Buildings on Ice: Making the Case for Thermal Energy Storage

Like many people in the green building world, I followed the design and construction of One Bryant Park, the high-rise office building in New York City that is being touted as the nation’s greenest. The building, likely to achieve LEED Platinum, was designed by Cook + Fox Architects and houses Bank of America offices and the headquarters of co-owner The Durst Organization. One Bryant Park’s wide range of green features—from rainwater harvesting and onsite waste-water treatment to optimized daylighting and a planned combined heat and power (CHP) plant—have attracted a great deal of attention.

But it was a feature hidden away in a sub-basement that I went to see recently: the building’s thermal energy storage (TES) system. Along with Mark MacCracken, P.E., the CEO of Calmac Manufacturing, which created the system, I entered through the building’s temporary scaffolding and slipped through a nondescript door in the lobby, leaving the building’s daylit grandeur for a catacomb of hidden hallways and stairways. Escorted by assistant chief engineer Dan Monahan of The Durst Organization, we dropped three floors from street level to a sprawling mechanical room with massive chillers, pumps, color-coded pipes of all sizes, and—what we had come to see—the 44 neatly arranged tanks where ice is made each night and melted each day to help cool the 2.1 million-square-foot (195,000 m²) tower.

Each of the 8'-diameter, 8½"-tall (2.4 x 2.6 m) insulated tanks holds over 1,600 gallons (6,100 l) of water and three miles (4.8 km) of plastic tubing through which 150 gallons (570 l) of glycol solution flows. When the water is frozen at night, each of these tanks holds 162 ton-hours (570 kWh) of cooling capacity, enough to provide cooling for about 10,000–12,000 ft² (930–1,100 m²) of office space, according to MacCracken.

Like a growing number of buildings today, One Bryant Park is using ice to allow daytime cooling loads to be shifted to nighttime, when electricity costs are lower. We’ll see how this practice not only reduces cooling costs but also significantly lowers electric demand charges and in many places reduces both pollution emissions and primary energy consumption.