Evaporative cooling

Evaporative coolers draw hot air from outside through a series of wet filter pads that are supplied with water from a tank at the base of the unit. Water from the filter pads evaporates, drawing heat out of the air and humidifying it. The cooled, moist air is then blown through the house.

Evaporative coolers work partly by cooling the air inside the house and partly by creating a cooling breeze. To work effectively, evaporative coolers need favourable external conditions and some windows and internal doors need to be left open so the cooled moist air can be exhausted from the house.

As evaporative coolers are an open system, they provide a continuous supply of fresh cool air through the home when in use, but unless conditions are favourable this open system comes with some negatives. Evaporative coolers can draw external pollutants such as smoke, dust and pollens into the home rendering them useless on bushfire, controlled burn, or high pollen-count days.

Ducted evaporative systems also require additional maintenance to weatherise them for winter to avoid hot air rising through the ceiling vents and ducts and leaving through the cooling unit on the roof.

Types of evaporative coolers

Ducted evaporative coolers are the type with a cooling unit located on the roof and ductwork carrying cooled air throughout the home to outlets in the ceiling. They are available in both standard and inverter models. Inverter models have a variable speed (or inverter-driven) motor, resulting in lower running costs.

Window/wall mounted, and portable evaporative coolers are available to cool small rooms or to provide spot cooling. These systems are cheap to buy but provide limited cooling potential and can be more expensive to run.

Ideal conditions

The efficiency and effectiveness of evaporative cooling systems can vary greatly depending on outdoor weather conditions. As the cooling effect of evaporative systems relies on evaporating moisture from the wet filter pad, they are limited by how much they can cool the air entering your home and will not work effectively in humid or extreme heat conditions. They work best in hot dry conditions.

If the outside air is humid, the cooling effect of the unit is limited because the water will not evaporate as easily from the pads. As a guide, Melbourne's average humidity on a summer afternoon is between 40 and 50%, while in Mildura it's between 20 and 30%. Both areas can use evaporative coolers, although they are more effective in Mildura's drier climate.

Running costs

Evaporative coolers use both electricity and water. Actual running costs will depend on the cooling capacity of the unit and the fan speed that you choose. Evaporative coolers are not subject to efficiency labelling requirements making it difficult to compare models.

Water consumption

Evaporative coolers use both electricity and water. How much water is used depends on the size of the unit, the humidity of the day, and the fan speed that the unit is set to operate on.

Ducted evaporative coolers must refresh their water supply otherwise it can become too salty, and a range of water management systems are used by different brands/models. If you are purchasing a ducted evaporative cooler, ask about the water management system used and what the typical hourly water consumption is likely to be in your area. If you have solar on your home, the water costs associated with evaporative cooling will likely out way any energy costs, making a refregerative cooling system more favourable.

Sizing

Sizing guidelines for evaporative coolers are based on airflow and the volume of the area to be cooled. It is important to seek an accurate sizing quote from a local retailer or installer who will also consider your local humidity levels.

Choose energy-efficient cooling

When selecting the right evaporative cooling system for your home, it is important to compare different models as efficiency can vary greatly. Evaporative systems aren’t subject to labelling requirements so speak to your installer about the benefit of different models.