How Much Cooling is Needed In the Datacenter

This is always one of the most interesting discussions when architecting any datacenter, server room or even communications IDF closet environment.  Most IT Managers feel most comfortable when the datacenter is so cold that you need to wear a coat to work inside it.  The typical datacenter room has a cold aisle temperature set-point of around 65 degrees and over temperature alarms set to around 75 degrees. (Obviously this varies with the capabilities of the environment and the sophistication of the operators)

There are several problems with philosophy.  The first is that it is challenging to maintain this level of temperature – with added complexity of both additional cooling equipment and datacenter layout.  The second is that it costs a whole lot of money to maintain the environment at such a low temperature.  This is driven to a large extent by the added cost of powering the extra air conditioning needed to maintain the low temperature, a key factor in measuring the efficiency of your datacenter.

Rather than perpetuating the status quo, the first step in developing cooling requirements should be to understand what the environmental requirements for the technology you are trying to cool really are.  Here is a quick look at some of the most common Datacenter components’ temperature specifications

From this table I will make the following broad generalizations (note – in a real analysis everything in the room must be considered):

• The server platforms all have an operational temperature range of between 50 degrees Fahrenheit and 95 degrees Fahrenheit (note: Symetrix DMX 4 has max of 90 degrees Fahrenheit)

• The communications equipment all have an operational temperature range of between 32 degrees Fahrenheit and 104 degrees Fahrenheit

• The UPS equipment have an operational temperature range of between 32 degrees Fahrenheit and 104 degrees Fahrenheit

Clearly, when we set our datacenter temperature set-points at 60 to 65 degrees Fahrenheit we are maintaining our equipment near the bottom of the allowable temperature range.

There are a few design practices that can be recommended from this information:

• Servers do not need to be maintained at a 65 degree Fahrenheit inlet temperature.  The actual set-point can be raised quite substantially to between 75 and 85 degrees Fahrenheit and they will run fine.

• The environmental needs of the server platforms are very different from those of the communications equipment and the UPS equipment.  This would drive a design that separates these three types of technology into different rooms with different environmental configurations

• For smaller  technology rooms like IDF communications rooms, where the technology is often limited to Communications Switches, how the environment is managed can be dramatically rethought, limiting supplementary cooling in many circumstances.

By changing the set-points of the datacenter we have the ability to consider alternate cooling schemes, including free air cooling in many parts of the country.  Many of these alternate schemes are less expensive to implement and certainly less expensive to run.  This is the area where we can affect the greatest improvement in datacenter efficiency

By removing mechanical, electrical and communications equipment from the room containing the servers we are removing both significant contributors to the heat load as well as equipment that can be run at much higher temperature.