Free Cooling for Data Centers: Strategies and Advantages

Much of today's discussion about improving the efficiency of data center cooling systems centers on sophisticated technologies like immersion and direct-to-chip cooling techniques. But depending on your data center's location and current cooling methodologies, there might be a much cheaper way to boost cooling efficiency and reduce energy usage: Free cooling.

As the term implies, free cooling offers a way of cooling data center infrastructure with virtually no energy use. However, there are some big caveats, and free cooling isn’t for every data center. Read on for details as we discuss the pros and cons of free cooling relative to other common data center cooling techniques.

What is Free Cooling in Data Centers?

In data centers, free cooling is the practice of dissipating heat without artificially cooling air or water. Typically, free cooling systems work by collecting air or water from the ambient environment, then circulating it into data center server rooms or individual server racks.

Free cooling is distinct from what’s known as mechanical cooling, which relies on refrigerants and compressors to cool air or liquid.

The Benefits of Data Center Free Cooling

The main benefit of free cooling systems relative to mechanical cooling is simple: Free cooling uses much less energy. In turn, it can boost data center power efficiency and sustainability.

Related:Heat Reuse Strategies for Liquid-Cooled Data Centers

This is because mechanical cooling systems require substantial amounts of electricity to power the equipment that removes heat. Free cooling systems are much more passive, so they don't require nearly as much energy.

That said, it's important to note that most free cooling systems are not totally energy-free. They often require fans or water circulators to move cooling mediums, and that equipment uses electricity – albeit much less than a typical HVAC compressor.

For data center operators, free cooling systems also offer the benefit of being low in cost to install and easy to operate and maintain, since they require few components. The fact that they don't involve refrigerants is also an advantage because there is no risk of leaking harmful refrigerants into the atmosphere.

The Challenges and Limitations of Free Cooling

While free cooling can be a great way to reduce energy costs and improve data center sustainability, there is a big caveat: Free cooling only works in certain locations and under certain conditions.

To operate a free cooling system, a data center must have access to air or water whose natural temperature is lower than temperatures inside the data center. As a result, free cooling is typically not viable for data centers in warm climates, during hot seasons or during warm periods of the day.

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Nor is it realistic for most data centers to cool servers using free cooling alone. Most facilities need mechanical cooling systems in place to sustain operations during periods when free cooling is not viable. This means that free cooling is a complement to, not a replacement for, mechanical cooling for the typical data center.

On top of this, free cooling systems that circulate water could lead to high volumes of water usage – which is already a challenge for many data centers. For this reason, data centers in regions where water is scarce may not be able to take advantage of free cooling, even if water in the environment is naturally cool enough to support this technique.

A final potential challenge is that IT equipment that runs at particularly high temperatures – as modern AI hardware may, for example – might not be a candidate for free cooling. Ambient air or water may not be cool enough to dissipate heat from this equipment at the rate necessary to prevent overheating.

How to Take Advantage of Free Cooling

Despite these challenges, the fact that free cooling is relatively inexpensive and simple to install means that data centers can often take advantage of free cooling – at least as an auxiliary cooling measure – easily enough.

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In many cases, installing free cooling is as simple as augmenting existing HVAC systems with air exchangers that can pull air from outdoors and circulate it through the same system that is in place to dissipate heat using mechanical cooling. By leaving the fans on but turning compressors off, you get free cooling, assuming the outdoor air is cool enough on its own.

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More complex free cooling systems – especially those that use cool water instead of air – are more complicated to install. But even in that case, pulling water from an external source, then blowing air over it and circulating that air through server rooms, is not especially expensive. It's the same basic process used in the case of mechanical cooling, except that instead of blowing air over pipes containing refrigerant that was chilled by a compressor, the system uses cool water to chill the air. This means this approach can be implemented by adding onto traditional HVAC systems rather than building an entirely new one.

Free Cooling and the Future of Data Centers

In short, although free cooling has distinct limitations, it also has clear advantages – and more important, it's a comparatively low-cost, low-complexity way to improve data center efficiency and sustainability.

In addition to considering more sophisticated cooling system improvements, like switching to immersion cooling, data center operators should evaluate whether free cooling could be a way of cutting electricity usage without having to rethink HVAC strategies from scratch.