Feature Cost Control Strategies to combat cost rises
Kenny Green, technical support manager at Uninterruptible Power Supplies, a Kohler company, discusses how a correctly chosen and configured UPS system can contribute to power savings
R
ising power costs are of direct personal concern to all of us - and they are to businesses as well. In a recent UPSL survey, over 85% of correspondents cited rising power costs as a major concern for their business. This represented an increase of nearly five percent on the 2010 survey results.
As this recent UPSL survey shows, rising energy costs are of increasing concern to businesses as well as indi- viduals. This is exacerbated by social and, increasingly, legislative pressure to exhibit green strategies. As a busi- ness’s data centre or ICT infrastructure and the uninterruptible power supply (UPS) that feeds it contribute signifi- cantly to its energy consumption, UPS efficiency comes under the spotlight.
In recognition of this demand, most leading UPS manufacturers now offer progressively more energy efficient UPS solutions. The once prevalent transformer-based UPS topology has largely been replaced by transformer- less implementations. As Fig. 1 (above) shows, these offer a near flat operating curve, achieving 96% effi- ciency at full load, reducing only to 95.5% at 25% load.
Even at full load, transformer-based solutions are a couple of efficiency points down, and as the load reduces to 25%, this efficiency drops away sharply - to around 86%.
This improved performance cre- ates energy savings directly. Yet fur- ther savings arise because better UPS efficiency reduces cooling energy requirements and costs. The example below demonstrates the possible cost savings available from transformer- less technology.
An example
The example concerns a user’s load of 80kW, with a power factor of 0.8. This presents a 100kVA load to the UPS. With either transformer-based or transformerless topology, this could be supported by two 120kVA modules and design power factor of 0.8 sharing the load equally in an N+1 redundant arrangement. Each module will be operating at 42% loading, which equates to just 91% operating efficiency for transformer- based types. By comparison, the transformerless units will deliver 96% efficiency. Assuming a cost of 9.0p/kWh - typical for commercial
S18 SEPTEMBER 2013 UPS & Standby Power
Above: Kenny Green, technical support manager at Uninterruptible Power Supplies
Below: most leading UPS
manufacturers now offer progressively more energy efficient UPS solutions
premises - the savings over five years amount to £24,015, with £6,000 origi- nating from cooling savings. Transformerless topology inherently produces an input power factor much closer to unity and less load depen- dant than a transformer-based UPS. This reduces the magnitude of the UPS input current, therefore the size of the cabling and switchgear. It can also reduce electricity costs. Transformerless UPS efficiency can be further improved, to around 98%, by operating in eco-mode. This means that the critical load is fed directly from the utility mains during normal operation, but switched through the UPS if the mains fails or transgresses tolerance limits for an excessive time. Eco-mode has increased in popularity as energy prices have climbed while ICT equip- ment typically protected by UPSs is better able to ride through short dura- tion power interruptions. A choice to go eco-mode must also be governed by the quality of the utility mains supply on the user’s site.
These efficiency improvements mean that UPSs can continue to pro- tect critical loads with minimal impact on the user’s energy bill. This is espe- cially true since, as we have seen, transformerless UPSs can maintain near full efficiency even at reduced loading. Redundancy, and therefore increased power availability, can be built-in. The UPS’s ability to protect is enhanced without excessive loss of power efficiency.
Uninterruptible Power Supplies
www.upspower.co.uk T: 0800 171 2320
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