Ask specialists in the field – IT managers or UPS and conditioning system suppliers – if availability affects efficiency and they will all answer in the affirmative without hesitation.
And if we were then to ask them how much it affects efficiency, after some hesitation, most of them would give a qualitative reply.
Help with this can be found in the IEEE Gold Book “Design of Reliable Industrial and Commercial Power Systems”, in which availabilities in relation to the most widespread architectures – N, N+1 and 2N – are given.
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The table below gives an example of the efficiency trend of the same UPS on the basis of redundancy.
| Availability | Probability of fault (5 years) | UPS load | UPS efficiency | |
| N | <99.993 % | >39.95 % | 60 % | 92.4 % |
| N+1 | 99.993 % | 39.95 % | 40 % | 91.9 % |
| 2N | 99.994-99.999 % | >29.8-16.6 % | 30 % | 90.8 % |
In the hypothesis of a load of 90 kW and a 160 kVA UPS with a rated load efficiency of 93%, operating 24 hours a day, the impact on the environment is shown in the following table.
| Load level | Efficiency | Losses | HVAC | CO2 | |
| N | 62 % | 92.4 % | 7.4 kW | 2.5 kW | 53 t |
| N+1 | 42 % | 91.9 % | 7.9 kW | 2.6 kW | 56 t |
| 2N | 31 % | 90.8 % | 9.1 kW | 3.0 kW | 64 t |
This shows clearly that the system’s required availability must be evaluated and calculated carefully on the basis of the level of service to be provided.
Tech Info – March 2010
HOW AVAILABILITY AFFECTS EFFICIENCY
by
MATTEO GRANZIERO
Technical Communication Specialist
SOCOMEC UPS
