AHU-3 Bearing Distress in a Leased Laboratory Building
You are the facility manager for a 12-story, 310,000 sq ft multi-tenant office and laboratory building. AHU-3 serves floors 9–10, including a tenant laboratory whose lease requires 99.5% HVAC uptime and imposes a $2,500-per-day service credit for missed targets. Vibration on the supply fan bearing rose from 4.1 to 11.2 mm/s RMS over six weeks, and bearing temperature is running 18°F above its commissioning baseline. Four corrective work orders in six months were closed after greasing and a note to “monitor.” The 60 hp motor is a 22-week lead item and there is no on-site spare. A rooftop crane lift requires three weeks’ notice and about $9,500 in permits and rigging. The O&M contingency balance is $18,000. Summer design load begins in three weeks. The CMMS backlog is 340 work orders, 62 overdue. The tenant has not yet been told anything specific.
1. What immediate actions do you authorize in the next 72 hours, and what evidence supports them? Address the SLA, spare strategy, and contingency budget.
Read the worked answer
The vibration level is the decisive signal. For a rigidly mounted industrial machine in this size class, 11.2 mm/s RMS falls in the highest severity zone under ISO 20816 guidance, and the six-week upward trend plus an 18°F bearing-temperature rise points to bearing degradation rather than a lubrication problem. Re-greasing and monitoring have already failed four times, so repeating that response is not defensible.
Within 72 hours I would:
- Reduce AHU-3 to the minimum safe operating condition and confirm the reading with a second sensor and oil analysis; if vibration continues rising, shut down rather than risk seizure.
- Start daily vibration and temperature readings and add infrared thermography on the bearing housing and motor.
- Request an emergency quote and lead time for a rental motor and for expedited OEM supply; simultaneously book the crane and permit window.
- Issue a factual tenant notice that describes the condition, the monitoring plan, and the contingency plan without promising an outcome.
- Escalate for emergency capital release. The $18,000 contingency will not cover a motor, rigging, and labor, so I would not pretend it can.
The SLA exposure of $2,500 per day and the laboratory’s business interruption outweigh the cost of a conservative response. A run-to-failure decision is not supportable here.
2. The owner asks you to defer the repair until after summer to protect the contingency. Build the decision rule you would use and state your recommendation.
Read the worked answer
I would compare the expected cost of failure with the all-in cost of planned repair. Expected failure cost equals probability of failure before peak load multiplied by the consequence: SLA credits, laboratory business interruption, emergency rental, overtime, possible water or smoke damage, and safety exposure. Given a rising vibration trend in the highest severity zone and an 18°F temperature rise, the probability is high, not remote. Even a conservative 30% probability against a $75,000–$150,000 consequence produces an expected loss larger than the incremental repair cost.
Decision rule: act now if the trend is in the highest severity zone, the consequence is material, and a planned repair can be executed before the risk peak. Defer only when the condition is stable, redundancy exists, and the consequence is low.
Recommendation: authorize the repair before summer design load. Fund it through the contingency plus an emergency capital request, not by draining the contingency and leaving the building exposed. If the motor cannot arrive in time, secure a rental motor or portable cooling unit and schedule the crane lift. I would document the owner’s decision either way, because deferral transfers the SLA and safety risk to the building without reducing it.
3. What do you tell the tenant and executive leadership, and what data do you track until the repair is complete?
Read the worked answer
I would send two different communications. To the tenant: a factual notice that AHU-3 has a bearing condition under engineering review, that monitoring and repair planning are underway, and that a contingency plan exists for temporary cooling if the unit must be taken offline. I would not speculate about cause or promise a date until the motor and crane are confirmed. To executive leadership: a one-page risk summary with the vibration trend, the SLA exposure, the funding gap, the recommended action, and the decision needed by a specific date.
Data to track daily: vibration in mm/s RMS, bearing temperature versus baseline, AHU-3 supply and return temperatures, work-order status and parts ETA, crane and permit milestones, and any tenant complaints. I would also record the deferred-maintenance history so the organization can see why four greasing work orders did not constitute a repair.
The communication principle is no surprises: tell the tenant what is known, what is being done, and when the next update will come. Document the notices and the owner’s funding decision in the lease file.