Industrial Exhaust System Replacement
The owner of this industrial building in New York state’s Capital Region had an exhaust system in a cleanroom research area that consisted of two parallel scrubbers with downstream exhaust fans both rated for 23,000 cubic feet per minute. The exhaust fans were located within the building, and the fan discharge was routed up through a fire-rated shaft several stories to the roof. The owner believed that the discharge ductwork was compromised and in need of replacement.
Erdman Anthony was called upon to design a new mixed-flow fan system located on the roof and to design the replacement ductwork in the existing shaft while minimizing the shutdown of the system for less than two weeks.
Erdman Anthony began to develop concepts for the ductwork’s removal and replacement in the enclosed fire-rated shaft, which did not have any interior access. Reuse of the shaft would require openings to be made on each floor to access structural supports and duct anchorages. These openings would need to be made prior to the shutdown, and any leakage from the compromised ductwork was a safety issue for the contractors doing the work and employees in the areas adjacent to the openings.
Given the concerns arising from the reuse of the existing shaft, Erdman Anthony reviewed alternative routes for the ductwork to get to the roof. An alternate routing up the outside of the building was presented to the owner and accepted.
The new route would require a steel frame to be built up the side of the building to support the two insulated and jacketed 36 inch-diameter duct risers. The ductwork extended across the roof to the fan on duct supports from the steel framing supporting the fan. The benefit of this concept was the ductwork and the fans could be fully installed, started, and tested prior to shutting down the existing system. This resulted in reducing the shutdown time to ten days in order to remove the old fans and associated ductwork, connect the new ductwork to the existing scrubbers, and balance the system.
The electrical requirements for the new fan system increased as compared to the original system, which was completely on a standby-generator system. The existing generator system was not capable of supporting both of the new fans. As a result, one fan was connected to normal power, and the other was connected to the standby power. Manual two-way disconnect switches were installed on each circuit serving each fan, per the owner’s request to allow via manual transfer for either fan to operate on emergency power should the other fan fail.
The design also included variable frequency drives on the new fans – initially for balancing purposes – to improve energy performance, as well as new building management controls to monitor air flow and pressure, alarms, and the operation of the variable frequency drives.