Swamp Cooler Types for Outdoor Use
An evaporative cooler, more commonly known as a swamp cooler or desert cooler, can generally be used for outdoor cooling as long as it is set-up correctly and rated for safe use in the kind of location where you will be using them. But some are easier to use for outdoor cooling than others.
Avoid styles that have air vents coming out the bottom of the unit. These are designed to be permanently mounted to the roof of a building with cool air vents leading from the unit down into the building.
Look instead for coolers with air vents coming out the side, or out of the top with air flow adaptes than can direct the air flow where you need it. Also look for features such as wheels that can make them easier to move around and use outdoors.
Swamp coolers are generally classified by how they work or by their size.
How They Work
- Single-stage swamp coolersare the most common and least expensive to purchase. They create more humidity than two-stage units -- as much as 70 - 80% relative humidity. This means their cooling will be most effective in only the driest climates and weather. The chart below shows the range of cooling you can expect from a single-stage unit.
Single-stage units with "direct" technology use the most basic technology: warm air blowing through the pads and the cooled air blowing directly out of the unit. These are the least expensive and easiest to find. Single-stage units with "indirect" technology add a heat exchanger to the unit. This may lower the amount of humidity produced by the unit, but it can also lower the cooling somewhat.
- Two-stage swamp coolers (also called "indirect-direct") produce less humidity than single-stage units -- around 50 - 70% relative humidity. But because of the way they are made, this does not lower their cooling effect. In fact, the air from these can be up to 6°F / 3.5°C cooler than air from a direct cooler. These are more expensive than similar units that use direct cooling, and also require more maintenance. They are mostly available in larger units, but this technology will gradually make its way down to smaller portable swamp coolers, too.
In the first (indirect) stage the warm air goes through a cooling chamber where it is pre-cooled. In the second (direct) stage this pre-cooled air is blown through the water soaked pads and then into the area being cooled. Because the air going through the pads is already cooled a bit, it needs less moisture to lower it to the desired temperature. Since it picks up less moisture, it picks up less humidity to provide the same degree of cooling as a single-stage unit. Less humidity means it can cool in a wider range of weather conditions than a single-stage unit.
- Another fairly new technology uses dessicants (materials such as silica) that remove moisture from the air. Fresh air first passes through this material to dehumidify it before going through the single-stage or two-stage cooling process.
Size
Smaller sizes, best used for "spot cooling" or "small area cooling" use fan blades smaller than 16 inches / 40 cm but 12 inches / 30 cm is most common. These small units seldom list their blade size in the product description. They usually look like a tall rectangle under 3 feet / 1 meter tall and less than 2 feet / 61 cm wide and deep.
Their cabinets are sleeker than larger sized units. You might prefer to have these in a room with you since they are more visually appealing than the larger units. Since they are small their water tanks are rarely more than 5 gallons / 19 litres. They range from as little as 250 CFM all the way up to 3,800 CFM.
Larger portable swamp coolers have fan blades that start at 16 inches / 40 cm and go up to 48 inches / 122 cm and more. They look like big screen TVs or huge computer monitors with a big fan in the back. They need large cabinets to house these large fans and water tanks of 10 to 65 gallons / 30 to 250 litres. Their cabinets may be as small as 24 inches / 60 cm square by 42 inches / 105 cm, but are usually over 3 feet / 1 metre square and deep, and can get much larger. Weights start at just under 100 lbs / 45 kg and can range up to several hundred pounds / kilograms.
They are powerful, moving thousands of cubic feet per minute and capable of cooling large areas. Yet they use very little electricity -- they rarely draw more than 10 amps at 115 volts (1150 watts). So even most of these large coolers can run on regular household currents.
Basic Parts of a Swamp Cooler
Knowing a little about a swamp cooler's parts can help you make smart choices in purchasing, maintenance and repairs.
Pads
The use of pads or "media" sets swamp coolers apart from other outdoor cooling methods. The pads are made of special materials and construction that allow them to be saturated with water yet still allow as much air as possible to flow through them.
They are traditionally made of pliable aspen wood fiber, called "excelsior." Another option is special wood fiber (cellulose) papers or kraft paper (cardboard) that are combined with resins and glues to form a rigid pad. They are also available in synthetic materials which can last a very long time but may not hold as much water as other materials. These are formed into any of a number of configurations designed to increase saturation and air flow.
These materials need to be able to hold moisture while resisting mildew. Because they are constantly exposed to water, pads are subject to developing mold and odors. They may be treated in a number of ways to keep them from developing and picking up impurities like bacteria, algae, mold, etc.
Because swamp coolers use fresh air, pads are exposed to dust and pollen and other contaminants, especially when being used for outdoor cooling. But the water that constantly flows over the pads also acts as a cleansing agent, gently washing these things off of the pads and into the waste-water drain. Many evaporative coolers also use air filters to filter the air before it enters the unit. With the combination evaporative coolers can be very effective air filters.
Impurities that stick to the pad (dust) or grow in the pad (mold) decrease their effectiveness. Though pads are treated and constructed to minimize this, they should be replaced regularly to ensure they are clean and effective.
Most swamp coolers are designed to take only a certain size of pads. Pads vary in thickness from 1 to 24 inches / 2.5 to 60 cm. The thicker they are the more water they can hold and the more cooling they can provide. More air flow is needed to get through the thicker pads, so the thickest pads are used in more powerful coolers.
Make sure you'll be able to get replacement pads for any evaporative cooler you buy. Prices and sizes can vary widely. Some coolers may use only one pad while others may use several.
Water Distribution
Water distributors are designed to provide continuous, even flow of water over the pads. Pads must be completely and constantly saturated. Any place on the pads that is not saturated is a place where hot air can come in to the room. If your unit is not cooling well, the water distribution lines may be clogged and need cleaning.
Pumps
Swamp coolers use simple recirculating pumps. They should include a feature that will simply shut off the pump when there is not enough water available. This protects the pump from any damage caused by overheating. It allows your cooler's fan to still operate, but you will not get the benefits of the cool air from evaporation when the pump is off. Instead you'll start to feel the air from the unit get warmer as the pads start to dry out because no water is being pumped over them.
Motors
Swamp coolers use either an axial or a centrifugal motor with either a belt drive or direct drive. Direct drive motors are generally more efficient than belt driven motors and need less maintenance. Belt drive motors are generally quieter. Motors may need to be lubricated each year or may have sealed bearings that are maintenance-free.
1- or 3-PHASE MOTORS
Since they require so little power, almost all evaporative coolers are powered by single phase motors. But as you're shopping around you may notice that some of the largest are powered by 3-phase motors. In fact, most motors larger than 750 W / 25,000 BTU use a 3-phase system.
3-phase technology can power these larger motors more economically than a similar single-phase system. 3-phase motors also tend to vibrate less and last longer than similar single-phase motors.
If you need one of these larger units, make sure it can work with your electrical supply. Some 3-phase coolers can operate on more than one voltage supply, making them very versatile as well as powerful.
Cabinets or "Housing"
A swamp cooler's cabinet (its outer "shell") is highly susceptible to corrosion, especially when placed outside for outdoor cooling. This can range from everyday exposure to the outside weather -- heat, wind, rain and snow, to dust and debris being pulled into the unit from fresh air, to mineral build-up inside from constant water use.
Cabinets that resist this corrosion not only continue to look their best, but also protect the working elements inside. Look for fiberglass or galvanized steel cabinets that have powder coated finishes. Painted cabinets may need to be repainted from time to time to maintain their appearance and keep corrosion in check. Also look for cabinets made of plastics such as tough, injection molded polyethylene. I've seen warranties for as long as 25 years on polyethylene cabinets -- than can be longer than the life of the cooler, itself.
