# Air Cooling
Air cooling is a data center cooling method that uses fans and air conditioning units (often within the computer room in the form of [CRAH](https://hydraulogistics.at/link/16#bkmrk-crah)s) to circulate cool air between IT racks, expelling the hot air from computing equipment.
Considered the most traditional cooling method, air cooling is used by approximately 80% of data centers. It is most suitable for smaller data centers, because it is sufficient for smaller heat loads while being cost-effective and easy to implement on a small scale. However, for larger data centers with a more significant heat load, air cooling is insufficient and must be supplemented or hybridized with other methods like [liquid cooling](https://hydraulogistics.at/books/chilled-infrastructures/page/liquid-cooling "Liquid Cooling").
In cooler climates, some data centers can reduce energy consumption by circulating ambient cool air to cool equipment (known as [free cooling](https://hydraulogistics.at/books/chilled-infrastructures/page/free-cooling "Free Cooling")), bypassing the energy-intensive process of conditioning the air.
On average, air-cooled data centers have a relatively inefficient [power usage effectiveness](https://hydraulogistics.at/link/16#bkmrk-pue) of [1.70](https://hydraulogistics.at/books/chilled-infrastructures/page/comparing-impacts-by-cooling-type "Comparing Impacts by Cooling Type"), but a near-zero water usage since they do not directly use water for cooling, not considering their [indirect water use](https://hydraulogistics.at/link/16#bkmrk-indirect-water-use).