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Off Grid Heating system

I'm designing a heating system for my soon to be built house, all will be in-floor, Staple up (thick AL plates) in the first and upper floor, in-floor in the basement.  system will be solar assisted with the backup a water heater thru FPHE.  I'm thinking about designing the entire system to operate on 24 VDC.

 there would by necessity be no outdoor reset, unless someone knows of a non-electric or DC capable resetting 3 or 4 way valve. a capillary-operated outdoor reset 4 way valve would be top notch for this application.

the system will be as follows: high temp of 100 supply temp supplying the upper floors exterior rooms, (house heat loss is about 12 BTU per SF at design temp) low temp of 85 feeding the slabs, and the bathroom floors (both bathrooms are very low heat loss, minimal exterior walls.  Zoning will be accomplished with wax cylinder operated zone valves and loop actuators.  System head loss will be about 8' at highest with 3 gpm.   I can build the DC relayboards to run the zoning and circs.   the domestic water would be circulated thru the FPHE by either a DC circ or an AC circ (because the water heater won't fire without AC anyway.) but I'd be able to operate off the heat stored in the tank, and what's picked up off the woodstove.

the solar side will be an 820 Gal non pressurized tank fed by 8 4'x10' collectors (PV powered loop) and a woodstove coil (definitely powered by a DC pump.) 

I would be using a PV panel on the roof to keep the batteries topped up, with an automatic charger if necessary. 

The big questions are: Has anyone out there done this before? specifically running the actuators on DC? 

does anyone know of a non electric or DC capable 3 or 4 way mixing valve that would do ODR?  I'm not married to ODR, as most of the above grade floors are really low mass, and the water heater will be firing at the same temp and rate anyway.

I already have the heater.

I'm considering the Laing D5 strong for circulation duties if I go the DC route.

This is one of those experiments that we do on ourselves, but not anyone else.  and if worse comes to worse, I can re-use the equipment and do AC.

thanks for your insights,

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