Evaporative Cooling

 

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Evaporative Cooling

An evaporative cooler has a fan which blows air through a wetted pad, where water evaporates into the air. This cools the air by extracting from it the latent heat of vaporization and the fan circulates the cooled air though the building.

There are many factors in evaporative cooling, below are the following main topics which will be discussed:

The System Typical Uses

Limitations

Cost

 

Typical Uses

It is most useful in hot, dry climates such as Arizona because as it cools, it adds moisture to the air. In climates with a higher relative humidity, the evaporative cooler wont be as effective.

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The System

The evaporative cooler consists of two basic parts: a fan and wetted pad.  The fan blows air through the wetted pad and cools the air by removing the latent heat of vaporization from it.  Some ductwork may be required to distribute air throughout the building.  There also needs to be an outlet for the hot air to exit.  This can usually be a window in the top floor or attic.  The air is cooled to a maximum of about 20.

 

http://www.eere.energy.gov/consumerinfo/heatcool/hc_cc_evaporativecoolers.html

 

 

The evaporative cooler is also environmentally friendly because they dont require as much energy as regular air conditioners. In addition, it doesn't use Freon which pollutes the environment.  It also acts as an air filter because the wetted pads catch and retain particles in the air that are blown in from the outside.

 

The Architect's Studio Companion

 

In the chart below, the yellow represents the optimum cooling conditions.

 

http://www.eere.energy.gov/consumerinfo/heatcool/hc_cc_evaporativecoolers.html

 

 

Amount of B.T.U.s removed based on how many gallons of water consumed per hour:

 

2 gallons.................17,400 B.T.U.'s removed
3 gallons.................26,100 B.T.U.'s removed
4 gallons.................34,800 B.T.U.'s removed
5 gallons.................43,500 B.T.U.'s removed

 

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Components

The major components of the evaporator cooling system are the evaporative cooling unit and the ductwork. In the chart below are normal dimensions for these components.

 

The Architect's Studio Companion

 

 

There are two types of evaporative coolers; a two stage and a single stage cooler.  The two stage (indirect/direct) cooler uses an air-to-water heat exchanger/ precooler which reduces the incoming air temperature without raising the relative humidity, then puts the incoming air through a direct evaporation stage, further reducing its temperature.  Usually only used when temperature is greater than 100. Single stage (direct) have three types of coolers. The most commonly used evaporative coolers are fixed fiber pad coolers, rotating pad coolers, and rigid-sheet pad coolers.

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Limitations

One of the limitations of the evaporative cooler are that it only cools about 20, creates more humidity and requires more maintenance than an air conditioner. The evaporative cooler is only a cooling unit; a separate unit will be needed for heat if necessary.  The cooler needs immediate access to outside air, which is not always available.

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Costs

An advantage of the evaporative cooler costs about half as much as a conventional air conditioner to buy (about $100-$300) and about the cost to operate. The operating cost uses about the same amount of energy as a  normal 120V outlet.

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This site was last updated 05/04/05