When asking the question of “Does evaporative cooling work?”, It’s important that the big picture is known.
There is no doubt, that evaporative cooling can be a cheap way to cool your home, but in Melbourne and other climates around Australia, there can be some serious drawbacks that are very costly. These disadvantages, are 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 the removal of 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 the main cities around Australia (regional office stations), out of 8760 hours in a year the table below shows you 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 to most other cities in Australia with lower humidity, so 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 and truly made up for with a less efficient home for heating. Hot air rises, and evaporative cooling vents are usually in the ceiling in each room. As an 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 that goes against 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.
If you take the draught effect side of things out of the equation and you cover up your registers every season, you are still left with areas on your ceiling which are uninsulated for heating during winter. It’s important 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 which need to be considered in the operation of the system.
If you already have an evaporative cooler, or you still want to go down this path, here are some things to think about.
Things to Look out for:
- 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. It can damage your evaporative coolers electric motor.
- Make sure the ducting that is 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.
There are some simple things you can do, without replacing your whole system.
For more information visit this article from the business spectator.