LA CROSSE, Wis. — How do you replace the air conditioning system in a 50-story, 1,750-guestroom hotel without guests being aware of the process? Very carefully.

The 1.2 million-sq-ft Sheraton New York Hotel and Towers, located in Manhattan near Rockefeller Center and the Theater District, had to do just that.

According to hotel property operations manager Ian Murray, the hotel re-evaluated its air conditioning chilled-water plant with an eye to ensuring continued system reliability and operating economy.

Built in 1962, the hotel was operating on its original chiller plant, including two 1,100-ton steam turbine-driven centrifugal chillers and one 400-ton electric centrifugal machine. Steam for the two large machines was supplied by New York’s district steam system.

The hotel retained Jaros, Baum and Bolles (JBB), a consulting firm, to evaluate the system and suggest chiller replacement. The consultant had to look not only at replacement chiller choices, but also at the physical planning requirements of a plant upgrade.

The challenge presents itself

The mechanical room of the hotel is located in a deep sub-basement and although quite spacious, access to it with large equipment is challenging. Any equipment moved in or out requires extensive planning.

The recommendation of the engineer, and the choice of the owner, was to replace the steam turbine machines with new, high-efficiency centrifugal chillers.

The analysis by JBB revealed that electric centrifugal machines could save significantly in building operating costs for the 24-hr operation. During off-peak hours, the hotel would be able to take advantage of low rates to operate at a cost of less than three cents per ton-hour versus nearly 10 cents for steam.

The equipment chosen to replace the two large steam units was a pair of 1,100-ton Trane “CenTraVac” two-stage chillers.

According to Murray, the hotel made the decision to order the high-efficiency chillers on the basis of long-term operating savings.

Another important requirement: The hotel insisted that it needed a continuous stream of chilled water. “We don’t have the luxury of shutting down the plant. In the hotel business, guest comfort is paramount,” said Murray.

For this reason, the job had to be designed for a time of year other than the peak cooling months.

Also, the first of the new chillers had to be on-line before the last old unit was taken off-line.

In the end, the work was completed between Nov. 18, 1996 and June 3, 1997.

Taking care of business

Trane sales engineer Stuart Gaffin worked with the owner, engineer, and Trane factory staff to order units with separable shells and compressor doweling. The purpose was to simplify unit disassembly and reassembly in the mechanical room.

Both the replacement equipment and the old equipment had to be maneuvered through a 7- by 12-ft opening cut in the concrete floor above.

The hotel environment had other implications for the conversion process.

The Sheraton had to install new electrical feeders and rearrange others to provide service to the new chillers. The challenge again was to do the conversion in a way that would be invisible to guests.

“To do that took some planning,” said Murray. “We needed to avoid interrupting service to any guestrooms and we were successful.”

The end result is a new, highly efficient chiller plant installed with virtually no impact on the convenience, comfort, or occupancy levels of the hotel.

And, as far as the hotel guests were concerned, it never happened.