. . . . . . . . . . about evaporative cooling

The Concept:

As the name implies, evaporative cooling works by evaporating water into the air stream.  This principle is best illustrated in a personal way by that chilling effect you feel when you come out of a swimming pool and a breeze blows across your body!  The chilling effect is caused by the evaporation process of the water drying quickly from your body.  The same thing happens when you sweat.  A "cool breeze" is just air flowing over your body evaporating the sweat.  It is natures way of keeping us cool during hot weather or physical exertion.

Using the "kiss" method (keep it simple, stupid), evaporative cooling is the use of this evaporation process to cool the air passing through a wetted cooling media.  The cooling media could be as simple as a wet cloth.  In fact, this process has been used for hundreds (if not thousands) of years.  Hanging a wet cloth over an open window cools the air passing through the cloth.  I would think that early civilizations that understood astronomy, built irrigation canals and impressive structures like the pyramids would have used this principle.

Now for some technical stuff!  Temperature is measured in two (2) important ways that relate to evaporative cooling. These are "dry bulb" and "wet bulb" temperatures expressed in degrees Fahrenheit or Celsius if you prefer.  There are several other measurements that reflect the amount of moisture in the air.  These are "dewpoint",  "grains of moisture per pound of dry air" and "pounds of moisture per pound of dry air", "absolute humidity" and "relative humidity".  The following brief explanation of these measurements will help in the understanding of this process.

Dry Bulb:  The ambient (surrounding air) temperature taken with a thermometer .

Wet Bulb:  The lowest temperature level of the air that can be reached by evaporatively cooling the air.

Wet Bulb Depression:  The difference between the Dry Bulb and Wet Bulb temperatures.  I.E.  if Dry Bulb is 100 degrees (f) and the Wet Bulb is 70 degrees (f), the Web Bulb Depression is 30 degrees (f).  The Wet Bulb Depression is used to determine the percent of efficiency of the cooling media.

Cooling Efficiency:  The percent of  the temperature drop across the media compared to the Wet Bulb Depression. I.E. if the Wet Bulb Depression is 30 degrees (f) (as in the above example) and the actual temperature drop measured across the cooling media  is 27 degrees (f), the cooling efficiency of the media is 90%.  (27/30 = .90).  The cooling efficiency is also referred to as "Saturation Efficiency" because it refers to the amount of moisture that is packed into the air.  100% Saturation Efficiency would indicate a temperature drop of 30 degrees (f)  in the above example of wet bulb depression.

Dewpoint:  The temperature at which moisture begins to form on a slick surface indicating 100% saturation of the air with moisture.  That is how the dew gets on the grass in the morning.  The dry bulb air temperature drops to the wet bulb temperature level.

Grains of moisture per pound of dry air:  A method of measuring actual water vapor (moisture) in a pound of dry air, Most often referred to as "humidity ratio".   I.E. 50 grains of moisture at 100 degrees (f) equals 12% relative humidity and 70 degrees (f)  wet bulb at sea level.

Pounds of moisture per pound of dry air:  Same as grains except weight of water vapor (moisture) is expressed in pounds.  In same example above, the pounds of moisture would equal .009 # per pound of dry air.

Absolute humidity:  Actual measurement of water vapor in the air.

Relative humidity:  The percent of moisture in the air compared to the amount of moisture the air could contain.  This is the most common reading to be reported in the weather reports.  The report of "100 degrees and 12% relative humidity (RH)" is the same as all the above examples.  Using the analogy of a glass half filled with water means the glass is 50% full.  It could hold an additional 50% at which point it would start to overflow if more water was added.

Evaporation Rate:  The rate at which water is absorbed into the air passing through the cooling media.  For practical purposes, this rate is measured in gallons of water per hour (or minute).

Cooling Media:  In the recent past, a common type of cooling media was "aspen" pad.  Literally wood fibers packed together loosely to allow air to pass through.  This type of media was packed into 2" thick slabs within a cloth mesh.  This pad was held on a wire hanger frame to support it within a metal frame.  Water was introduced across the top of this pad and air was pulled through it by a blower.  The cooling efficiency was only about 50% which was relatively poor.

Another type of pad used today is a slab of expanded paper to form a 2" thick media.  This media also has a  low efficiency (about 50%) in performance.  Both of these cooling media have a random water flow pattern and both have a short useful life (sometimes only 2 months in hard water, high temperature areas).

 The newest and most efficient media is  Premier Rigid Cooling Media.  This media is usually used in 12" thickness which performs at 90% efficiency at about 500 feet per minute velocity.  It is available in any thickness up to 24" which performs at (up to) 99% cooling efficiency.   The construction of this media is unique in that it has alternating, transverse flutes of 45 degrees and 15 degrees.  The 45 degree flutes carry the water (introduced over the top of the media) to the front of the media where the oncoming air forces it back into the media assisting in the thorough wetting of the media.  The air flows through the 15 degree flutes.  This media is made from a cellulose material with wetting agents and rigidifying saturants.  The useful life of this media is usually 2 to 6 or even more years.  Refer to section on "Rigid Media" from our home page for further information about this media.

The essence of  this little guide to understanding evaporative cooling is simple.  Adding water (in vapor form) to the air cools the air.  It also adds humidity to the air.  The mechanics of building evaporative cooling equipment is similar to any other ventilating or heating equipment with the exception that an evaporative cooling section is required.

   Refer to the next section "Why Evaporative Cooling" for additional information about this process.

 Premier Industries has been a leader in the manufacture of heavy duty & stainless steel evaporative cooling equipment for over 20 years. All our products are made in the USA, at our Phoenix, Arizona factory and carry a 10 year rust-through warranty.

Premier Industries' high quality evaporative cooling products

Stainless steel industrial evaporative cooler Portable mobile evaporative coolers commercial evaporative cooler swamp cooler Air Washer Intake and Make Up Air Cooler Evaporative cooling Upgrade for Swamp Coolers

Industrial Evaporative Cooler

Mobile Evaporative Cooler

Commercial Evaporative Cooler

Evaporative Cooling Module (Air Washer)

Converta-Pak upgrade retrofit for older coolers

Click an image to go to the product overview - see our home page for our complete product line


Why ask Why: The human race has been able to use up a great portion of the natural resources of the earth and has proceeded to pollute the air we breathe and (according to the experts) burn a hole in the ozone in the overuse of Chlorofluorocarbons (CFC's) which may cause global warming!  Conventional air conditioning is one of the major contributors of CFC's into the atmosphere.  An alternative type of cooling, which does not expel CFC's is highly desirable as one important step in the correction of this problem.  It is time to answer the question with why not Evaporative Cooling!

Evaporative cooling is a passive cooling method that does not expel CFC's.  It is 100% fresh air cooling which even helps to clean the air it cools.

Benefits of evaporative cooling:

Economy:  There is no compressor, condenser, chiller coils, cooling towers or heavily insulated piping used in evaporative cooling.  The cost of acquisition and operation is a fraction of conventional air conditioning and mechanical refrigeration systems. Maintenance costs are minimal requiring simpler procedures and lower skilled maintenance people.   An extra benefit is the cost payback due to its' low energy use and extended useful life of equipment being cooled by it.

Effective: Evaporative cooling has been used for thousands of years in various forms for comfort cooling and is still in common use around the world because of it's simplicity, low cost and effectiveness.  Unfortunately, many owners of buildings and specifiers of cooling equipment in the U.S. do not seem to realize that it is effective in all areas of the country rather than just in the hotter, drier climates.  ASHRAE Handbook, 1995, chapter 47, Evaporative Air Cooling notes "...dry bulb temperature reduction due to the evaporation of water always results in a lower effective temperature, regardless of the relative humidity level" and that ". . . (evaporative cooling) can provide relief cooling of factories almost regardless of geographical location."

 Increased Comfort:  In a large number of industries it is normal in hot weather to experience increased heat-related illness, lower productivity and increased absenteeism among workers. Many of these industries cannot afford the tremendous costs of conventional mechanical refrigeration or air conditioning, while they can afford evaporative cooling.  Quoting again from ASHRAE Handbook, 1995, Chapter 47, Evaporative Air Cooling  "evaporative cooling can alleviate this heat problem and contribute to worker efficiency with improved morale.  If the heat problem is not alleviated, increased absenteeism, high labor turnover and dangers to health and safety during the summer months.  Production declines in uncooled plants may range from 25% to 40% of normal on hot days."  

Health Benefits: Evaporative cooling is 100% fresh air cooling.  This means that all the air being cooled is brought in from outside.  It is also necessary to force approximately 90% of all the air coming into the building, out of the building, leaving a nice 10% positive pressure.  Today, the term "Sick Building Syndrome" exemplifies the result of continuously re-circulating the air inside the building.   The old saying that you can get sick in a hospital is true.  The air containing contaminants of all sorts is being breathed in by everyone.  In fact, the "no smoking" section of a public building is a joke.  The same air permeates the entire building and is shared by all who breathe it.  Fresh air would exhaust these contaminants quickly and harmlessly. Federal guidelines in building construction now require a percent of all air in the building be fresh air.  To further improve the air quality, the rigid cooling media used in today's evaporative coolers filters to near 1 micron size particles out of the air.

Improved Efficiency of Other Equipment: Evaporative cooling is commonly used to pre-cool the air passing over heat exchangers, motors and many other types of mechanical equipment.  A good example of this is a Precooler for air cooled condenser coils on conventional air conditioners.  The energy use of the air conditioner is reduced by as much as 50% in hot, dry periods.  The useful life of this kind of equipment is greatly improved by using evaporative precooling.   It is becoming common practice in the southwest U.S. to include evaporative cooling modules around equipment rooms for precooling purposes.

The answer to "Why Evaporative Cooling" is that it is Sensible cooling.  It is an important tool in helping to curb the excessive use of energy.  It helps clean up the atmosphere since it has no CFC's or HCFC's.  It is economical, effective, it has health benefits, improves worker and equipment efficiency and provides a much needed alternative to conventional mechanical refrigeration!


 Standard vs Custom Equipment:

There is much merit to the point that it is better to build the equipment to meet the need rather than change the need to fit existing equipment!  It depends on how much importance you place on matching the equipment to the application.  If the application is loosely defined and performance of equipment to meet the needs of that application is not critical, then standard equipment may be the better way to go.

If your needs are specific, and performance is a must, then it may be time to move up to custom designed, commercial / industrial duty, Premier Industries, Inc. evaporative cooling equipment. Custom design and manufacture is the answer to acquiring the exact equipment you need. With Premier Industries, Inc., the cost of custom equipment is usually not much higher than standard equipment and in many instances has been proven to be less costly.  We can provide assistance in design of evaporative cooling equipment. Starting with the size structure you want to cool, we can recommend equipment size and offer different alternatives that could save a lot of time and money.  If the need is to replace existing equipment, we can recommend units for that purpose.  Sometimes the existing equipment can be made to work effectively by upgrading to a higher efficiency using products like the Converta-Pak . Whatever the evaporative cooling need, it would pay to contact us.  A wealth of technical information is available at no cost!

Once the configuration is determined, Premier manufactures the equipment to the exact specifications.  The customer has the opportunity to order just what is wanted at very little, if any additional cost.

Refer to the various products Premier manufactures from our Home Page.  You will quickly see that we cover the complete spectrum of evaporative cooling equipment.

Send your specifications to us via e-mail (link below) or fax (602)-997-5998 or call us free at 800-254-8989.  We will be happy to quote on the cost for existing or future evaporative cooling projects.