An evaporative or swamp cooler can work in moderate humidity as long as you know what to do and why you're doing it.
The evaporation process that produces the cold air from the unit is the key to getting more cool from your cooler.
If you didn't already know, an evaporative cooling unit can keep you nice and cool during summer yet cost only a small fraction of the high running costs of air conditioning.
That's very attractive to a lot of people who need and want an economical as well as healthy temperature control solution in hot weather, but many are put off getting one because they are afraid the device won't work if the humidity gets too high.
Moisture, Air and the Chilling Effect of Evaporation
When water is evaporated, it makes use of the heat in the air as its catalyst in transforming water from its liquid form into vapor.
The heat is absorbed by and suspended in the water vapor, which lowers the temperature by a certain amount in the surrounding area.
The more rapidly the water evaporates, the greater the amount of heat is consumed and therefore the faster the temperature is reduced.
This is the exact process going on inside an evaporative cooler.
Water contained in a reservoir is pumped up and poured over a special absorbent cooling pad.
The pad has warm air from the room blown through it fast by a high power fan.
The water absorbs all the heat in the air and evaporates, chilling the air that is blown out the other side by the same fan.
That chilled breeze cools the ambient temperature in the room.
Evaporation Hates Humidity
The rate of evaporation of water is inversely proportional to the level of humidity in the surrounding area.
That means when the humidity level is low, the dry air can store a lot more water and evaporation occurs very quickly.
However, when the humidity level is high, the air is saturated with moisture which severely reduces its ability to absorb water vapor. In this case, evaporation happens slowly.
That's one of the reasons that hot, humid weather is more uncomfortable than hot, dry weather. The perspiration your body produces just sticks clammily to your skin instead of cooling you down by evaporating.
For exactly the same reason, very humid weather reduces the effectiveness of evaporative coolers. As the humidity level rises, the difference in temperature between the air coming from the cooler and the air in the room is reduced, until it eventually becomes little more than a fan in a box!
The big disadvantage here is that swamp coolers are not effective in a very humid environment. That is, unless you happen to know a certain clever trick to overcoming some of the problems.
Well, read on, because you're about to discover it!
Open or Closed Windows?
With a regular air conditioner, the room or building being cooled must be closed up tight for the process to be effective as well as economical.
However, the exact opposite is true of swamp coolers. These devices rely on getting a constant stream of fresh air to work effectively.
If your portable evaporative cooler doesn't seem to be cooling you down, the first trick is to make sure it's placed near to an open door or window. If you already have it by an open window, go ahead and open another window on the other side of the room.
This is to create a cross-breeze in the room, which will draw out the hot, moist air from the room. In general, 1 or 2 sq ft per 1,000 CFM of air cooling capacity is enough to cycle hot, humid air to the outside.
You should try experimenting some to get the flow just right. Adjust the window openings to see how wide they need to be open to create the best cross-breeze and control the amount of cooling your device will achieve.
Air Conditioning Dehumidification
Another trick you can use if you already have a central air conditioning system is to use its dehumidification characteristic to boost the swamp cooler's effectiveness.
By setting the central AC thermostat to a fairly high temperature, say around 80 degrees, it will run very economically yet still dry out the air sufficiently to allow your portable evaporative air cooler to come in and reduce the temperature to an even more comfortable level.
This trick also has some benefit to air quality, since it's not good for the lungs to breathe in so much very dry air as is produced by air conditioners. A swamp cooler hydrates the air making it kinder to the delicate lining of the lungs and creates a natural benefit to the respiratory systems of your family while providing coolness and comfort into the bargain.
Anyone for Ice?
Most manufacturers recommend the addition of ice to the water tanks in order to facilitate better cooling.
This may, on the face of it seem like a good idea. But the reality is ice in the water can actually hamper the cooling process of evaporation.
Here's why.
Adding ice to the water reduces the temperature of the water and while there may be some benefit from the fan blowing the colder air from the water's surface, the lower water temperature can slow the evaporation to vapor.
This reduces the volume of chilled evaporated air and slows temperature reduction. So its best to use regular, room temperature water for your tank and let the soaking and fanning process do its thing as it was designed to do!
In all cases where you think an evaporative cooler might not be working because there's no cold air coming out, take a moment to try a few things first before throwing in the towel and sending it back to the store with a barrage of complaints.
You may be pleasantly surprised at just how forgiving and effective these swamp coolers can actually be when you use them right to bring them back to life and re-turbocharge their chilling ways once again!