Design Review - Wood boiler with Oil Backup

[Newfiestang]

Folks, can some of the experts here please review this design and provide feedback. I am planning to replace my old conventional wood boiler with a new gasifier and integrate with my existing oil boiler.

I think this design will work but i am struggling with how to keep the oil boiler water temperature above 130 deg when the wood storage/boiler is above its setpoint and disabling the oil burner as my current setup does. With existing setup there is a circulator between the wood and oil boiler that is running continuously if wood boiler water temp is above 160 def. From what i can tell newer designs frown on this setup. I guess i could wire such that the wood boiler interlock logic allows the oil burner aquastat to remain in control but then the oil boiler aqustate will maintain the oil boiler min temp and call for burner to fire once in a while even if the wood/storage temp is above setpoint.

Anyway if the questions make sense please see dwg below and provide comments....much appreciated.

 

[Bad LP]

You close off the oil boiler flow when the wood boiler temp is proper. A simple zone valve closes any possible water flowing thru your oil boiler.

When the reverse is happening (wood cold/oil needed) it reverses.

I’m a far cry from an expert but have just a system. 100% seamless operation from LP to wood then back again. Weekend home designed to move in 100% of the time.

 

[Newfiestang]

Yes as I stated above I know how to disable it but if I do that the water temp in the oil boiler will eventually drop to ambient. Then if the wood temp drops and the oil is called there will be a long delay before oil boiler is back to usable temp. I am thinking maybe set it up as a zone and either with a timer or temp sensor have that zone cycle water through it from wood boiler storage.

Does this sound reasonable

 

[maple1]

An important consideration may be if your oil boiler can work as or is a cold start boiler.

 

[hobbyheater]

Your oil boiler what is its water capacity , cast iron or steel construction and how much does it weight ?

 

[Newfiestang]

An important consideration may be if your oil boiler can work as or is a cold start boiler.

It cant unfortunately thus my deli-ma

 

[Newfiestang]

Your oil boiler what is its water capacity , cast iron or steel construction and how much does it weight ?

Approx 15 gal, steel, and weighs about 350 pounds. Its an older version of the one linked below. Does not have the warn weather shutdown option as the new one states.

Caprice | NTI Boilers

ntiboilers.com

 

[Newfiestang]

Like I mentioned I guess I could just leave it in operation and just let its aquastat maintain min temp, think its 130 deg. It does this now anyway as its equipped with a DHW coil but I am planning to add an indirect DHW tank when i install the new system so the coil will be capped off I expect.

Actually just thought of something. If I dont need use the DHW coil any longer i guess i could use that coil connected to a zone of the supply manifold and just cycle water through it tpo keep the temp up. So I would need some sort of temp sensor fixed to the oil boiler, whats out there that will make this work?

 

[peakbagger]

The payback is definitely diluted with lack of cold start capability.

if you have several hours this course may be worth viewing.. It free and has a lot of info.

Hydronics for High Efficiency Biomass Boilers

This course examines best practices for combining modern, high efficiency wood-fired boilers with hydronic distribution systems.

www.heatspring.com

 

[hobbyheater]

When oil was my backup I had the oil boiler also heat the the storage tank ( 1,000 gallons)with some very impressive savings . An aquastat was plumbed into the top of the storage tank which turned the oil boiler on at 140 F which would run until the high limit was acheived then the oil would shut off.

 

[Newfiestang]

When oil was my backup I had the oil boiler also heat the the storage tank ( 1,000 gallons)with some very impressive savings . An aquastat was plumbed into the top of the storage tank which turned the oil boiler on at 140 F which would run until the high limit was acheived then the oil would shut off.

Never thought of that but at first glance it dont seem feasible but maybe im wrong. Furnace oil is about 95 cents a liter here where i live in Canada.

 

[Newfiestang]

The payback is definitely diluted with lack of cold start capability.

if you have several hours this course may be worth viewing.. It free and has a lot of info.

Hydronics for High Efficiency Biomass Boilers

This course examines best practices for combining modern, high efficiency wood-fired boilers with hydronic distribution systems.

www.heatspring.com

I've started reading that but I find most of these training courses get over the top sometimes for most users. I'm a instrumentation and controls guy and can follow most of the principles but some of this is deep.

 

[hobbyheater]

Never thought of that but at first glance it dont seem feasible but maybe im wrong. Furnace oil is about 95 cents a liter here where i live in Canada.

I,m also in Canada Northern Vancouver island BC .
My backup is now an electric boiler with a manual switch over, the oil boiler got used so little that my furnace oil started to gell .