Outdoor Wood Boiler and Electric Boiler Dual-Energy System Design

TheRadiator

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.

hot_rod

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

TheRadiator

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

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.

hot_rod

Info for sizing heat exchangers

https://www.caleffi.com/sites/default/files/file/idronics_29_na.pdf