CASE70 · Data centers · PUE / Fan operating state
Tracing a data-center PUE discrepancy to fan-only operation
A site-to-room PUE comparison triggers an equipment-level investigation. Fans operating without an active cooling call are examined before any change to the cooling sequence.
01 · CASE ANALYSIS
Start with the measurement discrepancy
The source reports site PUE 1.576 and room PUE 1.848: a difference of 0.272. That gap is a diagnostic signal, not a savings percentage.
Check the meter locations, aggregation period and IT-energy denominator before attributing the discrepancy to cooling equipment.
02 · CASE ANALYSIS
Follow the signal to operating state
Detailed equipment inspection identified fan operation when cooling was not active. Compare fan status and speed against the cooling call, valve or compressor state, supply/return temperatures and room conditions.
Fan-only operation can reflect ventilation, thermal protection or a valid sequence. Determine which running hours have no required service before changing controls.
| Measurement | PUE | Interpretation |
|---|---|---|
| Site | 1.576 | Check site energy boundary |
| Room | 1.848 | Check room boundary and IT denominator |
| Difference | 0.272 | Diagnostic gap; not a saving |
03 · CASE ANALYSIS
Test the revised sequence
Review schedules, manual overrides, fan minimum speed and the conditions that initiate cooling. Trial changes in a controlled operating window while checking rack temperatures and humidity.
Measure fan electricity and the overall cooling response under comparable IT load and outdoor conditions. A lower PUE caused by a larger IT denominator alone is not evidence of a fan saving.
04 · CASE ANALYSIS
Interpret the evidence
The source establishes an operating anomaly and a route for investigation; it does not provide an isolated final saving from switching fans off.
CASE38, CASE46 and CASE70 describe connected data-center work. Their observations should not be added as independent project savings.
| Signal | Question |
|---|---|
| Cooling call / valve / compressor | Is cooling actually requested? |
| Fan speed and power | What runs during no-cooling periods? |
| Supply / return / rack temperature | Is thermal service maintained? |
| Schedule and override | Does a valid sequence explain operation? |
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