Pumping Up Big John

When the domestic water-supply system at The John Hancock Center in Chicago began to show its age, the new pumping/control system that was installed did more than simply restore it to its original state. The system design improved the overall performance and versatility of the water-supply system, reduced maintenance requirements, provided dual-redundancy to guarantee continued operation and a...

05/01/2001


When the domestic water-supply system at The John Hancock Center in Chicago began to show its age, the new pumping/control system that was installed did more than simply restore it to its original state. The system design improved the overall performance and versatility of the water-supply system, reduced maintenance requirements, provided dual-redundancy to guarantee continued operation and also improved the quality of life for building occupants.

The existing domestic water-supply system—which serves the condominium portion of the building—was completed in 1968 and continued to operate daily, but maintenance costs were climbing. The association of condominium owners selected McGuire Engineers, Chicago, to spearhead the renovation design project.

The 100-story John Hancock Center is actually three separate facilities: retail stores and commercial offices occupy space from a concourse level through the 49th floor; above that are residential condominiums; and from the 93rd floor and up are elevator systems, building utilities, an observation deck, a restaurant and commercial television and radio broadcasting equipment.

Domestic water supply

The building's residential water system feeds 703 luxury condominiums from city water mains below the building by means of two 500-gallon-per-minute constant-speed pumps in the basement. These pumps pressurize the water and deliver it to a 30,000-gallon water-storage reservoir that begins on the 50th floor and extends upward to the 52nd floor, where the top of the reservoir serves as a utility space for the pumping and control systems.

The original condominium water-supply system used constant-speed vertical-turbine pumps, submerged in and supported from the top of the reservoir. Four "high-zone"-type pumps were designed to serve the uppermost portion of the facility, and three "low-zone" pumps were designed to serve the lower portion. The pressure output from these pumps was controlled by individual pressure-regulating valves attached to the discharge nozzle of each pump—a very common design in 1968. The inherent flaw in this design was apparent during nighttime and other low-flow periods, when the pumps operated at full-speed—with relatively no flow—causing internal pressures within the pumps to climb to their peak and resulting in considerable stress and eventual damage to the pump casings and mechanical shaft seals.

During an initial inspection, Richard Kviz, P.E., project plumbing engineer with McGuire Engineers, discovered a serious problem: the interior of the 30,000-gallon reservoir showed signs of advanced stages of corrosion, and its structural integrity was at risk. Kviz realized that the reservoir was in dire need of repair; otherwise, the system could run into a catastrophic situation. Unfortunately, the reservoir was the only means by which the condominiums could receive domestic water, and the reconditioning operation would take months to complete.

After analyzing performance requirements, the design team recommended that submersible-turbine pumps and variable-speed controls replace the outdated pumps. While such pumps are typically horizontally mounted, the pumps were installed vertically in this case, allowing multiple pumps to be placed side by side and submerged in the reservoir. This helped the design team deal with the limited amount of space in the 52nd-floor pump room.

Flexible design

To allow the reservoir to be repaired, the team designed a dual-feed piping system. During normal operation, the new system operates in a similar fashion to the original: the basement water-feed system supplies water to the reservoir; and the new pumps draw water from the reservoir.

Conversely, when draining the reservoir for rehabilitation, supply water from the basement pumps can be fed directly to the new high-zone pumps, completely bypassing the reservoir. Each of the new high-zone pumps was fitted with a special suction-inlet assembly. In addition, unique reservoir-bypass piping allowed supply water to go directly to the suction inlet of each pump, instead of going to the reservoir. Finally, a new "high-zone to low-zone" pressure-reducing station was installed to allow the low-zone fixtures to be supplied with the water provided by the high-zone pumps. Combined, these design features allowed the entire facility to operate without either the reservoir or the low-zone pumps.

For proper operation of the system in reservoir-bypass mode, it was crucial that a regulated pressure serve the high-zone pumps. For this reason, a temporary variable-speed control system was installed on the 100-hp basement-feed pumps.

Uninterrupted service

All new system components are designed and sized so that the reservoir and low-zone pumps can be taken out of service for the extended time period necessary, while providing an uninterrupted water source for the entire facility.

The new systems have met all requirements: the variable-speed submersible pumps use less energy, require less maintenance and permit the rehabilitation of the reservoir to be accomplished without disrupting the water supply.

For more information about pumps from Metropolitan Industries, circle 101 on the Reader Service Card.





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