Application of Economy Mode (eco-mode) in Data Centre Environments
Workspace Technology’s design team is constantly looking at ways to further reduce the PUE associated with data centre design. As part of this drive we encourage data centre operators to consider the deployment of more economic modes of operation for UPS systems.
What is Economy Mode?
Economy Mode or eco-mode functionality is the term used when UPS loads are run from the bypass instead of the inverter. This is the inverse of normal operation where the UPS bypass is waiting to accept the load if there are power quality problems.
UPS systems with eco-mode options are designed to provide the critical load with sufficient voltage (supply voltage should never be zero for longer than 20ms) to avoid load disruption.
Because in eco-mode the UPS is effectively off line a system efficiency’s of 98-99% can be achieved. The UPS system will constantly monitor the mains supply. If mains power deviations are monitored the system will automatically revert in on-line mode in typically less than 4ms.
Why deploy eco-mode?
The higher the UPS efficiency the lower the losses which in turn leads to a lower total cost of ownership and improved data centre PUE.
Typical ultra-high efficiency double-conversion UPS will typically performance at 96% at 50% load. This compare to >98% when the UPS is operating in eco-mode.
With the anticipated power cost inflation that is likely to take place over the 10 to 15 year life of the UPS eco-mode savings can be significant.
As can be seen over a 10 year period there are significant savings the can be made even with just 2% improvement in PUE.
The effect on a data centre PUE can be 0.025 which is a tangible improvement if the data centre PUE is < 1.20.
Implementing eco-mode is typically seen by many operators as an increased risk to the load. A number of area’s should be considered.
Mains Power Quality
When in eco-mode operation if the main monitoring system detects a deviation or quality issue the UPS will be returned to on-line mode. Typically the UPS will be configured to remain in on-line mode until the mains power has been stable for at least 30-60 minutes to prevent oscillation in times of mains instability. In the UK the eco-mode function can be sustained for at least 99.6% of the year however in area’s of power quality eco-mode is not advised.
Transient Voltage Surge Suppression
As good data centre design practice Workspace Technology recommends the installation of TVSS surge-suppression devices at key points within the power distribution scheme. This includes the main incoming panel, intermediately distribution panels and critical PDU’s. The installation of TVSS systems will ensure the critical load is protected from transient over-voltages (spikes) when operating the UPS in eco-mode.
Generator Back up
When emergency generators are implemented it is recommended that an inhibit signal is provided by the generator control panel to latch the UPS into on-line mode until mains failure is restored.
This will eliminate any issues will stability / quality of power and prevent the generator from being exposed to leading power factors that are typical with many critical load profiles.
Non-linear ICT loads and current harmonics
Total Harmonic Current Distortion (THCD) within I.T loads may be as high as 35%. When in online mode the UPS will isolate the mains supply from the effects of the I.T load harmonics. However when eco-mode is enabled, the mains transformer will be exposed to these harmonic effects. Workspace Technology will typically uprate the neutral conductor as a “good practice” design precaution to mitigate and potential issues when eco-mode UPS systems are deployed.
Workspace Technology recommends any new UPS system should support High-efficiency and eco-mode operation modes. We recommend that data centre operators should consider the configuration of eco-mode to help reduce energy costs and improve the overall PUE ratings. Workspace Technology’s expert electrical design team will ensure appropriate optimized engineering to give peace of mind to data centre operators when eco-mode is implemented.