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Make use of air movement in passive cooling - page 3

Windows

The word window was derived from the Old Norse word vindauga meaning wind eye. This also describes the purpose of a window: to provide an opening for the wind to enter a home.

Not so long ago, louver-type windows and top-hinged windows were the norm in hot regions. Side-hinged windows, for example, could be angled towards the wind and were able to catch any air movement. Sadly, this is no longer the case, as mass-produced windows reduced the choice and the affordability of air-conditioning made breeze-friendly windows redundant. Today sliding windows are the most common window type in Australia. They are cheap to manufacture, but open only half of the paned area.

Despite the best intentions of placing windows on the windward side of your home, you still won’t have much air movement indoors if you don’t allow for cross ventilation. You need to have similar-sized windows on the building side facing away from the wind.

Envelope design

The wind beneath the wings of an aircraft creates high air pressure and keeps the craft afloat. This is only part of the story, as the area above the wing is more or less sheltered from the airflow and, therefore, lacks air - so to speak. The low pressure above the wing literally ‘sucks’ the aircraft upwards. In slow-moving aircraft, such as gliders, this ‘sucking’ effect can be as much as 2/3 of the total lift created.

Was has this to do with our home? I’m sure you can imagine that a building placed perpendicular to the wind direction must withstand a considerable amount of wind pressure on the upwind side (like underneath the wing), in particular multi-story or tall buildings. On the downwind side, or lee side as the mariners call it, there is also an area with low air pressure – just like above the wing. The pressure difference increases with wind speed and provides an excellent source for cross-ventilation.

Building a home with the long face towards the prevailing wind is a logical conclusion, but not always practical. You can, however, design a home with recesses and bays that create many high and low pressure areas. Fins or projections can be incorporated in the design to channel the breeze or to create pressure differences.

Ventilation can also be considered when deciding on the floorplan. Ideally, the building should have single depths rooms, but a better solution would be to plan the airflow in advance to create flow paths for the requirements of individual rooms.

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