Removing Legacy UPS
Decommissioning legacy UPS (Uninterruptible Power Supply) systems can significantly improve Power Usage Effectiveness (PUE) at data centers by reducing electrical losses, cooling demand, and maintenance overhead associated with outdated and inefficient infrastructure.
Why Legacy UPS Systems Hurt PUE
PUE = Total Facility Power / IT Equipment Power
Legacy UPS units contribute heavily to the "Total Facility Power" side of the equation without directly powering compute load. Here’s how they negatively affect efficiency:
1. Low Energy Conversion Efficiency
Older UPS systems often operate at 80–90% efficiency, especially under partial load.
Modern UPS systems reach 96–98%+ efficiency, even at lower loads, using technologies like double-conversion ECO modes and modular topologies.
This means legacy UPS waste significantly more power as heat during AC-DC-AC conversion.
Less wasted energy = lower total facility power = better PUE.
2. Increased Cooling Demand
Inefficient UPS units generate more heat.
This additional thermal load requires more cooling capacity, raising power usage by chillers, CRAHs, and fans.
Decommissioning them reduces the total heat in the environment, allowing for scaled-back or optimized cooling.
3. Oversizing and Underutilization
Legacy UPS systems were often oversized to handle peak loads that never materialized.
UPS systems operate most efficiently at 60–80% load; below that, their efficiency drops sharply.
Decommissioning unused or overbuilt systems and replacing them with right-sized, modular UPS improves utilization and energy performance.
4. Redundant Infrastructure
Many older data centers built in the N+2 or 2N era have redundant UPS systems that may no longer be needed due to updated redundancy policies (e.g., moving to N+1).
Removing unneeded systems cuts unnecessary energy draw and simplifies power paths.
5. Battery System Inefficiencies
Legacy UPS batteries (often VRLA) require continuous charging and environmental control (temperature, humidity), which consumes power.
Decommissioning the UPS also allows for removal of these legacy battery banks, reducing both power and cooling needs.
Benefits to PUE from Decommissioning Legacy UPS
Efficiency Gain - Impact
Reduced conversion losses - Lower total facility power
Less waste heat - Reduced cooling demand
Better load matching - Higher UPS efficiency
Elimination of idle systems - Cuts power drawn by unused infrastructure
Opportunity for modernization - Adopt modular, scalable, and energy-efficient systems
Example Impact
Before: A legacy UPS running at 85% efficiency supports a 500 kW IT load. It draws ~588 kW, with ~88 kW wasted as heat.
After: A modern UPS at 97% efficiency draws only ~515 kW for the same load — saving 73 kW instantly, plus reducing cooling needs.
Final Thought:
Decommissioning legacy UPS systems is a high-impact move toward improving data center PUE because it attacks inefficiency at both the power and cooling levels. When paired with modern UPS technology and right-sizing strategies, it can dramatically lower energy overhead without compromising uptime or resilience.
