Natural Ventilation & Cooling

In commercial mechanical cooling systems there is a system of free cooling where colder fresh air from outside is mixed with air returning from the interior to the system to drop the temperature naturally rather than using energy to do the job. It is possible to do this in our homes when the temperature is lower outside than in – if the window and door openings have been located to take advantage of the seasonal and daily airflows and the layout has been organised to allow cross and through ventilation with natural breeze pathways.

One of the keys to feeling benefit from natural ventilation is the speed of airflow. Air needs to be flowing at a reasonable speed for it to induce evaporation from our skin – the method by which our bodies cool themselves – and this needs to be understood to achieve the desired result. Simply opening up all our windows may not provide sufficient air speed to convince us that it has any cooling effect. Speed is needed and is induced by reducing the opening size towards the wind and increasing the opening size away from the wind. The reduced wind pressure on the lee side of the house causes a slight vacuum  – sucking the air out of the house and the required replacement air, having to force its way through small openings, will have to speed up to make up the shortfall. This high speed air movement then convinces us, by inducing evaporation, that we are being cooled naturally without the need for mechanical cooling.

This is the same process we employ when we switch on ceiling fans and cool using much less energy than required for refrigeration systems.

Whilst this may not provide sufficient cooling on very hot days it can reduce the time that home owners feel the need to use energy through mechanical cooling to stay comfortable.