How Casa Pasiva recycled infrastructure for a breath of fresh air

For Chris Benedict, the archi­tect who led the retrofit of Casa Pasiva, the energy recovery venti­la­tors presented a conun­drum. The machines, which help a building conserve energy by balancing temper­a­tures of incoming and outgoing air, were a crucial compo­nent of the passive house retrofit of the afford­able housing complex in Bushwick, Brooklyn. But these large, bulky units are typi­cally designed for newly built single-family homes. The multi­family complex of 143 apart­ments across nine build­ings simply didn’t have the space, or the capacity for new duct­work, to house this key piece of technology.

“Architects and mechan­ical designers have tried a lot of different loca­tions for the machine and a lot of different strate­gies,” said Benedict. So she decided to try some­thing which, at that point, had never been done before: Taking advan­tage of the existing duct­work of the multi­family build­ings by installing energy recovery venti­la­tors on the roof.

Most New York City apart­ment build­ings have a common shaft that collects exhaust from apart­ments stacked on top of each other, connecting every apartment’s kitchen and bath­room to a roof fan, where exhaust ulti­mately is dispersed. 

Placing the ERV on this opening would be pioneering a new method, and could save Casa Pasiva the costs and hassle of replacing the entire development’s ventilation. 

The method took advan­tage of existing ducts to disperse exhaust air, and only needed to add new ducts for cycling in fresh air from the ERV into the apart­ments. Keeping the ducts also simpli­fied the new venti­la­tion system overall, which was a plus since, as Benedict mentioned, air ducts ​“are tricky.”

Ventilation is perhaps the most compli­cated part of retro­fits, espe­cially for passive houses, Benedict explains. Balanced heat recovery is a key tenet of the design philos­ophy, since it allows for a building to have fresh airflow while also main­taining an insu­lated exte­rior. But Casa Pasiva’s existing ducts were leaky and clogged, with malfunc­tioning fire dampers, which meant that the ERV couldn’t operate until those prob­lems were fixed. 

Once the ducts were patched and cleaned up, then came the chal­lenge of the ERV itself. ​“Finding an actual product that could work? It didn’t exist yet, so we had to modify some ERVs that were already on the market,” Benedict said.

The problem was the airflow rate of the existing exhaust shafts, which ranged from 60 to 230 cubic feet per minute (CFM) — much lower than was ideal for the new system they were trying to install. At the time, there were no outdoor units with CFMs that small, Benedict said. As a result, the team ended up bringing in a number of indoor ERVs from a company called RenewAire, and then adapted them for the roof by putting the machine in weath­er­proof housing.

Once the pieces were in place, the team 3D-modeled the new duct­work to make sure their plans would work. They then combined the new, the old, and the adapted: The weath­er­proofed RenewAire ERVs on the roof were connected to new inflow air ducts that ran down the building exte­riors. They were able to do this by drilling holes and connecting them to the inte­rior of the apart­ments, so that the machine could blow in fresh air. The existing shafts served as the outflow of dirty air, completing the ERV loop. 

The new ducts were inte­grated seam­lessly into the build­ings’ exte­rior insu­la­tion, another key part of the passive house trans­for­ma­tion. They were covered in foam and insu­la­tion, and even­tu­ally sealed with the stark, sleek façade that graces Casa Pasiva today.

“The roof becomes kind of the mechan­ical room of the building,” Benedict explained to Passive House Accelerator. ​“That way all the equip­ment is very easy to get to, and easy to repair or replace.”

What’s more, all this work was done in a way that was mini­mally disrup­tive for resi­dents, who largely remained in their homes throughout the reno­va­tion, explained Josh Shaffer, the capital plan­ning and sustain­ability manager at RiseBoro, who financed the project. This is because much of the duct­work and insu­la­tion was added on the exte­rior of the building, rather than interior.

“So it ended up being a real expe­ri­ence,” Benedict said. ​“I think it’s a great project. It’s a groundbreaker.”