My Mother's House Part V: Ductwork and Hybrid Energy

Learn more about the MOTHER EARTH NEWS earth-sheltered home that relies primarily on passive solar gain and a passive/active heat and storage system.

| May/June 1982

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    Hot air for our hybrid collection system is drawn form both the greenhouse and the round registers you see in the roof peak duct.
    PHOTO: MOTHER EARTH NEWS STAFF
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    The solar-heater air enters the storage bed (shown here before completion) at the far end and passes between the rocks.
    MOTHER EARTH NEWS STAFF
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    As you can see, our earth-sheltered house is — at least externally — nearing completion. We do have several more important features to discuss in future issues, however.
    MOTHER EARTH NEWS STAFF
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    The system can be switched from storage to heating mode with a single lever. That control does, though, manage an array of linkage rods that move three valves.
    MOTHER EARTH NEWS STAFF
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    The system can be switched from storage to heating mode with a single lever. That control does, though, manage an array of linkage rods that move three valves.
    MOTHER EARTH NEWS STAFF
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    Left: Storage Mode Right: Heating Mode
    MOTHER EARTH NEWS STAFF

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By the time you read this, MOTHER'S Eco-Village property will be getting ready to open its gates for the summer, and thousands of folks will have the opportunity to view our earth-sheltered house firsthand. We hope the building will have interesting features that will be relevant to nearly anyone's favorite energy-efficient housing concept.

During the ongoing planning process we've tried to remember that earth sheltering and/or passive solar design may not be every future homeowner's cup(s) of tea, so we've attempted — wherever practical — to experiment with an assortment of alternative heating and cooling techniques. In this issue, for example, we'll describe our hybrid-solar collection and storage system... a setup that — though not strictly necessary in a dwelling with the inherent energy efficiency of ours — has proved to be quite impressive.

Passive Solar Energy and a Ducting System

Because of the extensive use of glazing on the south side of our house, two areas can — on sunny days — become warmer than is necessary: The sun-heated air tends to gather both in the greenhouse and at the peak of the second-story roof. Of course, the presence of 90-degree-Fahrenheit-plus temperatures at those two locations doesn't pose a comfort problem for the structure's occupants (and it would be easy enough to vent the excess heat, anyway), but we simply couldn't bear to let all that warmth go to waste.

 

Consequently, we decided to set up a ducting system that could capture heat from both spots and either direct it to the floor area immediately or store it for future use. Essentially, during collection, warmth is pulled actively (by a 1/3-horsepower blower) from the greenhouse and from a triangular passageway that runs along the peak of the second-story ceiling.



The air is routed through ductwork (it's made from fiberglass board) to an enclosed rock storage area located beneath the east-end bedroom floor. The box was built from plywood (with a supporting framework) and insulated with polystyrene board, then the bottom of the container was lined with 8-by-16-inch concrete blocks placed on their sides and spaced about an inch apart. Our crew handpicked a little more than 10 tons of approximately 3-inch-diameter washed river rock to fill the storage bed to a level about 6 inches below the top.

To give our rock bed the capability of handling both storage and heating, we cut openings at the top and bottom of the east and west ends and then built plenums, from fiberglass ductboard, to encase each of the two pairs of openings. Each chamber has a valve inside which will join either its top or its bottom rock bed opening to the connecting ductwork.






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