in Greener Homes on 14 November 2010
Fans and ventilation will take the heat out of your bills.
Our electricity consumption spikes on hot summer days. But with utility bills soaring and climate change pressing, it’s time to turn off the air conditioner. There are cheaper ways to keep your home cool.
Andreas Sederof, from sustainable housing design firm Sunpower Design, says carefully planned cross-ventilation is a vital part of a well functioning home. It’ll help you harness each cool change on a stifling day and every fresh breeze in the evening.
If you’re planning to build or renovate, Mr Sederof’s first tip is that all windows are not equal. “To be effective, your windows must be sufficiently openable,” he says.
For example, awning windows, which hinge at the top, don’t allow as much breeze as casement windows, which hinge at the side like a door.
“Casements expose the whole opening of the window to ventilation,” he says. “In Melbourne, most cool changes come from the south and southwest. You can get the windows to act like chutes for the cooling breezes to enter the house.”
Mr Sederof’s second principle is to give the wind a free run of your home. “The building’s spaces should be organised in such a way that it allows cross-flow ventilation. It’s best to have the ventilating doors and windows opposite one another – like a good aerodynamicist, you need the air flow to be as unrestricted as possible,” he says.
According to Sustainability Victoria’s Air Movement guide, providing an outlet for the wind, as well as an inlet, creates wind speeds up to eleven times greater than only opening an inlet window. Larger outlet spaces to the north allow a greater volume of air to enter from the south.
Even if the southerly change hasn’t yet arrived, you can still passively cool your home each evening by venting the day’s heat.
“In summertime we often get still, clammy nights,” Mr Sederof says. “That’s when openable roof glazing, highlight windows or thermal chimneys can be very effective. Hot air rises, so it’s easy to evacuate. Cooling towers like those have been around for centuries in the Middle-East.”
When you open both a low window and a roof window (once the temperature has fallen outside) hot air will flow out and cooler air will enter. “If you’ve got low windows opposite small fern gardens or vegetation, you’ll replace that hot air with slightly colder air from the plants’ transpiration,” he says.
Ceiling or roof-mounted exhaust fans work on the same principle as high windows. They’ll extract hotter air from high in the room and draw fresh air through open windows. They can be either powered or passively operated. Make sure you choose models that have covers or dampers, or seal automatically if they’re not being used, so you don’t lose warmth in winter.
If your home doesn’t have good cross-ventilation, and you can’t retrofit it, ceiling fans are the next best bet. In hot weather, fans can make you feel a few degrees cooler. Mr Sederof recommends one fan for every 10 to 12 square metres.
“Fans rely on evaporative cooling. The air moving over your skin is what makes you feel cool,” he says. “But you have to buy decent quality ones – if you’re spending less than $200, they’re probably not good enough.”