Located on top of the central utility plant (CUP), we made our way to the refrigeration exhaust system fan. Once we arrived at the place where we would be taking our readings, we set up our equipment. Next, we drilled and prepared for a Pitot Tube Traverse. We put the variable frequency drive (VFD) in hand mode… nothing happened.
This particular exhaust fan serves a room containing the new chiller that serves a new hospital. The system was designed to operate in the event of a refrigeration leak. Once we realized the fan did not turn on, I called the control person for the project. They continued to tell me that they had no control over the system, so I then called the General Contractor we were working for. The GC connected with the facility engineers, who also informed me that they had no control over the system.
After discussing this with the mechanical contractor also working in the CUP, and continuing to work on it another hour or so, I was told that they could jump the alarm out. Once he did that, the system turned ON! And we headed back to the place where our traverse was located.
Conveniently, the VFD was next to the duct, installed on the wall. But then we discovered…30 hz! That’s it. The fan wouldn’t run over 30 hz. We took a traverse, and the fan was low on flow. We tried to put the fan at 60 hz, but it would not ramp up that high.
With years of experience, I found myself scrolling through the options and realized the VFD was locked out at 30 hz. Having made many friends throughout this industry, I called one I refer to as “the “drive guy.” He helped me unlock the drive, and we were able to get the drive to go up to 60 hz. We then tried another traverse. We got to 50 percent of design flow, and I had a hunch that the fan was running backwards.
Finding ourselves tracking down facilities to unlock the locked ship ladder located on the back of the CUP, we headed up to the roof to locate the fan, remove the cover, and verify whether the fan was running backwards. As it turned out, we had to call the electrician to switch the direction of the fan. He finally arrived, and to his disbelief, I showed him the fan was running backwards. He switched the wires within the drive and put it back together.
We took our traverse again, and to my disbelief, the fan was still only exhausting 50 percent. I headed back to the roof but quickly realized the ladder had been locked back up since I had told facilities we were done. After tracking facilities back down to unlock the ladder, I headed over to the fan, removed the cover, and found that the fan was still running backwards.
I called the electrician again, and he refused to believe me–until he spoke to his apprentice. After discussing it with the apprentice, they realized the wrong side was switched. They arrived to redo what was done previously and switch the correct side of the drive. After that was complete, we turned the system back on and took our traverse. Finally, we were making design flow!
Long story short, a few-hour job turned into an all-day affair due to one person not verifying direction at start-up. After that experience, I would highly advise anyone to verify direction prior to the start of any work. This goes for all mechanical equipment.
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