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Evaporative Cooling

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Potential Savings*
10 Year $ Savings:
up to $1,000
10 Year CO2 Savings:
up to 15,314 kg (equal to driving a car 102,100 km)1
Cooling Power:
strong – provides a powerful cooling effect in dry heat, but can’t operate in humid heat
Suitable Climates:
places with dry heat (eg VIC, ACT, inland NSW and SA). They shouldn’t be used in areas of high humidity or where severe water shortages exist.
*Savings are based on examples used in this article.

Evaporative coolers use water to provide cooling. The cooling unit draws warm air from outside and passes it over a number of water-soaked “cooling pads”. The pads absorb the heat, which in turn evaporates the water in the pads. The evaporated air is cool (similar to a sea breeze), and is blown into the room.

If you need the sort of cooling power that an air conditioner can provide, then evaporative cooling is your only real alternative. They are capable of delivering comfortable indoor temperatures of around 23 to 27°C, even if outdoor temperatures are nearing the 40°C mark. However they can only do this in areas with low humidity (around 30-40% humidity), such as inland areas. That’s because evaporative coolers actually add humidity to a room.

Types of Evaporative Coolers

Ducted and portable evaporative cooling

Rooftop ducted evaporative cooling unit (left) and a portable evaporative cooler (right)

Evaporative Coolers come in both portable and ducted versions. You can use a portable evaporative cooler to cool a single room (up to around 20 m2), but you’ll probably need a ducted system if you want to cool a large home.

When using portable evaporative coolers, you’ll need to manually fill the system with water. Ducted systems on the other hand are connected to your water supply, and so will automatically fill up water when required.

Financial and Environmental Savings

Here’s how evaporative cooling stacks up against a number of other cooling systems both financially and environmentally.

Cooling an Individual Room (an area of 20 m2)

Portable evaporative coolers almost match ceiling fans for cost-effectiveness and CO2 emissions. Unlike ceiling fans, they’re portable, need no installation, and can deliver a far greater cooling effect.

Compared to air conditioners, portable evaporative coolers could save you close to $1,000 over 10 years, along with 2.3 tonnes of CO2 emissions (equivalent to driving a car 15,400 km)1. Best of all they can almost match air conditioners in the level of cooling comfort they can provide.

Portable
Evaporative
Cooler
Air Conditioner
(reverse cycle)
Savings
Cost Installed $346 $815** $469
Annual Energy Cost $10 $63 $53
10 Year Total Cost $450 $1,450 $1,000
10 Year CO2 Emissions 454 kg 2,767 kg 2,313 kg
Figures based on 560 hours of cooling per year and an average electricity price of 21.9c per kw/h. Air conditioning unit compared was a 2.5KW reverse cycle unit with an EER of 4.82, and portable evaporative cooler was a 14L size, capable of cooling up to 20 sqm. Calculations assume 125KW of cooling per m2.

Cooling an Entire Home (an area of 100 m2)

A ducted evaporative cooling system costs a lot upfront to install – around $6,600 in our example for a high quality system with water saving technology. However our calculations showed that over 10 years you could end up around $1,600 ahead compared to a reverse-cycle ducted air conditioner or a ducted cooling unit added to a gas heating system.

A ducted evaporative cooling system hardly produces any carbon emissions. Over 10 years, you can expect to save around 15.3 tonnes of CO2 compared to a ducted air conditioner. That’s the equivalent of driving a car 102,100 km1!

Despite its low carbon emissions, ducted evaporative cooling uses a lot of water, which slightly reduces its appeal. Ducted systems frequently “dump” used water to prevent a build up of salt in the system, and therefore need constant refilling. Some new systems have significantly reduced water consumption (below 20 litres per hour), however many systems still use anywhere between 40 litres and 116 litres per hour depending on the house size, according to one study2. A system using 40 litres per hour would use more than 22,000 litres per year – the equivalent of a person’s showers for 10 months!3

Ducted
Evaporative
Cooling
Ducted
Air Con /
Add-On Cooling^
Savings
Cost Installed $7,415 $5,150** -$2,265
Annual Energy Cost $125 $477 $352
Annual Water Cost $54 $0 -$54
10 Year Total Cost $9,208 $9,917 $709
10 Year CO2 Emissions 5,462 kg 20,776 kg 15,314 kg
Figures based on 560 hours of cooling per year, an average electricity price of 21.9c per kw/h, an average water price of $2.31 per KL, and average water use of 40 litres per hour. Air conditioning unit compared was a 12.5KW ducted reverse cycle unit with an EER of 3.21, and evaporative cooling was a 12.6KW ducted unit. Calculations assume 125kw of cooling per m2.

Our Recommendation

If you live in a place with dry heat, and you need more than fans to keep you cool, then evaporative cooling is the way to go.

Whether you’re cooling a room or a home, think about portable evaporative coolers first – they use far less water than ducted systems, they require no installation, and they can be moved around the house. If you’re cooling multiple rooms you could just buy a number of portable units and keep them in different rooms. You’ll save a lot more money and a lot more water compared to a ducted unit.

If you need a ducted cooling solution, then we strongly recommend evaporative cooling over air conditioning, due to its lower running costs and lower CO2 emissions. If you’ve already got ducted gas heating, you can also install ducted evaporative cooling along with it – you can also use the same controller for both. This means you’ll have the lowest cost and lowest polluting ducted heating and cooling technologies in your home.

If you live in an area with water shortages, please don’t use ducted evaporative cooling, as it’ll worsen the water shortage. If you’re concerned about how much water you’re using, install a rainwater tank on your property to help offset your system’s water use. We’d also recommend zoning your ducted system so that only those areas that need cooling get it, saving you power and water.

 

1. Based on a car emitting 150 g of CO2 per km.
2. UniSA Institute for Sustainable Systems and Technologies, Technical Background Research on Evaporative Air Conditioners and Feasibility of Rating their Water Consumption, September 2009.
3. Based on one 10-minute shower per day using a 3-star rated showerhead with a flow rate of 7L/min.
** Represents 50% of the upfront cost of a reverse cycle air conditioner. The other 50% has been allocated to heating the room in winter.
^ Upfront costs, energy costs and CO2 emissions for add-on cooling are very similar to those for reverse cycle air conditioning, so these have been grouped together in this table.


© 2018 Start Sustainable Pty Ltd.