Decommission CRAC/CRAH units
Decommissioning CRAC (Computer Room Air Conditioning) or CRAH (Computer Room Air Handling) units can improve Power Usage Effectiveness (PUE) at data centers by reducing unnecessary cooling energy consumption, eliminating overcapacity, and improving overall cooling efficiency.
Quick Reminder: What is PUE?
PUE = Total Facility Power / IT Equipment Power
CRAC/CRAH units fall under "Total Facility Power", not IT load. So reducing their energy use directly improves PUE.
Why Decommission CRAC/CRAH Units?
Over time, data centers often:
Consolidate IT loads
Replace older servers with more efficient hardware
Move workloads to the cloud
Decommission legacy infrastructure
However, cooling infrastructure often remains unchanged, resulting in overcooling and energy waste. That's where CRAC/CRAH decommissioning helps.
How Decommissioning CRAC/CRAH Units Improves PUE
1. Eliminates Overcooling and Short Cycling
Too many active units can lead to inefficient airflow patterns, causing some systems to short cycle.
Decommissioning excess units ensures that only the right number of systems operate, reducing wasted energy.
Less runtime = less power draw = better PUE.
2. Reduces Fan and Compressor Energy Use
CRAC units use compressors, and CRAH units use fans connected to chilled water loops—both are high power consumers.
Decommissioning units that aren’t needed removes parasitic loads from the power equation.
Each unit removed could save kilowatts of continuous power usage.
3. Lowers Maintenance and Improves Reliability
Fewer units to maintain = more focused airflow optimization.
This enables more effective hot/cold aisle containment and variable speed cooling, further reducing energy use.
4. Reduces Cooling Redundancy Waste
Many data centers were built with N+2 or 2N cooling redundancy.
In practice, fewer units may be needed to maintain SLAs.
Decommissioning redundant units can optimize performance without sacrificing reliability.
5. Unlocks More Efficient Cooling Technologies
Removing legacy CRAC/CRAH units makes room for more efficient alternatives:
Rear-door heat exchangers
In-row cooling
Liquid cooling
Outside air economization
Example Impact
A single CRAH unit may use 3–10 kW, depending on fan speed and load.
Removing just 3 unneeded CRAH units running 24/7 at 5 kW = 131,400 kWh/year.
That’s thousands of dollars saved and a measurable improvement in PUE.
Impact Area - Benefit to PUE
Overcooling reduction - Lowers total facility power
Fan and compressor load reduction - Eliminates parasitic energy consumption
Improved airflow management - Enhances cooling efficiency
Reduced cooling redundancy - Optimizes energy use without impacting uptime
Space for newer systems - Enables transition to high-efficiency cooling
Final Thought
CRAC/CRAH decommissioning is a powerful strategy to improve data center PUE—especially in facilities that have downsized IT loads, upgraded equipment, or implemented better airflow containment. By eliminating excess or outdated cooling infrastructure, operators can significantly reduce overhead energy use while maintaining optimal operating conditions.
