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Introduction

Large commercial chillers are the backbone of many facilities, supplying thousands of tons of cooling through extensive piping networks. But even when the equipment itself is built to last, the structures that support it may not be.

During routine vibration data collection, our team identified excessive vibration not on the chiller, but on the piping support structure tied into the system. Follow-up testing confirmed the cause: resonance. This wasn’t a threat to the chiller itself, but to the facility structures that keep the chilled water system in service.

The Setup

The facility operates six chillers connected to a common chilled water header. The newest unit, a Trane 862 kW (≈1,156 HP) chiller operating at 4160 V and 3570 RPM, was piped into the header alongside the existing chillers. The chilled water lines are supported on heavy H-beam steel mounts.

While the supports appeared substantial, vibration monitoring revealed otherwise.

The Discovery

Routine data collection was performed with a Betavib King vibration analyzer using a TREA330 premium CTC Triax accelerometer, along with CTC cables and magnets.

The analyzer showed that while the chiller itself was operating normally, the piping supports were vibrating excessively. This triggered a deeper investigation.

To confirm the root cause, we conducted impact testing using the same Betavib analyzer with a single CTC AC192-1D accelerometer. The results showed that the H-beam supports had a natural frequency of ~59–60 Hz — nearly identical to the chiller motor’s operating speed of 3570 RPM (59.5 Hz).

When the chiller was online, vibration at the top of the support frame reached about 0.7 in/s peak at 1× running speed. Amplitudes increased from bottom to top, showing that the structure was resonating in its first bending mode.

Why Resonance Matters

It’s important to understand: the chiller itself was not in danger. Rotating equipment is designed to operate at 3570 RPM continuously.

The real risk lies in the facility structures being forced to vibrate at that same frequency. At 0.7 in/s peak, the piping supports were experiencing vibration levels high enough to cause long-term structural problems if left uncorrected.

This level of motion, repeated 60 times per second, can lead to:

• Piping chafing against the steel mounts, wearing through insulation, coatings, and eventually the pipe wall
• The risk of a hole in chilled water piping, leading to a catastrophic facility flood
• Fatigue cracks in welds and anchors
• Loosened hangers and piping supports
• Leaks at flanges and nozzle connections

“It’s not the chiller that fails — it’s the facility around it.”

Mitigation Strategies

To protect the facility, corrective actions must address the structural resonance:

1. Stiffen the support structure — add gussets, cross-bracing, or tie-backs to raise the natural frequency above ~75 Hz.
2. Add damping — apply constrained-layer damping or viscoelastic pads to reduce peak response.
3. Install a tuned mass damper (TMD) — placed near the top of the frame, tuned to ~60 Hz, to absorb vibration energy.
4. Isolate the piping — with spring hangers or isolators (within nozzle load limits).
5. Minimize excitation — alignment and balance checks can help, but the primary driver here was structural resonance.

Lessons Learned

This case highlights the value of routine vibration monitoring with professional-grade equipment. The Betavib King analyzer with CTC Triax sensors identified the abnormal piping vibration that visual inspection could not. Follow-up impact testing with the CTC AC192-1D accelerometer confirmed the resonance problem.

The key lesson: resonance doesn’t damage the chiller — it damages the facility around it.

To avoid that risk:

• Collect routine vibration data on both equipment and connected structures.
• Perform impact testing when abnormal motion is detected.
• Ensure piping supports are designed with natural frequencies well clear of motor running speeds and harmonics.

Conclusion

Routine data collection with the Betavib King analyzer revealed that the piping supports for a Trane chiller were resonating with its operating speed. Left uncorrected, this resonance could lead to pipe chafing, fatigue, and even a catastrophic flood — not because the chiller failed, but because the supporting structures could not withstand resonance.

By detecting the problem early, corrective action can be taken before the facility suffers costly downtime. As chillers grow larger and more powerful, vibration management must extend beyond the machines themselves to the structures that carry their loads.

Thank you Brian Franks with JetTech Mechanical LLC for sharing this informative article with us! 

Understanding the consequences that resonance has on equipment reliability