Outdoor wood boiler w/ propane tankless backup controller recommendations

atrufant73

Looking to redo a customer’s poorly installed OWB heating setup and re-pipe it with a propane back up. I have been reading the Bio-mass issue of Caleffi Idronics and as a plumber the piping is the easy part, but anything past wiring basic ZVCs/SRs Relays I am a little out of my realm as far as looking for a controller(s) to handle this operation, but I think I have an idea. This is what I am looking for this controller to do...
1. Primarily run the wood boiler, only kick on the propane back up when neccessary.
2. Outdoor reset
3. Make sure the tankless modulates correctly (0-10v signal?)
4. DHW input for indirect tank
In the Idronics magazine they mention an outdoor reset controller AND a delta T controller (I have never seen a delta T controller before) I think after doing a little bit of research I need a Tekmar 275 and that will solve all my problems but I would like to see what others have done and recommend.

motoguy128

Tankless cannot be used as a booster.  It must be in parallel. They are designed for high delta T. Most shut down when inlet temps are over 100f.  

Also is this well water?

Would be better to use a indirect and small inexpensive propane boiler as a backup.   Obviously more expensive. 

Other solution might be a 3 way valve controlled by aquastat.  Id the wood supply temp falls under 160 or 170f or some predetermined number the propane tankless takes over.   

GroundUp

Using a tankless is still poor practice, may as well leave it alone if that's the plan. What model OWB is it and what's wrong with the current installation? The vast majority of OWB are atmospheric/unpressurized and will require a heat exchanger to pressurize the indoor side, which I do not see in any of the drawings you show. Let's get some more information before you jump in with both feet. OWB make/model, current piping diagram with circulators, valves, and emitters labeled, and the ultimate goal with this job. As far as controls go, a simple aquastat on the OWB supply line as it enters the house to interrupt the TT on the switching relay or ZVC is all you need

atrufant73

This is what I’m trying to do. Its an outdoor unpressurized central boiler. Right now they heat 3 seperate buildings and they heat it all open to the atmosphere. Looking to convert one building with a plate hx and hopefully change the other building once they are happy with this install that I do.

atrufant73

This is the house that I am working in current setup. They don’t use the wood boiler for the hot water because they don’t know how to wire the pump and if it runs constantly how they have it then it pops the t&p constantly. 3 way zone valve to do the heating zone, but we are getting poor flow through the system for obvious reasons.

GroundUp

The T&P will not pop with 180 degree water. If it does, it is faulty. That is a typical DHW setup with OWB systems, but adding a Ranco or similar is easy enough. Long story short, a 24/7 circ series loop from the OWB to the DHW plate to the SH plate and back to the boiler is a given. Add in the LP boiler (not a tankless WH) with closely spaced tees as a secondary loop on the outlet side of the new SH plate so as to not backfeed the OWB unnecessarily (or reuse the 3 way to bypass the SH plate completely) and use a simple aquastat or Ranco style controller on the OWB supply line to the DHW plate to break the TT circuit to the LP boiler until temp falls below 130(ish). Break on rise, I believe they call it. That way everything will operate as normal with the OWB until the OWB temp being supplied to the house falls below 130, then the aquastat will make and tell the LP boiler to fire until the heat call is satisfied. When the OWB comes back up to temp, the TT circuit breaks again and resumes normal activity.