How cool should my data center be?

The 2011 thermal guidelines is the third installment ASHRAE has published on this topic.  The first was in 2004 and the second in 2008. Here are the major changes in the 2011 version:

  • Expansion of the environmental classes to accommodate different owner requirements, facility applications, and IT priorities
  • Introduction of the allowable thermal envelope which has wider parameters than the recommended thermal envelope

Here is a summary of the 2004 and 2008 recommended environmental ranges

 

2004

2008

Temperature

68°F –  77°F

(20°C – 25°C)

64.4°F – 80.6°F

(18°C – 27°C)

Humidity

40% – 55% RH

41.9°F – 59°F DP

(5°C – 15°C DP)

 

These guidelines were developed to achieve maximum IT equipment reliability with minimal energy consumption.  Since 2008, ASHRAE has determined that not every data center or every piece of IT equipment under the sun must follow these guidelines.  Since different data centers have different kinds of applications and IT equipment, the appropriate environmental ranges should accommodate a specific application.  The 2011 guidelines define different classes of data centers, each with its own recommended thermal envelope.  Here is the summary description for each class from the 2011 manual:

Class A1: 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.

Class A2: Typically an information technology space or office or lab environment with some control of environmental parameters (dew point, temperature, and relative humidity); types of products typically designed for this environment are volume servers, storage products, personal computers, and workstations.

Class A3/A4: Typically an information technology space or office or lab environment with some control of environmental parameters (dew point, temperature, and relative humidity); types of products typically designed for this environment are volume servers, storage products, personal computers, and workstations.

 Class B: Typically an office, home, or transportable environment with minimal control of environmental parameters (temperature only); types of products typically designed for this environment are personal computers, workstations, laptops, and printers.

Class C: Typically a point-of-sale or light industrial or factory environment with weather protection, sufficient winter heating and ventilation; types of products typically designed for this environment are point-of-sale equipment, ruggedized controllers, or computers and PDAs. 

The following table shows the 2011 thermal envelope guidelines broken out for each class.

2011 Thermal Ranges
2011 ASHRAE Thermal Ranges

You’ll notice that the recommended temperature and humidity ranges did not change from 2008, but that the allowable ranges are significantly more liberal.  You may be asking yourself: When should I use the recommended ranges and when should I use the allowable ranges? Here is what ASHRAE says:

Recommended:  The recommended envelope defined the limits under which IT equipment would operate the most reliably while still achieving reasonably energy-efficient data center operation

Allowable:  It is acceptable to operate outside the recommended envelope (i.e. in the allowable envelope) for short periods of time without affecting the overall reliability and operation of the IT equipment.

This means that for a mission critical facility (class A1) the following thermal ranges are acceptable for short periods of time.

 

Allowable Range

Temperature

59°F –  89.6°F

(15°C – 32°C)

Humidity

20% – 80% RH

 

The thermal ranges become even more relaxed for non-mission critical facilities.

This is good.  For a long time a lot of people have realized that we don’t need to operate our data centers at 65°F.  The unbiased voice of ASHRAE is now confirming this fact.  The only question remaining is what is the acceptable length of time to operate in the allowable range?  I guess we’ll have to wait for the next set of guidelines for that answer.  But for now, we can start making some changes to the way we currently operate our data centers and not totally freak out if we find an 85°F hot spot.  Maybe instead of asking ourselves how cold our data center should be, we should be asking just how warm it can be within allowable parameters.


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8 thoughts on “How cool should my data center be?

  1. Credit ASHRAE with giving careful consideration to this issue, but their language is convoluted at best. Why would the “allowable” temperature range be inclusive of much of the “recommended” range? If we’re defining “allowable” as a transient condition, then it would make more sense for the allowable and recommended ranges to be mutually exclusive.

    One interesting note that I think you’re missing, Dan, is the lower threshold of the recommended range. The minimum temperature of 18°C is fairly high — how many datacenters have you walked into which are dumping supply air into the space at much lower temperatures?

    Perhaps the biggest issue, though, is where this temperature is being recorded. In short, a 32°C temperature recorded at a single point within the facility is much more acceptable than a global average of 32°C. I assume here ASHRAE is specifying the cold aisle average temperature?

    1. You are right, 18°C (64°F) is high. I would say the majority of data centers have at least some area where rack inlet temperatures can be as low as 55°F because the supply air is conditioned to 55°F. The reason is because 55°F is an industry standard for building supply air temp which is way too cold to be dumping directly into the cold aisle for a data center. But most people still manage data centers like buildings which is not the right approach. I do not know why rack inlet temperatures less than 64°F could reduce IT reliability. My best guess would be that if the air is too cold, there would be significant amounts of thermal strain on the IT chips, which are probably quite sensitive.

      These thermal guidelines are set for the rack inlet air temperature. This is well defined in the guidelines. I just forgot to mention it in the post.

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  3. Without artificial cooling, the temperatures in the colocation centers can rise pretty high. The temperature rise may result in malfunctioning of the electronic equipments present there. Apart from the space provided at the colocation centers, the facilities also include redundant power supply, cooling and physical security. Air conditioning systems keeps the temperature as well as the humidity to a minimum at the data centers. Balancing both temperature and humidity is important in the space; since, in case the humidity falls and it’s dry inside, the data equipments and servers may get further damaged due to static electricity discharge problems.

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