Four floors below one of Manhattan's most iconic office buildings, something strange happens every night. Machines silently freeze half a million pounds of water into ice, roughly three city buses' worth. By morning, the ice has melted, and the chilled water cools the building throughout the day. CBS News reported in June 2025 that this is how Eleven Madison Avenue keeps itself air-conditioned, based on interviews with the company that installed the system. A study conducted by the National Energy Assistance Directors Association and published in May 2025 revealed that the average summer household cooling bill in the United States for June through September was estimated to be $784. The same CBS report cited this figure as the highest summer average in the 12-year history of the organization's records on cooling expenses.
Meet the "ice battery"
Manhattan's cooling system is called an ice battery, which accurately describes how it works. While a phone battery stores energy in the form of electricity, the ice battery stores "coolness." Holly Paeper, president of Trane Technologies' Commercial HVAC Americas business, which installed the Eleven Madison Avenue system, told CBS News the building freezes water at night, when electricity is cheap, and runs on that ice during the expensive afternoon hours.
"So, when everyone else is using their electricity in the middle of July to cool their building or to cool their homes, it's a big draw on the grid," Paeper said, according to the CBS report. "This building won't draw from that because it made its ice last night." Trane Technologies says the buildings with the system can save 40 percent on cooling, as stated in the company's own technical documentation.
