A modern on-line UPS system has many advantages especially when it comes to UPS energy efficiency. It provides protection against all types of power supply failure, filters a vast range of disturbances found in the mains supply. As such, provides more sensitive loads with a clean backup power supply. With extra storage capacity, it can be designed to support the critical load for instance. When an alternative supply such as a standby generator system is brought on-line, for typically 10-15 minutes but can be up to hours.
Your uninterruptible power supply UPS energy efficiency is important for two critical reasons. The first is running costs and the second is related to the UPS battery runtime available when the mains power supply fails. This article looks at five most effective ways you can maximise your UPS’s energy efficiency.
1. Right-sizing the UPS and backup battery power supply
Most users associate UPS energy efficiency with running costs, and this is certainly true with data centre UPS solutions. The higher its operational energy efficiency the lower the amount of energy wasted. UPS energy efficiency savings also mean lower heat output and therefore less load onto the local cooling system. Right-sizing UPS power system and load profile also help to ensure it is supporting a load profile within its optimum range.
On an old transformer-based UPS system, the UPS energy efficiency may only be 80-85% and within a highly loaded system. This is because in this older type of uninterruptible power supplies the efficiency profile tails off quite dramatically as soon as the load is less than around 70-80% of the UPS rating. In a more modern UPS system design, a load as low as 25% can still achieve high operating efficiency. The use of a modular UPS design also helps to right-size as the ‘correct’ number of UPS models can be used in this high-efficiency design to meet the load and any N+X requirements.
2. UPS battery replacements and refurbishments
UPS power systems can have a working life of ten to fifteen years or more provided that the device undergoes regular annual maintenance and cyclical refurbishment.
Uninterruptible power supplies include ‘consumable’ items which require regular placement and within their design life. UPS batteries are the most common example and are generally of the lead-acid 5-year or 10-year design life, requiring replacement around years 3-4 or 7-8 respectively and when used within a 20˚C ambient environment. Cooling fans are another example of a UPS consumable which should also be inspected annually and replaced according to fan manufacturer recommendations.
Around year five of operation, a UPS system should be considered for refurbishment. The principle works here include replacement of the AC and DC capacitors. The capacitors require replacement as they can dry-out and their self-healing characteristics are weakened to the point of a potential critical failure occurring. Capacitors use flammable polypropylene and at high internal temperatures can experience thermal runaway and cause a fire inside the uninterruptible power supply.
If your datacentre power system is at the eighth year of operation and requires a UPS battery replacement. It may be worth considering a complete UPS upgrade rather a refurbishment and especially if your legacy system is a transformer-based type. An upgrade to a transformer-less, modular UPS system can see energy efficiency improvements from 15-20% or more dependent on the load percentage and profile supported.
3. UPS ECO Mode
Running the uninterruptible power supply in its dedicated energy-saving mode, commonly known as ECO mode, can boost efficiency to 98-99%. It achieves this by in effect operating as a line-interactive UPS, so the load is powered by the bypass line with the inverter inactive but ready to take over if there’s mains supply failure or fluctuation. This short break in continuous power is the main drawback to using ECO mode, particularly with sensitive equipment.
4. UPS maintenance and routine inspections
Regular maintenance of UPS systems is critical to the availability and resilience of an uninterruptible power supply and should be budgeted for when first installed. Without regularly maintaining UPS systems, sudden failures can occur with over 80% caused by a poorly maintained battery set. However sophisticated a UPS may be, the fact is that uninterruptible power supplies have consumable parts that require regular inspection to ensure optimum performance including overall UPS energy efficiency.
5. UPS Remote Monitoring
Uninterruptible power supplies should be monitored over an Ethernet/IP network for alarm conditions. Continuously monitoring the UPS system can establish load patterns over time and provide enough time to respond to issues that could affect UPS energy efficiency and operational resilience. Two specific alarms that can indicate energy efficiency include:
Overload and bypass alarms: if the load connected to the UPS power supply is greater than its rated output, an alarm will be issued. If the overload is large enough or there is an internal fault condition, the uninterruptible power supply may go into bypass mode
Over temperature alarms: can indicate an internal fan failure or that ventilation into and out of the UPS cabinet is restricted. Long term higher internal ambient temperatures can lead to component damage as well as requiring fans to run at higher speeds.
If the battery set is within a separate cabinet or room, the installation of a separate battery temperature sensor is recommended.
UPS energy efficiency summary
Over the last two decades there has been a significant improvement in the datacentre UPS energy efficiency levels. The use of IGBT-based rectifiers and inverters has helped to dramatically lower fixed energy efficiency losses and flatted the efficiency curve out over a wide load range, from as low as 25% to 100% loaded. There have also be improvements in transformer design and the widespread introduction of modular datacentre UPS by many of the leading UPS manufacturers. Energy efficiency levels have risen from around 70-80% to around 96% for most online systems and 97-98% could eventually become the norm. However, there will always be the need to correctly size both the UPS and its battery set, monitor installations and ensure that they are correctly maintained if the design calculations are to be proven in use.
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