Not a single temperature: humidity in the data center

When it comes to data center microclimate, the issue of temperature is usually considered. This is understandable, since the temperature must clearly comply with certain standards, with an accuracy of tenths of a degree. But we should not forget that there are other important factors, including humidity.

It is obvious that water in liquid form for equipment of most types is deadly, so to speak. Too high humidity can lead to condensation of water, which can start the process of corrosion of vulnerable elements or even cause a short circuit, if it is very bad. Previously it was believed that the relative humidity should be maintained in the range of 40-50%. But, in fact, all this is not so critical.

True, the case is widely known when it was the humidity that affected the data center's performance in an IT company, Facebook. In the data center in Prineville in 2011, two clouds formed at once - digital and water, consisting of condensate, which gradually poured onto the equipment.
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This happened due to an error in the building automatic control system. The data center has significantly increased the temperature, in addition, the air constantly passed through the evaporative cooling system, saturating with water vapor. After some time, an area of ​​high humidity appeared near the server racks, practically a cloud, from which real rain fell.

All this led to the fact that some of the servers simply went down as they began to short power supplies. Of course, the company rather quickly solved the problem, but then everyone had to worry about it.

So what's up with humidity?

The fact is that in data centers for many years, one might even say, for decades, the relative humidity was maintained at the level of 45-50%. It was believed that high humidity significantly reduces the likelihood of static charge. Humidity at this level is still trying to maintain in some data centers, although numerous studies have shown that this is no longer necessary.

The fact is that static electricity, in most cases, does not pose a danger to equipment even at a relative humidity of 15%. If you take appropriate security measures, this figure can be reduced even to 8%. In any case, it is these figures that are given in the report, which was released back in 2014 based on the results of a study by the TC 9.9 Technical Committee of the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE). According to the authors of the study, reducing the level of relative humidity in the DC allows you to save energy and, consequently, improve PUE.



The fact is that to maintain a high relative humidity requires a rather large consumption of water and electricity. This situation is observed in the event that the data center equipment operates at elevated incoming temperatures in accordance with the ASHRAE recommendations for temperature conditions in 2008 and 2011.

Already in 2012, the same committee conducted an independent study in order to determine the real level of relative humidity at which the threat of damage to equipment and its components by static electricity can be avoided. During the study, various types of data center flooring were tested, as well as different types of shoes for employees. The full version of the results of this study is available here . In short, in any climatic zone it is not at all necessary to actively use humidifiers - as mentioned above, 8% of relative humidity is enough. This is especially true for data centers that are located in areas with a cool climate and that use free cooling.

What precautions?

Here we are talking primarily about the flooring with high-pressure laminate, concrete floors or current-scattering coatings. There is no problem with them, especially if you use shoes with minimal conductivity.

So here are some recommendations:

• The floor covering in the data center must have the ability to dissipate static electricity, as well as grounding;
• Employees and visitors of the data center should wear shoes with soles that have a minimum conductivity, the resistance should not exceed 10 ⁸ Ohms. Some DC operators require wearing special antistatic slippers;
• The temperature of the incoming air should be close to the values ​​of the corridor established by ASHRAE;
• In the cold corridor, it is necessary to measure the humidity, it is desirable to set the dew point to 4.44 ° C below the so-called conservative level. This will be the equivalent of a relative humidity of 15% at an inlet air temperature of 24 degrees. In the hot aisle, the relative humidity may be lower than elsewhere, since the relative humidity decreases with increasing temperature. It is worth remembering that ASHRAE did not test for values ​​below 8%;
• It is worth remembering about the antistatic bracelets and make them mandatory when working inside the equipment.

As for the upper threshold of humidity, this figure, recommended by ASHRAE, is 60%. This avoids the emergence of another problem - the dissolution of chemical compounds and air particles in condensate droplets in the air. This leads to corrosion of the components of IT systems. Named problem, by the way, is relevant for Asian data centers. In a humid climate and a polluted environment, equipment deteriorates more often than in data centers located in other regions.

Worst of all are cooling systems that can corrode for months and at one point simply fail. And this is already fraught with long downtime and financial losses, very significant losses. Even if the equipment does not fail, it begins to consume more energy.