The fact that there seem to be many poorly designed EACs on the market should concern everyone who cares about the environment. People who buy the poor units may well come to the conclusion that EACs, as a class, are ineffective and then buy the much more energy hungry refrigerated air conditioners, while had they bought a well designed unit in the first place they would have what they need and would save energy, money and unnecessary greenhouse gas production. The problem is often in the design of the individual unit, not in the evaporative cooling principle.
Any form of air conditioning is an active way of cooling your home. It is generally best to explore all possible ways of passively keeping your home cool before going to active methods. Another of my pages on this site discusses other ways of reducing your greenhouse impact.
The key point to remember about EAC is that the cooling effect is directly related to the amount of water that is evaporated per unit of time (per minute or per hour). The more water evaporated the more cooling effect.
The exceptionally high 'latent heat of evaporation' of water is one of the most remarkable properties of this most remarkable of substances.
The reverse process, condensation of water from vapour, is what powers hurricanes.
EACs cool the air at the cost of increasing the humidity. If you are to use them effectively you must manage the humidity in the room or building by bringing in some amount of dry air from outside. I would advise using an evaporative air conditioner in conjunction with a hygrometer (an instrument that measures air humidity).
It follows from the above that if the air is already humid an evaporative air conditioner will not be of much use. They are at their best where the air is hot and dry. They may not be the best choice in many coastal areas of Australia.
Even a simple fan is, to some extent, an evaporative air conditioner. It makes you more comfortable by providing a moving air stream in which your sweat evaporates quickly and with minimal discomfort.
Note the the Calorie (capital C) used in nutrition science is equal to 1000 calories (small c). The Calorie is also known as a killocalorie.
In these days of climate change it is important that we all try to minimise our greenhouse gas production. Using EAC rather than refrigerated air conditioning can help with this.
However, some EACs are very poorly designed; see the IXL model in the box at the right.
There are several types of evaporative coolers including some more expensive
models that are capable of producing cooler and drier air than can be
achieved by the more simple EACs.
More is given on these at the Home Energy page (see
Notes on this calculationThis calculation gives an approximate, but very useful value for the efficiency of the air cooler. One of the advantages of this calculation is that you do not need to know the relative humidity of the air.
What this calculation does not tell you is the capacity of the air conditioner. That is, the 'cooling power' of the air cooler will be equal to its efficiency multiplied by the volume of air passing through it per unit time.
I'd suggest that if the efficiency of your air cooler is less than 50% you should seriously consider demanding your money back. A good cooler should be capable of achieving efficiencies of 70% or better.
Sweating is another example of very effective evaporative cooling.
Mammals would not be able to live in anywhere near the range of habitats
that they do if the latent heat of evaporation of water was not as high
as it is.
Find the temperature of the feed air (the air going into the cooler) on the column of dark figures on the left and the humidity of the feed air in the row of dark figures along the top. The temperature that the cooler should be able to achieve is at the junction of the row and column.
For example, if the temperature of the air being drawn into the cooler is
32 degrees and its humidity is 30% then look at the row starting with
32 and the column coming down from 30%.
The number at the junction of row and column is 23.
So, this is the temperature (in degrees Celsius) of the air coming out of
your cooler, if it is reasonably efficient.
To use ice to cool a room is, in most cases, a bad idea. Making the ice in a freezer releases more heat than melting the ice takes from the room; and you consume electricity into the bargain.
Buying enough ice to cool a room or a home would be very expensive.
The amount of heat absorbed by converting each gram of ice into water is far less than the amount of heat absorbed by converting a gram of water into water vapour. Evaporating a gram of water takes something like ten times as much heat as melting a gram of ice.
The only situation in which I can imagine using ice to cool a room would be acceptable and wise is the price-responsive-load electricity case. Here the ice could be made using sustainable electricity at a time when power was plentiful and cheap, so that it could be used later to cool the room, when the electricity was in high demand and expensive.
Even better would be if you could arrange a tunnel for the air to blow through using the Coolgardie Cooler principle. Don't have too high expectations, I have experimented with the idea and was disappointed.
What I did was to place a fold-up chair on a larger table.
Then I put a large tray (I used a cat-litter tray, about 50 x 30 x
5cm) of water on the chair and a bath towel
so that it was in the tray and hung over each side.
Then I put another large tray on the table so that the excess
water from the towel could drain into it.
The fan was placed so as to blow through the tunnel I'd made and I kept the
top tray at least partly filled with water.
Water was absorbed by the towel (capillary action) and flowed slowly down
into the bottom tray, with some evaporating on the way.
The more water you can get to evaporate the more effective your cooler.
I have now used it in three summers in my small (insulated) shack. On the hottest days it does not sufficiently cool the whole room for comfort, but when it was directed on the people in the room, they will be comfortable.
From the rate of evaporation given above and figures in
we can calculate that this cooler cools a room at about the same rate that a
simple 750 Watt heater would warm the same room.
Put another way, the cooling effect (750W) is about 18 times the power
An authority (eg. government) should mandate the printing of the efficiency of a cooler on the packaging of all coolers. An authority could also enforce the conspicuous printing of the evaporative capacity of all EACs on their packaging. It could be given as the amount of water that the unit will evaporate at a temperature of, say, 28 degrees Celsius and a relative humidity of, say, 45%.
The cooling effect of any cooler is directly related to the amount of water that the conditioner evaporates each hour. This will depend on the temperature and humidity of the air as well as the efficiency of the cooler.
This would give a prospective buyer a good idea of how effective one EAC was compared to another.
If you cannot be sure that any unit you buy will be effective and efficient, make sure that the retailer will take it back if you are unsatisfied.
This page mainly refers to small, portable air coolers.
Of course a ducted evaporative cooler large enough to cool a whole house
should evaporate much more water and will consume more electricity (but
will consume much less electricity than a refrigerated air conditioner).
The recomended models of EACs in the article were:
The 'Effic.%' column is the 'Evaporative efficiency score' given in the Choice article. I measured an evaporate efficiency of 71% for my Convair Magicool; the Choice article did not state how they calculated evaporative efficiency.
Unfortunately the Choice article must be held in some doubt because there are indications that the author did not fully understand the principle under which EACs operate. In the 'How we tested' section Evaporative Efficiency is defined as "High evaporation efficiency means the cooler gets a better cooling effect for the water it uses." And in the 'What to look for' section it is suggested that buyers should look for units that have "Low water consumption rates"; exactly the opposite is the case.
Solar powered evaporative air cooling
Australian Commonwealth Scientific and Industrial Research Organisation
(CSIRO) researcher Steven White, of the Solar Cooling Research Unit, has
developed a new concept in evaporative air cooling.
The system will allow solar energy to be economically used to assist
evaporative air cooling in areas with high humidity.
An acceptable air cooler
Article in Choice
Calculate the efficiency of your cooler
Energy-efficient and cost-effective
IXL Icecap 2
Simple air cooler
Solar powered evaporative air cooling
What temperature should a cooler achieve?
Where not to use EAC