Pursuing Passive
Eschewing the ostrich stance, New York City has set assertive targets to reduce carbon emissions by 80% by 2050. Given the city’s density, that goal roughly translates into cutting carbon emissions from buildings by 60%. Achieving those reductions will require highly efficient new and existing buildings. Stepping in with some very practical guidance is the Building Energy Exchange (BE-Ex), a New York City-based nonprofit that supports energy efficiency in buildings through research, education, and exhibits on display in its Manhattan resource center. BE-Ex is releasing a report in early 2018 titled Pursuing Passive, detailing the steps required for a deep energy retrofit of a typical New York City multifamily building.
In partnership with the PHI, in Darmstadt, Germany, and Steven Winter Associates, in New York, BE-Ex chose to study an existing 16-story masonry building in Brooklyn that has 163 units and was built in 1950. It has a 21% window-wall ratio and zero insulation in its walls. Yes, that’s right, zero. “The building we selected is typical of postwar construction that is taller than seven stories,” says Yetsuh Frank, the managing director for strategy and programs at BE-Ex. There are estimated to be more than 300 million square feet of multifamily buildings that fit this profile, nearly 6% of all New York City buildings.
BE-Ex analyzed the strategies and construction methods needed to attain EnerPHit certification for the building, along with how the retrofit could be phased. As housing is always at a premium in New York, all retrofit measures would have to be implemented with the tenants in place.
The advantages and disadvantages of adding insulation from the exterior or the interior are covered in the report. Essentially, insulating from the interior is possible but not practical, as this work could only be done when units became vacant, and this approach doesn’t solve the primary thermal bridge issues of the existing building. Insulating from the exterior would create much less disruption. The big disadvantage of the exterior approach is the expense of erecting scaffolding for a 16-story building.
The good news from the PHPP model is that adding only 2 inches of exterior insulation and replacing the poorly performing windows would trim the building’s energy use by two-thirds. With 858 windows in the building, that cost would not be inconsequential, but triple-glazed windows with high-performance frames would bring multiple benefits, including greatly enhanced comfort for the occupants.
Heating and domestic hot water are currently supplied by a central steam plant, with hot water piped through the building 24/7. “Even if you meet the heating demand targets of Passive House with an improved envelope, this heavy hot water load swamps the primary energy cap,” says Frank. Cooling by window air-conditioning units doesn’t help either. Fortunately, the envelope improvements would reduce loads enough to make way for HVAC updates, such as possibly a variable refrigerant flow (VRF) system that could provide both heating and cooling. Ventilation could be supplied either by a centralized system, repurposing the existing exhaust shafts, or by new in-wall units for each apartment distributed at the perimeters.
The study is intended to provide a playbook of the different upgrade strategies and phasing options, while indicating some basic capital planning options for interested owners. Retrofit costs have been estimated, but at a fairly high level, says Frank, since real costs in New York City are highly dependent on labor costs, which can fluctuate widely. “If the study results in useful guidance for this segment of the building sector, we hope to do similar studies for different building typologies,” says Frank.