When the City of Atlanta finalized plans for a 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 Automated People Mover (APM).
"The Atlanta Airport Authority recognized that one of the most important current construction projects it had to undertake was upgrading that ventilation system to meet fire code requirements," explains Bill Borie, president of Borie Davis (Atlanta), the HVAC equipment representative that handled the APM project. The APM's previous ventilation system was adequate when the APM served the A, B, C, and D Concourses. However, in 1994, when Concourse E was added and the APM was extended, the fans needed to be upgraded to handle the additional flow and pressure, and meet National Fire Protection Association standards for emergency smoke evacuation. (Diagram shows airport layout.)
The City of Atlanta, owner of the airport, initiated the Hartsfield Development Program (HDP) in 2000 to enable the airport to meet future demands -- a projected 121 million passengers annually by 2015. Improvements underway include construction of a fifth runway, an additional concourse, and a four-gate expansion of Concourse E, which handles international operations. Overall infrastructure upgrades to the Central Passenger Terminal Complex (CPTC) included HVAC equipment, drives and control systems to increase system performance, enhanced compliance with industry indoor air quality standards (IAQ), and decreasing maintenance and energy costs.
"Although those improvements are important to overall passenger and airport employee comfort, as well as energy savings, the ventilation upgrades to the APM are a life-safety measure," Borie emphasizes.
A three-story underground substructure houses the APM and its maintenance facility and connects all concourses with the terminal. It includes nine four-car trains operating on a 3.5-mile loop track. The APM transports approximately 128,000 passengers per hour, carrying them from concourses to the baggage claim and ticketing area.
The system was retrofitted with four 6 ft diameter 125 hp reversible vane-axial fans capable of venting/exhausting the tunnel at 120,000 cu ft of air per minute. Four 125 hp ABB ACH Series drives control the fans, and the following benefits make them ideal for this application:
- 18-pulse design to eliminate potential harmonic distortion common in airport locations (which exceeds IEEE519-1992 recommendations);
- standard fireman's override;
- compatible with Johnson Controls' N2 Bus Serial Communication; and
- capacity to complement future tunnel expansion.
Harmonic Distortion Eliminated
"The only function of the ABB drives in this project is to control fan speed, whether for smoke extraction or general ventilation," says Dave O'Dell, ABB manufacturer's representative. "However, because the drives were installed in a voltage-sensitive facility, the issue of harmonic distortion also had to be addressed."
Since harmonic distortion may result in misoperation of sensitive electronic equipment, it is especially important that it be minimized in areas where there is a heavy use of voltage-sensitive electronic devices -- such as in airports where RF communications, computer terminals, and airport tower equipment are in constant use. ABB's 18-pulse design eliminates any potential harmonic distortion that is common with other drive types.
"Using the 18-pulse design provides a much cleaner electrical system, as well as getting the benefit of controlling the air volume necessary to satisfy the application," O'Dell says.
Drives Provide Precise Speed Control
The $3.4 million contract for mechanical and electrical equipment was awarded to W.B. Wallis & Co (Atlanta) and included the setup and installation of dampers, sound attenuators, programmable logic controllers, 56,000 ft of fiber optic cable, the fans and drives.
"We chose the ABB drives because this installation was a life-safety system and we wanted the Cadillac of drives," says Sam Green, W.B. Wallis vice president and project manager. "We use a lot of ABB drives in our projects and we count on their reliability. Plus, we have a good relationship with the ABB representative Dave O'Dell, and receive excellent service from our equipment representative Borie Davis, Inc. We did not consider using another company's drive."
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 backup controller are located at each of the two tunnel entrances, to monitor temperature and detect fire/smoke. The controllers communicate with each other and the fan drives via fiber optic cable installed in an adjacent utility tunnel.
"The fans are strictly there for fire emergencies, with a secondary task of providing ventilation, as the trains generate a lot of heat, especially when the outdoor temperature is higher," Green says. "The fans are placed at either end of the tunnel -- two in the underground maintenance facility and two on the rooftop -- so that in case of emergency, one fan can extract smoke and another can blow in clean air. The placement of the fans at the west end and at the east end of the tunnel was strategic so there would be a sufficient blow through/follow through airflow. The fact that we had two on the roof had nothing to do with air circulation, just a space consideration," Green explains. "There simply was no floor space at the terminal end of the tunnel to place two fans as large as these." (Shown here, rooftop installation.)
To provide tunnel ventilation, one fan at each end runs for 7 days, then alternates with the second fan to equalize wear. The fans run at speeds of 30-70%, depending on the heat generated within the tunnel. The ACH Series drives adjust to fluctuating load conditions, speeding up or slowing down fans when the load increases or decreases, keeping airflow balanced. In a fire or smoke situation, the fans ramp up to full speed. Without the ABB drives, the fans would need to run at the emergency ventilation flow rate at all times (constant speed operation), to ensure smoke extraction capability, which would mean higher operating cost and more energy consumption.
Firefighter's Override
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 firefighter's override. With the fireman's override activated, the drive will run the ventilation/extraction at full speed, ignoring any alarms or other commands. (Shown, one of the four 125 hp ACH550 Series drives from ABB used to power the fans.)
"It's a vital safety feature and unique to ABB drives," says Borie. "Other suppliers, in order to get that fireman's override feature, would require additional hardware in their drive."
The fans, manufactured by Twin City Fan and Blower (Minneapolis), are specially designed for smoke control applications and are tested to operate for one hour at 500°F.
"It's important that the fans can withstand the intense heat a fire can generate," Borie says. "Twin City tested the fans extensively -- and destroyed a fan in a high-temperature test -- to assure specification compliance. The fans are 100% reversible, allowing the flexibility of either exhausting or supplying clean air. Because a fire could occur at any point in the tunnel, the fan's wheel design had to be such that you could run the fan in either direction and move the same amount of air," Borie explains.
Clockwork Installation
The tunnel smoke-removal modification project was completed within a 330-day time frame and has been running without problems since January 2004.
"The installation went in very smoothly," Borie says. "We were not allowed to disrupt passenger flow through the tunnels. Fortunately, much of the wiring and internal construction was done in adjacent utility tunnels. It was after midnight and there was very little activity in the concourse, when the fans were finally tested in the tunnel. It was a good thing, because when the high-horsepower fans were turned on, large amounts of dust were blown through the tunnels. Airport cleaning crews came in hours early to clean up the tunnel for passengers trying to make early flights."
All parties involved with this installation met their schedules, and W.B. Wallis as the general contractor received a letter of commendation from the City of Atlanta Dept of Aviation for keeping to the timeline. Borie adds, "Twin City Fan and Blower Company and ABB were two key players in the overall success of the project."
