Hybrid heating, modern solutions

Take a trip to the base­ment of the International Tailoring Company Building at 111 4th Ave. in Manhattan and the two boilers might fool you into thinking that gas and oil still rule here. But the roof of the 13-story co-op tells a different story. 

Set against a back­drop of stun­ning panoramic city views are nine air-source heat pumps, neatly parked in three rows, whirring along to power the building’s heating and cooling.

When Local Law 97 (LL97) was passed in 2019, the International Tailoring Company Building had a choice: They could add more boilers to the base­ment, the cheaper option, or embrace elec­tric heat pumps, which would bring them into compli­ance with New York City’s mandate to lower building emis­sions. They ulti­mately decided to fuse the old with the new by creating a hybrid system, powered primarily by electricity. 

“LL97 changed [our] thinking and made us want to go more elec­tric,” said Eric Einstein, co-op board pres­i­dent. ​“That’s why we ended up with the mix we have.”

Before the rooftop heat pumps entered the equa­tion, Ecosystem engi­neers had to lay the ground­work. Their first step was to moderate the temper­a­ture of the existing internal pipe network — a two-pipe hydronic system — which previ­ously deliv­ered 45°F water in the summer and 160°F water in the winter to the 172 apart­ment units. 

Engineers’ goal was to estab­lish a lower target temper­a­ture of 100°F, allowing the heat pumps to run more effi­ciently, said Ben Milbank, senior project devel­op­ment engi­neer at Ecosystem.

To get the system where it needed to be, subcon­trac­tors hired by Ecosystem performed the tedious task of going into each apart­ment and replacing fan coils powered by the old oil and gas system with hybrid water-source heat pumps that run on elec­tricity. By the end, there were 192 new units in place. 

“This change, along with removing the natural gas-fired absorp­tion chiller, allowed the new system to operate effi­ciently with a lower temper­a­ture range,” said Milbank.

Ecosystem’s recon­fig­u­ra­tion created a low-temper­a­ture thermal network, a system that recy­cles waste heat. In the summer, excess heat goes back into the loop to warm up the domestic hot water; in shoulder season, it’s trans­ferred to another person’s apart­ment looking to warm up. Any left­over heat is disposed of by a series of large fan coils on the roof known as adia­batic coolers. 

In the winter, the in-unit heat pumps operate like the old system, which used two sepa­rate pipes with either hot or cold water to heat or cool, taking warm water in and blowing it across a fan to heat the apartment.

Meanwhile, the nine rooftop heat pumps service the entire system by sucking in warm air from the outside and injecting it into the tempered loop to heat the water.

That might be coun­ter­in­tu­itive, consid­ering how chilly the air gets in the winter. But, as Einstein points out, ​“Even on cold days, there’s heat out there, unless you’re an absolute Kelvin zero.”

On espe­cially frigid days, when the air source heat pumps can’t heat the water enough, two condensing gas boilers in the base­ment kick in, as a backup source of energy. Ben Milbank compared the system to a plug-in hybrid car: When used prop­erly, you make short trips on elec­tricity, and only rely on gas for longer distances.

By reducing the building’s reliance on oil and gas, the hybrid heat pump system has given the hundred-year-old International Tailoring Company Building a new lease on life. Even though the co-op isn’t running entirely on elec­tricity, it is still achieving LL97 compli­ance, and Milbank esti­mates the upgrades will reduce the building’s carbon emis­sions by about 80 percent – proof that a little compro­mise can get you a long way.

Milbank summed it up nicely: ​“If you aim for perfec­tion, I think we’re going to make a lot less progress.”