I don't see this being a practical thing to do. Lot's of work, very expensive for very little gain.

I would look for heat exchangers from old refrigerators, old air conditioners, car radiators to make solar collectors to heat up water and to heat up your greenhouse.

dcarch

dcarch,

Thank you for your input. Would you put this type up on the roof? They would block the sun light in the window boxes.

Eric

If you The Google 'solar hot water heaters', you will find hundreds of tinkerers doing the same thing - using the sun to heat hot water. Some of these are architects taking their ideas to the third world. IIRC there are several with the refrig heat exchangers, but mounted in a box outside. I looked at one for a hoop house project, but I had kid labor for free so used tubing instead.

Nonetheless, that design above doesn't have enough direct solar gain to work. I would take the box outside, insulate the heck out of it (where you are not that big of an issue), double-glaze it and make a nighttime cover. Then run your tubing/heat exchanger close together to make as much surface area and then out to the GH (well-insulated pipe). Return would have to be powered.

Dan

Dan,

Would you install the heat exchanger box on the ground in front of the greenhouse or on the roof? It would be harder to cover at night on the roof. I have the circulation pump already. 1" inline.

Without the heat exchanger.
Maybe someone can answer this. On the 40 gallon water heater label, estimates $416.00 a year to operate. This heater being hooked up to a closed loop system, would this be higher or lower. Seems like it would be lower, for your not adding cold water to reheat. Any Guesstimations?

Eric

All you need is to mount ~12" above benches for adequate head. You want gravity down, assist up. Your WH won't be pushing that much water. Much less to operate, and the return will be, as you say, warm. No guesstimate, sorry/

Dan

If you are going thru the trouble and expense of having solar hot water panels for the greenhouse, you may want to also have a by-pass loop to your house so that in the summertime you have hot water for your everyday hot water use in the house.

dcarch

dcarch,

That sound good too. I would have to research how to set up with a tankless water heater. I use a AquaStar on demand water heater.

Eric