Temperature and humidity design criteria

Use these temperature and humidity design criteria to ensure that your data center environment provides optimal conditions for your server operation.

The information technology equipment can tolerate a considerable range of temperature and humidity, as described in the server specifications for each server. Generally, the air conditioning system should be designed for 22 degrees C (71.6 degrees F) and 45 percent relative humidity at altitudes up to 2150 m (7000 ft.). This design point provides for the largest buffer in terms of available system time. If the air conditioning system fails or malfunctions, the computer will be able to operate until it reaches its specified limits. This buffer provides additional time for air conditioning repairs before the computer must be shut down. The design point has also been proven to be a generally acceptable personal comfort level.

The design points for temperature and relative humidity might differ in certain geographical areas.

Air conditioning control instruments that respond to + or - 1 degree C ( + or - 2 degrees F) temperature and + or - 5 percent relative humidity should be installed.

Computer room cooling is basically a sensible (as opposed to a latent) cooling operation. (Sensible heat is defined as the transfer of thermal energy to or from a substance resulting in a change in temperature: Latent heat is the thermal energy absorbed or evolved in a process other than change of temperature.)

Substantial deviations from the recommended design point in either direction, if maintained for long periods (that is, for hours), will expose the system to malfunction from external conditions. For example, high relative humidity levels might cause improper feeding of paper, operator discomfort, and condensation on windows and walls when outside temperatures fall below room dew point.

Low relative humidity levels alone will not cause static discharge. However, in combination with many types of floor construction, floor coverings, and furniture, static charges that are generated by movement of people, carts, furniture, and paper will be more readily stored on one or more of the objects. These charges might be high enough to be objectionable to operating personnel, if discharged by contact with another person or object. If discharged to or near information technology equipment or other electronic equipment, these charges can cause intermittent interference. In most areas, it will be necessary to add moisture to the room air to meet the design criteria.

Because temperature or relative humidity deviations for only a few hours will cause the floors, desks, furniture, cards, tapes, and paper to reach a condition that will readily permit the retention of a charge, it is recommended that the air conditioning system be automatically controlled and provided with a high or low alarm or a continuous recording device with the appropriate limits marked.

Server operating limits

Some individual servers might require special consideration and have more or less restrictive requirements. See your server specifications for specific environmental limits.

The typical server operating environment is shown in the following table. The server nonoperating limits are shown in the following Nonoperating Server Limits table.

Table 1. Typical server operating environment
Environmental criteria	Computer room limits	Office space air conditioned	Office space not air conditioned
Temperature	16 to 32 degrees C (60.8 to 89.6 degrees F)	16 to 32 degrees C (60.8 to 89.6degrees F)	10.0 to 40.6 degrees C (50 to 105.08 degrees F)
Relative humidity	20 to 80 percent	8 to 80 percent	8 to 80 percent
Maximum wet bulb	23 degrees C (73.4 degrees F)	23 degrees C (73.4 degrees F)	27.0 degrees C (80.6 degrees F)

The design criteria is shown is the following table.

Table 2. Design criteria
Environmental criteria	Design criteria
Temperature	22 degrees C (71.6 degrees F)
Relative humidity	45 percent
Maximum wet bulb	23 degrees C (73.4 degrees F)

The recommended design is shown in the following figure.

Figure 1. Recommended design

Note: The air entering the server must be at the conditions for operation before power is turned on. Under no circumstances may the server's input air, room air, or humidity exceed the upper limit of the operating conditions. This is the maximum operating temperature limit and should not be considered a design condition. Also, the relative humidity of the air entering the server should not be greater than 80 percent. This specification is an absolute maximum. The optimum condition is where the room is at the design criteria of 22 degrees C (71.6 degrees F) and 45 percent humidity.

Air temperature in a duct or an underflow air supply should be kept above the room dew point temperature to prevent condensation within or on the servers. When it is necessary to add moisture to the system for control of low relative humidity, one of the following methods should be used:

Steam grid or jets
Evaporation pan or pane
Steam cup
Water atomizers

Water treatment might be necessary in areas with high mineral content to avoid contamination of the air.

Note: In localities where the outside temperature drops below freezing, condensation will form on single, glazed window panes. Also, if outside temperatures are considerably below freezing, the outside walls of the building should be waterproofed or vapor sealed on the inside or, in time, structural damage will occur in the outside walls.

Server nonoperating limits

When the facilities are shut down, the nonoperating environmental specifications must be followed to prevent damage to the server and to ensure reliable operation when power is restored.

Table 3. Nonoperating server limits
	Server nonoperating limits
Temperature	10 to 43 degrees C (50 to 109.4 degrees F)
Relative humidity	8 to 80 percent
Maximum wet bulb	27 degrees C (80.6 degrees F)