Does evaporative cooling work?
When asking the question “Does evaporative cooling work?”, it’s essential to consider the big picture.
Thermal imaging of evaporative coolers in winter reveals valuable heat escaping from the evaporative cooler unit on the roof.
There is no doubt that evaporative cooling can be a cost-effective way to cool your home, but in Melbourne and other climates around Australia, there can be some serious drawbacks that are costly. These disadvantages are often not considered before an evaporative cooler is installed or sold to a consumer interested in keeping cool during summer.
Evaporative coolers can contribute to an additional 20-40% extra air leakage in a home. With the use of blower door testing, we have found that removing an evaporative cooling system with a mechanical damper can contribute to around 20% of the air leakage in a home, which is a massive overhead in winter for heating.
Based on the RMY (Reference Meteorological Year) weather file for major cities around Australia (regional office stations), out of 8760 hours in a year, the table below shows how many times a year heating or cooling could be needed:
Country the amount of hours with temperatures BELOW 10C the amount of hours with temperatures ABOVE 30C
Melbourne 1336 176
Sydney 331 68
Canberra 3192 109
Hobart 3609 17
Adelaide 1021 484
Geelong 2342 155
Woolongong 583 44
Bendigo 3609 109
Brisbane 342 66
Perth 743 471
CSIRO provided the number of hours in the different cities around Australia of temperatures below 10 °C and hours above 30 °C
Perth has a different ratio compared to most other cities in Australia, with lower humidity. Therefore, moving towards an airtight building envelope as opposed to continuous ventilation could be argued as being less beneficial.
Looking at the big picture of heating and cooling, what money you save from cheap cooling is well spent on a less efficient home for heating. Hot air rises, and evaporative cooling vents are usually located in the ceiling in each room. For example, have you ever noticed in summer that the top floor of a double-story home gets hot, and the bottom floor stays cold? In winter, an evaporative cooler produces the same effect but worse because that heat goes outside.
The other problem with evaporative cooling is how many of those limited hot hours above 30°C have high humidity. Evaporative cooling does not work very well with high moisture content in the air.
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f you take the draught effect out of the equation and cover up your registers every season, you are still left with areas on your ceiling that are uninsulated for heating during winter. It’s essential to clean your evaporative cooler professionally every year, which is another cost of using this technology. These issues will never go away, and they are additional costs that need to be considered in the operation of the system.
If you already have an evaporative cooler or still want to consider this option, here are some things to think about:
- Make sure the damper has rubber gaskets, but also ask them to show you the system.
- Ensure the vent outlets from the evaporative cooler are easy to close airtight. Also, be wary that it’s not a good idea to start the evaporative cooler if all your outlets are taped up or closed off, as it can damage your evaporative coolers’ electric motor.
- Make sure the ducting used in your install is insulated.
- Don’t forget you need to service the evaporative cooler yearly.
If you already have an evaporative cooler, cover up the vent registers with contact every winter or shop around because there are some great covers out there to reduce draught effect through these systems.
Have a look at our piece on improving your ducted heating energy efficiency too! There are some simple things you can do, without replacing your whole system.
For more information visit this article from the business spectator.
