Many historic neighborhoods across the United States are being renovated and revived. When done effectively, both charm and history can be captured, while making the homes more energy efficient. Retrofits of existing housing stock has inherent sustainability advantages, especially if deep energy retrofits dramatically boost performance.
In the Park Slope neighborhood of Brooklyn, a 120-year old brownstone was recently retrofit to become the first Passive House-certified project in New York City. This international standard results in a 90% reduction in heating bills. While seemingly identical Brooklyn brownstones contain meager amounts of insulation and conditioned air leaks from gaps and cracks, a Passive House certified project performs very differently.
The renovated brownstone is very well insulated, virtually airtight –and is heated primarily by the sun, occupants, and waste heat from appliances. A blower door test ensures that the home is properly air sealed and helps the builder pinpoint potential gaps if needed. Making an older home virtually airtight is no small feat, but Jeremy R.M. Shannon is demonstrating that it is possible on several projects he has worked on.
"A key element of Passive House design is airtightness," explains Shannon, principal architect for Prospect Architecture. "Without airtight construction, the best insulation available is wasted. To understand this, think of water leaking out of a cup. Regardless of how thick and strong the cup is, if you have a hole at the bottom, the water will leak out."
To ensure high indoor air quality, the brownstone has two Zehnder energy recovery ventilators, providing a stream of fresh, filtered air into the home – while removing stale air and fumes. The energy recovery ventilators can add moisture during the long dry winters and lower humidity levels during hot and humid Brooklyn summers. This minimizes the heating and cooling load of the building, by capturing warmth, coolness, and having the ability to lower humidity levels that boost occupant comfort.
Because of the air sealing, virtually no outdoor air can infiltrate the retrofit brownstone. With the Zehnder energy recovery ventilator, the air in the home exchanges with fresh filtered air every three hours. In addition, the ventilator pre-heats or pre-cools the incoming air depending on the weather conditions by recycling heat and coolness from the exhaust air before it leaves the home.
A Zehnder energy recovery ventilator offers many advantages over a typical bathroom exhaust fan or range hood because they:
- Both exhausts and supplies air, resulting in balanced ventilation throughout the home
- Impacts the air quality of the entire home and not just one room or space
- Captures energy from the conditioned air before it leaves the home
- Filters intake air, which is especially important in areas with high outdoor pollution levels or lots of allergen or asthma triggers in the air
- Has the ability to add or remove moisture from the air as needed
- Is automatic, not requiring occupants to turn the system on and off to be effective
Shannon has now worked on four historic renovations that meet the stringent Passive House standard, all with Zehnder energy recovery ventilators. These projects demonstrate that older buildings can exhibit both historic charm and sustainability.