The elegance of the ‘Tier’ structure is broken by EN50600-3

Published on 24th November 2014 by Ian Bitterlin

I know that there are a few folks who denigrate the Tier Classification system originally introduced by Uptime Institute as irrelevant in modern European data centre design but no-one can deny the simplicity and elegance of the natural progression from ‘least’ to ‘most’ resilient. It remains, in my opinion, a very useful structure for benchmarking a design in terms of concurrently maintainable and fault tolerance.
Anyway, imitation is said to be the greatest form of flattery so the ANSI (north-American centric) data-centre standards of BICSI-001 & TIA-942 reinforced the original four levels of the Uptime Tiers, which are so easy to articulate:
• One active path without redundant elements
• One active path with redundant elements
• Two paths, one active with redundant elements plus one passive path. This is best described as Concurrently Maintainable with some risk during system maintenance
• Two paths, both active, each with or without redundant elements. This has the Concurrent Maintainability attributes of ‘3’ plus Fault Tolerance to the worst possible single event
It is now very unfortunate that we can’t use the ‘Tier’ word (especially in conjunction with roman numerals, I to IV) as Uptime have fallen out with TIA and asked for their ball back. So we have Tier I-IV of Uptime, Data Centre Type I-IV of TIA-942 and F1-F4 of BICSI (there is an F0 but it doesn’t describe a data-centre as we know it, not having a UPS or genset) – and now comes along EN50600 with Availability Classes 1-4, or so we should have hoped. Why I say ‘hoped’ is simply so that, more or less, a Class X classification in EN50600 means that it was equivalent to the other classification systems.
But, no: In EN50600-3, the cooling section, of the Availability Classes have been shifted one step to the right – so Class 1 doesn’t exist, Class 2 is equivalent to ‘tier/type/F’ I/I/1, Class 3 is equivalent to II/II/2 (and so is NOT Fault Tolerant) and Class 4 is equivalent to III/III/3. So what about an equivalent to IV/4? Well, that is called ‘Enhanced Class 4’.
There are many conclusions that can be drawn but the basic problem is that a facility characterised as Class 4 in EN50600 is NOT a IV/IV/4 in the other systems and vice versa. The opportunities for marketing abuse and deception, let alone confusion, are many-fold.
The problem seems to have stemmed from confusion around the industry practice of building facilities with 2N power (like a Tier IV) and N+1 cooling (like a Tier III) and calling it Tier III+, but the result has rendered the EN Standard less than useful and may well lead to people either ignoring it or making false claims in marketing for ‘Tier 4’ facilities without reference to EN50600, and so deceiving prospective clients.
As engineers, we now have two problems;
• Tiptoeing around trying not to use the word ‘tier’ or mixing up roman and Arabic numbering systems – I’ve already found this frustrating, even in this blog
• Remembering to carefully explain to clients that a Class in EN cooling does NOT correspond to the same Class in the other systems - I’ve already found this very difficult in facility audits
So how could such a buggers-muddle arise? The Standard production process is a drawn out affair involving the national standards bodies of each member state and is best described as lining up a lot of birds in a row and hoping to hit them all with just one bullet. Hopefully each member nation puts forward a local committee that has expertise in all of the subjects, which doesn’t always happen. Then the editor has to get a draft in place based on all the ‘technical’ inputs and, finally, get resolution on the ‘final’ draft that goes for international voting. At that stage you have to hope that the countries that did not contribute abstain (or vote ‘yes’) rather than vote ‘no’ despite their lack of commitment during the creation phase. As you may appreciate getting a standard in place therefore has to have ‘consensus’ at many stages and, in addition, has to the approval of the editor. In the case of EN50600-3 the recommendation by some in the UK that the ‘four tiers’ was followed was ignored and some ‘expert’ (I know not from where) appears to have convinced the editor that 2N cooling was technically difficult – which is plain wrong as Tier IV/Type IV/F(4) cooling is actually easier to implement and control than Tier III/Type III/F(3) – and, in addition, that Tier 3+ was a ‘problem’. OK, so real Tier 4 cooling is rare and expensive – but it is Fault Tolerant, so you get what you pay for! The problem of even writing this down and making it clear highlights the ridiculous state-of-affairs we find ourselves in by the restrictions of using the terminology ‘Tier’! Of course, Tier III+ is actually only a ‘problem’ for the Uptime Institute as they insist on the principle of lowest-common-denominator.
EN50600 could have spelled the end of using the Uptime Tier Classification system in Europe but I suspect that the reputation, market standing, brand and history of Uptime will actually result in EN50600 being stillborn. There are plenty of examples where Standards are ignored in data centres – for example generator power rating to ISO – so ignoring EN50600 is more than possible. That is not to say that formal ‘accreditation’ by Uptime to their own Tier Classification will take-off, since they have had long enough to gain a foothold in Europe without appreciable success, but EN50600-3 has made the equivalence and clarity of Uptime/BICSI/TIA-942 very appealing and, certainly, less confusing.
I, as a member of the UK EN50600 committee, probably owe you all an apology for not being active enough, not being fully aware of the impending risk or insistent that it was wrong soon enough. So, it is a ‘sorry’ from me...


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Prof. Ian Bitterlin is the Chief Technology Officer for Emerson Network Power – the world leader in data-centre power and cooling infrastructure solutions and integrated DCIM software. Recognized in the industry as an expert mechanical and electrical engineer, Ian has produced numerous wh ... More

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