My Data Logging Monitoring Plan; One More Thing

In preparing my post on the details of how I decided what to log on the hot water system at the Newport EPA lab, I realized I forgot to fill you in on one of the targets I had identified in the monitoring plan I described in the previous post.  So, I will use this post to do that and then move on to the details of monitoring the heating hot water system.

In addition to the air handling systems serving the labs, which I had targeted for monitoring, there is also an air handling system serving the administration area, illustrated in the pictures below.

ASU2-5 02

ASU2-5 03

This unit is a fairly simple VAV system served by a supply fan that is equipped with a cooling coil, an economizer, and a relief fan, all serving VAV reheat terminal units which provide the zone level temperature control. 

I decided it was worth some logging attention for a number of reasons as described below.
Some of the clues that there might be an opportunity were contained in the log book that you can see sitting on the top left side of the AHU fan section in the top photo and in the indications shown by the variable speed drive displays shown in the bottom photo.

  • Ray Nevins, the lead engineer for the facility indicated that while he had only been
    working there for a couple of months, when he did his rounds, the unit seldom seemed to show any variation in speed. His logs showed the speed tended to float around in the 45 – 60 Hz range, indicating that the fan may be moving design flow most of the time.
    If that turns out to be true, then getting the system to function as a VAV system again would save some fan energy.
  • One reason the fan might run at full speed most of the time could be that the velocity controllers on the terminal units have failed or are not properly adjusted.
    Ray is new to the facility and has not been through the preventive maintenance procedure for the controllers, so he was not sure of their status from personal experience.  But, he was concerned that they may not have been serviced as regularly as might be desirable based on some of the records he had found.   In my experience, this is not unusual of terminal equipment, making terminal units good retrocommissioning targets. 
  • The controllers on these particular VAV boxes are pneumatic, and experience has shown that regular attention is all the more critical to ensure proper operation.  Otherwise, they can fail to full flow, and sometimes, full reheat, a very energy intensive failure mode.  Correlating logged data from the AHU
    with logged data from the hot water system may shed some light on
    the general status of the terminal equipment and help me quantify
    any benefits that could be realized from a focused RCx effort
    followed by more regular maintenance.
  • Oregon is a relatively mild climate, especially the Oregon coastal climate.  Thus a functional and properly tuned economizer can offer significant savings over mechanical cooling.  Logging the performance of the AHU, especially during the swing season that is currently in progress, will shed some light on how well this important energy conserving feature of the system is performing.
  • The Administration AHU should be able to operate on a schedule.  Unlike the rest of the laboratory, the administration offices are only occupied on weekdays from about 7am until about 5pm.  Thus, the administration AHU should be operating on a schedule.  Data logging will reveal if this is in fact the case and if there are opportunities to optimize the schedule or  the night set-back/set-up set points that keep the spaces from getting too far out of control when the system when it is not running.  Its easy to take obvious scheduling opportunities for granted, but experience has shown that what you is supposed to be happening may not be what is actually happening, especially on older control systems with limited alarm capabilities.

The bottom line was that while the Administration area AHU was a relatively small system, it also represented a system that had the potential to operate fairly efficiently but showed symptoms of some inefficiencies.  Dedicating a logger to the system for a couple of weeks will help me understand if a more focused effort is in order.

David Sellers
Senior Engineer – Facility Dynamics Engineering

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