Time to get back on my soapbox again…this time it is about “contaminants” in data centers as an excuse to avoid using fresh air cooling or having outside air enter the white space. The bottom line is that unless your data center is located in “an emerging country” then the odds of a contaminant-created hardware failure in anything like a short time frame are about the same as winning the lottery…assuming you take some pretty basic steps in the design.
Contaminant control, or more correctly, concern over contaminant control has been around for decades. I remember doing some research over 25 years ago on the impact of ozone on telecommunications equipment. Bell Labs, as it was known long ago, had performed some pretty interesting tests to document what could be a very real problem under the right circumstances. The results of those tests indicated that, with the exception of certain locations, the air in the equipment room was worse than the air outside so it made more sense to flush the room with outside air than to avoid bringing outside air into the space.
Particle and gaseous contaminants CAN be a problem if ignored. However, the extent of the problem and how quickly it manifests itself needs to be considered.
Phenomenon like copper creep and circuit bridging do occur…but only when the conditions at the server are right to support those failure modes. Two things generally need to be in place for the failure mode to even begin. First, there needs to be a fine coating of dust particles on the circuit boards. Second, the relative humidity at the board needs to be at the deliquescent RH…or the point where the dust starts to absorb moisture and become “wet”. If the RH is too low then dust might affect localized temperatures on the board but the mechanism to cause bridging simply does not exist. The converse is also true…no dust…then no mechanism even with a relatively high humidity level.
Dust can come from anywhere. Every time someone enters the data center they bring in some amount of dust particles. Every time a box is opened in the data center particles are created. And, yes, every time outside air is brought into the data center it is possible that dust can enter. In fact, a data center with no outside air is actually vulnerable to the worst kind of dust intrusion…uncontrolled infiltration through doors, cracks, pipe openings, or wind pressure. Maintaining a positive pressure in the white space helps to prevent infiltration and keeps the worst dust (and gases) out of the data center.
ASHRAE, through the TC 9.9 committee, has set a target for data center “cleanliness”. It is ISO Class 8. ASHRAE has also noted that ISO Class 8 conditions can be met with a MERV 8 filter…a common and inexpensive filter available at virtually any HVAC parts house. If the air being filtered is coming from the outside then ASHRAE recommends a MERV 11 or MERV 13 filter. These might not be quite as common as the MERV 8 but they are also readily available and can fit in a standard 2” filter rack.
The interesting side note about the ASHRAE recommendations is just how extremely conservative they are. ASHRAE recommends no more than 15mg/m3 of “fine” particles…defined as particles less than 2.5mm in size. However, IBM (who should know something about computers) has a limit of 150mg/m3 and a “fine” particle definition of particles less than 5mm in size.
Once again, owners are being led down a path to purchase cooling systems and equipment that fail to optimize their energy savings through an inflated fear of something that happens very rarely in the developed world and is easily controlled with proper filtration. Products such as our Aztec ASC indirect evaporative cooling systems are designed with MERV 14 filters in mind and can actually accept MERV 16 filters…the highest MERV rating point…that is suitable for operating rooms and can remove all bacteria and most tobacco smoke. This allows the Aztec system to optimize the use of fresh air cooling and use a more efficient heat transfer system than air-to-air heat exchanger systems…and still exceed the extremely conservative ASHRAE recommendations for particulate control.