625 North Michigan Avenue

High Rise Building Pressurization in Chicago, Illinois

Our work at this high-rise building started because of a severe building pressure problem during the economizer mode.  We discovered the large fan systems were moving excessive amounts of air, thus contributing to the relief problem.  During the first few years, AHU modifications were phased, with a major adjustment to slow the supply fans and rebalance the areas served by these units.  The following is a list of subsequent projects we developed over a total of ten years:

• Control upgrade for fan systems
• Control upgrade for chiller plant
• Control upgrade and mechanical improvements to provide more consistent condenser water for tenant computer room cooling units
• VFDs were installed on all five large constant volume fan systems.  This allows the fans to slow down during lightly occupied hours, thus saving fan energy.  The BAS is also programmed to slow the fan speed when the return air relative humidity gets above a setpoint during the summer cooling mode.  This reduction in airflow helps the system provide colder discharge air, and thus better dehumidification.
• Isolation control valves were added to the perimeter two-pipe fan coil risers to shut off heating water to different building exposures when the outdoor solar conditions cause those exposures to be sufficiently warm.
• A new more efficient burner was installed on one of the two old steam boilers, with the second boiler only operating as a backup.  Controls were added to this boiler plant to automate it and connect it to the existing BAS.