Designated a National Historic Landmark, the 45-story CBOT building is an art deco structure consisting of two towers. For many years, the air-handling system — including two large supply fans and two return fans — provided airflow for floors 10 to 23 in each tower. Installed in 1970, these old air handlers were becoming a cause for concern. Maintenance costs continued to increase, and the building owners wanted to ensure uninterrupted HVAC service to traders and tenants.
Carrying out the replacement posed unique challenges for general contractor Alps Construction and mechanical contracting firm Competitive Piping Systems Inc. (CPS) of Chicago. “The age of the building, the location of the equipment in the building, the need to keep the old system operational with a single weekend cut-over, and access were the most unique items about the retrofit,” said Adam Smith, project manager, Alps Construction.
The initial problem centered on how to move equipment to and from the two mechanical rooms that housed the air handlers, which were located on the 24th floor. The only access to those rooms was through a door leading into tenant office space where electronic trading and other activities take place.
The contractors knew they had to find another way to get men and equipment into and out of the mechanical rooms during the project; so they developed a different route. It led from the mechanical room through a small exterior opening cut to the outside, and then down to a sub-roof on the 23rd floor.
The difficulties involved in moving equipment via this route played a big role in the choice of new equipment. The original plan was to replace the old units with something similar, but given the access limitations, that idea no longer seemed feasible.
“The original blowers were ex-tremely large,” said Tom Muraski, vice president of CPS. “In order to get something that size into the building, we would have had to take out walls. It would have been a massive undertaking.”
Instead, the team chose a modular fan system from Huntair Inc. The company’s Fanwall system consists of a number of individual cube-shaped cells, each of which houses a fan, motor, and electrical connections. The number and configuration of these cells depend on the application and its requirements.
“The Fanwall components were of a manageable size to allow us to work around the existing equipment that remained in the penthouse and gain access through standard doors,” said Smith.
Because the modular fan system could be installed cell by cell, no significant structural changes were needed. With Fanwall fan cubes, Muraski explained, “We could bring the system up in small pieces and build everything onsite.”
Fanwall Technology systems are custom-configured by specifying the number of fans, as well as fan operating speed and wheel width and diameter. This allows each system to be optimized for maximum efficiency.
For this job, Environmental Systems Design, a global consulting engineering firm headquartered in Chicago, worked with Midwest Applied Solutions of Hillside, Ill., the Huntair manufacturer representative, to design two identical fan systems totaling 470,000 cubic feet per minute (cfm). Each system consists of a 130,000 cfm supply array made up of 21 Fanwall cells and a 105,000 cfm return array made up of 15 cells. The cells measure approximately 3 feet by 4 feet and weigh about 400 pounds.
One by one, CPS personnel brought the 72 fan cells up to the 23rd floor using a dolly. The installers then moved the cells outside onto the sub-roof where scaffolding and a hoisting rig lifted each cell up to a catwalk next to the mechanical room on the 24th floor. Finally, a construction worker wheeled the cells into the mechanical room through the temporary hole in the wall.
Another factor in the complicated installation was the requirement that airflow to floors 10 to 23 — in both towers — was never to be turned down during normal business hours. To meet this requirement, CPS divided the project into phases. First, while the existing supply fans were running, technicians demolished the old exhaust fans and replaced them with a new Fanwall supply system. Piping ran through the space designated for the new fan array, but this presented no problem, thanks to the flexibility of the modular system, according to the company. The array was simply split into two parts, one part five cells wide by three high and the other two cells wide by three high, allowing piping to run in between.
Once the supply Fanwall Technology systems were in place, CPS switched over power and ductwork to the new Fanwall array. It began functioning as the new supply system over the weekend. Finally, the contractor demolished the old supply fans and replaced them with a Fanwall array for the exhaust system.
The entire job, which included installing new coils and dampers, took about three months. All system shutdowns and startups occurred during nights, weekends, and holidays so that the project wouldn’t disrupt building operations during normal business hours.
No More Mission-Critical
The identically sized fans and motors that make up a Fanwall array operate in parallel to create the same airflow rate as a single, larger fan sized for the same duty. Due to this system redundancy, a fan/motor failure is only a high-priority maintenance issue rather than a mission-critical failure that disables the entire air handling system.
If one of the fan’s motors fails during operation, the VFD and control system increase the speed of the other motors so that overall system performance can be maintained at the same level during the time it takes to replace the failed motor. Losing one fan doesn’t noticeably affect the system’s operation.
Publication date: 01/16/2012