Evaporative coolers

While heat pumps are the most energy-efficient cooling system for our local climate, many homes in the Valley are equipped with evaporative coolers. These units perform best when the outside humidity level is low. Here is some information to help you get the greatest comfort and efficiency from your evaporative cooler.

What is an evaporative cooler?

An evaporative cooler is a box-shaped appliance with one or more porous surfaces that enable air to pass through. A fan inside the unit pulls outside air through the sides and into the house. To produce cool air, each porous side is fitted with a pad of water-absorbing material. Water is stored in a pan at the bottom of the cooler and a small pump lifts the water to the top of each side.

To effectively cool your home, each pad needs to remain damp, but not soaked. Dampness creates the most evaporation and, therefore, the most cooling. The amount of water the pump moves may need to be adjusted from time to time to properly dampen the pads.

Adjusting the air flow

Climate control inside a home with an evaporative cooler depends on proper air balance. To limit humidity, you need to make sure that the same volume of air flows out of your home as is pumped in.

You can attain balanced air flow by installing ducts in each room or opening windows when the cooler is in use. A window should be open just enough to allow air pressure inside a room to slowly and quietly close the door to that room. If the door closes forcefully, there is too little exhaust and the window should be opened wider. However, the window is open too far if the door doesn't move at all.

Checking unit size

To choose the right size evaporative cooler for your home, you need to determine how many cubic feet of air per minute (CFM) the unit can pump.

If you can't locate the CFM number on your evaporative cooler or in the owner's manual, the following formula will help you calculate it:

  • Multiply the square footage of your home by the average height of the ceiling (in feet).
  • Divide by two (air changes per minute).

Example: 1,625 sq. ft. x 8 ft. (ceiling height) = 6,500 CFM/2

Caring for your cooler

Have your cooler serviced twice a year, prior to the cooling season and midway through summer. Regular maintenance will help extend the life and efficiency of the equipment.

Before starting up the unit, perform these simple maintenance steps:

  • Remove old pads and thoroughly clean pad frames. Use a wire brush to scrape away scale. Paint all surfaces with a cooler protectant.
  • Drain and flush the reservoir. Scrape away scale and paint with protectant.
  • Clean the water distribution system, including the pump screen, pump impeller and water distribution tubes. Replace any cracked tubing. Lubricate the pump impeller with SAW 20 motor oil.
  • Inspect electrical wiring and switches for poor connections or worn insulation. Inspect the belt for cracks and wear. Replace or repair worn parts.
  • Adjust motor bolts for proper belt tension. Set the belt tension so that moderate hand pressure will depress the belt about one inch at the center.
  • Turn on the water supply and make sure water is wetting the entire cooler pad. Too little water will cause dry spots and reduce the cooler's efficiency.
  • Check the water level in the reservoir. Adjust the float valve to maintain about three inches of water.
  • Replace the cooler pads and reinstall the frames. Ideally, the first five steps should be performed at season's end. If you will not be using the unit during the winter, shut off the water supply and disconnect electricity to the unit. Then drain the water line to prevent possible wintertime freezing. Close the duct dampers and cover the unit.

Improving cooler efficiency

Evaporative cooler thermostats, available at many hardware stores, automatically turn off the cooler when the air reaches a desired temperature, making operation much more efficient.

Most evaporative coolers without thermostats have separate switches for the fan and pump. If your unit lacks a thermostat, allow your pump to run a few minutes before turning on the fan. This saturates the cooler pads.

Evaporative cooling vs. air conditioning

Evaporative coolers and central air conditioners both serve the same important purpose: keeping us cool. But these two systems operate very differently. Understanding the difference can help you get the most out of your system and minimize wasted energy.

Evaporative coolers cool air by filtering it through water, thus lowering its temperature. Evaporative coolers produce humid air because the air absorbs water during the cooling process. These systems work best when a small amount of outside air circulates into the home while the cooler is on.

Central air conditioners, on the other hand, work by taking humidity out of the home. These systems produce cold, dry air and work best in an airtight home.

Things to keep in mind

  • 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.
  • If you have central air, there is no need to crack a window or open a door to make the system more effective. In fact, this will make the system work harder and cost you more money.

Regardless of what type of system you have, make sure it is operating properly. Systems that leak water, make unusual noise, or that don't produce cold air are probably not energy-efficient and can increase your energy bill.

The pros and cons of evaporative coolers

The major advantage of an evaporative cooler is that its operating costs are typically half those of a central air conditioner. However, during the Valley's monsoon season (between July and August) humidity often rises and, when combined with high temperatures, limits cooler effectiveness. For that reason, few Valley homeowners rely exclusively on evaporative cooling.

  • Lower original equipment cost than air conditioners
  • Lower operating costs
  • Simple installation
  • Reduced control over temperature in house
  • Air is not cleaned as well as with an air conditioner
  • Need to open windows or vents to outside
  • Damp air can cause doors and wood furniture drawers to swell
  • Requires more maintenance than an air conditioner

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