Factoring winter humidity changes into data center maintenance
Tuesday, Dec 11th 2012

Winter weather brings months of colder temperatures and reduced humidity. For data center operators, environmental changes can present unique challenges for maintaining stable operating conditions for IT equipment. A recent Data Center Knowledge column by network power consultant Mark Silnes offered some steps facilities managers can take to ensure the low winter humidity does not threaten servers in their data centers.

Low humidity levels produce static electricity, which can damage the sensitive electronics of servers. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) recommends specific temperature and humidity operating ranges for IT equipment. Silnes noted that the ASHRAE recommended ranges for temperature and humidity are 64.4 degrees Fahrenheit to 80.6 degrees Fahrenheit and 41.9 degrees Fahrenheit dew point (DP) to 59 degrees Fahrenheit DP, respectively. While the allowable ranges for both temperature and humidity under ASHRAE guidelines are wider, Silnes explained that data center operators should conduct a detailed assessment of their facility and equipment before attempting to operate outside the recommendations.

Data centers can use IT environmental monitoring solutions such as those offered by ITWatchDogs to keep internal conditions within these windows. However, meeting ASHRAE guidelines for humidity can be more complex than simply installing a humidity sensor.

Relative humidity vs. absolute humidity
In a Data Center Journal column, Jeff Clark explained that, traditionally, data center humidity level recommendations were given as relative humidity percentages. This standard of measurement posed a challenge to data center managers, since relative humidity changes according to air temperature. Newer metrics for monitoring humidity recognize the importance of measuring absolute humidity, he said. By measuring dew point or the mass of water per dry air, data center managers can get a more realistic idea of the humidity range surrounding their servers.

Clark noted that the absolute humidity of a data center, as measured in grams of water per grams of dry air, should be kept between 0.006 and 0.011. Using a measure such as this rather than the previous recommendation of a range between 40 and 55 percent relative humidity allows data center operators to standardize measurements from one side of the server to another and to better manage the natural variability in outdoor humidity created by using free cooling.

More tips for handling low winter humidity
In addition to keeping humidity within recommended ranges during the winter, data center operators can handle humidity complications by taking a few additional precautions, Silnes noted. He recommended using intelligent cooling controls that give a holistic sense of data center temperature so that different cooling components are not working against each other.

"Without this type of system, a precision cooling unit in one area of the data center may be humidifying, while at the same time a unit across the room is dehumidifying," he explained. "The control system gives you visibility into conditions across the room and the intelligence to determine whether humidification, dehumidification or no action is required to maintain conditions at target levels. This way, reliability is automatic."

Data center operators can also schedule winter maintenance in anticipation of equipment failure. Silnes recommended checking for problems such as a clogged drain due to mineral deposits in the humidifier pan or other mineral buildup that might cause the humidifier to overflow onto the data center floor. He also recommended checking for debris in the condenser and dry coolers, which can hurt cooling system performance, as well as ensuring that heat rejection fluid does not freeze.

While some problems may proliferate in winter, cold weather can help economize data center cooling costs, he noted. By using environment management tools to carefully track temperature and humidity, data center operators can turn winter weather into an opportunity rather than a liability.