A Florida House With Natural Cooling

Although it cost no more than a comparable "surface" structure, this Florida home uses natural cooling and heating methods to satisfy most of its thermal management needs.

| July/August 1981

In north Florida's subtropical panhandle region—where summertime humidity can average a clammy 82% and temperatures in the 90's aren't even considered noteworthy enough to comment on—cooling a dwelling is usually of greater concern than is warming it. On the other hand, though, heating requirements can't be ignored altogether, since the region is subject to nearly 1,600 heating degree-days during its cold season.

Understandably enough, designing a passive solar home to suit such fluctuating conditions could present quite a challenge. However, the folks at Tallahassee's Mad Dog Design and Construction Company felt that, by coupling modern thermal conditioning methods with "tried and true" locally popular building techniques, they could come up with a house that would rely on natural cooling and heating yet be comfortable enough throughout the year to require little or no utility-supplied power.

A Well-Planned Design

Essentially, the Florida builders used several passive methods—backed up by two active systems—to insure a pleasant interior climate during the hot summer months. First and foremost, the earth-sheltered structure relies on natural ventilation, combined with heat-gain prevention, to maintain a comfortable internal environment. Borrowing from traditional local designs (which, of course, evolved to suit the area's climate), the Sunshine Staters utilized high ceilings, continuous attic-linked soffit vents, and strategically placed windows to encourage the flow of air throughout the house.

For example, the south-facing solarium/greenhouse area incorporates ceiling mounted outlets that can be opened, in case of overheating, to allow warm air to duct into the attic and out the soffit vents. Similarly, in the house itself—which is separated from the solarium by a quartet of sliding glass doors—unwanted warmth can be vented around four movable 8' X 8' insulated ceiling shutters. These horizontally hinged overhead "flaps" are mounted in light wells which are framed into the front of the attic and faced with acrylic glazing. When the electrically operated sky shutters are three-quarters open, pockets are formed, which accumulate warm air and direct it upward while permitting plenty of indirect light to brighten the rooms below.

Other heat-controlling elements in the unique design include [1] roof overhangs above the skylights, [2] solar screening over the greenhouse windows during the warmer months, [3] insulated draperies on the sliding glass doors, and [4] ceiling insulation with an R-value of 28. Additionally, the builders have taken advantage of deciduous trees to help shade the structure in the summer months.

Another factor that contributes to the energy efficiency of the Tallahassee residence is the dwelling's earth sheltering itself. Calculations made prior to construction had indicated that a large portion of the necessary tempering could be accomplished by using the soil as a massive heat sink, since about two-thirds of the building's wall area—as well as its entire floor—were slated to be below ground level. However, data gathered later showed that earth temperatures low enough for cooling purposes could be found only at a depth greater than five feet . . . so, to compensate for the fact that the earth-bermed structure was not wholly engulfed in soil, the Mad Dog designers merely insulated its surrounding earthen ramparts with a two-inch-thick Styrofoam beadboard skirt that extends outward eight feet from the home's concrete walls.

This protective "collar"—after being covered with waterproof sheeting and 12 inches of backfill—serves to minimize the effect of the sun and ambient air on the soil below (creating stable and comfortable temperatures at a depth of only four feet, even during the hottest months). It also provides an effective watershed that directs surface flow away from, rather than along, the sides of the building.

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