Home solar heating for less than $200? It's possible
How would you like to install solar heating in your home for under $200? Harry H. Briscoe, a mechanical engineer in Rome, Ga., says you can. He has developed an inexpensive solar system which is designed to supplement a conventional warm-air heating systems in new homes and small commercial buildings with gable roofs.
The Briscoe system is easy to install and operate, requires little or no maintenance, and is simple enough for the layman to understand and appreciate.Best of all, according to the developer, it requires a very low investment -- under $200 -- and offers a high return.
"It has always been my belief that consumer acceptance of solar heating can only be accomplished by a low-cost system," says Mr. Briscoe. "The high cost of the solar-heating systems now available prevent most people from considering them when building a new house or business."
Mr. Briscoe says that no other heating system can begin to approach his for simplicity, low initial cost, and attractive return on investment.
The Briscoe system consists of a solar heat-storage chamber located in the attic, a duct running from this chamber to the return side of the furnace in the basement, another duct running from the living area back to the storage chamber in the attic, a single-stage thermostat in the storage chamber, a two-stage thermostat in the living area, two temperature-controlled dampers, and two temperature-controlled roof ventilators.
The storage chamber runs the entire length of the roof, starting at the ridge beam and extending down from it as far as space will permit. Naturally, the larger the chamber, the more heat it will store.
The top or exterior of the chamber is constructed of translucent fiberglass panels which are the same color as the asphalt shingles used to cover the remainder of the roof. This permits the aesthetics of the building to be preserved with just a small loss of solar radiation transmission.
(A fiberglass panel will not admit as much solar radiation as a solar collector, but the loss is very slight -- not even a consideration, really, when the costs of the two are compared.)
The bottom of the chamber consists of black sheathing which absorbs light radiation passing through the fiberglass panels and also acts as an insulating medium. According to Mr. Briscoe, the entire chamber can be built for what it would cost to build a conventional roof. The labor required and materials used would be comparable.
At the center of the storage chamber, in a horizontal plane, is a duct routed to the ridge of the chamber. Its upper end is fitted with a temperature-controlled damper that automatically opens when the air in the chamber gets above 85 degrees F. and closes when it goes below 75.The other end of the duct is connected to the return side of the furnace.
If a building has central air conditioning, then a manually operated summer/winter damper is installed in the duct so that air from the solar chamber does not add to the heat gain during the cooling season.
A single-stage heating thermostat installed in the storage chamber next to the duct going to the return side of the furnace controls the automatic damper. Sensing the temperature of the chamber, it closes the damper at 85 degrees F. In the living space of the building is a two-stage thermostat whose first stage is in series with the thermostat in the solar chamber.
"Should the first stage of the thermostat in the living space close and the thermostat in the chamber also be closed, the blower in the furnace will be energized," explains Mr. Briscoe. "Solar-heated air will then be extracted from the storage chamber and distributed to the living area via the ductwork which is part of the building's conventional heating system."
If the storage chamber thermostat is not closed, the furnace blower will not go on, Mr. Briscoe points out.
Since there is a differential of approximately 4 degrees F. between the first and second stage of heating, the second stage of the thermostat would close, activating the main heating system to satisfy heat requirements.
The system also includes a second duct running from the living space back to the storage chamber. It allows the air from the living area to return to the chamber where it is reheated, then reintroduced to the living area by means of the furnace blower, continuing the cycle.
A diffuser equipped with a manually operated damper is attached to this duct in the living area and, in the heating season, is open. In the cooling season, it is closed, keeping hot air out.
Two temperature-controlled gable ventilators, positioned at either end of the roof, complete the Briscoe system.
Closed during the winter months, these ventilators decrease the heat loss from the solar storage chamber while allowing enough air infiltration to avoid a moisture condensation problem. In the summer, they open to relieve high attic and solar chamber temperatures.
"I found the best method for operating the ventilators to be a set of horizontally opening doors attached to the gable louvers in the attic," reports Mr. Briscoe.
"A piston assembly partially filled with freon 114, which I designed, determines the position of the doors," he adds.
The chemical properties of freon 114 are such that above 40 degrees F. it changes from a liquid to a liquid-vapor state, exerting a positive pressure within a closed container. This pressure forces the piston in Mr. Briscoe's design rearward, opening the ventilator doors. As the temperature drops, the pressure relaxes and the doors gradually close.
It should be noted that the Briscoe system is only adaptable to new construction because of the obvious difficulty and expense of removing, and then replacing, the upper portion of an existing roof. Used in this way, it provides the most economical supplementary solar heating available, Mr. Briscoe contends.
To demonstrate the efficiency of his system, Mr. Briscoe uses a 65-foot-long building in his home town of Rome, Ga. Facing south, it has a 240-square-foot solar storage chamber and requires heating six months of the year. Rome has about 10 hours of daylight in midwinter but the sky is overcast one-third of the time.
The average solar-heat gain through fiberglass panels is 114 Btuh (British thermal units per hour) per square foot. The cost of electricity in Rome is 2 1 /2 cents per kilowatt-hour. Natural gas costs 16 per therm (100,000 Btu); propane 43 cents.
Using these figures, the total heat gain per day of the panels (114 Btuh X 240 square feet X 10 hours) would be 273,000 Btu. A 30 percent overcast factor would reduce that figure to 261,288 Btu, and a 65 percent panel efficiency factor (determined by tests) would reduce it further to 169,837 Btu.
Taking this figure, 169,837 Btu, and factoring in the energy costs listed above for a 180-day heating season, the annual fuel cost savings will be $225 if electricity is used, $48.60 if natural gas is the energy source, and $131.45 if propane is the fuel.
At an installed cost of, say, $175, the Briscoe system would provide a return on investment of 133 percent the first year if electricity were the energy source. Natural and propane gas would return 32 percent and 79 percent respectively the first year.
Home and building owners in regions of the United States with higher degree days than Rome, Ga., could expect even better returns on their investments, Mr. Briscoe notes.
If anyone is interested in learning more about the system, the inventor can be reached at Central Electric Company, PO Box 1268, Rome, Ga. 30161.