Cooling a data center without AC

http://weblog.infoworld.com/sustainableit/archives/2008/09/intel_air_side.html

Intel has done a test, cooling a high-load data center model without using air conditioning, just ambient outside air. They did see a higher failure rate on the equipment, but not nearly as much higher as was expected. And the portion that used a simple, cheap cooling system without all the climate control of a true data-center AC unit had a lower server failure rate than full-on data-center-class AC yielded. My feeling is that it's not the cold air that's critical to data-center health, the servers will be entirely happy with 80-90F cooling air. It's mostly the dust and to a lesser degree the order-of-magnitude changes in humidity that cause most of the failures. Scrub the dust from the air (even cheap AC units do this, and simple filter systems can do it too) and keep the humidity in the 5-35% range (no need to control it to +/- 2%) and you'll give the servers 95% of what they want to be happy. And you can do that for a fraction the cost of a full climate-control system that controls everything to within 1%.