About time I posted my passive solar hot water heating system up here.
The core of the system is the tank. I framed up the sides just like standard 2x4 rough construction. The interior dimensions come out to be 3'x4'x4'. It's all marine treated lumber, built for the long haul. Inside the construction is 1" foil faced foam sheeting, then an EPDM pond liner. The lumber side of things is insulated with fiberglass insulation, just like a home. (excuse the mess)
The tank is filled with water just for heating purposes. I don't drink it or bathe with it- I filled the tank years ago and there it sits. The top is covered with a piece of plywood, a layer of 2" foam and wrapped in more rubber pond liner. That water gets pumped up through some panels on my roof:
There are 4 panels, 8'x4' each, for a total of 128 sq.ft. A small pump circulates the water up through the panels through 1" PEX. Here's the control system:
There's a sensor mounted to the panels on the roof and when the panels are warmer than the water in the tank the pump will turn on. The whole system is sloped at 1/2" per foot so that when it is not pumping the whole thing will drain back into the tank (important feature in cold winter climates). I have never had any freezing issues; the PEX lines to the roof are wrapped with that foam pipe wrap and it seems to work just fine.
So, that's the core of the system. From there I have a 100' roll of 1" pex that sits in the tank and that is what my well water goes to in order to get hot. By the time it passes through that 100' roll it will be the same temp as the tank water. This works amazingly well. Most of the year my pumps shut down when the tank hits 120*. It can heat hotter, but this seems to be the right balance for my system. If my tank hits 120, I can still depend on comfortably hot water for several days without sunlight, still in the 110* range. If all else fails , or if there is a long period of no sun, the output from the 100' pex heat exchanger passes through a tankless water heater.
The beauty of this is that the tankless heater is programmed for 107.5* and only turns on if the water temp is below that. If the water is 106* it will heat the water to 107.5*. If the water is 108*, it doesn't run.
I have the option to circulate my tank water through my floors, but I don't do it very often. It takes a lot of heat out of my tank by trying to heat my floors. I originally installed this system to heat my floors but once I discovered the beauty of the domestic water heating I pretty much just use it for that now. The newest addition is RMH option, but we'll see where that goes.
I can't take any credit for this system, Gary Reyes is the mastermind behind it. He outlines his build explicitly on his site: