The owners of this certified Passive House in Ann Arbor, Mich., cherish their nearly five-acre property, which backs up to a wildlife-rich estuary. Seeing its natural beauty from the house was a top priority. They wanted most of the glazing on the north side in order to optimize views of the prairie fields and to ensure privacy on the other sides of the house, which are subject to potential eyesores from future development. That orientation would limit exposure to desirable solar gain and heat energy. The solution was to incorporate a thermal storage and delivery system in the form of three Trombe walls. Of course, high-performance building materials and mechanical systems contributed to the house’s tight, energy-efficient envelope, which measures 0.6ACH50, but there were a few low-tech strategies at play, too.
Architecture as problem-solver
According to Michael Klement, principal of Architectural Resource, the design concept for the single-story ranch house was “21st-century Craftsman Prairie”—after Frank Lloyd Wright’s Prairie homes, which had their heyday in the 1920s. It is visually distinct for its long, extended horizontal lines meant to emulate the plains, and the two-story center section, which houses the guest bedrooms. The hip roof is notably detailed with 5-1/2-ft.-deep overhangs with a pronounced knife-edge. The overhangs are key. During the hot summer months, the walls (and interiors) are fully shaded; come late December, low winter sun is able to reach inside the house thanks to upwardly angled soffits.
Trombe walls can be used in conjunction with windows, eaves, and other building design elements to balance solar heat delivery. The upswept soffits expose as much of the wall as possible for heat absorption, while enabling sunlight to come in through the unobstructed upper portions of the windows.
The approach is from the southeast, which means the…
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6 Comments
Beautiful house. It’s sad to know that we don’t take advantage of free energy as much as we should. As I designed a handful of Trombe wall houses in NM, I learned that most of them failed in the comfort department; one side of the house was warm and other areas were cold.
For anyone wanting to use this great approach, there were two things I considered critical to overcome this deficiency, one, a very tight building envelope; and two, a low-speed, ducted fan on the ceiling of the Trombe wall rooms, circulating and distributing the warm air to the rest of the house via the air handler.
Great information, Armando. Thanks for sharing that strategy.
The house described has an insulated slab floor as well as Trombe wall. Likely that slab would stabilize interior temperatures across the interior space, as well as the mass of the Trombe wall on the south side of the house. However, the article also mentioned I-joists for the floors, so presumably the slab was covered by I-joists and finish flooring, which would reduce the effects of the slab’s thermal mass on stabilizing interior temperatures and storing excess heat for cooler periods.
I designed and built a superinsulated passive solar home in Colorado (not near passive house level insulation or air sealing), and found that a 4” tiled slab kept interior temperature fluctuations +/- five degrees F year-round. We didn’t need any supplementary heating or cooling in that main floor of the home over five winters (5,600 heating degree day climate).
https://www.greenbuildingadvisor.com/green-homes/a-passive-solar-home-from-the-1980s
The sunny and dry climate of Boulder, CO and New Mexico are ideal for passive solar gain in winter, and Ann Arbor is moderately overcast mid-winter. So not ideal for harvesting wintertime solar heat gains.
https://www.greenbuildingadvisor.com/article/a-quantitative-look-at-solar-heat-gain
You have to put windows somewhere, so using glazing on the south side is useful in cold winter areas, so long as you have access to unshaded sunlight during the winter months when the sun is lower on the horizon. Clever design of this Trombe Wall home with deep roof overhangs and soffit design: “Late December, low winter sun is able to reach inside the house thanks to upwardly angled soffits.”
I like the idea of the pressurized air lock between the garage and the house. It seems like that could be implemented at low electric cost with modern ECM fans. Any details on what was used?
I have my doubts about the wisdom of using concrete for thermal mass in a Trombe wall, now that we understand the carbon impact of concrete. And I've also seem good arguments for using a sunspace with minimized thermal mass instead of maximized thermal mass, well insulated from the conditioned space, with the idea being that the temperature drops rapidly at night, at which point your thermal losses through the glazing are reduced. And during the day it heats up quickly. Once it's warm enough, dampers are opened and fans are turned on to harvest that heat for the conditioned space.
I've read about some ways to reduce the carbon impact of concrete (besides avoiding concrete, which is one solution). Would be nice to see an article on that topic of substituting or adding materials to reduce or eliminate cement from the traditional concrete mix.
A couple of articles on concrete here in the last 2 years:
https://www.greenbuildingadvisor.com/article/concrete
https://www.greenbuildingadvisor.com/article/greener-concrete-horizon
But even with reduced carbon concrete, I would only use it for the applications such as foundations where it's hard to find a good substitute and it's serving an important function.
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