The humidity level in the data center: why it matters
The equipment used in the data centers places quite stringent requirements on the relative humidity of the air in the room. If it decreases below a certain level, electrostatic discharges may occur. As you know, static electricity can be dangerous for IT equipment in the data center. To minimize it, it is recommended to maintain a certain level of relative humidity in the data center premises.
Under the humidity of the air understand the content in it of water vapor. There are absolute and relative humidity. Absolute humidity is the density of water vapor in the air at a certain temperature. The higher the temperature, the more moisture can be contained in the air. The limiting amount of water vapor that saturates the air at a given temperature is called maximum humidity. Further moisture will condense. The problem of condensation - another problem, therefore, exceeding the maximum value of the level of relative humidity in the data center is also undesirable and must be controlled.
Relative Humidity is defined as the ratio of absolute humidity to humidity, the maximum possible at a given temperature, expressed as a percentage.
What should be the humidity in the data center?
On the basis of which documents or standards is moisture content standardized in data centers? In accordance with document SP – 3-0092: (Standard TIA-942, revision 7.0, February 2005) “Telecommunication infrastructure of data processing centers” clause 184.108.40.206. The “environmental performance parameters” of these parameters should be as follows:
- temperature with a dry thermometer: from 20ºС to 25ºС;
- relative humidity: from 40% to 50%;
- dew point: not higher than 21ºС;
- rate of change: not more than 5ºС per hour.
In addition, the specifications for IT equipment specify permissible values of humidity and temperature for specific hardware models.
Meanwhile, according to research carried out in 2014 on the instructions of the TC Technical Committee 9.9 of the American Society of Heating, Cooling and Air-Conditioning Engineers (ASHRAE), it is assumed that the relative humidity can be reduced to 8-15%, which will help save electricity and improve the energy efficiency indicator PUE but it requires certain measures of protection.
The flooring of the data center must have the ability to dissipate static electricity, as well as properly grounded. Employees and visitors of the data center should wear shoes with a sole with conductivity properties. Regardless of the level of humidity, it is recommended to always wear antistatic bracelets when working with equipment or when replacing parts inside the case.
If, when walking on an ungrounded raised floor with 80% humidity, the voltage of static electricity reaches only 250 V, then at 20% it is already 12 000 V: a spark discharge in this case can lead to failure of IT equipment or telecommunications systems.
To maintain a higher relative humidity, more steam is required, and, as a result, more energy and water consumption. After all, it is known that up to 40% of the total power consumption of the data center consists of cooling systems (if traditional freon or chiller systems are used).
To maintain the required level of humidity in the data center requires a fairly large consumption of water and electricity - it takes up to 15% of the electricity they consume.
Reducing the humidity level from the traditional 40-50% became possible with the advent of IT equipment in the data center, which operates at elevated temperatures: warm air retains more steam, and the data center can save electricity on evaporation systems for humidification (steam humidifiers).
If the humidity level is higher than the allowable values, condensation may form on the cold surfaces of the equipment, as a result - corrosion. This is one of the problems with data centers that use freecooling, where the outside air can be cold or humid.
In the data center, built on the architecture of cold and hot corridors, the likelihood of condensation is high in a cold corridor. Condensation on electronic components can be detrimental to IT equipment and cause a short circuit.
In the updated TIA-942-A standard, the humidity parameters are specified in the section:
220.127.116.11.1 Operational parameters
The temperature and humidity in the computer room should be maintained in accordance with the
requirements for equipment of classes A1 or A2 in ANSI / TIA-569-C.
The required temperature and humidity values for equipment classes A1-A4 and B.
Ie Currently, the maximum value of humidity for rooms of class A1 and A2 is 60%, for class B the allowable range is from 8 to 80%.
Designs and types of humidification systems
Air humidification is traditionally implemented either as a separate system, or as one of the modules of air conditioning systems, or as a ventilation system. Many large data centers install CRAC (Computer Room Air Conditioners), which control temperature and humidity, using built-in heaters and humidifiers. They maintain controlled temperature and humidity parameters in a given range.
As a rule, precision air conditioners are equipped with electrode-type steam humidifiers: the electrodes in the steam cylinder are energized, the water is heated to a boiling state, and thus we get steam through the steam distributor to the air flow.
Steam production at the same time can be adjusted by changing the level of occupancy of the steam cylinder. using a controller that maintains the required water level. If steam production drops below the required value, the filling valve opens to increase the water level in the tank. In the case of a reverse situation, the valve remains closed until the desired humidity is reached.
Controllers can display a set of various parameters, such as relative humidity of air, current in a humidifier, electric conductivity of water, steam capacity, error indication.
Depending on the conductivity of the water and the concentration of mineral salts in it, it may take several hours for the humidifier to enter the operating mode.
In the systems of precision air conditioning Schneider Electric, as in all similar systems, the module with a humidifier is installed directly into the body of the air conditioner and supplies steam to the air duct. The advantages of this approach are precisely maintaining the moisture parameters in a separate local volume, simple adjustment, and the ability to quickly replace the module.
There are also disadvantages: greater power consumption compared to spray or surface moisture, dependence on water quality. The latter, however, applies to almost all types of humidification, except for humidifiers on heating elements, which are usually used in separate ventilation systems.
There are different types of humidifiers: electrode, infrared, ultrasonic, etc. Each approach has its advantages and disadvantages, however, electrode steam humidifiers are the simplest solution in terms of installation, control and maintenance. Other types of humidifiers are more demanding on the content of impurities in the water. They are characterized by such disadvantages as mechanical clogging of the nozzles, the formation of plaque on moisturizing mats, white plaque in the case of using ultrasonic systems. And steam humidifiers with water purification systems are more demanding, higher operating costs. In addition, in the Russian context, water treatment systems are quite expensive, and the quality of water varies greatly in different projects, which entails high costs for water treatment.
In steam appliances, steam is formed as a result of boiling. They do not change the air temperature. The advantages of such plants include clean steam, regulation accuracy, ease of installation, low capital investment, low water quality, but they are characterized by high electricity consumption (about 0.75 kW per 1 kg of steam), power limitations (steam capacity within 1- 120 kg / h).
The most common types of steam humidifiers - electrode and tenovy. Electrode humidifiers have a lower cost, but are more expensive to operate, because they require regular replacement of electrodes and cleaning. The accuracy of maintaining the parameters they have is ± 5%. Electrode type humidifiers operate on medium hard water.
Humidification systems from Schneider Electric
To maintain the required humidity in the data center room, Schneider Electric air conditioners use immersion electrodes with the ability to adjust the production of sterile steam and automatically adjust the salt concentration in the steam cylinder, which allows the use of ordinary, unprepared water of varying degrees of hardness without chemical treatment or demineralization.
Thus, in Schneider Electric humidification systems, simple tap water is used. It merges into the drainage. Additional costs are minimal, only simple mechanical water purification is required. In the case of a high salt content, the electrodes can be quickly consumed, but the steam cylinders themselves are essentially consumable. On average, once a year they need to be changed (the frequency depends on the specific site).
What is the difference between humidifiers in ventilation systems from humidifiers in a precision air conditioner? In principle - only in the location, because in the case of a ventilation system, a steam distribution pipe is installed in the duct from the housing of the humidifier, which is located next to the duct. You also need to carefully select the installation location of the tube and its width and quantity.
Usually, precision air conditioners are equipped with standard steam humidifiers with the only possible rated power. The maximum steam consumption is selected based on the air consumption range of a particular model of air conditioner, i.e. within this range, the steam output of the humidification system is sufficient.
Among the components of the InRaw RP air conditioning system connected to the chiller are the humidifier (4) and the humidity sensor (12). InRow devices are equipped with temperature and humidity sensors to automate procedures for regulating operation. They are compatible with Hot Aisle Containment and Rack Air Containment insulation systems, which increase the efficiency of cooling systems.
In addition, in order to reduce capital costs, it is not necessary to equip all air conditioners with steam humidifiers - some air conditioners can be “cold only” models.
Monitoring of humidity in the data center can be carried out within the framework of DCIM. It gives a complete and accurate picture of the air condition in the room and an understanding of the processes occurring in the data center, including using it to control a sharp increase / decrease in humidity at a specific point due to changes in the data center structure or any actions to tune the equipment configuration. The indicators are removed from the humidity sensors at different points in the data center.
The use of hardware and software components of the DCIM (Data Center Infrastructure Management) system helps to reduce the cost of operating a data center, increase the impact of CAPEX, speed up decision making and implementation of data center infrastructure management.
All types of precision air conditioners by Schneider Electric can be equipped with humidity control systems, either by type (DX freon systems, CW chilled water systems) or by form factor (perimeter and intra-row).
The humidifier consists of a steam cylinder, a steam distribution pipe (installed directly at the heat exchanger outlet), filling valves and drainage, a water level sensor in the steam cylinder.
Proportional control of the operation of the humidifier (achieved by controlling the current passing through the cylinder electrodes and controlling the concentration of salt in the cylinder) allows increasing the efficiency of the system, reducing energy consumption and extending the service life of the components.
Humidity is measured in the cold corridor. It is advisable to set the dew point at 4.44 ° C below the equivalent of a relative humidity of 15% at an inlet air temperature of 24 degrees. In the hot corridor, the relative humidity may be lower than in other places, as it decreases with increasing temperature.
The task of designing, planning and creating the engineering infrastructure of data centers is to predict correctly, based on many factors. Different implementations of cooling and humidification systems are possible, even on the same site. If for small data centers there are typical solutions, then large objects are always unique. We must try to correctly predict the change in IT load in the data center. And, of course, do not forget about the level of humidity.