City and MTA Plan to Harness Thermal Energy in Lower Manhattan
A trio of Lower Manhattan subway stations is slated to chill out under a plan by the Metropolitan Transportation Authority to bring experimental climate-control technology underground.
On August 10, Mayor Zohran Mamdani announced that the Chambers Street stop on the J/Z lines (beneath the David Dinkins Municipal Building) and the Brooklyn Bridge-City Hall stop on the 4/5/6 lines (at Chambers and Centre Streets) will host a study of how thermal energy networks (TENs) can be used to capture, store, and transfer the excessive heat in subway stations that is now allowed to dissipate, harnessing it for use in buildings above.
TENs are an emerging technology that links buildings and nearby infrastructure through a network of pipes that siphon heat from where it is available but unwanted, to sites where it is (or will be) needed. The MTA plan also involves two other technologies: geothermal power and radiant cooling. The first envisions drilling boreholes 600 feet down into bedrock, a depth at which the temperature remains around 55 degrees throughout the year. The second hinges on running water through a network of pipes that link the place where temperature is to be controlled with those deep shafts. Liquid pumped down to the cool rock comes up chilled, and then absorbs heat from the surrounding air in the subway stations. As those pipes and the liquid inside heat up, they carry that thermal energy back to the bedrock, and cool off once again. All of this is accomplished using very little energy and generating only a fraction of the carbon emissions associated with air conditioning. In a further twist, hot air captured in summer can be sequestered for months at a time, allowing its release in winter, for use in nearby buildings for heat and hot water.
Mayor Mamdani said, “we now have an opportunity to make our subway platforms cooler and more comfortable while putting wasted heat to work during the winter. That means lower energy costs, a more resilient subway system and a cleaner energy future for New York City.”
Budgeted at $800,000, the feasibility study will gauge how much cooling can be achieved and the potential energy cost savings. If the results are encouraging, the City will begin design work on the system in early 2027. The preliminary plan calls for harvested energy to be distributed to four nearby buildings: City Hall, the Municipal Building, Surrogate’s Court, and the Tweed Courthouse. If built, the TENs system at the two subways stations would be the first in any American transit system.
Further along is a pilot plan now being implemented at the East Broadway subway station on the F line (near Essex Street). There, Toronto-based alternative energy startup Cascara is installing a “district energy” system that will achieve radiant cooling by circulating carbon dioxide (CO2) in both liquid and gaseous forms between two networks of pipes. Because liquid CO2 is always cooler than the gaseous form, it absorbs “waste” heat from its surroundings, thus chilling the air. This process converts the CO2 into the warmer, gaseous form, which then transports the captured heat to a location where it is needed, such as the hot water source in a nearby building. Once the heat has been expelled, the CO2 condenses back into liquid form, and the process begins all over.
MTA spokesman Mohamed Farghaly explains radiant cooling as “similar to the experience of walking through the refrigerator aisle of a supermarket—the refrigerator compartments aren’t exhausting cold air into the aisle, but you feel a drop in temperature just from being nearby.”
“The cooling system is designed to be modular, compact, and easy to install and maintain,” he says, “maximizing the opportunity to replicate this design at scale in the future if the pilot is effective.”
A Cascara spokesman says, “cooling is just another name for heat extraction. The ‘district energy’ plan consists of pulling heat from where you don’t want it, transporting it locally, and then inserting that same heat where you do want it, while harvesting a decarbonization bonus on both sides of that exchange.” The pilot program at the East Broadway station is slated run through the end of 2027, with Cascara underwriting most of the costs.