In the original system, chilled water was piped from the chillers at the basement level to the upper floors via a PVC riser in an interior pipe chase. The condensing water from the chillers is piped on a common loop to the cooling towers, which are on ground level alongside the building. The original cooling tower was a single-cell unit rated at 440 tons.

MORE CHILLER CAPACITY NOT THE ANSWER

In 1992, because of increasing heat loads from office computer equipment and increases in building ventilation rates, an additional 195-ton Trane Series R™ water-cooled screw chiller was installed. The chiller was included on the same chilled water and tower water loops as the original system. But, it was discovered that, although the additional chiller provided redundant capacity, it did not contribute to better building cooling because it was constrained by the limited cooling tower capacity and the undersized air handlers on the upper floors.

This was the situation when CB Richard Ellis took over management of the building in April 1998. Up until that time, the strategy had been to pre-cool the building in advance of weekday occupancy, sometimes starting as early as Sunday afternoon. Even so, on the warmest days, the building was unacceptably warm by mid-afternoon. Despite the fact that there was adequate chiller capacity, there wasn’t enough cooling tower capability to shed the excess heat. Further, there wasn’t adequate capacity in the airside plant to allow air volume at desirable levels. A solution was needed.

The management firm worked with the owner to develop a plan for improving the comfort level of the building. The challenge the engineers at CB Richard Ellis faced was designing a system that could be installed without interrupting tenants’ operations. This was particularly challenging given the tight clearances in the mechanical rooms on each floor. The engineering work was done during the second half of 1998 and the project equipment was bid in January 1999. Work began in July 1999.

PIPING IMPROVEMENTS

The new design involved both the chilled water distribution system and the airside plant. A new steel pipe was scheduled to be installed to replace the PVC riser. Coincidentally there was a failure on the PVC pipe just as the project was starting. The riser was temporarily repaired until the replacement steel pipe was in place. The eight-inch chilled water mains were replaced with 10-inch lines. Piping was replaced to each air-handling unit (AHU) to reflect the increased AHU size as well.

The entire central plant system was completely repiped to achieve a true primary-secondary chilled water system. The chilled water pumps were changed from constant speed to variable speed types.

Condenser water pumps were relocated to an area near the ground level cooling towers. This saved space in the building mechanical room and reduced pumping costs.

The existing single-cell cooling tower that was designed for 1,320-GPM was replaced with a new three-cell Marley cooling tower rated for 2,550-GPM. The cooling towers are designed for an operating range of 95-85 degrees F.

All of these cooling tower and chilled water plant improvements were made without taking the existing system out of service during the workweek. While parts of the cooling tower system were out of service during the building improvement process, a rental air-cooled chiller from Trane’s ChillerSource™ unit was installed. This chiller assured continuing chilled water service to the air handlers and fan-coils.

AIRSIDE CAPACITY DOUBLED

The airside part of the solution involved changing the air handlers on the upper floors to allow a supply of one CFM of conditioned air per square foot. The previous system had supplied only 0.54 CFM per square foot.

All of the air handlers on the upper floors were replaced with Trane Modular Climate Changer™ air-handling units. The clearances of the mechanical rooms on each floor were so tight that the old units had to be disassembled to be removed. The new units were also installed in pieces and assembled in place. The modular design of the Trane air handler made this possible. Work was scheduled so that one air handler was replaced each weekend until the project was done. In this way, disruption of customer operations was minimized.

Bruce H. Hall at CB Richard Ellis worked with Chris St. John in Trane Orlando to assure that the new air handlers and other equipment would fit in the tight spaces and could be disassembled if necessary. The Trane office also worked with the Trane Lexington plant where the air handlers are manufactured to stage deliveries to meet the week-by-week replacement schedule.

CONTROLS UPGRADED

In addition to the chilled water plant and airside improvements, the original building control system was replaced with a Tracer Summit™ system.

This improvement allows much closer monitoring of conditions throughout the building and increases system efficiency by optimizing chiller, pumps, and cooling tower operation. The Tracer Summit system also included a tenant services module. This software feature allows automated requests for temporary service schedule changes and simplifies the billing for special services such as night or weekend occupancy.

Trane wireless controls were installed on the VAV boxes on all of the upper floors. This simplifies relocation of sensors as areas are remodeled to suit changing future tenant needs. The management firm is able to reduce labor costs in facility remodeling. In addition, Trane UCP2™ controls were installed on the two older centrifugal chillers that will allow more complete unit diagnostics, monitoring, and optimization.

PROBLEM SOLVED

As a result of the HVAC plant improvements, the First Union Tower now provides control of the building environment, even during the hottest time of the year. With the waterside improvements, chilled water is delivered to the air handlers and fan-coils at 42 degrees F and returns at 57 degrees.

The new air handlers allow complete environmental control with specified fresh air makeup, even on the hottest days. Despite the increases in the size of much of the service equipment, building energy usage did not increase. Pre-cooling of spaces is no longer necessary and tenants can enjoy an optimum office environment.

For additional information, contact 651-407-3921 or www.trane.com.

Publication date: 09/02/2002