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Outdoor Wood Boiler and Electric Boiler Dual-Energy System Design

TheRadiator
TheRadiator Member Posts: 12
edited January 2023 in Radiant Heating
In my previous thread, I got suggestions for my outdoor wood boiler with cast iron radiators, in a dual-energy system:

https://forum.heatinghelp.com/discussion/185787/outdoor-wood-boiler-with-cast-iron-radiators-inside-and-an-auxilary-water-heater#latest

Here is our current design:

Draft 1:


Please take a look at the whole design and let me know whether I'm on the right track.

Comments

  • hot_rod
    hot_rod Member Posts: 22,022
    Why the 4 way mix valve on the wood boiler..while it can be used for return temperature it seems like an $$ solution. It would require a valve, actuator, controller and a circulator.

    The electric boiler may have a minimum flow requirement. With only one small zone calling, you may not meet that flow requirement. Check the manual for guidance

    If you do need a circ dedicated to the electric boiler, best to pipe it as primary secondary

    A thought below. 4 circulators, the 281, P1 is both a protection valve with circulator in one assembly. Built just for wood boiler use.

    One circ for the radiators, one circ for the radiant with zone valves. I’d use something like a Grundfos Alpha for zone circulators. They will adjust based on zones opening and closing. No need for a pump on each zone.

    So the electric boiler is a primary loop, the zones are secondaries, everybody gets the flow they need.

    Missing is a boiler over heat dump zone. With some control creativity you could force on P1 and any zone if the boiler reaches maybe 190 f or so. Just dump that excess into one of the zones
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    TheRadiator
  • TheRadiator
    TheRadiator Member Posts: 12
    edited January 2023
    I appreciate your input.

    I have checked the manual. The electric boiler requires a minimum flow rate of 7 gal / min. I've adjusted the design accordingly with the primary-secondary loop and to accurately reflect the number of radiators in our house.

    I gave each in-floor heat zone its own mixing valve and dedicated circulating pump for optimal temperature control. The electric boiler delivers 85C on the coldest day for the radiators. The upstairs in-floor heat is just PEX-pipe stapled to the wood floor, and thus only works well with higher temperatures. The basement in-floor temperature will be maintained at 35C.

    I think it would be a great idea to use the concrete in-floor heat in the basement as a heat dump zone.




    Another question I have is, can the water in my indoor circuit reach 85C with a properly sized heat exchanger when the wood boiler can only supply a maximum temperature of 85C / 190F? I guess with enough delta t it should work...
  • hot_rod
    hot_rod Member Posts: 22,022
    Thats better.
    Here is the 281 assembly for the boiler to pump and protect it.
    https://www.caleffi.com/sites/default/files/file/01224_na.pdf

    Also manifolds with the mix valves built in, plug and play.

    You can size a heat exchanger to get within 3-5 degrees of each size. It’s called close approach sizing. It does increase the size of the HX of course.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • hot_rod
    hot_rod Member Posts: 22,022
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream