Domestic Solar Water Heater
Installation of a domestic solar hot water system. The system was originally installed on a house in the early 1980′s and was in use for around 10 years. The system was removed and not used for the next 15 years. Some parts and components have disappeared.
The system is a water-based, open drain-back system. It requires a separate unpressuried storage tank and is freeze-proof. While this system is not as efficient as newer ones, it is the simplest and cheapest system for a DIY installation.
Solar Collectors
Two 8′x4′ flat-plate collectors from Solartech (cira 1983 – company is now defunct I beleive) are installed on the roof. Optimum angle for this location is 65 degrees from horizontal. The roof is only 30, but mounting them flat reduces the complexity of the mounting brackets and eliminates problems from wind. Should they prove inefficient they can be raised later.
The roof mount was built from 2 8-foot pieces of 2×2 angle iron bolted to 6 1-foot ‘riser’ pieces of 2×2 adjustable steel track. This type of track is typically used for installing gas, water, or electrical fixtures and was purchased as a 10-foot length from Fastenal for $30. This includes the spring nuts and bolts required to mount the angle-iron. All pieces were primed and painted with black rust paint.
The risers are affixed to the roof with 2 lag bolts each through the roofing into the rafters below. The holes were sealed liberally with roofing cement. The angle iron was bolted horizontally across the risers and are adjustable to obtain the optimum angle for drainage.
A material lifter ($80/day from United Rentals) made lifting the 65kg panels onto the roof much simpler. The material lifter is like a hand-crank operated forklift that can lift up to 700lbs 30 feet straight up. The lifter should come with 4 foot extension arms to make lifting panels, etc. more straight forward. This one did not come with extensions, so a couple of 2x4s were lashed to the tines of the lifter.
Heat Exchanger
At some point the original heat-exchanger coil was lost. A new one was built from 50 feet of 5/8″ O.D. copper refrigeration tubing, which is cheaper ($60 vs. $300) and more flexible copper pipe. Designing a proper heat exchange is complicated stuff – this one was built using the I-think-it-looks-like-the-old-one principle. It may or may not work, but it looks good.
heat exchanger coil
coil detail
The tubing was wrapped tightly around a 12″ diameter cardboard concrete form. A ‘tail’ was run through the middle of the form, then carefully bent to form the first loop in the coil. This tail will be the heated-water return, which will eventually be connected to the hot water tank.
To prevent the coil from turning into a giant slinky, two lengths of old copper pipe were wired to each loop. This gives the coil support and some ‘legs’ to keep the coil off the bottom of the tank. A 2″ spacer (a roll of masking tape) was inserted between each loop as it was wired in place to maintain the even spacing.