Free cooling is an approach to lowering the air temperature in a building or data center by using naturally cool air or water instead of mechanical refrigeration.
The prevailing air at many latitudes and elevations can be considerably cooler during certain seasons and times of day than the air that is warmed by data center equipment. By filtering, humidifying and introducing cooler prevailing air directly into the data center, it is possible to reduce or eliminate the use of industrial-grade CRAC systems. Cooling systems that use this approach are sometimes called air-side economizers.
Alternatively, a source of cold water from local rivers, lakes or ocean sources can be circulated into a data center and used instead of undergoing the traditional method of refrigerating a closed water loop with a chiller. Systems using this approach are often called water-side economizers, which can either be used to cool room air or directly cool cabinets and other systems.
In both cases, the industrial cooling systems would only be needed when the outside air temperatures become too high for free cooling systems like air- or water-side economizers to be effective. Consequently, the working life of installed cooling systems can be significantly extended. Reductions in cooling system use also mean drastic reductions in data center power consumption and service/repairs, lowering the energy and maintenance costs for facility owners. If prevailing conditions allow continuous use of air- or water-side economizers, industrial data center cooling systems may be eliminated entirely.
In actual practice, free cooling is not entirely free, because pumps, fans and other air/water-handling equipment is needed, and that equipment also requires periodic repairs and maintenance.