MOTHER EARTH NEWS Heats up With Solar Energy

As far back as the mid 1970s, MOTHER was going green. Solar energy was used to heat the editorial offices. Here's a look at the system, with diagrams.

| May/June 1976


Without thick fiberglass insulation, the 110-degree  water in these 550-gallon tanks would not stay warm at night.


It's been almost a year since MOTHER set out to warm 1,600 square feet of her editorial office space with the sun . . . and—as we reported on page 100 of our last issue—that original goal is now a reality. Today, MOTHER's editorial department is (at least in part) solar heated. And we're tantalizingly close to using the sun to supply a full 100% of the Btu's we need to warm that 1,600 square feet right through the winter!

The move to "sun power" began back in July 1975 when four Georgia Tech students—John Hansell, Jeff Sheppard, Scot Iseman, and William Bruning—began the conversion. By the end of the summer, some 30 solar collectors (with a total surface area of 675 square feet) sat atop the building in which MOTHER is housed. Then, that fall—as the college foursome started back to campus—MOTHER staffers Dennis Burkholder, Joe Lane, and Bob Pace took over. Aries Engineering, a Gainesville, Florida firm with expertise in the field of solar heating was also retained as a consultant.

What we eventually got for our time, effort, and money was a conventional, forced-flow (active) heating system in which thermal energy (warmth from the sun) is gathered in the rooftop collectors. This heat is then absorbed by 45 gallons of collector fluid (a 1:1 mix of Prestone and tap water) that is constantly circulated between the collectors on the roof and four recycled 550-gallon storage tanks in the basement. Once downstairs, the antifreeze/water mixture passes through a heat exchanger located inside one of the 550-gallon tanks . . . and, in this way, warms the water held in the large container. A pump then circulates water from the first tank into the other three storage units. This keeps the 2,000-plus gallons of water in the four tanks at a fairly constant 110° Fahrenheit.

In addition to passing through the basement heat exchanger, some of those 45 gallons of hot (usually 130° F) antifreeze/water solution can also be shunted from the rooftop collectors to a second set of heat exchange coils hanging from the ceiling of the 1,600-square-foot office that we wanted to heat. Here, a 1/4-hp fan blows air past the copper coils into ducting that routes the resulting warm breeze to vents throughout the editorial department. An ordinary thermostat automatically turns the fan on and off.

As you can see from the accompanying diagram, our solar heating system contains a total of three pumps: one which forces the Prestone/water solution around and around between rooftop collectors and basement storage tanks, another that pushes some of the same fluid past the fan in the editorial department, and a third which circulates the eight tons of stored water back and forth among those four downstairs tanks. The operation of the three pumps is coordinated by an electronic "black box" located in a shed next to the roof-mounted collectors.

This control box constantly monitors inputs from three sources: [1] a temperature probe on the upstairs collectors, [2] another probe inside one 550-gallon tank in the basement, and [3] the office thermostat. Whenever the temperature of the collector fluid exceeds that of the basement water by five degrees or more, the box comes alive and tells its solenoids to flip on both [1] the rooftop collector pump, and [2] the basement circulation pump. In this way, the heat which has begun to accumulate in the 45 gallons of collector fluid is automatically transferred to the storage tanks downstairs. (Conversely, in the evening—as the antifreeze solution begins to cool down—the black box "remembers" to turn off the same two pumps.)

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