Mechanical Service Corporation was asked to step in when a commissioning team and BAS contractor encountered numerous static pressure issues while performing startup services on seven custom AHUs in a new laboratory clean room facility. Pressurization is critical in all clean room facilities, and these puzzling issues were stalling the commissioning effort. Several MSC technicians were dispatched to the facility with various diagnostic tools including NIST data loggers, smoke pencils, and balancing hoods.
Our first and most basic task was to inspect all doors in the facility. Several were found to require adjustments to the closure mechanisms, some had faulty or missing floor sweeps, and others required repairs to correct issues with hardware failing to latch properly and popping open.
In the meantime, we set up NIST data loggers to measure pressures in areas lacking sufficient differential pressure transmitters (DPTs) to the BAS from which to collect usable data. We began in the clean perimeter corridor and checked the required pressure of +.05 in. WC to a temporary outside neutral reference using a Dwyer A306 static pressure tip. After a few days of data collection, we were surprised to find that other areas connected to the corridor were affecting the static pressure and VFD control, causing pressures to swing from slightly positive to slightly negative. It was extremely important to fix this area first as all of the airlocks leading into the process suites referenced the clean perimeter corridor for negative pressure. MSC recommended installation of a permanent, accurate neutral reference point for precise supply and exhaust VFD control.
Now, with an accurate reference point and control, MSC technicians were able to turn their attention to other issues that were holding up commissioning progress in the airlocks and process suites. NIST data loggers were used to check which areas the BAS could read and which it could not read. It became evident that many of the facility’s differential pressure transmitters were inaccurate and could not be properly calibrated. MSC recommended upgrading the existing DPTs with robust new pressure transmitters that could accurately read the clean perimeter corridor to the airlocks.
In addition to finding several static pressure sensor tips recessed in the walls and ceilings with kinks in the tubing, we discovered poor installation on dozens of pneumatic fittings that were leaking and required repair. The faulty fittings were identified by isolating the pneumatic tubing, applying a slight positive pressure, and bubble-checking the fittings.
MSC technicians worked with the commissioning team using temperature and humidity data loggers to record levels throughout the spaces, revealing trends in areas where the BAS could and could not read. Humidity and temperature problems that we uncovered and corrected included loop tuning issues and positioner problems on several actuators.
Once all of the issues had been resolved, MSC performed an uninterrupted 72-hour test over a weekend to prove the system could maintain pressure, temperature and humidity and allow on-time completion of the commissioning phase of the project.
Owners of the cleanroom facility were duly impressed with MSC’s ability to quickly and thoroughly resolve the many static pressure issues. They asked that we remain as part of the commission team to help guide the project to completion and awarded us their maintenance contract. MSC also assembled a detailed SOP for maintenance personnel, and we performed a critical parts analysis and provided the facility with a list of critical spare parts to be kept on-hand as backup in the event of a failure.