Short answer
Evaporative cooling works well when outdoor air is hot and dry, but loses effectiveness as humidity rises. Refrigerated cooling holds temperature and humidity in any weather, at higher energy use.
How does each type cool air?
Evaporative cooling passes outdoor air through wetted media. As water evaporates, it absorbs heat from the air, lowering its temperature and raising its humidity.
The air is then delivered to the space and exhausted, typically with doors, relief dampers, or exhaust fans providing the path out. There is no compressor and no refrigerant.
Refrigerated cooling uses a refrigeration cycle to remove heat and moisture from air, recirculating most of it with a measured amount of outside air. It controls both temperature and humidity, in any outdoor conditions, at the cost of compressor energy.
For how the refrigerated side works inside a packaged unit, see how a commercial rooftop unit works; terms such as sensible and latent load are defined in the glossary.
When does evaporative cooling work well?
Evaporative cooling performs strongest when outdoor air is hot and dry, which describes much of the year in Arizona's low deserts and in parts of inland Southern California.
Under those conditions it can lower supply air temperature substantially with modest energy use. It suits spaces that tolerate some humidity and benefit from high air change rates:
- Warehouses, stockrooms, and receiving areas.
- Garden centers and semi-open retail areas.
- Workshops and service bays.
- Back-of-house spaces where refrigerated cooling would be costly to run.
Where does it fall short?
The effectiveness of evaporative cooling depends on the wet-bulb temperature, which rises with humidity. During Arizona's monsoon season, and during humid spells elsewhere, evaporative coolers can lower air temperature much less and add moisture to the space.
Sales floors, offices, exam rooms, and spaces with sensitive merchandise, electronics, or records often need humidity control that evaporative cooling cannot provide on its own.
Other limitations to weigh:
- Air path. Evaporative systems need a path for air to leave the building. Closed buildings without relief can become humid and uncomfortable.
- Water use. Evaporative coolers consume water continuously while running, plus bleed-off to control mineral buildup.
- Water quality. Hard water causes scale on media and components, increasing maintenance.
- Hygiene. Standing water and wet media require regular cleaning and draining when out of season.
How do maintenance demands compare?
Evaporative coolers have fewer complex components, but they need frequent attention during the season: media inspection and replacement, pump and float checks, water distribution cleaning, bleed-off adjustment, belt and motor service, and seasonal drain-down and start-up.
Neglected coolers lose effectiveness and can develop water quality problems.
Refrigerated systems require a different kind of care: coil cleaning, refrigerant circuit checks, electrical and compressor checks, filter changes, and economizer verification. The work is more technical but often less frequent. Both types benefit from a structured maintenance program; the tasks simply differ.
What about energy and operating cost?
Evaporative cooling generally uses less electrical energy than refrigerated cooling under the dry conditions where it works well, because it runs fans and a small pump rather than compressors.
That advantage narrows when humidity rises and the cooler cannot meet the load, and it must be weighed against water use and maintenance. A comparison for a specific building should use local weather data, utility and water rates, and how the space is used across the year.
How should a portfolio decide?
Decide space by space rather than building by building. Questions to answer for each area:
- What temperature and humidity does the space actually need, and for which hours?
- Can the space accept high airflow and a path for air to leave?
- How does the space perform during the humid part of the season today?
- What does water supply and quality look like at the site?
- What does the existing equipment's condition suggest about timing?
When an existing cooler is failing, the same factors used for rooftop units apply. See repair or replace a rooftop unit: the decision factors.
What happens to evaporative equipment outside the cooling season?
Evaporative coolers should be drained and shut down for the off season, with water supplies isolated and media dried, to limit scale, corrosion, and biological growth.
Covers or dampers prevent unconditioned air entering the building through the idle cooler during the heating months. Each spring, a start-up visit refills the system, checks pumps and floats, inspects or replaces media, and resets bleed-off. Sites that skip these steps tend to see shorter media life, more scale, and odor complaints when the cooler first runs.
How does space use change over time?
A warehouse that was suited to evaporative cooling when it held bulk stock may now house packing stations, offices, or temperature-sensitive goods. A sales floor that once used evaporative cooling may now carry electronics or cosmetics.
Revisit the choice whenever the use of a space changes, rather than only when equipment fails.
What does REE do in desert climates?
REE Mechanical Inc. has an in-house team in Arizona and self-performs across Southern California, including the inland and desert counties.
We handle evaporative cooler installation and replacement as well as refrigerated rooftop units, so the recommendation can follow the space rather than the product line. For getting ready before the hottest months, read the peak-season readiness checklist.
Methodology: Written by REE Mechanical's team from field experience on multi-site commercial portfolios; standards cited link to the issuing body.