BUILD A WATER-WALL HOME

Enlarge Image Image Gallery [1] The Morgan home in Davis, California has 14,000 pounds of thermal mass stored in its water walls, yet the containers blend in so well with the house design that they're barely visible. Can you spot the black south side of the bench-high water wall in the window? [2] The dwelling's largest steel tank, a 2' X 8' X 8' container, absorbs sunlight shining through the clerestory windows. [3] This window bench water tank can absorb both solar and wood-heat radiation. PHOTOS BY BROCK WAGSTAFF

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In many ways, passive solar homes are superior to those with active (mechanically assisted) heating and cooling systems. After all, passive solar systems don't rely on auxiliary energy sources to perform (so they'll work even when the power is off) . . . are generally simple and low in cost . . . combine energy collection and storage functions . . . have a long life . . . need little maintenance . . . and can often be built and installed by the home handy person, without special training or equipment.

But precisely because such "non-moving" systems have no pumps or controls to circulate warm or cool air, they typically rely on one key element: the thermal mass that stores and gives off absorbed heat or cold. A number of different items can be used to provide this energy-holding capacity, but just about the most effective and economical "To a water wall term that is a shorthand way of saying "contained water for thermal mass in passive solar homes").

Water-wall systems deserve much greater recognition than they've yet received . . . for a number of reasons. First, they can be very economical, especially since such units can often be installed-in either new or retrofitted homes-with standard construction techniques. Second, they are effective for both heating and cooling, particularly in areas with low nighttime temperatures. (Some heat-storage mediums, such as phase change salts, don't work for cooling.) Third, water walls can be attractively accented or practically invisible, as desired. (Did you notice the water walls when you glanced at the photos?) Fourth, water is a more efficient storage medium than are the other common sources of thermal mass. (See Table I for a comparison of water, concrete, and phase-change salts.) Consequently, water walls take up less room than other storage systems. This allows the house to offer outside views-avoiding the claustrophobic sensations possible with full masonry (Trombe) walls, which often completely block off south windows-and permits the easy installation and operation of movable window insulation. And finally, the fine radiating and temperature moderating qualities of water walls make for very comfortable homes.

START WITHTHE (SOLAR) BASICS. . .

Building a water-wall structure can actually be a straightforward proposition. To begin with, the home should incorporate the basics of good passive solar design. The most obvious of these fundamentals is proper orientation: A major wall should face south. Likewise, most windows should be on the south, with some on the north . . . but comparatively few on the east and west. The dwelling should also have excellent insulation (a minimum of R-19 in the walls and R-30 in the ceiling) and weather stripping (infiltration can easily account for one half of the heat loss in a well-insulated but poorly weatherized building). The design should incorporate good summer shading, too . . . particularly on any east and west windows, which, if unshielded, can let in a surprising amount of the summer sun's radiation. Then again, the dwelling needs adequate natural, induced, or mechanical ventilation. And last, it needs double- or tripe-pane windows with some form of movable insulation . . . either thermal shutters or drapes.

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