During my presentation at the Wisconsin Focus On Energy event last week, I covered energy efficiency opportunities in data centers. As usual, I made the case that everything depends on the environmental conditions you want to maintain - essentially, what is the temperature and humidity tolerance you have for the air going into IT equipment?
Many data center operators are supplying air that is overcooled, and within a very narrow humidity range, oftentimes 45 to 55 percent. This drives excessive energy use, because chilled water temperatures have to be low, and humidifiers and dehumidifiers have to operate often (and in some instances we find some CRAHs doing one and some the other!).
I pointed out that these tolerance levels are a hangover from the days of magnetic tape and punch cards, and that IT equipment manufacturers specify a much wider allowable temperature and humidity range. In fact, many industry-leading operators have done away with humidity control altogether, and are pushing supply air temperatures into the mid-70 degrees F range.
The layman's version of this part of the story is: turn up the temperature (and widen your humidity tolerance) on your air conditioning and you'll save energy and money.
The follow-on part of the story is that higher and wider tolerances allow for longer operation of air-side free cooling. I showed a slide that I obtained from Mark Hydeman at Taylor Engineering in Alameda CA that shows that as you tighten your tolerances on humidity, you decrease the time that you can run on outside air.