Definition
Free cooling is any cooling strategy that rejects heat using naturally cold ambient air or water instead of, or before, running power-hungry mechanical refrigeration. The compressors and chillers in a conventional cooling plant are among the largest non-IT loads in a facility; free cooling sidesteps them whenever outdoor conditions are cold enough to do the work for free, hence the name.
Airside and waterside economizers
Airside free cooling, often called an airside economizer, pulls filtered outdoor air directly into the facility and exhausts the hot air outside, with little or no active chilling. Waterside free cooling instead uses a cooling tower or dry cooler to chill the water loop with cold outdoor air, keeping the indoor environment isolated. Both approaches can run partially: economizers pre-cool the air and mechanical cooling only trims the last few degrees on warm days.
Why it suits Bitcoin mining
ASIC miners tolerate a wide intake range and run 24/7, so they benefit enormously from free cooling. A Hashcenter sited in a cold climate can run on outside air for much of the year, slashing cooling overhead and improving its PUE. The trade-offs are air filtration, humidity control, and corrosion management, since outdoor air brings dust and moisture that must be handled to protect the hashboards.
Free cooling is most effective when paired with a sealed airflow path, so combine it with air containment and a well-designed hot aisle / cold aisle layout to keep the free cold air working for you.
In Simple Terms
Free cooling is any cooling strategy that rejects heat using naturally cold ambient air or water instead of, or before, running power-hungry mechanical refrigeration. The…