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Solar heat and hot water

Posted: Sat Feb 06, 2016 7:30 pm
by ijames
While surfing around I found these two web sites. I have not built either system but of all of the web sites I visited they seem to be the right combination of simplicity and utility. The first site,, describes a passive solar heating system. The solar heat drives the air circulation and it includes a passive air block so you don't have to do anything to stop heat loss at night (see for more discussion on this), so once it is built it uses no power. The web site gives construction details to build the panels into the outside walls of a shop, but you could also insulate the sides and back and just attach each panel to the outside of the wall with penetrations for cold air out and warm air in. He goes into a big discussion on the aerodynamic shape of his collectors, but the drawings he includes makes them look like just circular segments. You could almost just buy cheap venetian blinds, spray paint them black, and hang them upside down in the collector box and tweak the fin angle.

The second site, ... erview.htm, shows how to build an automatic drainback water heater for preheating the feed water into an existing water heater. It does use a small circulation pump but will passively empty the collectors each night so no need for antifreeze and no worries about pipes bursting. Their design has a hot water storage tank below ground level in a home crawlspace, with the collectors sitting on the ground. However, if you don't have a crawlspace you could just put the tank at ground level and raise the collectors a few feet to keep them above the top of the tank. With the tank inside the shop, any heat loss would just go towards keeping the shop warmer overnight. Great in the winter, no so much in summer :-). What I found most interesting was the construction of the hot water storage tank. Rather than buying a commercial tank and taking whatever dimensions you can find, you make the dimensions whatever is convenient for your needs, build it from a reinforced plywood box, and then use an EPDM rubber liner to make it watertight. No side or bottom penetrations to seal, the pipes go down through the lid. Simple and rugged. I think he needs heat breaks on his inlet and outlet lines, like used on a regular water heater, to stop the heat loss he was complaining about on the web site (just a loop that goes down and then back up would do it). You could make the storage tank somewhat bigger than a hot tank or the tank on a jet washer, and add a circulation pump and loop of pipe in the storage tank to circulate the hot water to preheat the hot tank or jet washer in the mornings so save $$ getting those going, and you could use the hot water for rinsing parts from either. In the summer you might even be able to heat the hot tank or jet washer completely with solar.

Anyway, just a couple of ideas for shop improvements that should pay for themselves in a year or three.