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Old UPS – Burning money faster than gambling

Given that it is quite feasible for energy saving upgrades on data centres to achieve a Return on Investment (RoI) of 30% p.a. or more, and given that even if you have to borrow the money at commercial rates you will be unlikely to be paying more than about 8%, it is a wonder that these schemes do not have a higher up-take. If, as many organisations do, you have cash in the bank then the attraction should be even greater with your deposits earning just 2% or 3% p.a. at best.

Could it be that the schemes on offer sound too good to be true and so are not taken seriously?

If that is your concern then let’s take a look at a couple of actual examples.

Example A – 40kW Local Authority Data Centre

Installation of enclosed hot aisle to 12 racksDate Centre Enclosure – Cabinets

(Plus associated air con modifications)

  • Cost – £12,000
  • Annual savings – £6,400
  • Pay-back time – 1.9 years
  • RoI – 53%

Example B – 800kW Data Centre belonging to major supermarket chain

Installation of fresh air free cooling

  • Cost – £220,000
  • Annual Savings – £86,000
  • Pay-back time – 2.5 years
  • RoI – 39%

Both of these examples relate to the cooling systems but there are equally attractive opportunities with other aspects of data centre infrastructure such as UPS upgrades.  The efficiency at full load of a typical 5 year old UPS will be 93% at best and quite possibly less.  At part load even the best performing units will be much worse.  Bearing in mind that if you are operating two UPS’s in an N+1 topology then even at full IT load each UPS will be at 50%  then you will see that you are very likely to be well down the efficiency curve.  So the starting point is to measure the actual efficiency at your of your UPS’s at your data centre’s actual working load.

The latest breed of UPS’s incorporate an “energy saver mode” in which the double conversion part of the circuit is bypassed and hence most of the losses are avoided.  These machines will deliver 98% efficiency at all loads.

So if we take a modest IT load of say 60kW we have:-

  • UPS input at 80% efficiency = 75.0kW
  • UPS input at 98% efficiency = 61.3kW
  • Saving = 13.7kW

To 13.7kW direct energy saving you have to add the associated cooling costs because, ironically, you have to pay to cool the UPS losses as these comes out as heat.  Even with efficient air conditioning this will add about 4.5kW so in total you reduce your energy consumption by 18kW which at 10 pence per kW-hour amounts to £15,768 p.a.

Swapping two 60kW UPS’s is likely to cost around £40k so your RoI should be about 40%.  Indeed, the potential energy savings and reductions in carbon emissions that can be achieved by simply replacing older UPS’s are so good that this is supported by the Carbon Trust and 0% loans are available to fund such projects, see

For a detailed survey and report on the your data centre and the opportunities that exist for energy savings contact James Wilman on 0845 9000 127 or contact us now