Wood Boiler and Buffer Tank


Old 10-13-14, 09:44 PM
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Wood Boiler and Buffer Tank

I am in the process of upgrading my current 1 zone baseboard hydronic system to a 2 zone system(1 zone baseboard and 1 zone radiant staple up) heated by both an oil boiler and a wood boiler. I will be plumbing the boilers in parallel, as they are currently in series and that was just a quick fix. Anyway, I am confused about the following:

The indoor wood boiler is my primary heating method. It's a Thermocontrol 400 and I want to add a 100 gallon buffer tank to the mix. I have no idea how to control it though. Currently the wood boiler has a strap on Aquastat that turns on a circulator pump that just blindly pumps water through the baseboards, so I get a heated house. But I would like the wood boiler to heat the buffer tank water directly when there is no call for heat from the room thermostats, and then pull that heated water from the buffer tank when there is a call for heat. I can't figure out the electronics side of the equation - what kind of relay or aquastat or thermostat or zone circulators or whatever would know to pump hot water into storage when there's no call for heat, and then pump hot water out of storage when needed?

It's annoying now because since it's a pretty manual system, I have to know exactly what size fire to build so I don't over heat the house or freeze to death. I'd like the storage tank to prevent the overheating by absorbing the wood boiler heat when necessary.

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Old 10-14-14, 04:56 PM
Join Date: Jul 2009
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There are a ton of schematics for piping the system.
First off a double aquastat can be used to turn the pump off once the water temp drops below a fixed point.
A thermic valve will allow the wood boiler to reach proper temp before heating the buffer tank and it will also provide some boiler protection.
You could do a 3 way or 4 way valve and pump, or even variable speed mixing to heat the tank.
The better the control system, the better your system will work, there is no substitution for proper controls.
I make use of differential control a lot, so if the boiler is say 10 F hotter than the current tank temp, the system would activate the pump and send the hotter water into the storage tank.
You could add ODR on to the oil boiler (ensure boiler protection) and with proper placement of the sensor, you can trigger the oil boiler to actively top up the output of the buffer tank if it was not above your ODR threshold.

There are many very creative ways to solve this situation. Come down to what you wanna spend though.

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