Be ‘eco’ cool and keep your cool
You don’t have to use much energy to keep your home cool through the hot months. Colleen Hawkes reports.
Hotter summers, cooler winters – we all know what climate change is doing, so it makes sense to consider sustainable options to keep the house cool over the summer.
Stuff talked to the Energy Efficiency and Conservation Authority (EECA) and architect Wulf Borrmeister of Christchurch, a specialist in sustainable design, about the best ways to ensure summer comfort.
And cross ventilation is at the top of the list. Opening doors and windows on opposite sides of the house will create a cooling draught – you can fit security latches so windows can remain open.
Borrmeister likes to take this one step further when designing houses, by providing high louvre windows on one side. ‘‘Because heat rises, it pays to have windows open at the top of the house to let hot air escape,’’ the architect says.
‘‘This creates a stack effect, pulling cool air into the house down low and releasing hot air up high.’’
But, ideally, it pays to reduce solar gain in the first place by keeping out the sun.
‘‘Properly designed roof overhangs, external shutters and window screens – movable or fixed – pergolas and awnings can be placed where they’ll block the most sun from windows and walls during the hottest parts of the day,’’ says Borrmeister.
EECA also recommends closing blinds and curtains to block out the sun’s direct rays.
Planting deciduous trees on the north and west sides of your home is another way to provide shade in summer.
The trees will lose their leaves in winter and allow sunlight through.
You can also use trellises for growing plants to shade your windows in summer.
Turning off unnecessary electrical appliances will reduce a home’s heat load. You can’t turn off the fridge, but opening a window nearby will help. You could also consider cooking on the barbecue to keep the heat outdoors.
Cotton bed linen rather than sheets with a polyester-cotton mix will help you sleep better at night. The same goes for clothing – natural fibres will keep you cooler.
Low-cost ways to cool
Fans are much cheaper to run than air conditioning, and there is truth in the hack from eco adviser Nelson Lebo, who advises placing a fan near a window facing outside to help speed up cross ventilation. You need a window or door open on the opposite side of the house, so the fan can pull the air through.
Heat pumps are another energy-efficient alternative, although EECA says they cost about the same to cool the house as they do to heat it – about 10 cents per kWh of heat released. This may be the only option for families who have homes with no eaves and west-facing children’s bedrooms.
EECA has the following suggestions:
■ Try using just the ‘‘fan only’’ setting, which helps you feel cooler by creating a breeze. This setting uses a lot less electricity than the full cooling mode. Keep your windows open while using the ‘‘fan only’’ mode.
■ Use the dehumidifying mode, if it’s the humidity rather than the temperature that’s the problem.
This mode uses less electricity than the full cooling mode. Shut your doors and windows in the rooms you’re dehumidifying.
■ Use cooling mode only on really hot days when the other methods aren’t enough. Close all your doors and windows in the rooms you’re cooling. It’s best to cool only one room as this is what most heat pumps/air conditioners are sized for. Set the thermostat to around 22 degrees Celsius. The room won’t cool down any quicker if you set it lower, but you are likely to use more electricity by overcooling.
■ Avoid using auto settings – if you forget to switch the unit off, it will start heating if the temperature drops below the thermostat setting.
■ Clean the filter of your air conditioner or heat pump regularly, following the manufacturer’s instructions.
Plan from the outset
The better insulated your home is, the cooler it will be in summer. Borrmeister says the time to think about comfort levels is at the outset if you are planning a new build or renovation. That includes window and door joinery, and double glazing as well as insulation and external shading.
‘‘These are often the aspects of your home that you cannot see, but that in the long term can contribute to significant cost savings in running your home and the overall health of your home.’’
Architect Evan Mayo of Hamilton says his practice likes to design for passive cooling alternatives and prefers to incorporate high and low windows. ‘‘We are using more screens and battens to create shade over windows and outdoor living areas. Even in my own home, we prefer not to rely on a heat pump.’’
Borrmeister suggests if you are serious about passive cooling and heating, you might like to build a certified passive house, which maintains a standard temperature all year round, or aim for a 6 Homestar (or higher) rating from the New Zealand Green Building Council.
The Superhome Movement can also help with advice on building healthy, energy-efficient homes.