Evaporative “swamp” coolers combine evaporation cooling with wind chill from a fan. The process and parts are fairly simple.
Hot, dry air is pulled into the cooler by the pump.
First, motors power the fans that draw water into the unit.
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.
Pumps supply water to be distributed.
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.
Then the water is distributed over fibrous pads.
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.
The pads hold the water long enough for it to evaporate and absorb the heat from that process.
The pads and the filters are swamp cooler parts that need to be regularly replaced. 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 swamp 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.
The same fans that pulled the hot, dry air into the unit blow the freshly cooled air out.
The size of the fan determines how much air flow a swamp cooler can produce. This air flow balances with the amount of water being evaporated to produce the most efficient cooling – up to 20º or more in hot, dry conditions.
Cabinets or “Housing”
The cabinet protects the mechanisms – especially important for outdoor use.
A swamp cooler’s cabinet (its outer “shell”) is highly susceptible to corrosion, especially when placed outside for outdoor cooling. This can range from every day 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.
Other Outdoor Cooling Methods
Swamp coolers combine two of the most effective outdoor cooling methods. But, as mentioned above, they have some limitations. You can maximize their cooling by combining them with other methods or devices, or other options may be more effective.
Take a look at our comparison page or our pages on other outdoor cooling methods:
- Outdoor fans combine well with swamp coolers, ensuring adequate air flow and distributing the cool air from evaporation.
- Misting fans are another kind of device that combines evaporation and wind chill to cool outdoor areas.
- Outdoor shades are a nearly universal solution that work well with any outdoor cooling method, including swamp coolers.
- Misting systems use a similar technology as swamp cooler, but in an open system that can cool larger areas.
- Portable air conditioners are especially suited to enclosed areas (tents, sheds, etc.) and special circumstances.