Firstly, we are not a fan of evaporative cooling. We never have been, we have never installed one however we have pulled out hundreds. We are certainly not saying they are rubbish, and they are better than no cooling at all, however there is just no comparison when comparing it to refrigerated cooling.
RUNNING COST COMPARISON
Is evaporative cooling cheaper to run? Yes and no! On a warm day the evaporative systems work quite well. They cycle on and off and are most likely just cheaper to run than a refrigerated cooling system. On a mildly hot day the evaporative cooler will need to run 100% of the time, because once the air stops, the cooling effect stops immediately, whereas a refrigerated system will remove the heat energy from the house. You would normally have the doors and windows closed, which will maintain the temperature for a longer time and the system will not need to run 100% of the time (maybe cycling 50% of the time or at least run the inverter compressor at low speed). In hot and humid weather, the evaporative cooling wouldn’t cope. It would be running flat out and have no effect at all. Therefore, no matter how cheap it is to run now, it doesn’t work when you need it the most!
HOW IT WORKS
Heat is an energy and you cannot just make energy disappear. Both the evaporative and refrigerated systems deal with the heat energy in different ways. The evaporative cooling just changes the heat energy from one form of heat to another form – sensible heat to latent heat. “See Sensible and Latent Heat – what does it mean?”. It draws in warm dry air from outside by drawing it across wet media. The water evaporates off and some of the water uses up sensible heat energy, transforming it into latent heat. It hasn’t removed the heat energy, it has just changed the form of heat. So now the air temperature is lower, but the humidity is higher. If we plotted the wet bulb and dry bulb temperature of the air, before and after the wet fill, and plotted the measurements on a psychometric chart, we would see that the air has the same heat content, just in a different form. The evaporative cooler actuals adds heat energy to the air being blown into the house. The heat content of the air increases, as the heat from the fan motor is being transferred to this air passing over it, so it’s actually adding heat to the air. An evaporative cooler is more like a heater.
Relative humidity and how your body regulates its temperature
Your body is a natural evaporative cooler. You get hot and the pores on your skin open, allowing water to the surface for it to evaporate off and this cools your body. If the air is already saturated with moisture from the evaporative cooler, your natural cooling effect is reduced, and you become sticky and sweaty. Refrigerated air conditioning reduces the air below the dew point and removes moisture in cooling. With this drier air, your body’s natural evaporative cooling works better and cools you faster. With the drier air refrigerated cooling produces, compared to evaporative cooling, you can run it at a higher set point, using less energy and maintaining your comfort.
HIDDEN COSTS OF EVAPORATIVE COOLING
Wonderful, you just had evaporative cooling installed and now you’re told you will need to leave your doors and windows open for it to work. You install security screen doors and flyscreens because you can’t sleep, there’s another $3,000 – $5,000 you weren’t expecting to spend. Now you still can’t sleep because it’s too noisy, the cats next door are fighting, the possums are running around at night. Installing evaporative cooling wasn’t such a great idea – the house is cooler however now you can’t sleep due to the noise!
MOISTURE
Using evaporative cooling creates moisture in the air. Everything is damp and moist, the towels in the bathroom don’t dry, mould is forming on the ceilings of the bathroom, the tiled floor tiles are wet and slippery due to the moisture in the air becoming condensation on the floor.
DAMAGE TO GYPROCK CEILINGS
Running an evaporative cooling system can cause damage to gyprock ceilings. Yes, that‘s right! We don’t think we have removed an evaporative system where the ceilings have not been wavy or sagging, due to the high humidity caused by the evaporating cooling. The plaster gets damp and starts to sag. Unfortunately, the only way to repair these damaged ceilings are to replace them, another huge hidden cost.
HEAT LOSS
Evaporative coolers create massive heat loss through the duct and vents. There is a direct pathway to outside. Yes, some have shutters, however they are very leaky. You can buy covers for the vents but that’s just a further hidden cost. The ductwork for evaporative coolers is very thin and we often see older units with uninsulated duct. The amount of additional heating that is required when you install evaporative cooling in Canberra is high. We have had customers who have experienced an increase of 10-20% in running costs in their gas heating winter bill once they had evaporative cooling installed. The additional cost in heating far outweighs any savings the evaporative has, over refrigerated cooling. We would normally size a larger system for a house that is keeping the evaporative system to allow for the additional heat loss. Therefore, keeping your evaporative cooling after having reverse cycle installed would be crazy however it is your choice.
People say they like the fresh air of an evaporative cooler not realising you can run your air conditioner with a door or windows open however it is just less efficient.
