Swamp cooler
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Swamp coolers (also called "evaporative coolers" or "Air coolers") are air conditioners used to cool buildings in dry climates. The technique they use is evaporative cooling, of which two types exist: direct evaporative cooling and indirect evaporative cooling. Evaporative cooling is especially well suited where the air is hot and humidity is low. However, in higher humidity areas, there are many proven cost-effective uses for evaporative cooling that make it the preferred choice. 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).
History
Different civilizations throughout the ages have found ingenious ways to combat the heat in their region. An earlier form of air cooling 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.
Evaporative cooler designs
Direct Evaporative Cooling (open circuit)- used to lower the temperature of air by using latent heat of evaporation, changing water to vapor. In this process, the energy in the air does not change. Warm dry air is changed to cool moist air. Heat in the air is used to evaporate water.
- similar to direct evaporative cooling, lowers the temperature of air by using latent heat of evaporation via some type of heat exchanger. The cooled moist air never comes in direct contact with products or environment.
Typical
Typically, residential and industrial swamp coolers use direct evaporative cooling and can be described as an enclosed, metal or plastic box with vented sides containing a radial fan (also centrifugal or squirrel cage), fan motor with pulley wheels and a water pump to wet the cooling pads. They can be mounted on the roof (down draft) or exterior walls (side draft) of buildings. To cool, the fan draws ambient air through vents on the sides and through the damp pads. Heat in the air evaporates water from the pads which are constantly re-dampened to continue the cooling process. Thus cooled, moistened air is then delivered to the building via a vent in the roof or wall.
Because the cooling air originates outside the building, a vent must exist to allow air to move from inside to outside. Air should only be allowed to cycle once through the system or cooling efficiency will fall. This effect is due to the air reaching the saturation point.
Cooler pads
Traditionally, swamp cooler pads consist of excelsior (wood wool) (aspen wood fiber) inside a containment net, but more modern materials, such as some plastics and melamine paper, are entering use as cooler-pad media. Wood absorbs some of the water, which allows the wood fibers to cool passing air to a lower temperature than some synthetic materials. The thickness of the padding media plays a large part in cooling efficiency, allowing longer air contact. For example, an eight-inch-thick pad with its increased interface will be more efficient than a one-inch pad.Evaporative (wet) cooling towers
Cooling towers are larger structures for cooling water or other working media to near-ambient temperature. Wet cooling towers operate on the evaporative principle and may be used in a swamp cooling arrangement. Cooling towers can be found on large buildings or on industrial estates.
With respect to drawing air through the tower there are three types of cooling towers:
- natural draft, which utilizes a tall chimney,
- fan assisted natural draft, and
- mechanical draft which uses power driven fan motors to force or draw air through the tower.
Misting systems
Misting system work by forcing water via a high pressure pump and tubing through a brass and stainless steel mist nozzle that has an orifice of about 5 micrometres, thereby producing a micro-fine mist. The water droplets that create the mist are so small that they instantly flash evaporate. Flash evaporation can reduce the surrounding air temperature by as much as 35 °F (20 °C) in just seconds. For patio systems, it is ideal to mount the mist line approximately 8 to 10 feet above the ground for optimum cooling. Misting is used for many different applications including orchids, pets, livestock, kennels, insect control, odor control, zoos, veterinary clinics, produce cooling, greenhouses, etc.
Photo of Misting fan.
Misting fans
A Misting fan is a similar to a humidifier. A fan blows a fine mist of water into the air. If the air is not too humid, the water evaporates, absorbing heat from the air, allowing the misting fan to work as an air conditioner. A misting fan may be used outdoors, especially in a dry climate.
Performance
Understanding evaporative cooling performance requires an understanding of psychrometrics. Evaporative cooling performance is dynamic due to changes in external temperature and humidity level. Under typical operating conditions, an evaporative cooler will nearly always deliver air cooler than 27 °Celsius (80 °Fahrenheit). A typical residential swamp cooler in good working order should cool air to within 3°C - 4°C (6°F - 8°F) of the wet-bulb temperature.Some rough examples clarify this relationship.
- At 32 °C (90 °F) and 15% relative humidity, air may be cooled to nearly 16 °C (60 °F).
- At 32 °C (90 °F) and 50% relative humidity, air may be cooled to about 24 °C (75 °F).
- At 40 °C (105 °F) and 15% relative humidity, air may be cooled to nearly 21 °C (70 °F).
(cooling examples extracted from the June 25, 2000 University of Idaho publication, "[Homewise]").
Advantages vs. refrigerated air-conditioning
Less expensive to install
- Estimated cost for installation is 1/8 to 1/2 that of refrigerated air conditioning
- 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.
- The constant stream of air from intake to vent through the building freshens the air in the building.
Disadvantages vs. refrigerated air-conditioning
Performance
- High temperature, high humidity outside conditions decrease the cooling capability of the swamp cooler.
- The air supplied by the swamp cooler is nearly 100% humid (but typically is only 80-90%).
- Very humid air prevents the evaporative cooling of sweaty or wet skin.
- High humidity in air accelerates corrosion. This can considerably shorten the life of electronic equipment.
- High humidity in air may cause condensation (which can be extremely hazardous if it happens inside electrical equipment)
- Swamp 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. Water softeners, bleed-off and refill systems may relieve this problem, however.
- Water line needs protection against freeze bursting during off-season, winter temperatures.
- Pollen, odors, and other outdoor contaminants may be blown into the building unless sufficient filtering is in place.
- The vents that allow air to exit the building may pose a physical security risk.
- Asthma patients may need to avoid evaporatively cooled environments.
References
See also
- Air conditioning
- Cooling tower
- Cooling tower system
- Pot-in-pot refrigerator
- Dew point
- Evaporation
- Humidity
- HVAC
External links
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