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Uninterruptible power supplies

How Much Will I Save?

The UPS market is diverse, and devices vary greatly in cost and efficiency. Table 1 below reflects the results of a recent market survey of the price and full-load efficiency of all types of UPSs manufactured or sold in Canada.


Table 1
Market Survey of Uninterruptible Power Systems:
Capacity, Price and Efficiency

 Capacity Range   Price Range
(CAN$) 
 Efficiency Range 
 250 VA–500 VA  150–300  70–94%
 501 VA–1000 VA  200–900  60–85%
 1000 VA–6 kVA  450–7500  70 – 90%
 6 kVA–30 kVA  > 10 000  80 – 90%
 Above 30 kVA  > 25 000  85 – 95%

Efficiency is not a strong factor in the pricing of UPSs; installed features and optional accessories create most price variation. However, the following example shows the significance of choosing efficient equipment:

A building owner has a choice of purchasing one of two 2-kVA UPSs, either a basic unit with a full-load efficiency of 70 percent or another unit with a full-load efficiency of 90 percent. What would be the expected energy savings if the more-efficient UPS were bought instead of the basic unit?

Savings would depend on the loading profile and the cost of electricity. For a constant full load with a 0.9 power factor, and assuming a cost of 8 cents per kWh, the expected energy savings from choosing the efficient UPS would be $400 a year.

Table 2
Comparison of Annual Cost of UPSs
with Different Efficiencies

2-kVA UPS Standard Unit High-Efficiency Unit
Full load efficiency 70% 90%
Power factor 0.9 0.9
Cost of electricity (kWh) $0.08 $0.08
Annual energy use (kWh) 22 526 17 520
Annual energy costs $1,802.08 $1,401.60
Annual savings $400.46

For variable-load conditions, savings depend on the part-load efficiency and the loading profile of the particular UPS. Offline UPSs generally have higher part-load efficiencies than online or line-interactive UPSs. Consult the supplier before making a purchasing decision.

Next: Purchasing Tips