Home / Tools / Free-cooling hours map
Original data · 45 US markets · NOAA 2020 to 2024How many hours a year can the chiller stay off?
At ASHRAE W32 water and a 10°F approach, a dry cooler alone carries the load 90% of the year in Ashburn, Virginia, and between 51% (Miami) and 99% (Los Angeles) across 45 US data center markets. Pick a water class and see every market.
Facility water class
Air on the coil
Every market, ranked W32, 10°F approach
| # | Market | Full free cooling, dry | With adiabatic | Chiller hours / yr | Design dry bulb |
|---|---|---|---|---|---|
| 1 | Los Angeles, CA | 99% | 100% | 1 | 85°F |
| 2 | Seattle, WA | 98% | 100% | 2 | 87°F |
| 3 | Hillsboro, OR | 94% | 100% | 21 | 96°F |
| 4 | Boston, MA | 94% | 100% | 2 | 91°F |
| 5 | Santa Clara, CA | 94% | 100% | 15 | 94°F |
| 6 | Cheyenne, WY | 93% | 100% | 0 | 91°F |
| 7 | Pittsburgh, PA | 93% | 100% | 1 | 90°F |
| 8 | Minneapolis, MN | 92% | 100% | 4 | 92°F |
| 9 | Secaucus, NJ | 91% | 100% | 0 | 92°F |
| 10 | Columbus / New Albany, OH | 91% | 100% | 0 | 91°F |
| 11 | Ashburn, VA | 90% | 99% | 4 | 95°F |
| 12 | Cincinnati, OH | 90% | 99% | 0 | 92°F |
| 13 | Chicago, IL | 90% | 99% | 6 | 92°F |
| 14 | Des Moines, IA | 90% | 99% | 5 | 93°F |
| 15 | Denver, CO | 90% | 100% | 15 | 96°F |
| 16 | Manassas, VA | 89% | 98% | 4 | 94°F |
| 17 | Quincy, WA | 89% | 100% | 74 | 100°F |
| 18 | Philadelphia, PA | 88% | 99% | 1 | 94°F |
| 19 | Boise, ID | 87% | 100% | 103 | 101°F |
| 20 | Omaha / Council Bluffs, NE | 87% | 99% | 15 | 95°F |
| 21 | Reno, NV | 87% | 100% | 73 | 99°F |
| 22 | Richmond, VA | 87% | 99% | 6 | 95°F |
| 23 | St. Louis, MO | 86% | 98% | 12 | 95°F |
| 24 | Sacramento, CA | 86% | 100% | 125 | 102°F |
| 25 | Atlanta, GA | 86% | 99% | 1 | 93°F |
| 26 | Charlotte, NC | 85% | 99% | 2 | 94°F |
| 27 | Raleigh, NC | 85% | 98% | 10 | 95°F |
| 28 | Albuquerque, NM | 85% | 100% | 34 | 97°F |
| 29 | Louisville, KY | 85% | 99% | 7 | 94°F |
| 30 | Salt Lake City, UT | 84% | 100% | 120 | 101°F |
| 31 | Kansas City, MO | 84% | 98% | 19 | 96°F |
| 32 | Nashville, TN | 84% | 99% | 10 | 96°F |
| 33 | Oklahoma City, OK | 82% | 99% | 69 | 99°F |
| 34 | Memphis, TN | 80% | 97% | 23 | 97°F |
| 35 | Fort Worth, TX | 73% | 97% | 215 | 104°F |
| 36 | Abilene, TX | 73% | 99% | 296 | 105°F |
| 37 | Jacksonville, FL | 71% | 94% | 16 | 96°F |
| 38 | Dallas, TX | 69% | 96% | 202 | 103°F |
| 39 | Austin, TX | 69% | 97% | 276 | 104°F |
| 40 | Houston, TX | 69% | 91% | 87 | 99°F |
| 41 | San Antonio, TX | 67% | 94% | 280 | 103°F |
| 42 | Las Vegas, NV | 62% | 100% | 972 | 112°F |
| 43 | Mesa, AZ | 57% | 99% | 1,022 | 111°F |
| 44 | Phoenix, AZ | 54% | 99% | 1,363 | 113°F |
| 45 | Miami, FL | 51% | 87% | 0 | 93°F |
What the water classes mean
ASHRAE sorts liquid-cooled IT equipment by the warmest facility water it accepts. Warmer water means more hours when outdoor air can do the cooling alone.
| Class | Supply water to the IT equipment |
|---|---|
| W17 | up to 63°F |
| W27 | up to 81°F |
| W32 | up to 90°F |
| W40 | up to 104°F |
| W45 | up to 113°F |
How it is calculated
- Hourly dry-bulb and wet-bulb readings, 2020 to 2024, from the NOAA Local Climatological Data station nearest each market. About 8,760 hours a year per market.
- Full free cooling: the hour's air temperature plus the dry cooler approach is at or below the class supply temperature. The chiller is off.
- Partial: the air can still pull the return water down part of the way (return is taken as 18°F above supply). The chiller trims the rest.
- Adiabatic: air on the coil is taken 85% of the way from dry bulb to wet bulb.
- Design dry bulb is the temperature exceeded 0.4% of hours, about 35 hours a year.
Source: NOAA National Centers for Environmental Information, Local Climatological Data. Public domain. Updated 2020 to 2024.
Questions engineers ask
What is free cooling in a data center?
Free cooling means rejecting the heat with outdoor air alone, with the chiller compressors off. A dry cooler does it whenever the outdoor air, plus the cooler's approach, is colder than the facility water temperature the IT equipment needs.
What are the ASHRAE water classes W17 to W45?
ASHRAE groups liquid-cooled IT equipment by the warmest facility water it accepts: W17 is up to about 63°F, W32 up to about 90°F, W45 up to about 113°F. The warmer the class, the more hours a dry cooler can carry the load alone.
How is the free-cooling hours number worked out?
From five years of hourly NOAA weather records (2020 to 2024) at the airport station nearest each market. Every hour counts as full free cooling when the dry bulb plus the approach is at or below the supply temperature of the chosen water class.
What does adiabatic pre-cooling change?
Wetted pads cool the air entering the coil toward the wet-bulb temperature on hot hours. In dry climates such as Phoenix or Reno that adds a large share of free-cooling hours. In humid climates the gain is smaller.