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Our first Sustainability Chats - virtual green tour - was this past Thursday, May 28th. UWL Professor Scott Cooper took us around his Driftless region passive solar home showing us the impressive yet attainable passive building aspects he has implemented. Thank you to the Cooper's for touring their home and for everyone who joined us live!
Did you miss the live event? Don't fret! CLICK HERE for the video recording.
You can also read more about Scott's build and passive solar homes in Wisconsin below.
Passive Solar Homes in Wisconsin
by: Scott Cooper
An all electric home has several advantages over a traditional house that uses natural gas or propane. Not having a gas line reduces the risk of fire, improves indoor air quality by not burning anything inside the house, and eliminates a monthly gas fees. With the addition of photovoltaic solar panels, an electric home can be net zero by producing as much electricity as it uses, reducing use of fossil fuels and releasing more carbon dioxide into the environment. There are concerns that prevent some home builders from going all electric in Wisconsin including initial costs, concerns about staying warm in a harsh winter, and energy storage. Many of these issues have been solved through decreased costs, improved technology, and net metering with progressive electricity suppliers like Riverland Energy Cooperative. Net metering credits customers for surplus kWh produced in the summer and draws from these credits in the winter as they use more energy than they produce. To be connected to the electrical grid, customers still pay monthly basic service costs. Energy efficient building designs are incorporated in passive solar houses including: capturing and trapping heat from the sun through south facing triple pane glass windows, thermal masses to store the heat, and well insulated air tight walls and ceilings (Figure 1)
One example of a passive solar house was built in 2016 on Brice Prairie in Onalaska Wisconsin. This two bedroom, two bathroom house has 1600 square feet of heated living space, along with a breezeway, garage, and shop above the garage. An 8.4 kW photovoltaic system produces all of the energy used by the house for heating, air conditioning, lighting, charging a plug-in Prius hybrid, and other electrical needs (Figure 2). The key to the success of this house is a passive solar design that includes triple pane windows mostly facing south, 12” thick double stud walls insulated with dense packed cellulose (R43) and a well insulted ceiling (R75). The floor is a 4” thick concrete slab on 8” of foam (R27) which acts as a thermal mass to store heat and not lose it through the ground. The walls have vapor barriers on the outside (Tyvek) and inside (Intello) to prevent moisture build up (Figure 3). Because the house is airtight an energy recovery ventilator (ERV) runs constantly pulling stale air from the bathrooms and kitchen and releasing conditioned fresh air into the bedrooms and living room. For back up heat in the winter there are Fujitusu minisplit heat pumps on each floor that also serve as air conditioners in the summer. By having each indoor unit connected to a separate outdoor exchanger these units can produce heat even at outdoor temperatures of -15 degrees. Finally, the house has an off peak electric line that runs a Steffes thermal storage unit and an electric water heater. Other energy saving devices include an induction stove top, energy star appliances, LED lights, and a heat pump condensation clothes dryer.
Building a passive solar house adds about 10% to the costs of building the house. Not having to install a conventional heating and ventilation system with lots of ductwork saves money that can be used to invest in better insulation and windows. Because there is no forced air, passive solar houses typically have open floor plans (Figure 4). Compared to similarly sized houses built using traditional methods, a passive house can use 60-90% less energy each year and the additional building costs will be recovered within 12-15 years at current energy prices. Last winter, when outdoor temperatures dropped to -30 degrees and the house was easily kept at a setting of 65 degrees with supplemental heating downstairs, and nothing required upstairs. All electric, passive solar houses are a comfortable and energy efficient option even in a cold climate like Wisconsin.
Figure 1: Basic elements of a passive solar house, © 2018 Richard Pedranti Architect www.richardpedranti.com.
Figure 2. Picture of the house showing a 4kW photovoltaic system attached to a 1” raised seam metal roof.
Figure 3. Cut away model of the wall design. Left panel shows the outside of the wall lined with Tyvek and a 2”x6” load bearing stud. Right panel shows the inside stud lined with Intello. Cellulose is blown between the walls and electrical wiring is run along 2”x3” boards behind the drywall to minimize penetration of the Intello vapor barrier.
Figure 4. View from the inside of the house.