NEW YORK, NY — The Durst Organization, a major Manhattan commercial property owner, has chosen an Off-Peak Cooling (OPC) system to reduce the overall cost of energy in its 20-year-old building on the Avenue of the Americas.

The OPC system, supplied by Calmac Manufacturing Corp., Englewood, NJ, uses less expensive nighttime electricity to produce ice in 8-foot storage tanks. The ice is then used the following day to cool the building. Shifting the electric load from more costly on-peak hours to off-peak hours significantly reduces energy costs, since on-peak prices are at least double and can be up to 10 times the nighttime rate, according to Calmac.

Building air conditioning systems traditionally work by blowing air past coils containing chilled heat transfer fluids. The fluids are cooled by a chiller, which must operate whenever the air conditioning system is on. Building owners using traditional air conditioning systems, therefore, not only use more on-peak electricity, they incur higher peak-demand rates for that electricity. In contrast, during peak-demand periods, buildings that rely on OPC technology are cooled by using small pumps to move the ice-cooled fluid past fans that blow cool air into the building, says Calmac.

OPC is a proven technology that is used in schools, hospitals, office buildings, supermarkets, and warehouse outlets. However, the Durst Organization’s usage of OPC marks the first time that this technology will cool a Manhattan building, according to Calmac. While the ice storage tanks are ordinarily installed outdoors, they can also be buried in the ground, installed on roofs as well as within the building itself.

In this case, 28 tanks were installed in the basement of the 41-story building. “Beyond the cost-saving aspect of Off-Peak Cooling, we selected this technology because it reduces peak electrical load on the grid. This, in turn, lowers the need for building new power plants with all the siting issues that accompany them and reduces the need for utilities to bring a dirty, peak-shaving plant on-line,” said Jody Durst, co-president of the Durst Organization. “For every four buildings that use OPC, a fifth could be cooled without increasing daytime electrical demand.”

The Durst Organization received funding from the New York State Energy Research and

Development Authority (NYSERDA) for an ice storage plant feasibility study and was subsequently awarded over $200,000 under the NYSERDA Peak Load Reduction Program for its implementation.

For more information on Off-Peak Cooling, visit the Calmac website at

Publication date: 08/19/2002