FIGURE 11 THOMASON SOLAR HEATING SYSTEM, USING ROOF-MOUNTED, SINGLE-GLAZED COLLECTORS WITH OPEN WATER FLOW

The tank is surrounded on all sides by 25 tons of fist-sized stones contained in a 10 x 7 x 30-foot bin. When rooms need heat, a blower blows air upward through an array of stones to the rooms. A reflective (but nonmetallic) near-horizontal roof (15 x 40 feet) or sunporch over the swimming pool directs additional radiation to the collector. A fraction of winter's heat need is supplied by solar energy: 85 percent in (mild) 1973-74 winter, 75 percent in a typical winter. Source of auxiliary heat is an oil furnace. In summer, an air-conditioner capable of 34,000 Btu/ hour output is operated at night (when outdoor air is cool and city demand for electricity is small) to cool and dry the stones. During the hot humid day, the stones cool and dry the air circulated to the rooms. (It is said that an air-conditioner of half this output would suffice.)

Although some leading solar researchers regard Thomason's system as inefficient, the inventor is actually pursuing its commercial production, and it may currently be used in more operating solar homes than any other single system. While the Thomason system uses forced air heating, it is designed to minimize the need for sheet metal ducting, using instead the existing spaces behind the building walls and between the joists to channel the hot air. In one Thomason-type application inspected by the study team, the builder had used wall board to construct a central duct, which could not be accommodated within the wall spaces.

The Phoenix Project of City of Colorado Springs--This solar heated home is a direct result of the energy crisis. In June 1973, the City of Colorado Springs imposed a moratorium on the connection of new loads to its gas distribution system because of gas shortages. The projected procurement rate created a sudden and substantial interest in other energy sources, and after a consulting study, a committee of local professional and business people backed by the mayor worked with the National Science Foundation to design and build a model solar heated home. This home was completed in September 1974 and has been occupied by a family since January 1975. Figure 13 shows the house, and Figure 14 is a graphic representation of the operational concept.

Designed to accommodate a middle income family of five, the house is a two-level 2,190 square foot dwelling, excluding the finished family room in the basement. A heat transfer fluid (Dowtherm J) is heated in the solar collectors and flows to a coil in an underground storage tank where the heat energy is transferred to water. The hot water is passed through a house heating coil where the energy is transferred to a forced air heating system used to heat the rooms. Backup heating capacity is provided by a two-step electrical resistance air heater in the house duct, which cycles automatically on thermostat demand when the stored water is not hot enough to handle the heating requirement.