Independence Center

The HVAC/mechanical system at Independence Center I is based on a complex and flawed design that dates back to the original construction of the building. Each of the two towers has two air handlers per floor which supply conditioned air to electronic VAVs on each side of the floor. The problem is that both air handlers are connected to a common supply air duct that makes a complete circle around the floor. Regardless of whether one air handler or both are running, air will move around the circular duct to all VAVs. Although each air handler is supplied with a VFD and an isolation damper to prevent backflow, one air handler cannot supply the minimum flow to all VAVs on the floor.

The original Johnson Controls system was incapable of producing a control strategy to handle partial occupancy on the floor. To exacerbate this situation, there were several tenants with a small footprint that paid for 24-hour occupancy. The end result was that both air handlers would run 24/7 on all floors containing these full-time tenants, even though they only occupied a small space. Johnson Controls technicians had worked on this problem for years and spent a great deal of time on site trying unsuccessfully to solve this problem.