Theres no arguing with the fact that data centres and server rooms use a lot of energy. And one of the biggest contributors to the energy bill is the cost of data centre cooling, especially when using conventional chiller units. Cooling server rooms consume a staggering 1% of the worlds energy. Its not surprising then that data centre operators are increasingly interested in the concept of free cooling or the use of fresh air. In most data centres and server rooms the air-conditioning runs continuously, even when its cold outside. And in the UK, its sufficiently cold outside to not need server room air conditioning for almost nine months of the year, because the ambient temperature remains below 15°C. Its a pretty obvious solution: when its cold outside, just bring the fresh air inside to cool the server room. It is still possible to filter the air and control the humidity but the free-cooling approach uses a lot less power than running standard air conditioning chiller units. And because todays computer equipment is a lot less sensitive to slight variations in temperature and humidity than it used to be, fresh-air cooling is an increasingly attractive solution for many data centre operators.