Evacuated tubes to radiant & hot water?

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Bloemie

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I am considering using evacuated solar water heating to be my primary radiant floor heating source and using electricity to be the backup up near lake Ontario Zone 5. I prefer the idea of closed loop, in the event something freezes. The house will be on slab and I am planning to add concrete block walls for extra thermal mass and considering a cistern for added heat storage.

My question is more about
1) Would you use 1 closed loop for floor and solar or split it into 2 loops with heat ex-changers.
2) If I fed this through a Hot water tank heat exchanger, the temperature would be low for house hot water. What would be my options to modulate one section as hotter in a closed loop system, so that when the solar heated evacuated water heats the hot water tank at a higher temperature than the floor at a lower? I cant turn off the flow to the floor if the solar water is hotter than the floor system requires and I need to bypass the water heater if the temperatures are too low.

Suggestions?
 

Fitter30

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Think i would pipe the system like a boiler system with two solar heater tanks. One for dhw the other for floor heat. Controls for two control (zone valves) valves with dhw priority. Injection or a mixing valve for temp regulated floor temp. Worked on one evac tube system 15 years ago 50°f overcast 160° water. A drain down system needs to be incorporated with tube system to keep it from overheating the water. If using heat exchangers still need tanks for volume or the system would never water temp under control. Bigger the tanks easier to control. Boiler could be added with control valves to bypass tubes or boiler. Someone that is program savey could design a program to operate all the controls. This won't be a inexpensive system.
 
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Bloemie

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I was hoping I was missing something easy, but the variable temp of solar evacuated tubes and the need for a backup heat source makes it a tough business case for "Free and Friendly" heat.
 
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