Callaway's new Sibley Center has energy ideas home greenhouse planners can use - conservatory design

Flower & Garden Magazine, Oct-Nov, 1984 by Edwin C. Symmes, Jr.

Callaway's New Sibley Center has energy ideas home greenhouse planners can use

The spectacular new $5 million conservatory at Callaway Gardens, Pine Mountain, Ga., is more than a floral showcase. It is a demonstration of several advanced concepts of energy conservation and solar use that will be watched eagerly and studiously by people involved in greenhouse design, including home gardeners. Some of the ideas deserve trial on a home greenhouse scale.

The landscape architect, Robert Marvin, set out to "introduce people to nature' in the overall 5-acre design, which merges outdoor gardens with those indoors. In the process he and the other designers incorporated many energy-related ideas using state of the art materials and systems.

The entire Sibley Center is a complex of gardens, each one temperature controlled, ranging from a tropical greenhouse to two outdoor gardens. As in home greenhouses, plants with similar needs are grouped together for ease of maintenance.

Insulation

The roof is a double layer of cream-colored translucent fiberglass fabric similar to that used on the Pontiac, Mich., Silver Dome. The two layers have an insulating air pocket between. This slows escape of heat in winter, and penetration of the powerful Southern sun in summer. The walls are 4-inch-thick glass blocks. These again provide insulation. The earth's insulating ability was used by creating a high berm on the cold north exposure of the structure.

Arrangement of Plants

Large trees planted on the berm help buffer winter winds and force them up and over the major indoor display house. Even the interior plants follow this principle, as medium size trees on the north perimeter help temper the colder air there. Progressively shorter plants toward the south let in the sun, and lead the cooler air downward toward the front of the building where cold tolerant plants are located. Only deciduous trees (leaf-shedding) are used along the south side. They allow sun to enter in winter, but shade that side in summer.

Heating

The radiant heaters used at Sibley Center are a major departure for greenhouses, as they heat "things' instead of air. Even though they are electric, they are energy cost efficient. They have been placed selectively in locations that need extra warmth, without heating an entire area.

Ventilation

The entire south wall opens. It consists of 26 glass doors, each 24 feet high, that fold away, letting in the outdoors on mild days. This abundant air circulation creates a buoyant atmosphere quite different from the usual greenhouse air, and it is expected to provide a healthful environment for plants.

High velocity fans are installed near vents far up on the north wall for moving large volumes of air, but it is expected that they will be used sparingly. The entire interior is dotted with smaller overhead fans equipped with lighting fixtures, just like home ceiling fans, to keep air stirring gently and distribute the warm upper air down to ground level.

Evaporative Cooling

An automatic mist system covers the main display area. Another area receives the splash from a 22-foot waterfall. Visitors can walk behind this waterfall to view a fern grotto. Both of these systems effectively cool the air in summer for both plants and people.

Building Orientation

In mid-Georgia, where Callaway Gardens is, the perfect solar alignment is 15 degrees east of south. The "south' wall of Sibley Center actually faces this compass reading exactly.

Solar Energy Use

The roof is built at three different heights. These levels allow sun to enter when low enough in winter, and keep it out when it is high overhead in summer. In a home, an overhang accomplishes the same purpose. Massive rock walls inside the structure absorb and store warmth by day and radiate it back into the interior space at night. These walls provide a root-hold for thousands of ferns and other plants. The stone planter-wall idea could be adapted in home greenhouses or plant rooms, although in a much smaller version than the 300 tons of rock used at Sibley.

Another "heat bank' is the shallow pool of water that winds like a stream through the plantings. Its bottom is painted black to absorb all possible warmth. The water gathers heat during the day and releases it, along with humidity, to the greenhouse atmosphere at night.

Photo: LEFT: Glass blocks, four inches thick, make up all but the south facing walls. They have insulating value. Overhead fans positioned throughout the structure move warmed upper air down to lower levels.

Photo: RIGHT: The south walls, facing on an outdoor garden, consist of high doors which may be folded open on mild days. Also glimpsed here are the roof panels (two layers of fiberglass fabric); and a solar pool that contributes a warming effect in winter.

Photo: Rock walls, graduated plantings, and sloped areas all serve functionally to conserve warmth and provide suitable growing conditions.