When the City of Atlanta finalized plans for the capital-improvement project at Hartsfield-Jackson Atlanta International Airport, an integral part of the 10-year, $5.4 billion project included upgrading the ventilation system of the underground Automated People Mover (APM). The APM’s previous ventilation system was adequate when the APM served the A, B, C, and D Concourses. When Concourse E was added and the APM extended — now 3.5 miles long, handling 128,000 passengers an hour — the fans required upgrading to handle additional flow and pressure to meet National Fire Protection Association standards for emergency smoke evacuation. The $3.4-million set up and installation contract for mechanical and electrical equipment was awarded to W.B. Wallis & Co. (Atlanta, GA).

altThe system was retrofitted with four 6' diameter, 125-HP reversible vane-axial fans capable of venting/exhausting the tunnel at 120,000 cubic feet of air per minute. The fans, manufactured by Twin City Fan and Blower (Minneapolis, MN), are specially designed for smoke control applications, able to run in either direction to move the same amount of air, and are tested to operate for one hour at 500°F. Supplied by ABB (Norwalk, CT), four 125-HP ABB ACH Series drives control the fans. The 18-pulse design eliminates harmonic distortion, which can adversely affect voltage-sensitive electronics, such as those in airports, where RF communications, computers, and airport tower equipment are in constant use.

The ABB ACH Series drive interfaces with two Johnson Controls DX-9100 series extended digital controllers, which communicate tunnel conditions that determine fan speed. A digital controller and back-up controller are located at each of the two tunnel entrances, monitoring for temperature and fire/smoke. The controllers communicate with each other and the fan drives via fiber optic cable installed in an adjacent utility tunnel.

To provide ventilation in the tunnels, one fan at each end runs for a seven-day time period, then alternates with the second fan to equalize wear. The drives adjust to fluctuating load and heat conditions, keeping airflow balanced. In fire or smoke situations, the fans ramp up to full speed. The fans’ full-speed operation is critical during a fire or smoke situation, and to ensure the fans do not shut down, the drive is equipped with a standard fireman’s override, which, when activated, will run ventilation/extraction at full speed, ignoring any alarms or other commands. Without the drives, the fans would run at the emergency ventilation flow rate at all times, meaning higher operating cost and energy consumption.


The tunnel smoke-removal modification project was completed within a 330-day time frame and has been running without problems since January, 2004.

Motion Control Technology Magazine

This article first appeared in the June, 2006 issue of Motion Control Technology Magazine.

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