In low-humidity areas, evaporating water into the air provides a natural and energy-efficient means of cooling. Evaporative coolers, also known as swamp coolers, use this principle. By passing outdoor air over water-saturated pads, the water in the pads evaporates, reducing the air temperature by 15° to 40°F before it is directed into the home.
How Evaporative Coolers Work
When operating an evaporative cooler, windows are partially opened to allow warm indoor air to escape as it is replaced by cooler air. Unlike central air conditioning systems that recirculate the same air, evaporative coolers provide a steady stream of fresh air into the house. Evaporative coolers cost about half as much to install as central air conditioners and use about one-quarter as much energy. However, they require a supply of water and need more frequent maintenance than refrigerated air conditioners. They are only suitable for areas with low humidity.
Sizing and Selection
Evaporative coolers are rated by the cubic feet per minute (cfm) of air they deliver to the house. Most models range from 3,000 to 25,000 cfm. Manufacturers recommend providing enough air-moving capacity for 20 to 40 air changes per hour, depending on the climate. (NREL 2001)
Installation
Evaporative coolers can be installed in two ways:
- Central Location: The cooler blows air into a central location. This works well for compact houses that are open from room to room.
- Ductwork Connection: The cooler connects to ductwork, which distributes the air to different rooms. This is required for larger houses with hallways and multiple rooms.
Most residential evaporative coolers are installed in a down-flow arrangement on the roof. However, many experts prefer ground-mounted horizontal units, which are easier to maintain and less likely to cause roof leaks. Small horizontal-flow coolers can be installed in windows to cool a room or section of a home. Portable evaporative coolers on wheels are also available but provide only a slight cooling effect and are limited by the humidity within your home.
Operation
Key Features
- Two Speeds and Vent-Only Option: Ensure your evaporative cooler has at least two speeds and a vent-only mode. The vent-only mode allows the cooler to function as a whole-house fan during mild weather by operating without the water pump.
Adjusting Air Movement
- Window Adjustments: Control air movement by adjusting window openings. Open windows or vents on the leeward side of the house to provide 1 to 2 square feet of opening for each 1,000 cfm of cooling capacity. Experiment to find the right windows to open and the correct amount to open them.
- Too Much Open: If windows are open too far, too much hot air will enter.
- Not Enough Open: If windows are not open far enough, humidity will build up in the home.
Temperature and Humidity Control
- Targeted Cooling: Open windows in areas you want to cool and close windows in unoccupied areas to regulate temperature and humidity.
- Security Concerns: If open windows create a security issue, install up-ducts in the ceiling to exhaust warm air into the attic as cooler air comes in from the evaporative cooler. Evaporative coolers with up-ducts will need additional attic ventilation.
Air Filters
- Dust Reduction: Optional filters can remove most of the dust from incoming air and reduce the tendency of coolers to pull water droplets from the pads into the fan blades. If your evaporative cooler does not have an air filter as part of the original equipment, it can be retrofitted during or after installation.
Evaporative Cooler Maintenance
Regular maintenance is essential to keep your evaporative cooler running efficiently.
Routine Maintenance
- Monthly Checks: In hot climates where the cooler operates often, check the pads, filters, reservoir, and pump at least once a month.
- Pad Replacement: Replace the pads at least twice during the cooling season, or as often as once a month during continuous operation.
- Pad Cleaning: Some paper and synthetic cooler pads can be cleaned with soap and water or a weak acid according to the manufacturer's instructions.
- Filter Cleaning: Clean the filters when the pads are changed or cleaned.
Seasonal Maintenance
- Major Cleaning: Evaporative coolers need a major cleaning every season. Drain and clean the cooler regularly to remove sediment and mineral buildup.
Safety Precautions
- Disconnect Electricity: Be sure to disconnect the electricity to the unit before servicing it.
Two-Stage Evaporative Coolers
Two-stage evaporative coolers are newer and more efficient. They use a pre-cooler, more effective pads, and more efficient motors, and don't add as much humidity to the home as single-stage evaporative coolers. These are most often used in areas where daytime temperatures frequently exceed 100°F.
Drawbacks of Evaporative Coolers
- Humidity: Evaporative coolers should not be used in humid climates because they add humidity to the air in your home.
- Cooling Capacity: They do not cool your house as low as an air conditioner would.
- Maintenance: They require simple maintenance about once a month.
- Roof Installation: If installed on the roof, routine maintenance can cause roof deterioration and may require using a ladder.
- Water Use: Evaporative coolers continually use water, which may be a concern in areas with limited water supplies.
Take Action
Consider an evaporative cooler for energy-efficient cooling in low-humidity areas. Ensure proper installation and regular maintenance for optimal performance. For more information, explore ENERGY STAR® certified products to help you save energy.
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