• A swamp cooler is an evaporative cooler, also called a desert cooler or air cooler, used to cool air. Through the use of the natural phenomenon of water evaporation, warm air is cooled and blown into a room or home, cooling the occupants. The process relies on the contrast of wet-bulb (humidity) and dry-bulb temperatures (thermometer temperature). The greater the contrast, the more benefit the cooler will be to the occupants. But if the two rise together, the benefit begins to lessen until there is no reason to turn on the swamp cooler.

• Parts of a Swamp Cooler

• Swamp coolers have a metal case, or frame, that fits over the cooler parts. The frame is box-like and vented and holds an electric motor with pulleys, a fan or blower and a water pump. The inside walls of the frame are lined with pads made of cellulose. These pads a replaced every season with new ones. When the swamp cooler is turned on, these pads are continually wetted with water by a water pump. A fan inside the box frame pulls warm, outside air through the wet pads which automatically cools the air by evaporation. The cooled air is then released through vents into the house or room. The cooled air is generally around 20 degrees F cooler than the outside air. If humidity outside is 10 to 20, percent then the cooler can cool the air up to about 30 degrees cooler. The higher the humidity goes, the less effective the cooler becomes. Swamp coolers can be mounted on top of the roof or at windows or openings on the sides of buildings.

  Climates for Swamp Coolers

• Dry climates are best for swamp cooler use. Swamp coolers are popular in the southwest United States due to the consistently low levels of humidity. Evaporative cooling is a dynamic system, meaning its effectiveness changes according to external temperatures and levels of water in the air.

Evaporative cooling is especially well suited for climates where the air is hot and humidity is low. For example, in the United States, the western/mountain states are good locations, with swamp coolers very prevalent in cities like Denver, Salt Lake City, Albuquerque, El Paso, Tucson, and Fresno where sufficient water is available. In worldwide, Spain, Australia, Turkey, Middle Asia, Africa and Middle East contries are perfect places to use evaporative air cooling. Evaporative air conditioning is also popular and well suited to the southern (temperate) part of Australia. In dry, arid climates, the installation and operating cost of an evaporative cooler can be much lower than refrigerative air conditioning, often by 80% or so. However, evaporative cooling and vapor-compression air conditioning are sometimes used in combination to yield optimal cooling results. Some evaporative coolers may also serve as humidifiers in the heating season.

In moderate humidity locations there are many cost-effective uses for evaporative cooling, in addition to their widespread use in dry climates. For example, industrial plants, commercial kitchens, laundries, dry cleaners, greenhouses, spot cooling (loading docks, warehouses, factories, construction sites, athletic events, workshops, garages, and kennels) and confinement farming (poultry ranches, hog, and dairy) all often employ evaporative cooling. In highly humid climates, evaporative cooling may have little thermal comfort benefit beyond the increased ventilation and air movement it provides.

Civilizations throughout the ages have found ingenious ways to combat the heat in their region. An earlier form of air cooling, the windcatcher (Bâd gir), was invented in Persia (Iran) thousands of years ago in the form of wind shafts on the roof, which caught the wind and passed it through water and blew the cooled air into the building.

Nowadays Iranians have changed the windcatcher into an evaporative cooler (Coolere Âbi) and use it widely. There are 9,000,000 evaporative coolers in central Iran, and in just April – May 2006 130,000 evaporative coolers were sold in Iran.

Evaporative cooling was in vogue for aircraft engines in the 1930s, for example with the Beardmore Tornado airship engine. Here the system was used to reduce, or eliminate completely, the radiator which would otherwise create considerable drag. In these systems the water in the engine was kept under pressure with pumps, allowing it to heat to temperatures above 100 Celsius, as the actual boiling point is a function of the pressure. The super-heated water was then sprayed through a nozzle into an open tube, where it rapidly boiled and released its heat. The tubes could be placed under the skin of the aircraft, resulting in a zero-drag cooling system.

However these systems also had serious disadvantages. Since the amount of tubing needed to cool the water was large, the cooling system covered a significant portion of the plane even though it was hidden. This led to all sorts of added complexity and the systems were always terribly unreliable. In addition this large size meant it was very easy for it to be hit by enemy fire, and practically impossible to armor. British and US attempts to use the system turned to ethylene glycol instead. The Germans instead used streamlining and positioning of traditional radiators. Even its most ardent supporters, Heinkel's Günter brothers, eventually gave up on it in 1940.

Evaporative cooling was used in some automobiles, often as aftermarket accessories, until modern vapor-compression air-conditioning became widely available.

Nowadays, evaporative cooling is widely used in China also since 2000. Because of high electricity cost, more people in China start to use evaporative cooling, instead of traditional air conditioning.  When numerous chinese people want to buy evaporative air cooler, China has became the biggest manufacturer of evaporative air cooler. With low producing cost and high efficient working, China made evaporative air coolers are most competitive in international market. Among these manufacturers, Fujian JINGHUI Tech grow fastest, because the company only focus on evaporative cooler products. This company export most coolers to abroad market.
 

A simple example of natural evaporative cooling is perspiration, or sweat, which the body secretes in order to cool itself. The amount of heat transfer depends on the evaporation rate, which in turn depends on the humidity of the air and its temperature, which is why one's sweat accumulates more on hot, humid days: the perspiration cannot evaporate.

A recent application of evaporative cooling is the "self-refrigerating" beverage can. A separate compartment inside the can contains a desiccant and cooling liquid. Just before consumption, the desiccant comes into contact with the cooling liquid, inducing evaporation.

Evaporative cooling is a very common form of cooling buildings for thermal comfort since it is relatively cheap and requires less energy than many other forms of cooling. However, evaporative cooling requires an abundant water source as an evaporate, and is only efficient when the relative humidity is low, restricting its effective use to dry climates. Evaporative coolers are colloquially referred to as swamp coolers in the U.S. In other places they are known as desert coolers.

Evaporative cooling is commonly used in cryogenic applications. The vapor above a reservoir of cryogenic liquid is pumped away, and the liquid continuously evaporates as long as the liquid's vapor pressure is significant. Evaporative cooling of ordinary helium forms a 1-K pot, which can cool to at least 1.2 K. Evaporative cooling of helium-3 can provide temperatures below 300 mK. Each of these techniques can be used to make cryocoolers, or as components of lower-temperature cryostats such as dilution refrigerators. As the temperature decreases, the vapor pressure of the liquid also falls, and cooling becomes less effective. This sets a lower limit to the temperature attainable with a given liquid.

Evaporative cooling has recently been observed to operate on a planetary scale on Pluto, where it has sometimes been called an anti-greenhouse effect.

On Earth, trees transpire large amounts of water through pores in their leaves called stomata, and through this process of evaporative cooling, forests interact with climate at local and global scales.

Evaporative cooling is also the last cooling step in order to reach the ultra-low temperatures required for Bose–Einstein condensation (BEC). Here, so-called forced evaporative cooling is used to selectively remove high-energetic ("hot") atoms from an atom cloud until the remaining cloud is cooled below the BEC transition temperature. For a cloud of 1 million alkali atoms, this temperature is about 1μK.

It is also Evaporation that is at the heart of the typical compressor based Air Conditioner; only that once its refrigerant evaporates inside the "evaporator" coils, the refrigerant gas is recycled to the compressor and condensor; instead of a "swamp cooler's" water, where it only evaporates once and then is discarded, typically vented to the outdoors.

Two-stage Evaporative Cooling, or Indirect-Direct. Traditional evaporative coolers use only a fraction of the energy of vapor-compression or absorption air conditioning systems. Unfortunately, except for in very dry climates, they may increase humidity to a level that makes occupants uncomfortable. Two-stage evaporative coolers do not produce humidity levels as high as that produced by traditional single-stage evaporative coolers.

In the first stage of a two-stage cooler, warm air is pre-cooled indirectly without adding humidity (by passing inside a heat exchanger that is cooled by evaporation on the outside). In the direct stage, the pre-cooled air passes through a water-soaked pad and picks up humidity as it cools. Since the air supply is pre-cooled in the first stage, less humidity is needed in the direct stage to reach the desired cooling temperatures. The result, according to manufacturers, is cooler air with a relative humidity between 50 and 70 percent, depending on the climate, compared to a traditional system that produces about 70-80 percent relative humidity air.

In practice, it is simple to predict swamp cooler performance from standard weather report information. Because weather reports usually contain the dewpoint and relative humidity, but not the wet bulb temperature, a Psychrometric chart must be used to identify the wet bulb temperature. Once the wet bulb temperature and the dry bulb temperature are identified the cooling performance or leaving air temperature of the cooler may be determined:

LAT = DB – ((DB – WB) x E)

LAT = Leaving Air Temp

DB = Dry Bulb Temp

WB = Wet Bulb Temp

E = Efficiency of the evaporative media.

Evaporative media efficiency usually runs between 80% to 90% and the evaporation efficiency drops very little over time. Typical aspen pads used in residential evaporative coolers offer around 85% efficiency while celdec type of evaporative media offer efficiencies of 90% + depending on air velocity. The celdec media is more often used in large commercial and industrial installations.

As an example, in Las Vegas, Nevada with a typical summer design day of 108°F DB/66°F WB or about 8% relative humidity, the leaving air temperature of a residential cooler would be:

LAT = 108° – ((108° – 66°) x 85% efficiency)

LAT = 72.3°F

However, either of two methods can be used to estimate performance:

• Use a Psychrometric chart to calculate wet bulb temperature, and then add 6°F–8°F as described above.
• Use a rule of thumb which estimates that the wet bulb temperature is approximately equal to the ambient temperature, minus one third of the difference between the ambient temperature and the dew point. As before, add 6°F–8°F as described above.

Some rough examples clarify this relationship.

• At 32 °C (90 °F) and 15% relative humidity, air may be cooled to nearly 16 °C (61 °F). The dew point for these conditions is 2 °C (36 °F).
• At 32 °C (90 °F) and 50% relative humidity, air may be cooled to about 24 °C (75 °F). The dew point for these conditions is 20 °C (68 °F).
• At 40 °C (104 °F) and 15% relative humidity, air may be cooled to nearly 21 °C (70 °F). The dew point for these conditions is 8 °C (46 °F).

Because evaporative coolers perform best in dry conditions, they are widely used and most effective in arid, desert regions such as the southwestern USA , Middle East and northern Mexico.

Advantages

Less expensive to install

• Estimated cost for installation is about half that of central refrigerated air conditioning.[8]

Less expensive to operate

• Estimated cost of operation is 1/4 that of refrigerated air.
• Power consumption is limited to the fan and water pump vs. compressors, pumps, and blowers.

Ease of Maintenance

• The only two mechanical parts in most basic evaporative coolers are the fan motor and the water pump, both of which can be repaired for very little and often by a mechanically able homeowner.

Ventilation air

• The constant and high volumetric flow rate of air through the building reduces the age-of-air in the building dramatically.
• Evaporative cooling increases humidity, which, in dry climates, may improve the breathability of the air.
• The pad itself acts as a rather effective air filter when properly maintained; it is capable of removing a variety of contaminants in air, including urban ozone caused by pollution, regardless of very dry weather. Refrigeration-based cooling systems lose this ability whenever there is not enough humidity in the air to keep the evaporator wet while providing a constant trickle of condensate that washes out dissolved impurities removed from the air.

Disadvantages

Performance

• High dewpoint (humidity) conditions decrease the cooling capability of the evaporative cooler.
• No dehumidification. Traditional air conditioners remove moisture from the air, except in very dry locations where recirculation can lead to a buildup of humidity. Evaporative cooling adds moisture, and in dry climates, dryness may improve thermal comfort at higher temperatures.

Comfort

• The air supplied by the evaporative cooler is typically 80–90% relative humidity; very humid air reduces the evaporation rate of moisture from the skin, nose, lungs, and eyes.
• High humidity in air accelerates corrosion, particularly in the presence of dust. This can considerably shorten the life of electronic and other equipment.
• High humidity in air may cause condensation. This can be a problem for some situations (e.g., electrical equipment, computers, paper/books, old wood).

Water

• Evaporative coolers require a constant supply of water to wet the pads.
• Water high in mineral content will leave mineral deposits on the pads and interior of the cooler. Bleed-off and refill (purge pump) systems may reduce this problem.
• The water supply line may need protection against freeze bursting during off-season, winter temperatures. The cooler itself needs to be drained too, as well as cleaned periodically and the pads replaced.

Miscellaneous

• Odors and other outdoor contaminants may be blown into the building unless sufficient filtering is in place.
• Asthma patients may need to avoid poorly maintained evaporatively cooled environments.
• A sacrificial anode may be required to prevent excessive evaporative cooler corrosion.