You Learn Something New Every Day

In data centers, it is common to deploy power and cooling systems in a redundant configuration.  This is to say, there will be more equipment installed than is actually required, so that if one system fails, there is at least one system there to pick up the load.  This is usually expressed as ‘N’ for the number of units required, ‘N+1’ for the needed number of systems plus an additional, 2N for twice the number required and so on.  Well, I learned recently on a data center project that I am trying to wrap up that running all systems in tandem for cooling actually produces energy savings because of the energy required for fans or equipment to start.  So even though they have N + a number of redundant chillers or CRACs, all units would run at the same time and at a lower capacity thus sharing the load.

I should caution that this is specific to a particular project and the input of a mechanical engineer (which I am not) is required to make an ultimate determination. I am told that this is a common energy savings strategy for larger data centers with chiller plants carrying a redundancy or with large CRAH units.   This comes as a surprise to me after meeting clients who advocated alternating equipment on a schedule to balance run time for equipment, which must seem preferable to designating a primary unit and wearing the unit out and having to rely on the backup system while the primary is maintained or replaced.  I’ll be interested to learn more.


1 Response to “You Learn Something New Every Day”

  1. 1 geoffala
    December 28, 2011 at 6:38 pm

    This is the same reason that it’s more efficient to run multiple power supplies in servers (AC power) at half capacity than a single one at full capacity. The reason for this is in the power conversion. You never get a 100% efficient AC-DC conversion, and as a power supply approaches capacity (typically around 80-90%) its conversion efficiency decreases VERY rapidly, resulting in a lot of wasted power (and heat).

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