Page 16 RAIN July 1979 Another· Solar Water Heater Jeff Paine - Ev.en in the cool and cloudy Pacific Northwest, it's time for home.owners to install solar hot water heaters. What we're learning here ought to be good news for the rest of the country. The economic case for such solar applications continues to brighten as utility rates soar and newly" implemented Oregon state a.nd federal tax credits reduce solar costs up to 55 percent As for the remaining 45 percent actual cost, that investment • can be returned upon sale of the home with the additional market value a solar hot water system adds. So don't let the initial $2500 or more contractor installed price scare you away- over the long term your expenditure will be returned along with virtually free energy dividends. If you want to install a sofar hot water system yourself-or at least understand some of the finer details-the following information should prove useful. The drain down system. described is being installed locally at workshops sponsored by Portland Sun-a local non-profit educational group which offers solar workshops, classes and consulting services. Their address is 3334 S. W. 1st Ave., Portland, Oregon 97201. -JP Opting for a Drain Down System: Drain c;lown systems circulate pure, drinkable water between a solar collector and a storage tank. When temperatures fall below 40 degrees F., the collector water is drained fr:om the system 'by a thermostatically controlled valve. Put simply, this type of system outperforms antifreeze protected systems: Pure water absorbs heat more readily than antifreeze solution. Consequently, the required collector area and coolant pumping rate are less than a comparably performing, more expensive antifreeze system. Drain systems also offer additional cost savin,gs in that a heat exchanger-required to transfer heat from collector antifreeze solution to the storage tank-is not needed with a system based on pure water. He-re are some good tips to help with your drain down installation: Sweat Soldering: .Rigid type M copper pipe was used to con-· nect the two tanks and solar collectors. Copper costs less than steel pipe and is easier to install. Any'hahdy person can cut • an9 solder the fittings together with readily available hand tools. It is important to polish the surfaces of the pipe and fitting with sandpaper or coarse steel wool in order to·remove all traces of oxide which can reduce the bonding strength of the solder. Be sure.to remove the sharp inside edge of the cut pipe with a knife so water friction and the pump workload are minimized. After coating with flux, and inserting the pipe and fitting together, heat the underside of the joint with a torch and touch the solder to the top of the fitting. The solder should be melted by the heated metal, not the torch flame. Overheating the joint may burn the flux a·nd weaken the joint. Different types of solder are used. ·Inexpensive 50/50 tin/ lead solder is used for joints outside of the collector. Temperatures inside a solar collector can reach 400 degrees F., so use more heat resistant and expensive 95/5 tin/antimony solder on the ,collector plumbing. For perfectionists, brazing is the best method for connections inside the solar collector. _ .. ''Pru~re..l(elitl VAive, from Collldor--Hof s~pplt --srae - Cold-from Strut Therme{; tG~ it. Controi PAt\ef Code Requirements: Notice from the drawipg, 3/4 inch copper pipe is used between the street water meter and the hot water tanks. Downstream from the water tanks, 1/2 in'ch pipe can be used. Plastic PVC pipe cannot be used inside the house. High temperatures deform it and chemicals can leech into the hot water. The backup tank must be fitted with a temperature /pressure relief valve drained by a pip·e pointing downwards within 2 feet of the floor. If installed on a wooden floor, the . backup tank must rest on a drip pan drained by a metal pipe to the outside ofthe building. A temperature/pressure relief valve is not required on the solar tank, but one should be installed near the hottest part of the system, the outlet pipe of the collector array. i'f an electric panel is near the water tanks, be aware-of the code requirement for an adjacent 30 inch by 3 foot deep access area clear of all obstructions. All fittings on the pump, drain valve, and the pipe to and from the collector are usually 1/2 inch diameter: Temperature sensors on the collector and storage tank activate a control thermostat which can shut the pump off and open a drain valve when freezing conditions occur. This empties the collector water through a n<:!oprene drain tube into a floor drain or a sink. You can also run the drain tube outside the house, but be aware that ice can build up, block the drainage, and freeze the collector. Be sure the electrical components carry a UL label and run their wire inside flexible armoured cable or else an inspector may cond~mn your system. Copper/Steel Corrosion: Wherever dissimilar metals are in contact in the presence of water, rapid corrosion will occur. To minimize this, a dielectric union should b'e installed. The plastic coupling inside this fitting prevents actual copper/steel contact. Homes with soft water have less bimetallic corrosion than homes with well water or hard water, so an inspector may c:: 0 ... IU -a. 5 r,)
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