Passive cooling by natural ventilation, salt bath modelling of combined wind and buoyancy forces.

We examine conditions under which the natural forces of wind and buoyancy may beharnessed in order to provide ventilation for cooling. Steady-state, displacement flows drivenby combined buoyancy and wind forces are simulated at small scale in the laboratory using aPerspex box to represent a generic room or single-spaced building. Density differencesnecessary to simulate the stack effect are produced using fresh and salt water solutions. Windflow is simulated by placing the box in a flume tank; the flume produces a flow of water pastthe box and this flow is used to represent the wind. By measuring salinity and the position ofthe stratification within the box, equivalent temperature profiles and ventilation flow rates innaturally ventilated buildings are deduced.Results of these experiments are compared with the predictions of a theoretical model.It is shown that if ventilation openings are located so the wind assists the stack-driven flowthe ventilation may be significantly enhanced and passive cooling achieved. The coolingcapacity of the ventilation system is shown to depend upon the relative magnitudes of thewind and buoyancy produced velocities, the area of the openings and the height of the space.It is shown that by harnessing the wind to assist the buoyancy-driven flow it is possible toi) reduce the temperature of the warm upper layer, ii) increase the depth of the lower layer atambient temperature and iii) increase the ventilation flow rate.