Choices To Evaporative Cooler Designs

There are many choices in the current market. Direct Evaporative Cooling (open-circuit) allows you to reduce the temperature by using the latent warmth of evaporation. This transforms water to vapor. This process does not alter the energy of the air. The warm, dry atmosphere changes into cool, humid air. Heat in the air evaporates the water.

Indirect Evaporative Cooling (closed-loop) is similar in function to direct evaporative cooling but involves some heat exchanger. The conditioned environment never comes into direct contact with the cooled, humid air.

Evaporative cooling is also available in two-stage evaporative cooling (or Indirect Direct). Traditional portable evaporative cooler use only a small fraction of the energy used by vapor-compression and absorption air conditioning systems. However, they can make people feel uncomfortable if the humidity is too high, even in extremely dry environments. Two-stage Evaporative Coolers do not produce the same humidity levels as single-stage models.

In the first stage, a cooler with two stages pre-cools warm air indirectly without adding humidity. This air is passed through a water-soaked pad in the second stage. As it cools, it will pick up humidity. Air is less humidified because it is pre-cooled before it reaches the second-stage evaporator. Manufacturers claim that the result is cool, humid air with a relative humidity range of 50% to 70%. This will depend on the climate. The relative humidity will be around 80% in a traditional system.

Cooler Pads

It is common for cooler pads to contain excelsior (wood wool, aspen wood fiber) – within a containment net. Modern materials like plastics, melamine, and paper are becoming more popular. Wood can absorb some of this water which allows wood fibers to cool passing vapor. As it allows for more air contact, the thickness and efficiency of this padding are important. For example, a pad with an eight-inch thickness will be more efficient than a one-inch.

Comparison To Air Conditioning


Installing Is Less Costly

The estimated cost of installation is between 1/8 and 1/2 the price of refrigerated AC conditioning

Operate At A Lower Cost

Operation costs are 1/4 the cost of refrigerated air.

The fan and water pumps consume less power than compressors, pumps, and blowers.

Ventilation Air

The building’s age-of-air is dramatically reduced by the constant and high volumetric flow of air through it.

Evaporative cooling can increase humidity in dry climates. This may help to improve thermal comfort.



High humidity and temperature can decrease the cooling ability of the evaporative coolant

No dehumidification. However, this is not a requirement in design. Evaporative cooling adds moistness to the air. This can improve thermal comfort in dry climates.


Air from the evaporative cooler is generally 80-90% relative humidity

The evaporation rate for moisture from the skin and nose, lungs, and eyes is reduced by humid air

Corrosion is worsened by high humidity. This can affect the life expectancy of electronic equipment.

High humidity can cause condensation. This is a problem in certain situations (e.g. Condensation can occur in electrical equipment, computers, and old wood.


A portable evaporative cooler requires a constant water supply to hydrate the pads

Water with high mineral content can leave deposits on the interior and pads. Water softeners and bleed-off systems can reduce this problem.

Protect your water supply line from freezing in winter. It will be necessary to drain the cooler and clean it regularly.