Removing Legacy UPS Systems
Outdated UPS systems waste energy as heat and inflate cooling load. Decommissioning them is a high-impact way to improve PUE.
By Nate Bruns
Decommissioning legacy UPS (Uninterruptible Power Supply) systems can significantly improve PUE by reducing electrical losses, cooling demand, and maintenance overhead tied to outdated, inefficient infrastructure.
Legacy UPS units contribute heavily to Total Facility Power without directly powering compute. Here’s how they drag down efficiency.
1. Low conversion efficiency. Older systems often run at 80–90% efficiency, especially under partial load. Modern UPS reach 96–98%+ even at lower loads using double-conversion ECO modes and modular topologies, meaning legacy units waste far more power as heat during AC-DC-AC conversion.
2. Increased cooling demand. Inefficient UPS units generate more heat, which requires more cooling from chillers, CRAHs, and fans. Decommissioning them reduces total heat and allows cooling to scale back.
3. Oversizing and underutilization. Legacy UPS were often oversized for peak loads that never materialized. UPS run most efficiently at 60–80% load; below that, efficiency drops sharply.
4. Redundant infrastructure. Many older facilities built to N+2 or 2N have redundant UPS that may no longer be needed under updated N+1 policies.
5. Battery inefficiencies. Legacy VRLA batteries require continuous charging and environmental control. Decommissioning the UPS lets you remove those battery banks too.
Example impact
A legacy UPS at 85% efficiency supporting a 500 kW IT load draws roughly 588 kW, wasting about 88 kW as heat. A modern UPS at 97% draws only ~515 kW for the same load, saving 73 kW instantly, plus reduced cooling. Paired with modern technology and right-sizing, removing legacy UPS dramatically lowers energy overhead without compromising uptime.
