Investigation On The Natural Ventilation In Courtyards With Thermal Pressure

Natural ventilation has the potential to form a relative comfort inner air environment in buildings with low energy consumption,therefore energy-saving efficiency can be obtained.Due to its own special structure courtyard-style buildings, the chimney effect can be used to induce natural ventilation in courtyards.In the present study,the features of thermal effect in courtyards are investigated and analyzed.A continuous monitoring was conducted to estimate the inner and outer thermal environments in a courtyard in Shanghai in summer,the data show that the chimney effect can makes a relative comfort thermal environment in the courtyard,and the effect is more obvious in afternoon.The numerical results indicate that whether there exists a thermal pressure in the courtyard,there is almost no variation of natural ventilation of the windward side rooms.The natural ventilation efficiencies of the leeward and side rooms can be improved when the hot pressure is increased.If there is a heat source inside the courtyard,by decreasing the internal pressure in the courtyard,the pressure drop between indoor and outdoor can be increased,and the overall ventilation efficiency can thus be enhanced.The numerical results also show that for different aspect ratios of buildings,the thermal pressure varies with the increase of the height of a courtyard building,heat sources in a single room only affects the ventilation of the room itself,i.e.,the effect of aspect ratio of building and internal heat source in rooms for the courtyard's natural ventilation can be ignored.The result also show that there exist a critical height h, when the height of the building H is higher than h,the air exchange rate is proportional to H,and the classical formula for calculating the change rate is suitable;when the building height H is less than h,even in small outdoor wind speed,the natural ventilation in a courtyard can not be estimated by the formula mention above.The values of h are affected by many factors,such as the intensity of inner heat sources,the scales and configurations of the buildings,etc..In order to obtain the air exchange rate,an empirical formula is given by the regression of the numerical results.