building systems

heating strategies

cooling strategies

     natural ventilation
     natural ventilation feasibility study

policy strategies

consumer notes

     consumer notes

Evaluation of the potential use Natural of Ventilation in
a typical residential building in China

The first part of this study consisted in an overall estimate of the available potential to use wind and buoyancy driven ventilation in conjunction with night cooling strategies as a mean of obtaining improved thermal comfort conditions in a typical chinese apartment.

This estimate was done for three cities situated in different climatic zones (Shanghai, Beijing and Canton). A typical residential building was analyzed, taking into account its geometry, materials, average infiltration caracteristics and typical occupancy (internal heat gains). Using weather data generated by the Chinese software Medpha (see chart below) and basic wind data from ASHRAE a simulation of the temperature profiles obtainable using passive night cooling strategies was done (supposing the use, if necessary, of simple forced ventilation during the night and ceiling fans during the day). The ventilation rates were obtained using a natural ventilation simulation tool (Vent). These estimated ventilation rates were then inputted into a night cooling analysis tool (Lesocool).

Night cooling strategies give better results with a low night time temperature and a high variation during the day so that more heat can be exchanged with the structure. The Beijing climate has this characteristic, Shanghai has a lower temperature spread as well as other urban characteristics (close building implantation) that make the application of passive strategies less effective.

A night cooling procedure involves maximum ventilation during the night in order to extract heat form the building fabric, during the day minimum ventilation rates are maintained and the building fabric is used an internal heat sink.

The results obtained are encouraging and show that these passive strategies have the potential to improve living conditions during the warm months of the year. Obtaining the same internal conditions (for the case shown in the chart above) using air conditioning would involve a monthly energy spending of (approximately) 6.2 GJ (5.88x106Btu). With this type of solution one obtains not only savings for the users (depending on the cases they might not be able to afford air conditoning at all) and also decreased environmental impact.

The next step in the project consists in the development of a multi-zone (whole building) software tool for "passive" architecture design. This tool uses tri-dimensional partition of the interior of the building to be modeled. This modeling approach will provide more precision and detail than currently available whole building models while remaining fast enough to be used for whole year real weather analysis.

The main strong points of this tool are: a numerical procedure that starts from the heat gains and outside temperature and predicts the internal temperatures of the rooms, the possibility to deal with the spatial distribution of internal heat sources (which in many cases are the main source of internal air movements) with increased precision (gains in the walls and in the lower or middle part of the space etc…) and improved coupling with the thermal mass of the walls (taking into consideration the velocity of the air currents adjacent to the walls).

This model will be used to study the natural ventilation/night cooling system that will be part of the prototype design to be developed next year, possibly in conjunction with an optimization algorithm (currently being developed by L.Caldas).

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Last modified on December 12, 2000 by
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