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How Does An Evaporative Cooler (Swamp Cooler) Work?

An evaporative cooler, swamp cooler, desert cooler, and a wet air cooler cools air through the simple process of the evaporation of water. Evaporative cooling works by utilizing water vaporization. The temperature of dry air drops significantly through the transition of liquid water to water vapor and water vapor is essentially evaporation. This process can cool air with much less energy than with refrigeration. In extremely dry climates such as the Southwest portion of the United States, evaporative cooling has an added benefit of also moisturizing the air which prevents things from becoming to dry. Evaporative cooling always requires a water source and must constantly have water to operate and cool the air.

What CausesEvaporative Cooler “How It Works” Animation

How Does Evaporation Lower Temperature?
When warm dry air passes over a water source a part of the water will always be absorbed by the air. The more hot and dry the air is the more water will be absorbed and the air is attempting to equalize itself. The water molecules will become gas in the hot and dry air and this process uses energy to change the physical state of the water. The heat will always transfer from the higher temperature of the air to the lower temperature of the water. When this occurs, the air is naturally cooler. Evaporation stops when it is too hot and the air becomes overly saturated and not able to hold more water.

How Does an Evaporative or Swamp Cooler Device Work?
An evaporative cooler is really just a large fan that blows air through water soaked pads producing a cooling affect. The fan pulls hot outside air through the pads and into the cooler and blows the cooled air out.

Evaporative Cooler Pads
The Evaporative Coolers pads are most commonly made of wood shavings. Wood is a great material because it absorbs and holds moisture while resisting mildew. These wood pads should be replaced every season and cost about $40 for a set of good ones that will last.



Evaporative Cooler Water Pump
A small recirculating water pump located inside the cooler pumps water through supply lines that distribute water to the top of the cooling pads. When water reaches the top of the pads the water saturates the pads by dripping through them constantly. The water goes through the pads and collects in the bottom of the cooler. The small recirculating water pump sends the collected water back to the top of the pads and this is a continuous operation.

Evaporative Cooler Float Valve
Water is continually lost through evaporation so a float valve is needed and adds water to the bottom of the cooler (sump) when the level gets low. During very hot conditions a cooler can use from 5 to 20 gallons of water per day depending on the size and CFM of the unit.

Evaporative Cooler Fan
The fan has 2 functions, it pulls in hot air and pushes out cooled air. The coolers fan pulls the warm outside air in and through the pads. This is where evaporation occurs and the temperature drops around 20 degrees. The same fan blows this cooled air through the side vent and into the home or garage and cools the area by 20 degrees.

How Efficiently Can Swamp Coolers Cool An Area?
The temperature of cool air blowing out of a cooler will always depend on the temperature and the humidity of the air going into the unit. Also an evaporative cooler works the best at the hottest time of the day because of humidity levels and varying temperatures.

How To Pick The Correct Size Evaporative Cooler For Your Home?
For a swamp cooler to cool effectively it has to be the proper size for the area which is needing to be cooled. A small window unit will not cool a large room. The output of evaporative coolers are rated by CFMs (the cubic feet per minute of air that the cooler can blow into your home). Figure out the cubic feet of space that is needing to be cooled and then divide whatever that number is by two. This will give you the CFM rating for the correct size of swamp cooler that is needed.

So if you have a 2,000 square foot home with 10 foot high ceilings:
2,000 x 10 = 20,000 cubic feet
20,000 % 2 = 10,000 CFM needed

How does an evaporative cooler work?

How a Desert Cooler Works (EVAP COOLER)

Benefits of Evaporative Cooling?
Evaporative cooling provides a complete air change and this occurs every one to five minutes pushing out hot inside air and any smoke or odors and pollution that may be present in the home.
Evaporative coolers and swamp coolers use as much as 75 percent less electricity than air conditioning does.
An evaporative cooler costs less than half as much as an air conditioner and it will cool the same sized area.
Swamp coolers operate on 120 volts meaning they don’t need special high amp circuits like air conditioners require. An evaporative cooler can be plugged into any outlet unlike air conditioners.
Evaporative cooling adds more moisture to the air that helps to keep wood and fabrics from getting dryed out.
Evaporative cooling doesn’t require as much ductwork as an air conditioning system requires.

Swamp cooler wiring schematic diagram

SCHEMATIC – Evaporative Cooler Wiring Diagram

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4 thoughts on “How Does An Evaporative Cooler (Swamp Cooler) Work?”

  1. Water is not coming through the water distribution lines. I bought a new pump but it is still not working

  2. The space to be cooled is of size 21.5m X18m X3mh and the condone area of 18mX 12m x 6m high.
    These two separate areas will be served by one unit.
    Note that the highlighted space needs a temperature of 16-18 degrees, this particular space will be fully insulated whereas the first one serves the normal temperature of 20 to 24 degrees.
    For this, the room measures 21.5m x18M x 4m will separately have it’s independent unit to serve at 20/24 degrees the unis must be able to operate humidity level of 65% and ambient temperature 28 to 31 degrees.

  3. DIY Project Help Tips

    You simply have the belt too tight. If you adjust the motor and the fan pulley too tight on your swamp cooler, the motor will shut off temporarily as it is overheating and it is thermally protected. Loosen the belt between the fan pulley and the motor pulley by sliding the motor closer and you should be good to go. The belt should not be so tight that it stresses the motor to the point of overheating.
    If you leave the motor to sit for about 20 minutes after it overheats, does it turn back on?

  4. I have to replace everything on my swamp cooler such as the motor, bearing , belt, and it still starts to turn and then it stops and motor gets hot what am I doing wrong. Please help.

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