The technical term for swamp coolers is evaporative coolers. These systems are able to cool a home without using a refrigerant system which can save a lot of money on operating costs.
A traditional air conditioner uses electricity to run a compressor which pumps refrigerant to cool the home.
An evaporative cooler gets its cooling power from water instead of refrigerant.
This is how they work.
Most of us have felt the effects of evaporative cooling. When you exit the water after swimming, the water that is left on you evaporates and cools you off. The same principle can be used to cool your home.
When hot, dry air comes into contact with water, the air loses some of it’s heat to the water. This in turn causes the water to evaporate (change from a liquid to a gas). The water vapor is absorbed into the air raising its’ relative humidity. This is a basic direct evaporative system.
This system consists of a sump (reservoir) with a float valve, a pump, pads, and a fan. The float valve automatically maintains the water level in the sump. The pump takes water out of the sump and distributes it to the pads. The water runs through the pads, which are traditionally made from aspen wood, and back into the sump. The fan pulls outdoor air through the pads where it is cooled and moisture is added. Then the air is pushed through a duct system into the home.
This basic system can be used to cool the home but it has some limitations. In areas where the outdoor relative humidity is above 50% these units are less effective. Under these conditions, the unit can raise the humidity of the indoor air to unacceptable levels. This is how they become known as swamp coolers.
These units typically come in three styles which are portable units, window/wall units and ducted units. The two basic types of these units are direct and indirect evaporative coolers.
Indirect evaporative units replace the pads with a heat exchanger. Water is pumped through the inside of the heat exchanger and air is circulated on the outside. The air loses some of its’ heat to the water and then is supplied to the duct system. These systems do not add moisture to the air supplied to the home. This lowers their cooling capacity.
The latest innovation is a two stage unit. This unit uses both direct and indirect evaporative cooling. In the first stage the air is precooled by the indirect method. Then the air passes into the second stage where moisture is added and it is cooled more through the direct method. Then the air is supplied to the home.
This system has a higher capacity and still maintains a comfortable humidity level.
The size of these units is expressed in cubic feet per minute (cfm). This refers to the amount of air the units supply to the home.
The usual method for finding the size of unit required is to divide the volume of the home by 2. To find the volume of the home, measure the square footage of floor area and multiply by the ceiling height in feet.
The typical system should provide 20-40 air changes per hour. This means that the the air in the home should be removed and replaced 20-40 times per hour.
For these systems to work there must be a free flow of air out of the home. Traditionally this was accomplished by opening windows. A rule of thumb was that you required two square feet of opening per 1000 cfm.
Today there are special ducts that are mounted in the ceiling and open to allow the air to escape to the attic. The attic must be properly ventilated to prevent excessive moisture.
This allows you to maintain the security of the home. Another benefit is that the ducts can be distributed in individual rooms to provide more even temperatures throughout the home.