Sunday, August 08, 2010
Swamp cooler is an inexpensive way to beat the heat
By Ann Robinson and Annie Schwemmer
Last week we discussed the basics of cooling system upgrades in regard to central air conditioning. However, in this dry, desert climate, central air isn't the last word on effective cooling systems.
Another natural and energy efficient option is an evaporative cooling system.
An evaporative cooler produces effective cooling by combining a natural process — water evaporation — with a simple, reliable air-moving system. Fresh outside air is pulled through moist pads where it is cooled by evaporation and circulated through a house by a large blower.
As this happens, the temperature of the outside air can be lowered as much as 30 degrees while using as much as 75 percent less electricity than air conditioners.
Evaporative cooling systems are more energy efficient because they use a simple, natural cooling process. Even our bodies use evaporation. We perspire in hot weather and through evaporation the sweat dries and lowers our body temperature. The same concept applies in nature.
Whenever dry air passes over water, some of the water will be absorbed in the air. That is why evaporative cooling naturally occurs near waterfalls, rivers, lakes and oceans. Because evaporative cooling adds moisture to the air, they are also known as swamp coolers.
Central air conditioning is a closed system, basically recycling inside air. For air conditioning to function properly, doors and windows should be closed. Evaporative cooling, however, uses outside air, so for proper air circulation, the cooled outside air must be allowed to escape.
Some windows should be strategically opened to pull the air through the house and out so the newly cooled air will flow easily.
Leaving doors and windows open is therefore not a sin when you have evaporative cooling.
Evaporative coolers can be placed on the side of a house or on the roof (though they are large and not terribly attractive, so placement should be considered carefully).
They often have only one point of entry, which is best placed in the most central location possible. From there, air can be directed through the various rooms by simply opening and closing doors and windows.
Evaporative coolers can be hooked up to a duct system, but they cannot share the metal duct system for your forced air heating system because the required air volume for the two systems is different.
Evaporative coolers not only take less energy to run, they are less expensive to purchase and to maintain. They have only a small motor and minimal working parts.
For the swamp cooler to work, the pads need water. Small distribution lines supply water to the top of the pads. Water soaks the pads and, thanks to gravity, trickles through them to collect in a sump at the bottom of the cooler. A small recirculating water pump sends the collected water back to the top of the pads.
Since water is continually lost through evaporation, a float valve — much like the one that controls the water in a toilet tank — adds water to the sump when the level gets low. Under normal conditions, a swamp cooler can use between 3 gallons and 15 gallons of water a day.
The pads can be made of wood shavings — wood from aspen trees is a traditional choice — or other materials that absorb and hold moisture while resisting mildew. Aspen wood pads, also called excelsior, need to be replaced every season or two, and generally cost $20 to $40 for a set.
Like any cooling system, the size of the unit must match the area it is expected to cool. While the output of air conditioners are rated in BTUs (British Thermal Units), evaporative coolers are rated by CFMs (the cubic feet per minute of air that the cooler can blow into your home).
Whether it is for a single room or a whole house, there is a simple formula for determining the proper size of swamp cooler you need. Figure the cubic feet of space you want to cool, and then divide that number by two. The quotient will give you the CFM rating for the proper-size swamp cooler.
The main drawback of swamp coolers is that they depend on dry outside air to operate effectively. This is usually not a problem in Utah, but we do have our occasional muggy days. When it is humid in the summer, swamp coolers will be significantly less effective in cooling your home.
If you have both an evaporative cooler and central air unit, do not run them at the same time. Doing so would cause the two systems to work against each other.
Overall in dry climates, evaporative cooling can be a less expensive, more efficient way to beat the heat. Living in the desert has its perks! As always, we welcome your home architect design questions at firstname.lastname@example.org.