This NYC high-rise is using heat pumps and waste heat to cut fossil fuels

Buildings everywhere need to get off fossil fuels in order to help the world avoid climate catastrophe. Yet owners of large commercial buildings in New York City are especially feeling the pressure: The groundbreaking Local Law 97 takes effect this year, requiring buildings of more than 25,000 square feet to meet specific emissions limits, which become more stringent in 2030, or face hefty fines.

One cutting-edge retrofit project is underway at the corner of Hudson and Charlton streets in lower Manhattan. The 17-story Art Deco office building, built in 1931, is ditching its fossil-gas boiler for uber-efficient electric heat pumps that are both heaters and air conditioners. They’re key components of a system that aims to heat and cool the building more efficiently by capturing thermal energy that would otherwise be wasted.

The state is backing the demonstration project, which could serve as a model to decarbonize the more than 6,000 high-rises that punctuate New York City’s skyline. As part of the Empire Building Challenge, the New York State Energy Research and Development Authority (NYSERDA) awarded $5 million to the 345 Hudson project in 2022, which also has more than $30 million in private funding.

Project leader Benjamin Rodney estimates that once the project is complete in 2030, the building will use 25 percent less energy than a conventional design and reduce greenhouse gas pollution by 70 percent relative to 2019 levels. As the grid cleans up, he expects the figure to climb to 90 percent by 2035. The deep emissions cuts will allow the building owner, Hudson Square Properties — a joint venture of Hines, Trinity Church Wall Street, and Norges Bank Investment Management — to avoid more than $200,000 in fines annually starting in 2030.

But more importantly, it could help other building owners determine how best to eliminate emissions — a crucial task given that nearly 70 percent of the city’s carbon pollution stems from the fossil fuels used to heat and power its buildings.

A single heating and cooling system instead of two less efficient ones

Like most New York City high-rises, 345 Hudson Street was originally kept toasty or cooled down via two separate systems. On cold days, steam has been pumped through radiators; when the weather’s warmed up outside, chilled water has flowed through pipes and absorbed ambient heat, which has been released via a cooling tower on the roof.

But dumping that thermal energy into the sky instead of redirecting it is a wasted opportunity, according to Rodney, who is vice president of construction at Hines. Buildings often need cooling and heating at the same time in different spaces, especially in the shoulder seasons; for example, while a data center whirring away on one floor needs cooling, an office area on another could use that heat.

To redistribute heat, Rodney’s team is installing a kind of thermal circulatory system. It’s a network of new and existing pipes that will carry a constant flow of water around the building. Each floor will have a heat pump that can then tap into or reject heat from this system in order to keep its occupants comfortable.

The design — an example of a thermal energy network — is far more efficient than having two isolated conditioning systems that don’t interact, Rodney said. ​“You’re creating this energy balance throughout the building.”

Rodney’s team is installing the water-source heat pumps floor by floor as tenant leases expire, with four in place so far, he said.

This phased approach ​“is a fantastic way to turn the building over” because it’s much less disruptive to occupants, according to Ted Tiffany, senior technical lead at the Building Decarbonization Coalition, who was not involved in the project.

The retrofit also includes three air-source heat pumps on the roof that can provide additional heating or cooling using the outside air as a thermal source or sink. Another system sitting atop the building, called an energy recovery ventilator, will deliver even more efficiency gains by using air leaving the structure to precool or preheat filtered air coming in.

What’s more, the high-rise will get some help from a nearby building. 345 Hudson’s water-based network will be physically connected to 555 Greenwich Street, its next-door neighbor, which already has an energy-efficient ground-source heat-pump system.

Underneath 555 Greenwich are 68 foundation columns, or piles, reaching 120 feet into the ground, where the temperature rarely dips below about 45 degrees Fahrenheit, even in the depths of winter. The heat pump uses this stability to its advantage: It’s connected to water-and-antifreeze-filled pipes within the piles that allow it to move heat efficiently into and out of the subterranean environment. The system is also a seasonal battery that can squirrel away excess warmth during the summer for when it’s needed in the winter.

Heat redistribution within and among buildings is more common in Scandinavian countries, Rodney said. But this project ​“is one of the first times that heat is being shared in this way … for New York and the United States,” said Jared Rodriguez, principal at Emergent Urban Concepts and an adviser to NYSERDA on the Empire Building Challenge. He added that utilizing energy resources efficiently is a critical part of the playbook for retrofitting large buildings, hence the importance of trying out ways to recycle their heat in the U.S.

In the future, other edifices could join the thermal energy network connecting 345 Hudson and 555 Greenwich. That would drive down carbon pollution further by reusing more heat instead of throwing it away, helping relieve some of the pressure on the grid as heating continues to electrify, Rodriguez said.

Even during hot summer days when office buildings may be pushing out a lot of heat, there are entities like laundromats and large hotels that need it, Rodriguez noted. He can picture that future: ​“City Winery is not too far away, and they have a big hot-water load.”