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Using ASHRAE specs for data center metrics

What are temperature and humidity values that will be acceptable in a multi-vendor installation and where are they measured?

The Ashrae Book, Thermal Guidelines for Data Processing Environments, provides environmental classes and environmental specifications. The IT manufacturers were well represented on the Ashrae Committee TC 9.9 resulting in the environmental classes and specifications being universally accepted by the industry.

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It has been common practice to operate data centers at fairly low temperatures such as 68 degrees Fahrenheit and at fairly high humidities such as 50% relative humidity. Some of the habit to operate at these conditions may be a carryover from the original mainframe days and may be compounded by conservatism.

IT equipment including servers and network equipment have many applications including ones that are external to the data center and therefore different operating conditions such as unoccupied, lights off, or unconditioned. The Ashrae Thermal Guidelines Book addresses this variation by establishing 4 different environmental classes.

Equipment environment - Class requirements
ClassAir conditioningEnvironmental controlExample
1Yes tightServers and storage products
2YesLooseServer and storage products (outside of data center)
3YesNoWorkstations,PCs and printers
4NoNoPoint of sales equipment
ASHRAE 2006

Class 1 is typically a data center with tightly controlled environmental parameters (dew point, temperature, and relative humidity) and mission critical operations; types of products typically designed for this environment are enterprise servers and storage products.

Environmental specifications are provided for each environmental class. The environmental specifications include both recommended values and allowable values.

Recommended Environmental Conditions: Facilities should be designed and operated to target the recommended range.

Allowable Environmental Conditions: Equipment should be designed to operate within the extremes of the allowable operating environment. In addition to the allowable dry-bulb temperature and humidity ranges, the maximum dew point and maximum elevation values are part of the allowable operating environment definitions.

For a Class 1 Environment, the specifications are:

Equipment environment specifications
ClassAllowable dry bulb(°F) Recommended Dry Bulb (°F)Allowable % relative humidityRecommended % relative humidity
159 to 9068 to 77 20 - 8040 - 55

Having this published vendor neutral environmental specifications is very beneficial for both the design and operation of data centers. However, what really makes this powerful is that Ashrae also defines where to measure the air thereby adding critical clarity and avoiding dispute. The Equipment Environmental Specifications are based on the equipment air inlet.

About the author:Beaty is the chair of ASHRAE technical commitee TC 9.9 (mission critical facilities, technology spaces, & electronic equipment)

This was first published in July 2006

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