By Jay Fox

New York University has long sought to be a leading voice in sustainability. Since their first pledge to reduce emissions was issued in 2006, the university has taken decisive action and plans to be carbon neutral by 2040, according to NYU Chief Sustainability Officer Cecil Scheib. As NYU is the largest private university in the United States—with more than 15,000,000 square feet of leased or owned space to accommodate its approximately 50,000 students and 20,000 employees—this will inevitably mean performing deep energy retrofits on the older buildings in the university’s portfolio.

Scheib notes that the university is considering high-performance and all-electric options in every retrofit, and that they are committed to obtaining LEED certification (Silver minimum) for every project involving a substantial renovation or new construction. However, they have also explored more aggressive strategies when refurbishing some buildings, as was the case with the retrofit of Rubin Hall, a student residence near the university’s core campus in Greenwich Village.

Despite these challenges, the team found that certification was possible and within reach if the university opted to certify through what is known as EnerPHit’s component path. Rather than measuring the overall performance of the building (which is the more conventional route), following the component path means meeting minimum efficiencies on individual components based on conditions specific to the building and the climate.

The university decided to go through with EnerPHit certification via the component path, which has sparked interest in others within the public and private sectors. In New York City alone, there are hundreds of millions of square feet of multifamily housing constructed using similar materials and methods as Rubin. Much of that housing is similarly inefficient and will need to be upgraded to comply with Local Law 97 (the Climate Mobilization Act), which places more stringent regulations on emissions for buildings over 25,000 square feet. When the city enacted the groundbreaking law in 2019, very few buildings of this typology had been successfully retrofitted, and a host of interested parties were hungry for pilot projects to provide real-world guidance on how it could be done.

Consequently, the university applied for and received grants from the utility company Con Edison and the New York State Energy Research and Development Authority (NYSERDA). NYSERDA provided $2 million to the project through their Carbon Neutral Economic Development program (now known as the Building Cleaner Communities Competition).

After several years of modeling and planning, onsite work officially began at the end of the 2023 spring semester. It was completed in time to allow students to move in for the fall semester of 2024, which is impressive given how much work needed to be accomplished.

Rubin was originally built with structural steel columns and beams with cast-in-place concrete floor plates. The uninsulated walls were clad in 4 inches of red brick over 8 inches of terracotta block. As noted in our previous coverage of Rubin Hall from September 2022, it was designed to be heated by oil furnaces and steam radiators, while opening the window was the sole means of ventilating and cooling the rooms. That’s a lot of open windows, a lot of wasted heat, and a lot of city noise (and smells) that wafts in.

The enclosure update included a rethinking of the wall assembly (see Figures 1 and 2) and replacing the windows with triple-pane models from Schüco, USA. FXCollaborative Senior Associate Jena Rimkus notes that visiting the manufacturer’s shop and working with the production and QC teams for Schüco, USA helped to ensure that the customized windows met performance targets.

Like many historic buildings, Rubin’s air barrier was the existing plaster on the inside of the exterior wall. Rimkus explains that it was cracking and separating from the terra cotta backup wall. “The project included creating a new air barrier with exterior sheathing board and transition membranes,” she explains.

“Periodic localized air testing convinced everyone on site that their full attention was required to achieve air tightness,” she adds. “The contract also requested a point person, called the Building Envelope Construction Manager, responsible for the work and all trades involved in the air tightness of the envelope. This person really did a good job of chasing down issues and making sure the sub-contractors were clear on what needed to be done to achieve the project goals.”

Rimkus additionally notes that bringing a contractor on for pre-construction services during the design phase was vital to the team’s success. “It allowed everyone to get ahead of field conditions by performing exploratory probes to get a better understanding of what is behind finishes and testing existing envelope materials to identify the best insulation,” she explains. Ultimately, the team decided on 4 inches of open-cell spray foam, which raised the R-value of the wall assembly to 20.7.

The upgrades to the HVAC system were also extensive (see Figure 3), as the entire heating system had to be replaced and both cooling and ventilation systems had to be introduced using existing building floor openings. The new ventilation system includes rooftop dedicated outside air (DOAS) units.

“This major retrofit of the HVAC approach included numerous challenges and modifications to fit the new equipment on the roof, in the cellar, and to find vertical routes for HVAC distribution,” says WSP Senior Vice President Jeffrey Rios. “Largely, the building was able to accommodate these new systems. There were a few required modifications to the design that came up during construction, including rerouting the path of some ventilation air due to existing shaft areas being smaller than originally assumed/indicated in existing drawings.”

Rios says the air source heat pumps controls were another example of a lesson learned.  The heat pumps require consistent water flow to operate properly, and minor adjustments to the control of the modules and pumping systems allowed for more consistent and reliable operation.

“Another lesson learned, based on the student rooms remaining comfortable even when some mechanical systems were not on, is that the Passive House envelope performance did its job; this was real proof that the reduced loads resulting from very low air infiltration and the higher performance façade minimized the heating and cooling capacity needs,” he says. “The lesson learned is to trust and verify, through testing, that these values are achieved and account for the reduced loads in the HVAC systems.”

“One of the challenges we had in achieving air tightness at the exterior was the proximity of the mechanical risers to the exterior wall which created tight conditions that were hard to seal,” Rimkus adds. “In hindsight, fewer risers on each floor or installing a floor mounted fan coil unit in the corner with risers feeding directly into the unit may have alleviated this challenge. Another challenge was sealing all penetrations through the air barrier which followed the interior wall of each room.  Another way to approach the air barrier would have been to demo a few feet of the interior walls where they met  the exterior wall so that the air barrier carried around the interior face of the exterior wall rather than the interior of each room.”

The university is confident that the retrofit has made Rubin more comfortable and more efficient, even if comprehensive performance data has yet to be collected. “It will take a year or more to get full energy data to compare predicted energy use to actual energy use, but so far, the limited data we do have looks excellent and savings are exceeding modeled performance,” Scheib says.

More generally, he notes that the students are comfortable. “In addition to the improved temperature control and the addition of air conditioning, the rooms are a lot quieter since the addition of the triple-pane windows.”