I read this article about an Australian University to Save £200k by a variety of energy saving schemes, one of which was to use local UPS systems instead of a central UPS system.
There are course, pro’s and con’s for each approach, but I hadn’t considered the efficiency angle before. When you look at it as a whole, then there is no way lots of individual UPS systems can be more efficient than one big one. Most centralised UPS systems will operate at no more than 50% load (due to redundancy -so if one UPS fails the other can support 100% load), and this is where a lot of efficiency is lost. Most UPS systems will be more efficient at full load than at half load (or less).
With point of use UPS systems, if you wanted to maintain redundancy, the same effect would occur. You would have two systems running at half load. Since each UPS system also requires its own onboard controller, you would think that this power loss would add up throughout the data center, in order to make the data centre less, rather than more efficient.
However, the real gain with using local systems is that you can size them exactly. With a centralised system you need to define what the maximum power consumption will be now, and at any time in the future and put in the according UPS (or opt for a modular system – but this is another blog entry). It is likely therefore, that in most early data centres, the centralised UPS are running no where near their 50% loading, whereas with local point of use systems you can just add systems as and when needed, thereby ensuring that you’re not wasting power by not having the UPS operating at its sweet spot.
We’ve actually used this approach for a customer recently. He has a small computer room, that has been built up over the years and has no overall UPS support. We’ve gone in to help and look at the options. The simplest approach seemed to be to put in a 10KVA UPS and wire this in to the existing infrastructure. This would give him the UPS support he needed. However, as his data suite was provided power by several circuits we would need to run in a new power feed. We would need to add PDU’s at the output of the UPS. We would then need to wire these into the existing circuits. All of a sudden, the actual cost of the UPS started paling into insignificance with the added installation costs.
As a result, we looked at individual UPS to fit into each rack and power the server and associated equipment individually. All of a sudden the numbers started to make sense. The KR1000J is more than enough for his servers, and occupies only 2U of rack space. So the customer has opted for individual UPS systems, saving an astounding £5,000 on a centralised system!