July 1979 RAIN Page 17 not r~quire dielectric unions in some.~ocatio~s. Oi1~side:of wall plumbing inspector told me corrosion from the copper/steel coverings, such as water tank connections, d1electnc unions are - ·contact should not be a problem since there isn't any water not required by the .code, but use them anyway for extra pro- flowing between the two metals. After insulating, this heat tection. Dielectric flex connectors·can be'used instead of :.e~ch,1rtge:r,storage tank should work almost as well as comunions if you prefer. Being fl~xible, they simplify attaching · mer~ially available versions costing a lot more. For more. pipes to tanks, but they are expensive and more restrictive to detai'l$ on this 'device, see the following reference section. water flow. • If you have installed or lived with a solar water heater, any Gate Valves: In order to shut the system oft, 3/4 inch gate valves are installed between the two tanks. Globe valves should not be used, as they are restrictive and reduce water pressure. Normally, the top and bottom valves are open, the middle · valve shut. Should the solar collector or tank require repairs,· the middle valve is ope.ned and the other two shut, enabling , the backup to operate without interruption. Insulation: A very important requirement for good performance is insulation. Storage tanks must be insulated at least • • with 6 inches of R-10 batfing. But don't insulate over any wires or electrical conn~ctions. Underwriters Laboratories says heat can build up to dangerous levels. Often overlooked is the_ need to get both storage tanks off the cool concrete floo_r with an insulated wooden platform or a couple sheets of styrofoam. Collector pipe runs, and the 3/4 inch hot pipe between the tanks can dissipate a lot of heat too unless well insulated. Arma-flex, a hollow foam material, is excellent for this purpose. When installing it, avoid slitting longitudinally and cementing it back together::J he glued seam looks bad, never holds together very long, and leaks a lot of heat. To prevent this, slip uncut Arma-flex over the pipe before you solder the fittings. When soldering, keep the insulation away from the heat with vise grips clamped to the pipe. Also important is to run all pipes inside the heated portion of your house. Do everything possible to minimize heat losses f:r;om pipe runs, or your solar system performance may disappoint you. Pipe Slope: The collector to storage pipe run must slope at least 1/4 inch per foot of horizontal run to insure proper drainage and freeze protection.·During the summer, heated water will emit air which can block pipes ang cause overheating damage unless the pipe slopes uniformly ;away from the e.ir bleed/vacuum break valve atop the collector. The solar collectors must also slope properly to insure adequate drainage. Tilt the outlet side of the collector support frame at least 2 inches above t}:le i.nlet or supply side. Try to mount the collector frame on an overhanging eave, so any leaks from the roof p_enetration by the frame attachment will not damage the house interior. The Antifreeze Alternative: In climates where frequent·freezing and thawing temperatures occur, antifreeze systems are less likely than drain down systems to suffet from freeze damage. The collector solution cannot freeze so long as the owner maintains an adequate level of antifreeze concentration. On the other haqd, draindown systems rely upon mechanical safeguards for freeze protection. So long as these components operate properly, the system won't freeze. But should an electric valve, a vacuum break valve, a temperature sensor, or a thermostat malfunction-or if the pipes are not installed properly-freeze·damage will result. This lesson was learned during Portland's unusually cold winter last year, when marry drain down systems froze up. . • Unlike drain down systems, antifreeze systems require~ heat exchanger storage tank. You can build this component yourself; accorg.ing to Tim Woods, a CETA solar technician. He buys new factory second hot water tanks from a plumbing distributor. Starting at the 'bottom of the tank, 60 feet of 1/2 inch·soft copper .tubing is wrapped around the tank. To increase heat conduction, the tubing is coated with 1/2 inch Thermon T85, a heat transfer mastic. It takes 5.tubes or $30 of this stuff to do the job adequately. Soldering-the tubes on the tank can heat damage its rust protective glass lining. A information you are willing to share with Rain would be ap- •preeiated. I am especially interested in experiences with thermosiphoning or pass1ve water heating systems. All you folks wh9 have .purchased Rain's Solar Water Heating Workshop Manual are urged to speak up! • • Instruction Manualfor a Solar Hot Water Heater Unit, by Clackamas Coqnty CETA Solar Project, $1.50, available from: Clackamas CETA Solar Project P.O. Box.215 Marylhurst, OR 97306 _ The Clackamas CETA Solar Project trains teenagers to build and install, free of charge, solar hot wate,r systems f9r low income homeowners. So far, 14 systems have been installed, costing $500 each for materials. If you want to build your own version of this design, obtain a copy-of these step-by-step . instructlons. (This solar project is looking for free, donated - materials. If you have Jny unwanted patio door glass, exterior plywood, or lx2 or 2x4 lumber, call Tim Woods, 636-5101.) Build Your Own, Solar Water Heater, $7.95 .fr.om: ~ Garden Way Publishing • Charlotte, Vermont 05445 One of the most detailed descriptions available on building your own active solar hot water system. "SDHW Systems: What Experts Look For," February, 1979, by Daniel C. Lewis, pp.16-19. "Domestic Hot Water," March 1978, by Robert 0. Smith and John MeeJ;cer, pp. 16-24. Solar Age, $2.50 each plus $1 handling on orders of $5 or more, available from: ' Solar Age P.O. B.ox 4934 Manchester, NH 03108 The SDHW article offers an excellent discussion of system components with suggestions from the experts. "Domestic Hot Water" describes what went wrong with a large solar hot water project sponsored by a utility company. 1 Tax Credit Eligibility Criteria for Residential Alternative Energy Devices, free from: Oregon Department of Energy Room 111 • , / Labor and Industries Building Salem, Oregon 97 311 Toll free access: 1-800-452-7813, ext. 4040 At pr~sent, the DOE eligibility requirements for a 25 percent tax credit on a solar hot water system are ridiculous. Your system must provide 10 percent of your home's "total energy consumption," including space he.ating. This total is estimated from your home's square footage of habitable space. Everyone knows hot water consumption depends upon the number of residents, not the size of the house or how much space heating it requires. But unfortunately, if you live in a large old,\lninsulated house, or live alone, a solar hot water system eligible for a tax credit would have to be excessively oversized and ex'pensive. Help is on the way, however. By September 1979·, SB 33 7 should be enacted by the Oregon State Legislature, changing the eligibility requirement to 50 percent of your hot water consumption. Sp if you live in an old house, wait unti~ this bill passes the legislature before starting-your project. CT□ D
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