Keeping It Neutral–On Carbon
Energy Use Case Study
Images courtesy of PERC
Project: Net Zero Energy Ready Home
Location: New Fairfield, Connecticut
Designer: Chris Trolle/BPC Green Builders
The Challenge: To create a zero-energy ready (ZER) LEED Platinum home in a rural, lakeside location in the state of Connecticut.
Energy Conservation Solution: Chris Trolle is co-founder of BPC Green Builders. He points out “With each of the [Zero Net Energy or Zero Energy Ready] homes we do, we focus on a very robust thermal envelope.” This project features a highly insulated, airtight envelope incorporating double-wall construction with R-33 blown cellulose insulation, an R-72 roof, and triple-pane low-e windows.
Energy System Solutions: Although ZNE construction relies heavily on the efficiency of the building envelope, the home’s performance can benefit from optimizing systems as well. First, the house meets all of the criteria to install a 9-kilowatt (kW) solar photovoltaic (PV) system to meet the electricity needs of the house. An electric-powered air-source heat pump heats and cools the space while an energy recovery ventilator brings in fresh air, all with nearly zero duct leakage. For heavier loads of winter space heating and domestic water, a hybrid approach was incorporated to supplement the electrical components. “The fuel the client chooses to use is based on their budget and local availability,” says Trolle. Since propane is a cleaner alternative to fuel oil and can be used nearly anywhere, including beyond the natural gas grid it was the fuel choice in this case. To keep the home warm during the coldest part of Connecticut’s winters, a 90 percent AFUE propane boiler with a 40-gallon propane tank serves an in-floor radiant heating system on the first level. Propane also provides domestic hot water heating. Instantaneous gas combination boilers are an energy-efficient option for space and water heating “with a very compact unit,” Trolle says. Because of their size, these tankless units can be located close to the point of use to reduce energy lost while transferring hot water throughout the home.
Results: All of the energy related features help the home earn a code-recognized Home Energy Rating System (HERS) score of 39. At the time it was completed, adding a 9kW PV system would have brought it down to a HERS score of 2.
CONCLUSION
There is no longer any reason for architects and designers to think that carbon-neutral design is for the future – it is critically important that every current project pursues that goal now. This is abundantly true for the embodied carbon found in the materials and products that we specify and incorporate into our designs. It is also true for the operational carbon generated to provide heating, water, and electricity to the building over its full-service life. There are options and opportunities now to create fully carbon-neutral buildings as well as hybrid solutions that leverage a variety of renewable energy sources with some more conventional, but lower carbon, choices. Design professionals have an abundant choice of tools, standards, and information sources to achieve better results now. Those who take advantage of it will achieve more sustainable buildings that meet all other project requirements while providing energy needs with drastically reduced or even zero carbon emissions.
Altogether, these and other design strategies are helping architects to meet the challenges of a post-pandemic world.
Peter J. Arsenault, FAIA, NCARB, LEED AP, is a nationally known architect and a prolific author advancing carbon neutrality by design. www.pjaarch.com, www.linkedin.com/in/pjaarch