Rеvuе des Energies Renouvelables
Volume 7, Numéro 2, Pages 125-134
2004-12-31

A Dynamic Mathematical Model To Predict The Performance Of Passive Cooling System By Evapo-reflective Roof For Hot Dry Climates



Authors : Bencheikh H. . Bouchair A. .

Abstract

A dynamic mathematical model used to predict the performance of passive cooling system by evapo-reflective roof in buildings for hot arid climates has been developed. The cooling system consists of a roof composed of concrete ceiling and flat aluminium plate, separated with air space partially filled with rocks and small quantity of water. Low emissive aluminium sheet with white painting on the upper surface, reduces the heat transfer by radiation during the daytime, an external treatment of the roof used to provide mass transfer to the outside (water vapour). At night, the temperature of the aluminium sheet falls below the temperature of the rocks water upper surface. Water vapour inside the roof condensates and falls by gravity. This heat pipe effect carries heat outwards. Heat exchange is improved by radiation between two humid internal surfaces. The efficiency of this cooling system is studied using finite differences method. Numerical calculations performed for different external temperatures and solar radiation show that the cooling produced by such system is significant. As a result of this, the mean air temperature in the room may be kept a few degrees over the minimum outdoor temperature throughout the day. Allowing natural ventilation of the building in the evening could further, lower the indoor air temperature by 3 to 4°C. The work is continuing.

Keywords

Evaprative cooling, Evapo-reflective roof, Hot dry climate, Night ventilation, Dynamic model.

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