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The potential application of Passive and Hybrid Downdraught Cooling to residential buildings is explored using an experimental facility constructed and tested in Seville, Spain. The experiment was devised as a prototype of the downdraught evaporative cooling system for the Nottingham University entry to the 2010 Solar Decathlon Europe competition.
The experiment shows that peak evaporative cooling is obtained with an airflow rate of 2000 m3/hour (about 25 air changes per hour) and an evaporation rate of 8 L/h of water. The resulting indoor temperature in the space can be from 1 to 2 degrees above the inlet temperature. Wind forces can improve the performance but are not reliable and the air supply inlet should therefore be baffled to prevent negative impacts.
Naturally driven evaporative cooling requires a control system which can vary the water supply rate in response to changing internal and external conditions. The use of exhaust fans can provide reliable performance, irrespective of external wind pressures, which suggests that a hybrid system (a combination of naturally and fan driven airflow) will be more robust in responding to variable conditions.