Data Centres continue to be in demand and the trend is set to grow with more consumerisation of IT and the growth in cloud computing. This means there is an increasing reliance on data centres to support critical systems ensuring maximum availability.

Another key industry focus is the reduction in energy consumption of the data centre. Whilst improvements in the power usage of IT equipment has become the main focus of the chip and server manufacturers, data centre cooling has become particularly important and here we are seeing some very different approaches.

Free cooling is widely recognised as an effective solution to enhance data centre efficiency, reduce operating costs and lower Power Usage Effectiveness (PUE). However, with the drive to be more efficient there are now many different options available to data centre owners and operators. The challenge is to consider the choices affecting all aspects of the facility not just efficiency.

In most facilities we accept the fact that we need to have fans to move around the air, so with the free cooling approach we are essentially referring to compressor free cooling. This is achieved by using low ambient air temperatures, but currently there are two very different options available – “fresh air”, using external air being drawn directly into the data centre from outside, or “recycled air”, using the same air re-circulated within the data centre.

At present most designs have mechanical systems as back up and so overall the capital expenditure and ongoing operating costs are broadly the same for “fresh air” and recycled air” options, so there is little to choose between the two based on price. Efficiency levels are also largely comparable, with both able to operate in the sub 1.2 annualised PUE.

Despite these similarities, there are also some glaring differences that should be considered by anyone considering a free cooling solution for any data centre refurbishment or new build project.

CONTAMINATION

With “fresh air” solutions there is a risk of contamination by introducing fresh air and so the additional time and cost for necessary changes of filters needs to be considered, especially in built-up urban areas. The other consideration with contamination is the effect to the availability of the facility. With incidents such as fire, smoke or other fumes often the fresh air systems need to be turned off and so a secondary system with 100% of the cooling capacity is required.

This backup system is rarely efficient and so when used, draws significant amounts of power. Typically this can be more than the IT systems and the impact of this Peak PUE of over 2 is in oversizing generators, switchgear and electrical systems and in having to keep this power in reserve.

BUILDING RESTRICTIONS

Fresh air systems pose other challenges which limit their use such as the need to have external access for ducting the air in and out of the facility. In particular, for refurbishments or installations in an existing property this is a key consideration at the design stage that cannot be ignored, especially for landlocked rooms, because of the potential for additional building work, cost and security.

A DIFFERENT APPROACH

An example of an alternative approach that does not use fresh air is PGS in Weybridge. This facility utilises Keysource’s high efficiency system Ecofris to recycle the internal air and not introducing any fresh air. This type of solution overcomes all of the considerations above and having operated for over two full years is an excellent example of true annualised PUE figures. With a full 2N cooling system and an annualised PUE of 1.15 it is one of the most efficient facilities currently in operation. However with a Peak PUE of 1.5 it provides significant indirect savings on electrical systems and more power available for IT.

THE BIG OPPORTUNITY

The one next big step for data centre operators will be to consider removing the chillers altogether. This poses a challenge to those with a fresh air approach because it is not only temperature rises that require the use of the mechanical cooling but other events outside of operators control.

In contrast, a system such as Ecofris that is optimised for efficient operation in all situations, we can consider removing the chiller. For the warmer hours of the day when temperatures rise above 24 degrees centigrade, control systems can start to elevate the supply air temperatures within the data centre up from 22 degrees. With most servers able to operate at much higher temperatures and ASHRAE increasing the allowable limits this strategy could not only further reduce capital expenditure but also improve efficiency.

There are many benefits of free cooling, but there are key decisions to be made during the design process. Any data centre owner or operator should take a close look to ensure any planned solution meets their requirements in terms of risk, availability, efficiency, maintenance and construction.