= In Line Thermostat

Overflow Seepage

Above: A schmematic of the translucent solar dome system in operation. Computer art by Bo Atkinson.

Overflow Seepage

Synergy Experiments

New Solar Seepage

Insulated Walls

Above: A schmematic of the translucent solar dome system in operation. Computer art by Bo Atkinson.

time shut off is automatic and powered by heat loss alone.

Thermostatic valves are used in cars to block radiator coolant flow when engine is cold. In domestic plumbing, the related devices are relief valves for boiler safety and scald-prevention on furnace type water heaters. This latter device, often called a "mixing valve" may be adapted for solar use. However, its operational range is suited only for very hot solar collection. More moderate and weather variable solar collection prefers wider ranges. These ordinary mixing valves were not durable for my temperate climate solar use. I tried both low and high temperature pistons. The active working part is a small piston which extends upon heating and retracts upon cooling. This movement is factory set by materials which have specific ranges of thermal expansion. Field adjustment can slightly alter the response range but perhaps not wisely. I "burned out" many of these hardware store "mixing valve" pistons using lower range settings on days during which temperatures soared too high for the low setting. Also these valves are not intended to close tightly. Eventually, I gave up and returned to manual solar operation.

After years of studying monthly industrial junk mail, finally my search paid off. I found a high quality thermal piston valve. For years now I have severely tested these industrial valves in a much more strenuous furnace application. These industrial thermal valves handle much wider temperature ranges, even above boiling, and keep working very reliably. I find it humorous that solar heat which collects in large pipes is considered a nuisance by industrialists. So, some versions of these valves are specifically intended to "dump" instead of reap solar hot water. Don't expect this supplier to be interested in humble solar projects, as a solar purveyor might. Therm-O-Tech Inc. is the manufacturer, 800-288-GURU for literature and a local dealer. "TV/HAT valves" are the simple in-line variety. These come with high quality (X or 38 inch) compression pipe fittings. And the valves really close tightly, as they should, effecting fully automatic control. Check out their other creative applications for thermal valves. I suspect competitive brands could exist somewhere on earth, but I remain uninformed about them at this writing.

Many factory set ranges are available including 90°F, 105°F, 125°F, 145°F, 155°F, 180°F (most interesting for solar). Switching between two or more high and low settings, depending on climate and momentary household demands could improve performance during cool weather. But one valve alone can satisfy low cost users. For economy I prefer a setting somewhat lower than my targeted temperature: perhaps using a 105°F in-line thermostat valve. Then I adjust a (cold, input, series connected) needle valve wide open on cool days, but just slightly open on very hot days. This really secures a very large measure of carefree automation using just one valve during all weather.


More heated water seems to be needed on cloudy, cooler days. Solar heated water must be stored for those rainy days. A 150 gallon storage tank has sufficed, but we plan on doubling capacity to extend our range in sunless weeks. In Maine the rain sprays playfully, in chains. Extended storage difficulties are quietly accepted with solar.

I couldn't find an ideal storage tank. Each suffered some drawback. I searched beyond the domestic market into industrial journals. In the mid '80s, high density polyethylene (HDPE) tanks offered the best economy at roughly $1 per gallon of capacity. These tanks were rated at 180°F (maximum recommended heat exposure). I accidentally verified that hot steam indeed melts this plastic. Coated steel tanks seem to rust out. Super alloy tanks were super expensive. Homemade cement technology is one of my specialties, but the disadvantages dissuaded me. The larger mass of cement tanks dilutes the collected heat (especially on small solar fills). Concrete tanks demand more elaborate structural support. We opted for a tank made from high density polyethylene.

Tank altitude is of consequence. I traded away my attic "high altitude" tank and settled my tanks below attic floor level. Height is important to get wanted water pressure, though presently I partly enjoy adequate pressure even with only one foot of drop. My worst inconvenience with insufficient drop is that I must blow air bubbles out at the tap. This is required only after tank has been emptied and the new hot water fill has only just started.

In addition to tank altitude, tubing installation needed straight runs without vertical meandering, which traps the air bubbles. As it is I could provide air vents above every upward bend, to purge bubbles automatically, but maybe I enjoy a little folly in my system now and then. This vertical meandering of tubing is no problem downstairs at a 10 foot drop between tank and faucet. The air bubbles quickly purge out downhill regardless of the status of tank filling or trapped air. Downstairs tap water is available immediately, even as the tank begins filling. The pressure is adequate for cold/hot mixing faucets, using 12 inch pipe fittings.

Frequently our system fills all available storage before the day is done. We are home to turn it off. I have never installed a float valve. These inexpensive valves could shut off flow once the tank is full regardless of continued collector heating. Several upgrade options could utilize this extra heating, but I have been distracted. Life is too great.

System Operation

Our local ground water contains iron and other minerals. The iron stains are many, even my outdoor fountain grows some sort of mineral loving algae ooze at the house-fed inlet. I recirculate the fountain water through our pond, garden and water table. I'm learning to love this. In concert, our solar collector sheds considerable rust after a freeze. The tank collects the rust at the bottom. Seasonally a blast of water from the garden hose stirs up and flushes the sediment out. It's a great cleaning system.

I prefer drinking the water from our system. The unpleasant, local, natural occurring gases are vented off by the low pressure tank. Holding the water overnight also helps to degas the water. This is a bonus — low cost purification! Our copper pipes offer many worse metallic spoilers to the list. Even the "new" silver solder lacks for flavor.

Even though my collectors have been exposed to attic dust for many years, I have never had a problem getting plenty of hot water. A slight dust coating clings to the outer pipe surfaces. I could use a garden hose to wash it off, but my attic floor was never perfected for leaks. I tried very hard to get things right, just running a bit late.

Synergy Experiments

Synergy integrates functions. I thought why not combine roof sheathing, attic greenhouse, air/water heating, and air conditioning. It was tough experimenting on our living space, but we happily lost ourselves dreaming of a greater purpose.

My solution called for a translucent dome. Translucent because transparent sheathing tends to cost more and privacy befits attics. A translucent dome act like a lens, "tracking" the sun while standing still, and a whole upper house envelope is obtained. Construction waste is minimal, but challenges are multiplied. The northern sky provides high quality visual light and adds some usable summertime solar gain.

By comparison, glass adds more cost to a home-made dome building. Even today, the future outlook toward progressive, insulated, light admitting sheathing is not a transparent material. Today's fashionable plastic, polycarbide is acceptably transparent only without insulation. You can't see much through "insulating" polycarbide: a hollow, extruded, channel sheet. Nor is the R value considerable. High insulating value that is more equal to foam boards is potentially available in an opaque material called silica areogel or frozen smoke. Currently the problem is scarcity and the cost of this translucent insulation. Today small supplies are produced in Sweden and Germany. Why the world isn't beating a path to supply it perplexes me. Silica areogel was invented 30 years ago. It is more ozone friendly and has a higher R value than styrofoam and is less toxic during a house fire. Its chief component is silicon. Why is the market so stuck on traditional window walls instead of light/heat utilizing walls and roofs? Thanks to the Freedom of Information Act, you can acquire extensive article reprints on aerogels from The Tech Transfer Group, Lawrence Livermore National Laboratory, POB 808 L-322, Livermore, CA 94550, phone 510-422-2646. We need some brave capitalist to rescue this under-represented technology.

Occasionally, in my travels I notice simple tubing collectors fastened above the roof surface. In temperate climates, these "open air" installations of tubing would benefit with a sheathing cover. Tubing alone gains solar radiation (heat), but loses heat through conduction and convection to the atmosphere and/or wind. In the tropics we couldn't care less. In cooler climates sheathing concentrates much more of the precious heat into the system. The difference in Maine is useful versus useless.

During summer, my solar attic works as a thermal fan. Dome geometry enhances the continuous venting. Maine's hottest summer nights are usually cool enough to continue thermal venting all night, resulting from daily stored attic heat. We open up the ground floor for soft night breezes, even wetting down our cement floors (occasionally), for more cooling. During heat wave daylight hours, we close up the ground floor, keeping it cooler for Alda's cut flower business. Cost-free air conditioning is a nice feeling.

Above: A marriage of the old and the new. Solar water heating and space heating/cooling on a New England cape-shack. Photo by Bo Atkinson

Dome Costs

The 42 foot diameter dome shell materials cost us roughly $3,000 in 1979. The material list was: five foot by 50 foot fiberglass sheathing rolls, cedar 1x4's, scrap aluminum battens, nails, screws, sealants, maybe 200 feet of boards for scaffolding and the upper plate, and a cord of unsawn poles for permanent interior support. I built it single handed, starting in spring and finishing (almost) by winter. The first floor and deck were built in prior years. I spent more than that building other interior structures. Just to complicate things, I built the dome to cover half the original renovated cape shack. Fiberglass was the best priced, plain sheathing in the '70s and '80s. Today, newer plastics might compete.

For large purchases of sheathing, products and prices are most competitive with greenhouse suppliers in any region. A monthly magazine called Greenhouse Managerputs out a yearly Buyer's Guide of extensive listings of suppliers nationwide. Their publisher's number is 800-433-5612.

Find courage

Too often, limitations force us to rig half-built projects/experiments temporarily and even seasonally. The home-baked and recycled appearance of our creations discourages those indoctrinated to support "professional" appearances. We should smile more on this reflection. At least we are home and not coveting the spoils of mindless nationalist wars. Very good! Our egos are kept unflattered, and plenty of alternative home work piles up. Yes, very appropriate blessings keep us inspired. Thanks for those extra special solar baths, that provide that worthful lift!


Author: "Bo" Robert Atkinson, RR 1 Box 2079, Freedom, ME 04941 • 208-342-5796. Feedback and dialog are welcome.

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