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How to Calculate UPS Costs to Run

Published by Jason Koffler on 01 December 2018

In today’s interconnected world, clients, customers, and other users of organisational data and other services need constant access to information. “Life happens” is rarely an acceptable excuse when loss of data access could threaten anything from profits to lives. This means that a UPS, or uninterruptible power system, remains vital to those whose systems are relied upon regardless of what external conditions may cause interruptions of sources of energy.

While having a UPS is extremely important to many businesses, government agencies, and other organisations, they do not come without cost. Those using a UPS need to know how to evaluate efficiency levels to keep costs down.

What Is UPS and How Does It Work

Certainly, power outages do happen. Regardless of whether they come from severe weather, internal wiring problems, brown or blackout conditions, a UPS unit ensures continuity of power and access to important systems.

UPS units provide backup power, usually from a battery, in case the power shuts off or voltage falls below a sufficient operational threshold. A UPS unit also protects sensitive and fragile equipment from the potential damage of power surges.

UPS units can come in three different types, depending on what devices and types of organisation rely on it for power continuity.

A standby unit represents the most basic type of UPS. It puts the system on battery power in case of power outages, brownouts, or surges. Residences and small businesses usually utilise this system to keep home security, point of sale, simple computers, and other devices running.

A line interactive UPS utilises a specialised system that does not necessarily have to automatically switch to battery power to keep devices operational. The system can regulate power availability on its own through either brownouts or surges. The systems that rely on a line interactive UPS are usually more sophisticated than those which only need standby power. These include gaming systems, home theatre systems, small to mid-level servers, and devices having comparable power needs.

Double conversion UPS systems ensure a completely seamless transition when external power is limited or unavailable. It takes in AC power, stores it as DC, then converts it back to AC for use. Other types of systems automatically switch on DC, which can create an infinitesimal break. Double conversion UPS systems are generally used for the most complex and high-end systems, such as large servers, major telecommunications facilities, and mission critical IT equipment.

Many UPS units use lithium-ion technology rather than the traditional sealed lead acid version often used as car batteries. Lithium ion units take up half the space but have a much higher power density. It allows for more power to be stored during periods when costs fall.

What Factors Into UPS Efficiency Calculations

UPS efficiency is based on how much power gets lost when the unit is used in the event of externally sourced power failure. In other words, when the power is out, limited, or surging and the UPS unit kicks on, how much of that power is required to run the unit itself and how much is available for the systems it powers.

For example, if a UPS unit has 96 per cent efficiency, that means that it uses four per cent to power the unit with the rest available to run the system connected to it.

UPS units, however, do not maintain the same levels of efficiency all of the time. Only when the UPS has a full load will it maintain its rated efficiency. For example, when a 200 kVA UPS rated at 98 per cent efficiency operates at 20 per cent of its capacity (40 kVA), the unit only realises an efficiency level of 85 per cent. This fact is important to remember when considering UPS unit efficiency.

The age of a unit also plays a role in UPS energy efficiency. Units sold between two and three decades ago enjoyed only an 83 to 85 per cent efficiency level. The introduction of transistors and other technologies boosted this to the 97 to 98 or more per cent seen in more modern units.

How to Calculate UPS Efficiency

The following formula is standard for calculating energy wastage and UPS efficiency:

(UPS kW Rating x Load % ) / UPS Efficiency) – (UPS kW Rating x Load % )) x (24×365) x kWh Price

Below are examples of cost savings based on kilowatt levels:

100kW UPS

100kW UPS at 90% load is 92% efficient = £7,198 pa

100kW UPS at 25% load is 70% efficient = £9,855 pa

500kW UPS

500kW UPS at 90% load is 92% efficient = £35,992 pa

500kW UPS at 25% load is 70% efficient = £49.275 pa

Below is a formula that shows more energy efficiency calculations

((UPS kW Rating x Load % ) / UPS Efficiency) – (UPS kW Rating x Load % )) x (24×365) x kWh Price

Shows a modular UPS system running costs at 97.5% efficiency at 90-25% load:

100kW UPS at 90% load is 97.5% efficient = £2,213 pa

100kW UPS at 25% load is 97.5% efficient = £590 pa

500kW UPS at 90% load is 97.5% efficient = £10,613 pa

500kW UPS at 25% load is 97.5% efficient = £2,948 pa

Common Mistakes in UPS Efficiency Evaluation

Many UPS purchasers and owners miss the boat on potential efficiency savings because of incomplete understanding.

For example, manufacturers always publish their efficiency ratings based on a 100 per cent full load of stored power. Quoted efficiencies generally only apply when the UPS is at 80 per cent or more load on the first day of operation. As was stated before, as the load percentage drops, efficiency does as well. This, however, is not necessarily an even correlation.

Percentages matter, even small ones. Owners often make the mistake of considering annual savings on efficiency differences. During a given year, these can be quite small. Over the life of a UPS unit, which should last at least ten years, the accumulated savings will generally be fairly significant.

Examples of Eaton UPS Efficiency at different loads.

Eaton’s Premier series UPS units , 93PM ,93PS , 93PR & 9395P are achieving up to 97% efficiency in double conversation with above 96% efficiency for load profiles 25 – 100% *.

9395P efficiency results during site testing
Load ►1.0
100%
75%
50%
25%
Efficiency [%]
96.5
96.9
97.1
96.6
9395P efficiency results during site testing
Load ►0.8 Lead
100%
75%
50%
25%
Efficiency [%]
95.7
96.1
96.2
95.5
9395P efficiency results during site testing
Load ►0.8 Lag
100%
75%
50%
25%
Efficiency [%]
96.2
96.6
97.1
96.3

*Note: When below 0.9 leading Power Factor loads is applied, this efficiency is slightly reduced.

Also important, efficiency drops considerably in relation to load when the percentage drops below 30 per cent.

In Conclusion

UPS energy efficiency is important, not only to know but also to understand. Efficiency and potential savings go much deeper than the published efficiency rating. Calculating efficiency levels on different units and understanding how they work can make a huge difference in costs over the life of the unit.

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