Evaporative coolers, also known as swamp coolers, rely on the evaporation of water to provide cooling. They work best in dry climates where the outside air is hot and low in humidity. The evaporative cooling process cools the air by evaporating water, which requires heat to change from liquid to vapor. This heat is taken from the air, resulting in cooler air being blown into a space.
Evaporative coolers have some optimal temperature ranges in which they work most efficiently. The effectiveness of an evaporative cooler depends on the temperature and humidity conditions both inside and outside the space being cooled. There are some general guidelines regarding evaporative cooler operating temperatures, but many factors impact their performance.
How Evaporative Coolers Work
Evaporative coolers pull hot, dry outside air through damp pads. As the air passes through the pads, the water evaporates and absorbs heat from the air, causing the air temperature to drop. The cooled air is then circulated into the home or building.
Three key factors impact evaporative cooler efficiency:
- Outside air temperature – The hotter and drier the outside air, the more cooling potential it has.
- Outside air humidity – The drier the air, the more moisture it can absorb.
- Inside vs outside temperature differential – A larger differential allows more heat transfer.
Ideal Temperature Range
Evaporative coolers work best when the outside air temperature is between 75-100°F. Temperatures above 100°F contain too much heat for the evaporative process to overcome. The maximum cooling differential is about 30°F less than the outside air temperature.
So with an outside air temperature of 100°F, the evaporative cooler can potentially cool the inside air to around 70°F. At temperatures above 100°F, evaporative cooling effectiveness drops off.
Factors Impacting Evaporative Cooler Efficiency
Many factors influence how efficiently an evaporative cooler can cool a space at a given outdoor temperature. Consider the following when determining the ideal temperature range for your evaporative cooler:
Outside Air Humidity
An evaporative cooler works by adding moisture to dry air. If the outdoor air is humid, there is less opportunity for evaporation and cooling.
Most evaporative coolers become ineffective at outdoor humidity levels above 60%. Higher humidity means the air has less capacity to absorb moisture.
Size of the Space
A larger space requires a more powerful evaporative cooler to reach and maintain the desired temperature. A smaller evaporative cooler may not keep up well on hotter days in a bigger space. Select an appropriately sized unit for the area you need to cool.
Insulation and Windows
Well-insulated spaces with energy efficient windows retain cooled air better. Homes with poor insulation and leaky windows make an evaporative cooler work harder to maintain indoor temperatures. Proper insulation keeps cool air in and warm air out.
Shade and Sun Exposure
Direct sun exposure heats up a home significantly. Proper shading, awnings, and landscape plants help reduce heat gain from sun. Minimizing solar heat gain improves evaporative cooler efficiency.
Number of Occupants
The more people in a space, the more body heat is generated. Large crowds or gatherings create additional cooling demands. A properly sized evaporative cooler accounts for occupancy.
Internal Heat Sources
Heat emitting appliances like stoves, ovens, and incandescent lights raise the internal heat load. Running these when using an evaporative cooler decreases its effectiveness. Schedule heat generating tasks for early or late in the day.
Optimal Evaporative Cooler Temperatures by Climate
The ideal operating range varies by climate. Here are some general evaporative cooler temperature guidelines for different regions:
Southwest (AZ, NV, UT, NM)
- Optimal outdoor temperature range: 85-110°F
- Maximum indoor cooling: 20-25°F below outside temperature
- Minimum outdoor humidity: 30% or less
The hot, arid desert climates of the Southwest allow evaporative coolers to work exceptionally well. Efficient cooling can be achieved with outdoor temps up to 110°F.
Central Plains (CO, KS, NE, OK, TX)
- Optimal outdoor temperature range: 80-105°F
- Maximum indoor cooling: 15-20°F below outside temperature
- Minimum outdoor humidity: 40% or less
The Central Plains have lower humidity levels that permit good evaporative cooler performance. As humidity increases near the limit, efficiency suffers.
Southern States (AR, LA, MS, AL)
- Optimal outdoor temperature range: 80-95°F
- Maximum indoor cooling: 10-15°F degrees below outside temperature
- Minimum outdoor humidity: 50% or less
Higher humidity in the South restricts evaporative cooling capabilities compared to drier western climates. Avoid using the cooler when humidity is above 50%.
Pacific Northwest (ID, OR, WA)
- Optimal outdoor temperature range: 75-90°F
- Maximum indoor cooling: 10-15°F degrees below outside temperature
- Minimum outdoor humidity: 50% or less
The Pacific Northwest has periods of heat and dryness permitting intermittent evaporative cooler usage. Humidity levels fluctuate more widely in this region.
California Coastal Areas
- Optimal outdoor temperature range: 65-85°F
- Maximum indoor cooling: 8-10°F degrees below outside temperature
- Minimum outdoor humidity: 50% or less
The moderate climate along the California coast allows for only modest evaporative cooling effects. Coolers are not well suited to foggy or humid days.
Seasonal Variations
Outdoor temperature and humidity change throughout the year in most regions. While evaporative cooling works great in summer’s peak heat, performance declines in cooler and more humid months. Units are often only used seasonally.
Spring
As temperatures climb from the milder weather of spring, evaporative coolers start becoming useful. Pay attention to humidity levels as warmer spring days can still be fairly humid. Turn off the cooler when humidity crosses over 60%.
Summer
The hot and dry conditions of summer are when evaporative coolers work at peak performance. Utilize them for maximum savings and cooling. Monitor humidity on monsoon days or tropical weather systems.
Fall
Cooling demands ease up in fall as temperatures gradually moderate. Use the evaporative cooler judiciously once daytime highs dip back below 80°F for consistent effectiveness. Turn it off when humidity rises.
Winter
Evaporative coolers are generally shut down for the winter when humidity is high and temperatures are cool. Some units can be converted to low humidity circulation mode to pull in fresh outdoor air.
Operating Costs
One of the main benefits of evaporative coolers is lower energy consumption compared to traditional air conditioners. The operating costs are much less. Here are some typical electrical usage numbers:
Cooler Size (sq ft) | Electrical Use (kW) |
---|---|
500 | 0.3 – 0.5 |
1000 | 0.4 – 0.7 |
2000 | 0.6 – 1.0 |
3000 | 0.8 – 1.2 |
4000 | 1.0 – 1.5 |
At electricity rates of $0.12/kWh, a 2000 sq ft evaporative cooler costs about $0.12-0.20 per hour to run. This is compared to $0.60-$1.00 per hour for an equally sized central AC unit.
Evaporative coolers use about 1/8th the electricity of traditional air conditioners. The water consumption is also minimal – around 3-5 gallons per hour depending on size.
Maintenance
Proper maintenance ensures an evaporative cooler works efficiently when needed. Recommended maintenance includes:
- Inspect water pump and lines for leaks.
- Check the float valve to ensure proper water flow.
- Clean out mineral deposits from drain bleed-off line.
- Replace cooling pads when they become coated with mineral deposits.
- Clean air filters to maintain proper airflow.
- Check belts for tightness and wear.
- Clean out dust and debris from motors and vents.
- Seal any air leaks in the cooler ducting or wall mounts.
Following the manufacturer’s advised maintenance schedule helps prevent issues and ensures satisfactory performance. Neglected coolers are more prone to breakdowns and poor cooling capability.
Conclusion
Evaporative coolers provide an energy efficient way to keep your home cool in hot, arid climates. They work best when daytime temperatures are between 75-110°F depending on humidity. Colder or more humid conditions decrease their effectiveness. With proper maintenance and understanding your local climate, evaporative coolers can be an economical cooling solution for drier regions. Monitor outdoor temperature and humidity regularly to determine when your evaporative cooler will perform optimally.