For 10-1/2 months per year on average, the seawater system effectively cools Purdy's Wharf. During the remaining six weeks, cooling is provided by conventional chillers; however, the seawater is used to cool the condensers of these units.

The project involved using the virtually endless supply of cold water that is in close proximity to Purdy's Wharf. This was done by transferring building heat to the cold harbor water through a series of cooling loops and heat exchangers. The unique design, believed to be the first of its kind, was also intended to serve as a demonstration of a technically and economically viable technology.

The seawater cooling system consists of two main loops. In the first loop, centrifugal pumps draw cold seawater from the bottom of the harbor, and then circulate the seawater through heat exchangers that are located in the basement mechanical room of the building to be cooled. The warmed seawater is then returned to the harbor floor.

The second loop carries the building's cooling water. In the heat exchanger, this water is chilled as heat is transferred to the seawater. A pump then circulates the chilled water throughout the building.

Finally, cool air is delivered to each floor by an air circulation fan that moves the warm building air through a cooling coil that is part of the cooling water loop.

To minimize pumping costs, the seawater pumps are located as close to the seawater level as possible.

The seawater installation was so successful that a similar system was installed in the recent Phase II development of Purdy's Wharf. The Phase II tower is a 22-story building that is 12 percent larger than the original tower. The second system uses staged pumping to further economize on energy use.

Publication date: 01/23/2006