One of the solutions that has been on the radar for a while and seems to be in the news recently is compressed air, so we have been looking at this as an alternative to battery back-up on UPS’s. The attraction of the compressed air system is that it can be stored at temperatures above 25°C (unlike lead acid batteries which deteriorate rapidly above this temperature and ideally should be kept at around 22°C). This made compressed air look particularly useful as we are currently designing a number of data centres to run on free-cooling and were hoping to avoid the need for any compressor based cooling at all. Unfortunately the cost of the compressed air system is prohibitive at the duties we require of 150 – 250kW for these particular projects, it being around 7 times the cost of a battery system for a similar autonomy.
At higher duties, say 1 MVA upwards, and especially when comparing with a diesel rotary (DRUPs) system, compressed air is competitive on price as well as offering higher efficiency and lower maintenance costs.
Other compressed air news has come from Peugeot-Citroen, who are developing a hybrid power system which will use the momentum of the car to charge a compressed air cylinder (regenerative braking). A compressed air driven motor will then assist the petrol engine, helping to achieve a claimed 80 mpg and CO₂ emissions of just 69 g/km. Launch is planned for 2016.
TATA Motors, in collaboration with French engineering company MDI, are also developing a compressed air powered vehicle which will be refilled from charging stations in a similar manner to battery powered cars.
Of course compressed air powered transport is not new and has been around since the 19th century, one of the early adopters being the Paris tram system (possibly a reason for the current “French Connection” with Peugeot-Citroen and MDI).
The one I particularly like though is inventor Jem Stansfield’s air powered motor cycle which has a top speed of 18 mph, a range of 7 miles and re-charges “in a few seconds” (he says).
The principle reason for the resurgence of interest in compressed air and other re-chargeable power systems is that the problems associated with storing electricity continue to hamper the development of electric cars. To bring us neatly back to the world of IT and data centres, Dr Fred Schlachter of Lawrence Berkeley Laboratories said at a recent symposium on scalable energy storage that “there’s no Moore’s Law for batteries”. Apparently, unlike the seemingly never-ending increases in computer processing power, improvements in battery performance are slowing. The present technology, based on Lithium-Ion, has its limitations and Schlachter believes that any break-through will only come with a change in chemistry.
So in summary if your data centre is under a 1MVA IT load and cost is any kind of driver compressed air UPS are probably not the best route to take. However if your facility has over a 1MVA IT load and especially if you are entertaining a diesel rotary UPS solutions then compressed air is definitely something to investigate further.