Online Monitoring Case Study - AHU Motor & Fan Bearing Defects

Applied Diagnostics Ltd - Precision with Pride

Introduction

This Air Handling Unit is situated on a roof with poor access for maintenance and routine monitoring. Due to its criticality an on-line monitoring system was fitted to alert engineers to any potential maintenance issues such as bearing wear or fan imbalance. The motor drives the overhung fan via 3 V-Belts, which is supported by rolling element bearings at each end of the shaft.

AHU Motor Bearing Trend

*

AHU Fan Balance & Bearing Trend

*

Actions / Conclusions

Following the installation and configuration of the on-line system the benefits were immediately apparent. The following information relative to fan condition was available allowing a Pro-Active maintenance strategy to be adopted:

  1. The Drive End Fan bearing reading was slightly high, possibly due to lack of lubrication.
  2. The Drive End Motor bearing was extremely high, most likely due to genuine wear.
  3. The Fan balance was acceptable for a unit of this size.

The on-line system was configured to react in the following manner:

  1. Local Panel Alarm illuminated to alert operators to AHU maintenance issue.
  2. SMS sent to site engineers to alert them to AHU maintenance issue, including the drive end Motor and Fan bearing vibration levels.
  3. E-mail sent to Applied Diagnostics engineers to alert them to AHU maintenance issue, including the drive end Motor and Fan bearing vibration levels.

The following corrective maintenance actions were taken following the received alerts:

  1. Applied Diagnostics engineers collected frequency spectrum data from the local panel vibration outputs. A severe motor bearing defect and dry fan bearings were diagnosed.
  2. Site engineers replaced the motor, which had the effect of reducing the trend to acceptable levels. The fan bearings were lubricated, which initially produced a slight trend reduction. However the trend started to increase again and the fan bearings are now scheduled for replacement at the next available opportunity.

Motor Bearing Damage Photo

*