In hot climates ventilation can be a useful means of cooling dwellings, if the outside air is cooler than that inside the dwelling. Often, in hot regions the outside air is so hot during the day that cooling by ventilation is of no benefit until the evening when the outside air cools. Ventilation can then be beneficial, and can be promoted by a sun-warmed cavity or 'solar chimney' added to a building on the sunward side. The cavity may be of any material of high thermal capacity. Heat from the sun is stored within the walls and heats the air within. The cavity is closed at the top and bottom by dampers. These, when opened in the evening, allow the buoyant hot air contained within to rise, drawing cooler outside air into the building. This process continues until the stored energy is consumed. The performance of a typical cavity in inducing ventilation into a house is studied experimentally and theoretically. The measurements are made on a full-scale model under steady-state conditions. Cavity width and air inlet area are important parameters in this study. Measurements are made on the temperature and velocity of the air. Observations on air flow patterns in the room and the cavity are made. A dynamic model is developed based on a finite-difference technique, and used to examine the performance of the cavity in various circumstances. The results show that air movement can be produced by a sun-warmed cavity if the dimensions of inlet and cavity width are kept to certain values, and that thermal comfort can be improved. List of symbolsA Area (m~) c Specific heat capacity (J kg-1 K-1) C~ Ventilation conductance (m2 K V~l-1) g Gravitational acceleration (9.8ms-2) ht Convection heat transfer coefficient (Wm ZK 1) h, Radiation heat transfer coefficient (Wm-2K-I) M Mass flow rate (kg s-~) R Thermal resistance (m2K W-1) t Time (s) T Temperature (°C) x Distance (m) v Velocity (m s-1) V Volume (m~) tv Cavity width (m) Y Cavity length (m)

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An experimental study of passive cooling roof was carried out for a typical summer day of June for Laghouat in Algeria. The proposed roof design is composed of a metal plate ceiling over which lies a bed of rocks in a water pool. Over this bed is an air gap separated from the external environment by an aluminium plate. The upper surface of this plate is painted with a white titanium-based pigment to increase the radiation reflection process during daytime. Several passive modifications have been introduced to the roof in order to reduce indoor air temperature in hot climates. An experimental investigation, employing passive procedure, has been carried out to study the possibility of reducing air temperature in buildings. The results show that the air temperature can decrease with a range from 6 to 10°K. This decrease can further be lowered by 2 to 3°C if night natural ventilation of buildings is allowed.