Electricity and water operating costs
An evaporative cooler trades a large compressor for a fan, a small pump, and water. Its running cost depends on three things: fan and pump power, run-hours, and how much water you consume at local prices.
Electricity
A cooler's electrical draw is mostly its fan motor, plus a small recirculation pump. Because it has no compressor, DOE says evaporative coolers can use about one-fourth as much energy as central air conditioners.[1] The best number is your own: read the nameplate watts or use a plug-in energy meter on portable units.
Air conditioners draw more power in extreme heat. DOE notes conventional air-cooled condensers use about 10% more power for each 10 °F (5.6 °C) above 95 °F (35 °C).[1] Use realistic hot-day AC power when comparing.
Water
Consumption is evaporation plus bleed-off or flushing. Evaporation rises with airflow and with how dry the air is. DOE cites seasonal estimates for a 1,500 ft² home without bleed-off of 2,980 gallons (Santa Fe), 7,261 gallons (Albuquerque) and 12,457 gallons (Las Cruces, New Mexico), and says to increase these by 50% with a bleed-off valve (SWEEP 2007).[1] Estimate yours with the water use calculator. Remember sewer charges if your utility bills them by water volume.
Worked example (illustrative inputs, not typical values)
| Evaporative cooler | Air conditioner | |
|---|---|---|
| Electrical power | 0.5 kW | 3.0 kW |
| Run time | 8 h/day × 120 days = 960 h | |
| Electricity at 0.15 per kWh | 480 kWh → 72.00 | 2,880 kWh → 432.00 |
| Water: 45 L/h × 960 h = 43.2 m³ at 1.50 per m³ | 64.80 | none |
| Season total | 136.80 | 432.00 |
The amounts are in whatever currency your tariffs use. With these inputs water is almost half the cooler's cost, so where water is expensive, or electricity is cheap, the gap narrows. Run your own numbers.
Costs the calculator leaves out
- Pads and maintenance (see the maintenance guide).
- Time-of-use or tiered tariffs and demand charges.
- Installation, ductwork and relief vents.
- Comfort differences on humid days, when a cooler may simply not achieve the same result.
Sources
- U.S. DOE Building America Solution Center (PNNL), "Evaporative Cooling Systems"