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Choosing a cooling system

Fans

Fans are the most energy efficient form of cooling. They are the cheapest to purchase, cheapest to run, operate quietly and are suitable for rooms of all sizes.

Portable and ceiling fans

Portable and ceiling fans produce a cooling effect by moving air over your warm body, helping to evaporate the moisture from your skin. Fans do not reduce actual room temperatures or humidity levels.

Considerations:

• Head clearance for ceiling fans should be 600-900 mm.
• When purchasing a portable fan, look for oscillating feature and variable speed control.
• Mount ceiling fans higher than existing light fittings to avoid flickering shadows, or install a unit with light attached.
• The fans should be reversible to assist with heating in the winter.

Whole house fans

Whole House Fans use moving air to create naturally cooling cross ventilation in rooms, while expelling hot air from the roof space.

A single fan unit is installed inside the roof space with a ceiling shutter immediately below. The fan creates a strong updraught, drawing fresh air in through windows.

Air from rooms flows through the house and rushes through the ceiling shutter into the roof space. It is then forced out via exhaust vents under pressure created by the fan.

Considerations:

• fan size is related to the cubic area of the home
• a minimum height of 900mm is required in the roof space
• system is located over a walk through area e.g. hallway or top of staircase.
• adequate roof exhaust vents required for high volume air flow
• a roof mounted canopy can house the fan if there is no roof space

Evaporative coolers

Evaporative coolers cool and filter the air. Hot outside air is drawn through a water-moistened filter and then blown through the house.

To work effectively, windows and/or doors must be left open so this moist air can be exhausted from the house. Evaporative coolers are generally more suitable for areas where humidity is low.

Types of evaporative coolers include portable units (suitable for small rooms up to 25m2), fixed room units located in an external wall/window (suitable open areas 30-50m2) and ducted central systems which are installed in the roof and suitable for whole home cooling.

Considerations:

• Site the unit on the side of the house which receives the prevailing hot winds. This avoids too much heat leaking in from the open windows and doors that exhaust the air.
• On high humidity days the highest fan speed should be used. If it is a very humid day, turn off the water supply to the cooler and run the fan only.
• Water consumption for evaporative coolers depends on the natural humidity of the day.
• Evaporative coolers do not work on a thermostat. They run for as long as you leave them on.
• During winter, ducted units on the roof should have covers placed over them and ceiling vents closed to stop excessive heat loss.

Refrigerated air conditioners

Refrigerated air conditioners remove heat from the air inside the home and transfer this heat outside. They cool, dehumidify and recirculate room air as a closed system (windows and doors must be shut). Reverse cycle models also provide heating.

Refrigerated air conditioners have the highest running and purchase costs, and are therefore best suited to very hot climates where other cooling options cannot provide the required comfort level.

Types of refrigerated air conditioners include portable units suitable for small rooms up to 20m2, window/wall units suitable for single room up to 50m2, split system units suitable for one or more rooms up to 60m2, and ducted split systems suitable for whole home cooling.

Considerations:

• Always look for energy rating labels on single phase domestic air conditioners - an energy efficient model will be cheaper to run than an energy inefficient model. The more stars you see, the more you'll save.
• Consider purchasing a system with inverter technology - which can significantly improve the air conditioner's efficiency.
• Rooms in which the air conditioner is being used should be closed off so the room air is recirculated eg windows and doors remain shut
• Whole house systems should be zoned to cool living and sleeping areas at different times
• Ductwork should be well insulated and sealed to prevent condensation
• If possible, locate window/wall units on the south side of the house. Shade the unit if it is exposed to full sun during the day (but don't restrict air flow over it).
• Set thermostats at 26-27ºC for summer cooling. Each degree you lower the thermostat may increase running costs by up to 15%.

Comparative costs

Cooling systems	Purchase/install cost	Running cost
Portable fan	Up to $100	< 1c/hour
Ceiling fan	$70 - $200	1c/hour
Portable evaporative cooler*	$200 - $400	1-3c/hour
Fixed evaporative cooler*	$1000 - $1300	4c/hour
Ducted evaporative cooler*	$2000 - $3000	8-12c/hour
Portable air conditioner	$800 - $3000	6-8c/hour
Window or wall mounted air conditioner	$500 - $3500	22-30c/hour
Split system air conditioner	$2000 - $5000	20-28c/hour
Ducted air conditioner	$5000+	40-60c/hour $1 hour (150m2)

*evaporative air coolers are not recommended for use east of the dividing range due to the high humidity

What size air conditioner should I buy?

Getting the size right is important. An oversized air conditioner will result in over cooling and frequently turning the system on and off to compensate for this will wear it out. One that is too small won't be able to cool the area.

Air conditioners are measured according to their heating or cooling output capacity (in kilowatts - kW). That is the amount of heating/cooling that will be moved into the room. This is expressed as kW capacity. Some suppliers express output as BTU (British Thermal Units) - this is an old measurement.

As a guide:

• a home with no insulation requires approximately 140w/m2 (0.140kW/m2)
• a home with ceiling insulation requires 100w/m2 (0.100kW/m2)
• a fully insulated house requires 70-80w/m2 (0.07-0.08kW/m2)
  

The following table contains the required cooling outputs for rooms of various sizes (to be used as a guide only):

	20m2	30m2	40m2	50m2	60m2
No insulation	2.8kW	4.2kW	5.6kW	7.0kW	8.4kW
Celing insulation	2.0kW	3.0kW	4.0kW	5.0kW	6.0kW
Fully insulated	1.6kW	2.4kW	3.2kW	4.0kW	4.8kW

Homes that are insulated require air conditioners with lower heating/cooling outputs because they can trap the cool/warm air - in summer an insulated home will not get as hot as an uninsulated house.

Ceiling height is not as important so the figures above are based on heat flow rates through walls, ceilings, roofs and floors. However, ceiling sweep fans will help move warm/cool air back down to floor level in rooms with very high ceilings (eg cathedral ceilings).