A blizzard can rage outside in -40C weather but inside the airtight Passive Home it may as well be June. "If it gets too hot you have to train yourself to open a window in winter," says Dr. John Eckfeldt of his home in Isabella, Minn. "After all, you aren't paying for the heat."
In fact, Dr. Eckfeldt and his wife, architect Nancy Schultz, need to check the outdoor thermometer to dress for the weather. "It feels like you are in a thermos and outside elements don't have an impact," he says.
Isabella is nestled in the Superior National Forest north of Lake Superior near the Iron Range, where iron ore has been mined since 1884. It is one of the coldest regions in the lower 48 states. The Canadian border is 40 kilometres north over the pristine Boundary Waters Canoe Area.
The Isabella Eco Home, as it is known, is a certified Passive House. The Passivhaus concept was pioneered in 1991 by physicist Wolfgang Feist in Darmstadt, Germany and today represents the highest energy standard for commercial and residential buildings. To be certified you must slash heating energy consumption by about 90 per cent - an achievement precisely modelled and measured by the U.S. Passive House Institute.
Innovations of the Passive House include ultra-thick insulation, doors and windows engineered to withstand cold and walls that encase the home in an airtight shell to retain heat. The Isabella Eco Home has 12-inch staggered double wall stud framing, 30-inch heavy timber framing on the roof and a continuous air barrier to minimize heat loss.
Another critical component is the lungs of the home - a mechanical heat recovery ventilation system. "In most buildings you lose much of your heat by warm air moving out and cold air moving in - so the control of air movement is key," Dr. Eckfeldt says. According to the rules, the Passive House air-tightness pressurization test result must be 0.5 air changes per hour - a standard about 10 times more stringent than in the U.S. Energy Star program.
The Isabella Eco Home heat recovery system reminds Ms. Schultz, owner of Compass Rose - an architecture firm that specializes in sustainability planning - of a 20- by 20-foot waffle iron with corrugated baffles. "The warm air going out passes side by side with clean, cold air coming in and heat is exchanged efficiently," Ms. Schultz says. "You need a big surface area for a counter-current exchange."
Passive House is a deceptively gentle description for an aggressive project kicked off by Dr. Eckfeldt and Ms. Schultz, passionate environmentalists, in 2007. "We took on net-zero energy [the home's annual net use of energy is zero]in a cold climate to challenge ourselves and see if we could push the envelope," says Dr. Eckfeldt, vice-chair for clinical affairs in the Laboratory Medicine and Pathology Department at the University of Minnesota.
Passive House standards, like old-fashioned passive solar homes, use non-mechanical means, including south-facing site placement, to get optimal solar collection from their triple-paned windows. "This is your first line of defence," Ms. Schultz says. "Then your active systems can be smaller."
The Isabella Eco House collects energy through 92 solar heat collector vacuum tubes and a photovoltaic system on the garage roof.
One of their most acclaimed features is their experimental solar thermal storage system of 9,000 cubic feet of sand and taconite beneath the home's insulated slab. Dr. Eckfeldt calculated heat values in various metals and found taconite pellets, which are almost pure iron oxide, refined from a local low-grade ore, had three times the heat storage capacity of sand or gravel. They bought nearly 20 truckloads from a nearby plant.
They employ an electric boiler and wood-burning stove in the winter months, as required. When the boiler malfunctioned in December, 2009, for 10 consecutive days of sub-zero weather, the home still stayed at 10° C thanks to its energy-conscious construction. Their measurement and control system is industrial quality to integrate the complex medusa of tubes, thermostats, controllers, fans, pumps and monitors. To achieve net zero energy use, they sell power back to the grid in summer during peak demand to offset what they buy during Minnesota's "dark months."
According to Ms. Schultz, who is accredited to design and evaluate buildings for LEED (Leadership in Energy & Environmental Design) certification, the Passive House designation is more difficult than a LEED rating because it is based strictly on the energy required to run the house - five BTUs per square foot. "One of the shortcomings of LEED is that there is no guarantee your energy model is the same as real-life operating performance," Ms. Schultz says. "The Passive House model is very prescriptive and gives you a baseline. Then they require you to test the performance once it's built. In LEED you can still have a leaky building depending on other points to offset - like rain collection."
The couple says their windows and doors are castle worthy - big, beautiful and amazingly engineered. Some weigh a ton each and sailed from Germany to Montreal, then overland to Minnesota by train and truck. Ms. Schultz and a German-speaking Amish friend did a factory tour prior to buying Mueller windows. "There were high performance windows in fibreglass but I did a Life Cycle Assessment (LCA) of sustainability and wood is best," says Ms. Schultz who laughs, "they are filled with krypton gas but they may as well have been kryptonite."
The couple recognizes their 2,134-square-foot home, at $500 per square foot conservatively, may not have payback in their lifetime. Asked what she would do differently, Ms. Schultz did not hesitate. "I would make the design simpler," she says. "But it is hard not to love it - I did not expect the comfort level."
Christopher Straka, principal with Vert Design, admires the pioneer work of the Isabella Eco Home. Mr. Straka, an environmental designer, received certification early in 2011 for Canada's first Passive House, the Rideau Residences, in Ottawa. A key attribute is that the windows and heating equipment, made in Canada, kept costs to about $235 a square foot. "That is comparable to a custom home at about $200-$225 per square foot," Mr. Straka says.
Mr. Straka notes that Canadian building codes lag, even with a tradition of field research that dates to the Saskatchewan House in the 1970s. He hopes that the principles of passive energy efficiency can be more widely legislated. "The bottom line is - we pay for energy," he says. "The Passive House movement is the future of green building."
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