“Passive” vs “active” equipment alarms: Know the difference, save 100X in costs!


“Passive” vs “active” equipment alarms: Know the difference, save 100X in costs!

Recently, our service team learned of a major equipment breakdown that ended up costing a processor a lot of money. What was unfortunate about this breakdown was that it could have been prevented at a cost of about 1/100th of the final repair bill.  This huge savings would have been possible if only plant personnel had recognized the importance of troubleshooting “passive” equipment alarms before they became a damaging and expensive “active” alarm.

Here’s what happened:  A processor relied on a single, large central chiller for plant-wide process cooling. The chiller was equipped with two refrigeration circuits, with each circuit served by dual compressors. The dual-circuit, dual-compressor design enables this large chiller to handle a wide range of chilling loads with a high degree of efficiency.

Over a period of days, one of the two chilling circuits began to experience a series of “passive” alarms. (Passive alarms are “warning signs” that indicate a problem that could lead to a future failure, but allow the equipment to keep running.) These alarms indicated flow-switch, pump, and pressure faults in one of the refrigeration circuits. The processor cleared all of the faults and chiller operation continued. However, no troubleshooting action was taken.

Days later, a much more serious “active” alarm occurred, indicating low suction pressure in the same chilling circuit, and the chiller shut down. (Active alarms trigger equipment shutdowns to prevent imminent harm to personnel or to equipment.)  In this case, the low suction pressure alarm meant that the circuit was not providing the dual compressors with an adequate flow of refrigerant. So, the compressors not only couldn’t remove heat from the evaporator circuit, essential to maintaining process cooling, but they were starved of the refrigerant fluid that provides them with internal cooling and lubrication.

During the brief chiller shutdown triggered by this alarm, experienced personnel should have recognized this as an “active” alarm with the threat of imminent damage and undertaken immediate troubleshooting and repairs.  However, those on the scene did not. Instead, they simply reset the alarm and restarted the chiller, not realizing that the malfunctioning circuit had recovered just enough refrigerant pressure to enable the chiller to limp along. Over the next five hours, the cycle of chiller alarms, shutdowns and resets occurred numerous times until a compressor overload occurred, blowing the main fuse. Only then was the chiller technician called in.

The technician quickly found the root cause of the problem:  The thermal expansion valve that should have regulated the pressure in the refrigerant circuit wasn’t working. The circuit board that controlled it had failed. Had the decision been made to troubleshoot any of the passive alarms or the first “active” alarm resulting in chiller shutdown, the cost of replacing this single bad circuit board would have been about $150.  But it would have required someone with enough experience and training to recognize the alarm situation and make the decision to temporarily cut chiller capacity (run on one circuit only) and adjust production levels enough that this brief and relatively easy repair could be made.

Minus that person, the cost was more than 100 times higher!  The repeated chiller restarts with low refrigerant pressure caused extensive damage to compressor blades, resulting in a spray of metal shavings throughout the refrigeration circuit and necessitating replacement of both compressors, along with damaged controls and components.  The total bill for chiller repair exceeded $15,000 in parts and labor.  In addition, the processor had to operate the plant at one-half chiller capacity for an extended period, since days of part acquisition and repair were required.

As this case clearly shows, it pays to understand what “passive” and “active” alarms are and how to respond when they occur. In summary:

  • Any passive alarm is a warning sign, warranting troubleshooting action, even though your equipment can continue to operate.
  • Multiple passive alarms, especially of similar types, indicate the need for more urgent troubleshooting and repair. Your equipment is still running, but serious trouble may be brewing. Troubleshoot and repair as soon as possible. Delays will only make the problem worse and the cost higher.
  • Any active alarm (equipment shutdown) indicates that equipment damage or personnel injury is imminent. Immediate root-cause troubleshooting and repair is essential before the equipment is returned to service.

I urge you to get your personnel the training they need to understand and identify the severity of equipment alarms and make prompt, accurate decisions about how to respond. Training is readily available from all auxiliary equipment manufacturers, so take advantage at your earliest opportunity!