Facility Door Problem Traced to Negative Pressure

A customer recently contacted MSC with HVAC problems they were having at their large facility that seemingly originated with doors. Occupants began noticing that doors – in the lobby, on the loading dock, etc. – would not close and lock properly, creating not only a nuisance but a serious security issue. When adjustments to door hardware did no good, facility workers began to suspect that negative air pressure was at the root of the cause. Extremely negative pressure within the building was pulling in air from open doors and other access points, causing not only the door issue, but complaints of a wind tunnel effect when entering the building and walking down certain corridors.

After confirming a negative pressure problem, MSC looked at the design of the existing HVAC system. The building had large recirculating air handling units with plenum returns on each floor. Supply air was provided by fan wall systems in the air handlers, along with VAV boxes and in-line return air fans. The difference was made up by fresh air brought in through duct work with flow stations connected directly to the outside. All of the air handlers had an economizer cycle and a large array of general exhaust from bathrooms and kitchen areas. MSC concluded that the HVAC system, if working to design intent, should have resulted in slightly-positive building pressure.

MSC technicians next analyzed the building’s total pressurization through flow stations where available, and by traversing areas where they were not. Several issues were quickly identified, including VFD malfunctions on supply air fans, flow stations that were out of calibration, and flow stations that were improperly located in turbulent areas, leading to inaccurate readings. Once the appropriate fixes were made and flow station sensors recalibrated, MSC was able to perform a rebalance of the system and make a few simple sequence changes that brought the building back to slightly-positive pressurization. Building staff were provided training on proper sequence as well as airflow quantities on supply, exhaust, fresh air intake, general exhaust, and economizer cycles. In the end, MSC had not only repaired the HVAC system and satisfied their client, they’d solved the initial problem: entrance and loading dock doors that failed to latch.

Mechanical Service Corp. 
41 South Jefferson Road 
Whippany, NJ 07981 
732-884-5000
http://www.mscnj.com