Power Boost

12/01/2005


The American Museum of Natural History in New York City is one of the world's preeminent scientific and cultural institutions. Each year, more than 5 million visitors tour the AMNH complex, which consists of 25 interconnected buildings, the earliest dating back to 1877.

The existing emergency power system wasn't quite that old, but it was definitely in need of an upgrade. In 2002, AltieriSeborWieber LLC (ASW) won the RFP to upgrade emergency power systems, and what they found—both new and old—say firm principals, wasn't unexpected.

The relatively new was a 1,000-kW diesel-fired generator in place to serve six buildings, including the new Rose Center for Earth and Space. But for the other 19 buildings, it was the old. Roughly one million sq. ft. was served by a 20-year-old 156-kW generator. ASW's task was to design an upgrade for emergency power distribution and lighting systems for the buildings it served.

The first step was to interview the museum staff and prepare a comprehensive emergency load study. The designs for new systems also had to account for space renovations for the next 10 years. ASW engineers recommended installing a 1,500-kW diesel-fired emergency generator for life-safety loads, with provisions for a second 1,500-kW genset in the future for redundancy, and also to serve as standby for non-critical loads. At the same time, the 156-kW generator would be retained for existing critical IT loads.

One of the most challenging parts of the project was finding space for the system and locating a route for emergency feeders to each building. The venerable 156-kW generator was housed in a small concrete-block building addition. This structure was not only occupied by the generator room, but it also housed, rather snugly, 23-in. condenser water piping that connected the building's cooling towers to the central chilled-water plant.

In other words, there was no space in the old generator room for new equipment and no suitable interior space to be found within any of the other existing buildings.

With no room indoors, the team went outdoors. A service yard between two of the buildings proved almost ideal. The only drawback was limited access. And by definition, limited, in this case, meant the site could only be accessed via two narrow tunnels that ran below various portions of the complex. In other words, equipment in the service yard would have to be designed in a manner that would allow passage through the tunnels.

The ensuing acoustic walk-in enclosures were fabricated so that they could be transported in pieces and reassembled on-site. A 14-in. diameter flue runs 75 ft. high from the generator to clear the cooling towers, which are on a platform 42 ft. above the generator enclosure.

A second enclosure in the service yard houses the main emergency switchgear. The enclosure is two-hr.-rated, with a 24-in. raised access floor to ease installation of cabling between the switchgear and the ductbank distribution system.

The system of ductbanks and manholes to distribute emergency power and control wiring from the switchgear enclosure to the related buildings posed other significant challenges for the design team. Installation of ductbank below the service yard required careful planning and coordination because of the need to demolish and reinstall existing aging pavement and drainage systems.

Where ductbanks meet buildings, pull boxes are mounted on the building exteriors to facilitate the transition. Immediately inside each building at the pullbox location is an emergency distribution room that contains disconnect switch, automatic transfer switch (ATS), step-down transformer and emergency distribution panelboard. When it was necessary to locate emergency distribution deeper within the building, or to pass through one building to another, two-hr.-rated MI cable was used for emergency feeders.

Two innovative technologies add to the enhancement. First, the ATS specified for the project features computer-based load monitoring that allows facility staff to monitor generator load and status. The monitoring system records loading, and will be helpful whenever future emergency power system loads are proposed.

Second, a new fuel-oil piping system follows the ductbank route. Piping runs approximately 90 ft. from a recessed wall-mounted filling station to a buried 6,000-gal. double-walled fiberglass storage tank. The tank has a computer-monitored leak detection system and the capacity to power the generator for more than two days at full load. Incidentally, say firm principals, installation of the tank required weeks of hammering through solid rock beneath the service yard.

The original emergency distribution within each building had been minimal. ASW reconnected all the existing emergency panelboards to the new distribution system and provided additional capacity in each building. Also, new emergency risers and panelboards were added to serve upper floors of the buildings.

This is another point where careful and well-planned coordination was vital. Risers were typically located within interstitial space behind exhibit display cabinets. Core drilling for riser installation had to take place during off-hours so as not to disturb museum staff and visitors.

Finally, upgrades to emergency illumination throughout the buildings were essential. In several areas, egress lighting did not meet code requirements. ASW conducted after-hours surveys to determine existing emergency lighting levels and figure out methods to supplement these systems. Enhancements included installing additional emergency lighting fixtures within existing galleries and egress paths, as well as rewiring existing lighting circuits to the new emergency power system. Original controls for emergency lighting circuits were removed to provide a fail-safe system.

In a word, the project was all about coordination. All work for this complicated project was scheduled to minimize disruption to normal building operations. Moreover, the upgrade was performed in conjunction with a separate infrastructure upgrade of the 77th Street electrical service, with necessary coordination among AMNH and two contractors. The icing on the cake of this successful project is that the building teams completed both projects within 16 months and on schedule.





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