Very little energy is needed to make a well-designed house comfortable. Appropriate insulation, which is essential for a comfortable house, combined with passive solar design and a draught-proofed building, can create low or even no energy requirements for heating and cooling.
Even for existing homes there are many ways to reduce energy bills, improve comfort and help the environment.
Passive design principles can increase comfort and reduce the need for cooling, by insulating your home and shading windows from summer sun. However, many existing homes do not include good design features, and climate change is bringing higher night-time temperatures, so cooling equipment may be needed at times.
Ask yourself the question
The better insulated, shaded and draught-proofed a house is, the smaller (and cheaper to buy and run) the cooling unit needed, and the less often it needs to run.
When choosing a cooling system, ask yourself a few questions. Does the air require cooling or will creating a cooling breeze be enough? How big an area needs to be cooled? How often and for how long is cooling needed?
The three major methods of mechanical cooling are fans, evaporative coolers and air-conditioners.
Fans should be the first choice for mechanical cooling and, with good design and insulation, they can often supply adequate cooling for acclimatised residents in all Australian climates. They circulate air but do not reduce temperature or humidity. Typically, the air flow created by a fan provides a similar improvement to comfort as reducing the temperature by around 3°C.
Choose fans for lowest greenhouse impact
Fans are the cheapest cooling option to run and have the lowest greenhouse impact.
Fans have a wide variation in efficiency: a Choice test showed ceiling fans used from 54W to over 100W. Check power consumption before buying and make significant savings in long periods of operation.
Your second choice for mechanical cooling should be evaporative coolers, except in humid regions. Evaporative coolers work best in climates with low humidity as the air has greater potential to absorb water vapour. They are significantly less effective in climates with high humidity.
Some doors and windows must be open for evaporative cooling to allow hot air to escape from the house. Smaller and older units do not use a thermostat, just a fan speed control. Newer, whole-house systems can be fitted with electronic thermostats and timers.
Operating costs can be low as only the fan and a small water pump use energy. However, many units have inefficient fans and fan motors that consume more energy than necessary. Some modern evaporative coolers use far less energy than older models: check with manufacturers.
Watch those power bills
Evaporative coolers can increase heating bills and allow a house to heat up faster when not operating, because large volumes of air can be sucked out of the house through the evaporative unit. Many modern units have automatic seals when not in use. Otherwise, close off ducts and cover the roof unit in winter to reduce heat losses.
An indirect benefit of an evaporative cooler is that it tends to pressurise the house, keeping out bugs and dust.
If thermal comfort cannot be achieved with passive design, fans or evaporative cooling, consider air-conditioning. Air-conditioning can give a higher degree of comfort in any climate. However, it consumes more energy and creates more greenhouse gases.
For efficient air-conditioning, the house or room should be sealed and highly insulated with bulk and reflective insulation. Windows must also be shaded from the summer sun.
Purchase costs vary depending on the size and type of air-conditioner, and efficiency varies widely between units and models. Systems using inverter technology and advanced design can show energy savings of up to 40% over standard units.
Air conditioners are available as portable, wall, window, split and ducted systems. Fixed systems need to be installed by a licensed refrigeration mechanic/electrician.
An alternative is solar air cooling, which works by using a fan or ventilator to extract hot air from the roof space and replacing it with ambient air, to minimise heat transfer to the ceiling space below. The effectiveness of removing hot air from the roof space is very sensitive to roof colour and presence of reflective foil under the roofing, for example, a dark (or unpainted steel) roof absorbs an enormous amount of heat.