a year, windows are crucial parts of building envelopes. The current trend to reduce the heat losses by building- components has resulted in many modifications of the design work of windows in order to improve the thermal performance and the indoor climate. The improvements of window constructions have resulted in a higher surface temperature on the inner pane and considerably lower downdraught, which in turn has created an opportunity to introduce unconventional design of the heating and ventilation systems.
In displacement ventilation the airflow pattern in a room is mainly guided by the convection flows from the heat sources present in the room. This implies that the air in the breathing zone mostly comes from the lower parts of the room, where the air often is less polluted by pollutants originating from persons or electrical appliances present in the room.
Wall-mounted air conditioning systems including window-type and split-type air conditioners are widely used in Asian countries. However, these systems blow cold air directly into the working space perpendicular to the mounted wall and may make people affected by these air conditioners experience discomforts such as draught and uneven temperature distribution. Now a wall-mounted air conditioning system is expected to effectively implement the displacement ventilation system for space cooling and cold draught avoiding.
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