Issue link: http://cp.revolio.com/i/634770
16 | THE DATA CENTER JOURNAL www.datacenterjournal.com a lthough a few big-name technology companies are boasting facilities in which peripheral functions such as power distribution and cooling use relatively little energy, most companies trail far behind. In 2013, for instance, a Digital Realty Trust survey of large businesses (greater than $1 billion in yearly revenue or more than 5,000 employ- ees) found that the average power usage effectiveness (PUE) of North American data centers was 2.9. is number means that for every watt of power consumed by the servers and other computing-related equipment, almost two watts are con- sumed by cooling, power distribution, uninterruptible power supplies (UPSs), lighting and so on. Even if energy prices remain unchanged over time, this average rating implies a tremendous amount of waste both in physical resources and in dollars among major data center operators. anks in part to changing ASHRAE guidelines, however, data center opera- tors have an opportunity to slash cooling costs through free cooling—essentially, the use of outside air rather than mechani- cally chilled inside air. And the benefits aren't limited to companies operating in the Arctic Circle, according to a Green Grid white paper ("Updated Air-Side Free Cooling Maps: e Impact of ASHRAE 2011 Allowable Ranges"). e publication notes, "Virtually all of North America and Europe, and more than 90 percent of Japan, can operate without mechanical cooling if data center owners can allow oc- casional incursions into the higher end of the ASHRAE class A2 and A3 ranges." In other words, free cooling is almost always sufficient, possibly with some mechani- cal backup for the rare cases of relatively extreme weather conditions. But free cooling involves more than just opening the windows (which most computer rooms lack anyway). Outside air still requires proper distribution to avoid hot spots in the data center, and this process consumes power. Moreover, fresh air may be nice to breathe, but humid- ity variations and contaminants can spell trouble for equipment. Hence the need for proper filtration, which introduces its own set of challenges. cLeaRing The aiR Seasonally and even daily, outside air conditions can change—oen rapidly. ese changes in temperature and humid- ity can be a challenge for free-cooling im- plementations. In addition, contamination introduced to the computer room from outside can damage sensitive equipment; the kinds of contaminants can vary de- pending on the location, such as whether it's in a rural or urban environment and whether it's near a saltwater body. More- over, because a data center requires large volumes of air for cooling, even low levels of contamination can be a problem. According to a 2011 ASHRAE white paper, major IT hardware vendors have reported a rise—albeit a small one—in equipment failures owing to air contami- nation. A variety of changing conditions have led to this increase, including the use of lead-free solder, operating temperature and humidity changes in the data center, decreasing electronic-component sizes and increasing densities, and construction of data centers in polluted areas. Corrosive contaminants, in combination with these factors, can damage equipment—visibly so in many cases. According to David Carlile of 3M Purification Inc., "Since most data centers in the U.S. that use some (or only) 'free cooling' are located away from industrial/manufacturing areas, the primary concern is airborne particulates. ose in drier, rural areas are more likely to experience periods of excessive airborne dust clouds." Particulate contamination can be characterized by the concentra- tion and corrosivity. "Data centers outside the U.S. in high-density areas (e.g., Asia) would also need to be concerned about industrial pollutants and the related corro- sivity of those airborne contaminants. All data centers near saltwater areas should be especially careful owing to salt corrosion- related issues." One of the keys to successfully implementing free cooling is proper "con- ditioning" of outside air to make it suitable for use in the data center. Doing so in- volves infrastructure and energy. Obvious- ly, running a fan takes power—although typically less than running a mechanical air conditioner. Carlile notes that "depend- ing on the configuration, air movement can make up the bulk of the cooling cost, especially in free-cooling configurations." Complicating the situation is the necessity of filtration. Imagine blowing through a straw; next, imagine blowing through a pinched straw. e latter case obviously takes more effort than the former. "Using 'low energy' air filtration and/ or optimizing the air-filtration selection can reduce the fan energy cost signifi- cantly," said Carlile. A filter that does its job while interfering as little as possible with the air flow is the best solution. One way to measure the effect of the filter is the drop in pressure from one side to the other (∆P). Going back to the straw analogy, when air hits the pinch, pressure builds upstream, but downstream pressure is lower since it faces no obstruction. For a filter, a higher ∆P means the fans must Free cooling involves more than just opening the windows (which most computer rooms lack anyway). Outside air still requires proper distribution to avoid hot spots in the data center, and this process consumes power. Moreover, fresh air may be nice to breathe, but humidity variations and contaminants can spell trouble for equipment. Hence the need for proper filtration, which introduces its own set of challenges.