Keeping your cool in a data centre

Cooling is one of the most important aspects of a data centre, reflected by the wide array of techniques and strategies that have emerged as solutions. The chosen approach for a facility will often be regarded as one of its defining features, especially for the more unusual solutions such as Yahoo's Compute Coop facility, which features an ambient air system resembling an enormous chicken coop.

Active servers constantly produce heat, and when multiplied to the tune of several hundred in a data hall, the temperature can quickly spiral out of control if not kept in check. Just 20 minutes without proper cooling can see temperatures increase to the point of a critical systems failure.

For example a recent failed software update in a Microsoft data centre caused an unexpected temperature spike that saw Hotmail and Outlook going entirely offline for around 16 hours, leaving millions of users without email access.

A prolonged outage like this is the worst nightmare of every data centre manager, making cooling one of the highest on-going priorities of any facility. As server technology advances, racks are able to run more efficiently and produce less heat, and also operate effectively at higher temperatures. However, temperature must still be carefully controlled and monitored at all times.

Despite this, there is actually no clear consensus on what exactly this temperature needs to be. ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) recommends facilities maintaining a temperature of between 18-27°C (64.4-80.6°F), granting a surprising amount of flexibility.

Even with PMB Holdings' years of experience as property developers, this was a new challenge for us as we entered the data centre market with our facility the MK DataVault, as there are few buildings that need temperature control on this scale. Most of our previous projects, such as The Blade building in Reading, which is an office block, need little cooling beyond keeping offices pleasant to work in.

Alongside finding a reliable cooling solution, there is also a need to be as efficient as possible, and the vast amount of energy used by the sector has received a great deal of negative press. Reputation aside however, it is also just good business sense to be as efficient as possible, especially with cooling. Data centres could be spending as much energy on cooling servers as it takes to run them, with some cooling systems representing up to 42 per cent of a data centre's energy usage.

Chiller units are widely used in the industry but use a large amount of energy and contribute to significant overheads in energy costs. This lead us to investigate the many 'free cooling' options available for the MK DataVault, and we eventually settled on a natural air system due to the combination of efficient energy usage and lower costs. This has become an increasingly attractive option for data centres, and a survey by The Green Grid found that natural options saved 20 per cent on energy costs and seven per cent on maintaining cooling systems. Aside from direct energy usage, air-side economisers have been found to save 76 million gallons of water compared to water-side systems.

As the system draws natural air in from outside the centre, when the outside temperature is low enough it requires no additional cooling at all. On warmer days or when extra cooling is needed, it can easily be supplemented with additional cooling methods.

Despite its advantages, natural air cooling isn't suitable for all data centres. Humidity is a major problem for the system and facilities in hot and humid locations will need to look for other options. This is one occasion where our British weather comes in useful, and many countries with cool climates have enjoyed growing investment from the data centre sector for this reason. Facebook for example opened a facility in Northern Sweden, just 60 miles from the Arctic Circle.

As part of the drive to be as efficient as possible, heat recovery has become a popular addition to the system. This sees the hot air removed from the servers transported elsewhere for other uses, such as heating the entrance or offices at the facility, or even piped further away to heat housing or greenhouses. Ironically heat recovery is actually impractical for natural air cooling as the system is so efficient that only low grade heat is captured, which is of little use for reclaiming.

Like most technology sectors, the data centre industry benefits from an extremely fast pace of innovation and advancement. While free cooling techniques now provide extremely efficient cooling solutions, the industry is never far from its next innovation and it will be interesting to see which new solutions become the norm over the next few years.