Natural air conditioner

Our tips for keeping your home cool this summer, using insulation and natural ventilation.
 
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01 .Introduction

Small fan

There's a number of ways ýou can keep your home cool during the hotter months. But preventing your house from getting too hot should be your first priority. Make sure it's properly insulated, draught-proof, shaded and ventilated. If you're renovating your home, or building a new house, consider designing it as energy-efficiently as possible. 

What's actually feasible to cool your existing home depends on several factors:

  • Are you living in a unit or renting your home? If so, you may not be able to make structural changes or install certain appliances; in this case a portable air conditioner may be what you are looking for.
  • Even if you're living in your own house, your choice may be limited — by the block's orientation or size for example.
  • How much are you willing to spend on a cool home? While some preventive measures, such as installing insulation, can lower your energy bill and pay for themselves in the long run, you may not be able to afford the upfront cost. Cooling appliances, on the other hand, always cost extra money: you need to buy them, in some cases have them installed, and pay running costs. So is your comfort worth an air conditioner or will a fan do?
  • What climate are you living in? An evaporative air cooler won't work well in humid conditions for example. A refrigerative air conditioner will, but you won't need a reverse-cycle model if your winters aren't cold enough for heating.

What do you need? 

Our decision guide helps you to find out what's most appropriate for your situation.

Warm House Coll House book

You can also find out more about keeping your home at a comfortable temperature using energy-efficient strategies in the CHOICE book, Warm House, Cool House

 
 

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02.Preventing heat gains

 

Heat always tries to move from warmer to colder areas - for example, in summer from the hot outside of your home to the cooler inside. By limiting the amount of heat that enters your home you may be able to get by without a cooling appliance. As well as making your home more comfortable to live in, this will keep your energy bill down.

Energy-efficient house design

  • If you're building or extensively renovating a house, the right design and materials can take advantage of the sun and prevailing winds to help regulate indoor temperatures. Ideally, the house will prevent or remove excessive heat gains in summer, while admitting and storing the sun's energy in winter.
  • The house should be elongated, with one of the long sides facing north.
  • Room temperatures will vary depending on how much they're exposed to sun and wind. For example, north-facing rooms will be the warmest rooms in winter and can get hot in summer. In most parts of Australia, living areas should face north (to take as much advantage as possible of the winter sun), bedrooms and studies east or west, and service rooms (such as the laundry) south.
  • Brick walls and a concrete floor slab can even out the temperature in north-facing rooms in summer, and store the sun's energy in winter to warm the house in the evening.
  • North-facing windows should be large; east, west and south-facing windows small.
  • Windows and doors should be aligned to allow cooling summer-evening breezes to flow through the house (cross-ventilation). Small windows in opposite walls are better than large windows in just one.

Insulation

  • Insulated ceilings and walls reduce the heat flow between the outside and the inside of your home, keeping it warmer in winter and cooler in summer.
  • In summer, up to 35% of the heat in your house enters through an uninsulated ceiling, while 15% to 25% gets in through uninsulated walls.
  • Insulating the ceiling should be the number one priority for every house owner. However, to make the most of insulation in summer, it's essential you provide shading for east, north and west-facing windows. If you don't and the interior does heat up, the heat can't escape easily because of the insulation (the so-called oven effect). Your house may stay hot for a long time, even if outside temperatures drop.
  • Draught-proofing your home will also help keep the summer heat out. For example, close off unused pet doors and fireplaces, and seal windows with insulation strips.
  • See our insulation buying guide.

Shading

  • External shading (such as trees or bushes, eaves, awnings or shutters) is more efficient than internal (such as blinds or curtains) for preventing heat gains.
  • Shade all east, north and west-facing windows in summer, especially if your house is insulated.
  • While you should shade north-facing windows in summer, make sure they let in the winter sun. Deciduous trees are one way of achieving this: while their canopy provides shade in summer, they lose their leaves in winter. Artificial shading such as eaves, pergolas or adjustable blinds and shutters can do the same job.
  • East and west-facing windows should be shaded by vertical blinds or shutters, because eaves or pergolas won't block out the low morning and afternoon sun.

Ventilation

  • Air moving through your home will increase the evaporation of perspiration, making you feel cooler.
  • While you can use various appliances to create an artificial breeze, the right house design can take advantage of natural breezes.
  • Keep your windows shut during the day when it's hot, but open them in the evening once it's started to cool down.
  • Trees and bushes can help channel breezes towards your house.

03.Cooling appliances

 

Fans

Fans are cheaper to run and buy than evaporative coolers and air conditioners. However, they don't reduce the room's temperature, but influence how warm your skin feels: the air movement created by a fan increases the evaporation of perspiration, which makes you feel cooler.

  • Desk and pedestal fans can be plugged into normal power points. They're portable and - depending on the size - direct the air around either a person or a room. Prices start at less than $20.
  • Ceiling fans cost from about $60 (though are typically priced about $200 and up) and usually have to be installed by an electrician. They can improve the comfort of a room.

Evaporative coolers

These devices cool by evaporating water. A fan draws warm air from the outside through a series of wet filter pads. The air's heat evaporates the water, cooling and humidifying the air, which is then blown into the house. It's important to ensure good ventilation so the humid air doesn't accumulate inside.

The higher the outside humidity, the less efficiently evaporative coolers work, as the humid air from outside won't be able to evaporate much more water from the filter pads.

Size doesn't really matter. Of course, a larger, more powerful air cooler will have a stronger air flow and be able to blow cool air over a larger area; but essentially they don’t need to be matched to the size of the area like refrigerative air conditioners do.

Unlike air conditioners, you don’t have to seal the room or house. In fact, you need to keep a couple of windows or a window and door open because the cooler needs this air flow: it sits in front of an open window or external door and draws the outside air through it.

Don’t place the cooler in the middle of a room because it’ll just recycle its own moist air, adding more and more moisture. And make sure there aren’t any curtains close enough to be sucked into the unit.

They're cheap to run, but don't have a thermostat.

  • portable model plugs into a normal power point and is best placed close to an open window. Its water tank must be kept filled (as a rough guide, they use up to 4 L per hour). Look for a model with a water-level gauge, variable fan speed and adjustable louvres. Expect to pay from around $100.
  • A window-wall model is usually fitted into an external wall or window, and permanently connected to your power and water supply. Prices start at about $1000.
  • ducted system is permanently installed (usually in the roof) and ducted to ceiling outlets throughout the house. It uses about 25 L of water per hour, so may not be the right choice if your water supply is limited. A ducted system will cost from around $2000.

Note that evaporative coolers can only cool; they can't be made reverse-cycle like a refrigerative air conditioner.

Refrigerative air conditioners

Similar to fridges, refrigerative air conditioners pump heat from the hot inside of your home to the outside - that's why they're also called heat pumps.

They're very efficient, work in any climate, and are particularly useful in humid conditions, as they also dehumidify the air. Reverse-cycle models can also heat your home, because even cold winter air contains usable heat that can be pumped into your home.

Before you buy an air conditioner, it's important to know the size you need. As a rough estimate, you'll need a cooling capacity (or output) of about 125 watts per square metre for a living area, and about 80 watts per square metre for a bedroom. However, the ideal size depends on many factors, such as the climate where you live, your home's insulation and how well it's sealed, and the shape and orientation of the room.

Air conditioners are more expensive to run than fans and evaporative coolers. Domestic models carry an energy rating label: look for one with as many stars as possible - it'll save on your energy bill, and helps to protect the environment.

Also remember that each degree cooler you want your home in summer can increase the running costs by up to 15%.

Try to shade your air conditioner - for example, by providing an awning - without restricting its airflow. When you're expecting a hot day, turn it on early rather than wait until your home gets hot.

  • portable model can cool a room of up to about 20 square metres. It can be plugged into a normal power point. Expect to pay around $500 to $1300.
  • A window-wall model is usually installed in a window or external wall, and can cool rooms and open-plan areas of up to 50 square metres. While smaller units can be plugged into a normal power point, larger ones may require additional wiring. Prices start from under $500.
  • split-system air conditioner consists of a compressor unit that's installed outside, and one or more indoor air outlets. They're usually used to cool one or more rooms, or an open-plan area, of up to 60 square metres. Prices start from under $1000.
  • ducted system is usually installed in the roof or outside on the ground, and ducted to air outlets throughout the house. Costs start from around $5000.

Getting cool, staying cool

Preventing your house from getting too hot should be your first priority. Make sure it's properly insulated, draught-proof, shaded and ventilated. If you're renovating your home, or building a new house, consider designing it as energy efficiently as possible.

Q1: Are you uncomfortable for more than just a few days during summer?

No: No action required.
Yes: If you've taken all the preventive measures you can and your home is still getting too hot, you may need a cooling appliance. Go to Question 2.

Q2: How big is the area you want to cool?

Personal space: Consider a portable fan
Room: Go to Question 3.
House: Go to Question 4.

Q3: (Single room) In what type of climate do you live?

Humid: Consider a ceiling fan or a pedestal fan. If that doesn't seem sufficient, a portable, window, split-system refrigerative air conditioner may be for you.
Dry: Consider a portable or fixed room evaporative air cooler.

Q4: (Entire house) In what type of climate do you live?

Humid: Consider a ducted refrigerative air conditioner.
Dry: Consider a ducted evaporative air cooler.

05.Cooling calculator

 

If you've decided you need an air conditioner to cool your home, this calculator will help estimate the required capacity of a room or split-system air conditioner. It is not relevant for ducted systems.

This tool is adapted from CSIRO's publication Room heaters and coolers - choosing the best size (by permission CSIRO Australia).