Evaporative coolers use a substantial amount of water, which could present a problem during times of drought. Depending on the severity of the drought and how much water your cooler uses, you may want to look into the following options:

  • Install a thermostat and timer on your cooler so it only operates when necessary.
  • Use a two-speed blow motor. Operating at low-speed uses less water and is more energy efficient.
  • Inspect your cooler monthly and perform maintenance as necessary to be sure that your cooler is operating efficiently.
  • Use alternative methods of cooling, including fans or an air conditioner if you have one. (However, be sure not to precool air using an evaporative cooler before turning on an air conditioner. This causes the air conditioner to use more energy).
  • Install a bleed-off clamp on your bleed line to limit the amount of water drained. This could save 4 to 14 gallons per hour depending on your system!
  • Re-use bleed water in your yard for irrigation. (But don’t forget to adjust your current sprinkling schedule appropriately!)
 Figure 1: El Paso Water is currently promoting water restriction clamps for their customers. Bend the metal and slide plastic tubing into clamp. Tighten screw into desired position.
Figure 1: El Paso Water is currently promoting water restriction clamps for their customers. Bend the metal and slide plastic tubing into clamp. Tighten screw into desired position.

In addition, below are some “Cool Rules” developed by Water Wise of the University of Arizona Cooperative Extension for saving water during a drought.

  • Be brave, delay turning on your cooler until the outside temperature reaches 85 degrees rather than turning it on when it is 79 degrees. You will use 50% less water.
  • Turn on the water pump a few minutes before turning on the fan. This saturates the pads first, making your cooler more efficient.
  • Open a window a crack in the rooms you are cooling. This will draw the cooled air through these spaces.
  • Use ceiling fans to circulate air within your home.
  • In the evenings, operate your cooler fan without the water pump. Cool air will be moved through your house without using any water.

Evaporative Cooler Water Use

Evaporative coolers use a substantial amount of water to run. Systems with bleed valves and sump dump systems use the most water. This should be taken into consideration in areas where water is expensive or in short supply.

A study conducted by the University of Arizona’s Office of Arid Lands Studies at the request of the city of Phoenix tried to quantify exactly how much water is used by evaporative coolers. The study found that average daily water use was 66 gallons per day, or 14,000 gallons per year (212 days of cooling). Coolers without a bleed valve used an average of 3.5 gallons per hour, while the coolers with a bleed valve used 10.5 gallons per hour. The percentage of household water used by the coolers was 25.8% for households without air conditioning, and 15.8% for all houses. On average, coolers ran 2,100 hours during the summer (Karpiscak et. al. 1998). Similar results were found in a study conducted in El Paso, Texas (Tarquin 1999).

Average water use (gal/hr) Average run time (hr/yr) Yearly water use (gal/yr)*
Without bleed 3.5 2,100 7,350
With bleed 10.5 2,100 22,050


*Extrapolated from Karpiscak et. al. 1998 study.
Source: Karpiscak et. al. 1998

In general, the amount of water used by your evaporative cooler will depend upon its size, air movement, and the relative humidity of the air. All things being equal, a 4500 CFM cooler uses less water than a 6000 CFM cooler. However, the most important difference is water usage rates for evaporative coolers is the use of bleed water.

Thermostats and timers can be utilized to decrease the amount of water (and energy) used by evaporative coolers. A thermostat can be set to a certain temperature so that the evaporative cooler is only used when necessary. In addition, timers can be used so that the evaporative cooler can turn on just before residents get home.

Water Savings

There are a variety of water saving opportunities for your evaporative cooler. The best way to save water with an evaporative cooler is to have a re-circulating system that does not bleed off water. This is the best option for coolers that operate with soft water. However, if your cooler is operating with hard water, you may need to install a bleed line. To curb bleed water use, you can install a bleed-off clamp on the line to minimize the amount of bleed. These clamps could save you between 4 and 14 gallons per hour, depending on your system! If your system does bleed water, try to re-use the water on-site for your outside landscape. This will indirectly save you water from irrigation (so remember to adjust sprinkling schedules appropriately!).

Regardless of your system, there are things you can do to decrease water use in general. Some are listed here:

  • Install a thermostat and timer on your cooler so it only operates when necessary.
  • Use a two-speed blow motor. Operating at low-speed uses less water and is more energy efficient.
  • Inspect your cooler monthly and perform maintenance as necessary to be sure that your cooler is operating efficiently.
  • Turn on the water pump a few minutes before turning on the fan. This saturates the pads first, making your cooler more efficient.
  • On cool evenings, you can operate your cooler fan without the water pump. The fan will bring cool air into your house without using any water.
  • Use alternative methods of cooling, including ceiling fans or an air conditioner if you have one. (However, be sure not to precool air using an evaporative cooler before turning on an air conditioner. This causes the air conditioner to use more energy).

Evaporative Cooler Wastewater Savings

Any evaporative cooler that uses a bleed valve to flush a portion of the re-circulating water and/or water from its reservoir produces wastewater. Coolers without a bleed valve use an average of 3.5 gallons per hour, while the coolers with a bleed valve use 10.5 gallons per hour, (Karpiscak et. al. 1998), thus coolers probably generate about 7 gallons of waste water per hour. The wastewater can either be drained to the sanitary sewer system or reused on-site.

Wastewater from an evaporative cooler can be re-used for irrigation purposes. Irrigation is a natural use for this water since the hot, dry conditions that often spur cooler use also spur irrigation demand. However, evaporative coolers also typically function in desert areas where the water has a high concentration of salts. This is a concern for plants that are sensitive to water with a high mineral concentration. In a study conducted by the University of Arizona’s Office of Arid Land Studies, it was found that coolers with a bleed off system produced wastewater with total dissolved solids (TDS) of 375 to 4,043 Mg/L. In general, water with a TDS below 5,000 Mg/L can be used for most irrigation (Karpiscak et. al. 1998). Nevertheless, you may want to research specific plants before irrigating them with the wastewater.

In addition, continual use of your cooler may cause overwatering. This is especially true if you don’t move the bleed-off hose regularly to different areas of your landscape. Alternatively, you can connect the bleed line to an underground irrigation system, such as drip irrigation, as shown below.

Figure 1: An example of a bleed line that connects to drip irrigation. Source: Aquacraft
Figure 1: An example of a bleed line that connects to drip irrigation. Source: Aquacraft

Evaporative Cooler Energy Savings

Evaporative coolers use a relatively low amount of energy, especially when compared to air conditioners. It has been estimated that a 1,600 square foot home will annually use 1,500 kilowatt hours for an evaporative cooler, versus 6,000 kilowatt hours for a refrigeration system. Thus, evaporative coolers can help save energy and money.

Table 1: Estimated energy usage and cost for evaporative coolers and air conditioners operating in a 1,600 square foot home.

Annual kWh Cost per kWh Annual Cost
Evaporative Cooler 1,500 $0.10 $150
Air Conditioner 6,000 $0.10 $600

Although evaporative coolers have relatively low energy use, there are a few things you can do to insure that you avoid wasting energy (and water). Be sure that you install a thermostat and/or timer on your evaporative cooler so that it only functions when necessary. In addition, many coolers are available with two-speed blower motors. Often you will only need your cooler to operate at a low speed, which is the more energy efficient mode.

Some homes have a combined system where the same ductwork is used for an evaporative cooler and air conditioner. In this case, make sure that you don’t precool the air in the house using the evaporative cooler before turning on the air conditioner. Refrigeration systems use more energy if they have to remove moist air brought in by evaporative coolers.

Benefits and Costs

The costs and benefits of owning and operating an evaporative cooler must be weighed by prospective users. Some of the pros and cons are listed below.

Benefits:

  • Provides cool, comfortable indoor environment for dry, hot climates.
  • Uses between one-tenth and one-third of the energy that air conditioners (AC) use.
  • Uses no ozone-depleting chemicals.
  • Relatively inexpensive compared to AC units.
  • Bleed water can often be reused for on-site irrigation.
  • Repairs and maintenance are fairly simple.
  • Operates as an open system that brings in fresh air, rather than re-circulating air.
  • Maintains natural humidity levels inside that help to keep furniture and fabrics from drying out.
  • Evaporative cooler pads filter incoming air.
  • Less noisy than AC units.

Costs:

  • Require frequent maintenance.
  • Only work under dry conditions.

As far as hard costs, evaporative coolers are less expensive than air conditioners. For example, a 4500 CFM evaporative cooler costs about $700 to purchase and install. A similarly sized AC unit would cost about $2,500. In addition, repair parts are often more expensive for AC units than evaporative coolers. Below is a cost sheet that estimates annual utility costs for evaporative coolers and AC units.

Table 1: Estimated annual utility costs for evaporative coolers and air conditioners.

Water Usage (kgal.) Cost per kgal† Annual Water Cost Electric usage (kWh) Cost per kWh Annual Electric Cost Total Annual Cost
Evaporative Cooler 19 $2.84 $53.96 1500 $0.10 $150.00 $203.96
Air Conditioner 0 $2.84 $0.00 6000 $0.10 $600.00 $600.00


† Based on the national average water and sewer costs.
Source: “Evaporative cooler water use” by Martin Karpiscak of Arizona Cooperative Extension. Accessed April 11, 2003.

Environmental Benefits

Evaporative coolers offer a few environmental benefits. Mainly, evaporative coolers use a relatively low amount of energy to cool your home. In fact, they use between one-tenth and one-third of the energy that air conditioners use. As a replacement for AC, coolers can help to curb your home’s overall greenhouse gas emissions. In addition, evaporative coolers don’t use ozone-depleting chemicals. Evaporative coolers are also a fairly quiet method of cooling. Nevertheless, some evaporative coolers use a large volume of water to operate, especially if they have a bleed line.

Sources: Karpiscak, M.M., et. al. 1998. Evaporative cooler water use in Phoenix. Journal AWWA, 90(4): 121-130.

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