ASHRAE, the professional body for cooling engineers, is working on a standard for data center efficiency, which could create controversy in the industry. 

The new standard includes recommendations for the maximum power usage effectiveness (PUE) that should be achieved by data centers in a given location (see table below), but some in the data center industry believe the body is being too prescriptive, in an echo of the criticism which surrounded ASHRAE’s previous foray into this field, in 2010. 

Emerson Liebert EFC free cooling unit
– Emerson Network Power

Mandatory PUE?

The ASHRAE 90.4 Energy Standard for Data Centers (draft published here) standard has been in prospect for some years from the American Society of Heating Refrigeration and Airconditioning Engineers (ASHRAE).

It was first announced in Feburary 2015, and a further draft is now available for comment. 

ASHRAE  is the source of the 90.1 standard which applies to energy efficiency in buildings generally, andwhich is widely referred to in building regulations.

That standard contains an addendum covering data centers, which caused controversy over fears that it might mandate a particular type of cooling technology (the “economizer”), although ASHRAE maintained that innovation would be allowed by facilities meeting the standard. 

Since then, the group  has decided that a separate building standard document is needed - and once again raised fears that, it will be too prescriptive. In particular, mandating specific PUE scores may not be popular.  

“You shouldn’t use formal standards in a rapidly growing, fast-moving industry,” said Don Beaty of DLB Associates, a past chair of ASHRAE Technical Committee 9.9 (TC9.9) for data center technology, according to a report by Rich Miller on Data Center Frontier.

The standard includes sections covering the building itself; its heating, ventilation and air conditioning; its electrical systems; its water heating; its lighting; and its other systems. Most of these simply refer to the existing demands of the 90.1 standard, but the electrical and heating and ventilation systems have more detail. 

Within the secton for heating, ventilation and air conditioning, there are two “compliance paths”. One is based on the mechanical load component (MLC), defined in the standard and calculated from the specification and/or performance of the climate control equipment in the facility. There is an alternative, based on the data center achieving better than a specified PUE, according to its location.

Climate zone tables listing most countries are available here, the zones within the US are listed here, and on a map here (and elsewhere). As examples, Singapore would be in 1A, the US spans from 1 to 8, the UK is in 4 and 5. 

Comments on the draft are still open and  can be made here

Power Usage Effectiveness (Design PUE) Maximum
Climate Zone Design PUE
1A 1.61
2A 1.49
3A 1.41
4A 1.36
5A 1.36
6A 1.34
1B 1.53
2B 1.45
3B 1.42
4B 1.38
5B 1.33
6B 1.33
3C 1.39
4C 1.38
5C 1.36
7 1.32
8 1.30