Add on Wood Boiler

Rob_36

I’m adding a gasification wood boiler, a BioMax 60, and hot water storage to our hot water heating system. The existing system is a Buderus oil boiler with indirect DHW, cast iron base board zones, radiant zones and Tekmar tn4 controls.

I put together a rough diagram of how I think this would look. A brief description of how I think the control logic would be follows:

When wood boiler fires, wood pump is on.
If no call for heat, 3-way directs to storage.
When there’s a call for heat, if storage temp > primary loop temp then storage pump on.
If storage temp < primary loop, then 3-way directs to primary.
If boiler temp drops, then oil boiler fires for heat to primary loop.
Oil would only supply to primary, not to wood boiler or storage.

Does this logic sound correct? Does this piping layout allow this? Do you know of tn4 controls for this type of setup? I've talked to Tekmar's tech support a few times and there didn't seem to be an obvious answer. I just sent them a diagram, so I'm hoping to hear more on Monday. Any thoughts would be appreciated.

Thanks, Rob.

hot_rod

here is how I piped mine

I used a series of setpoint and differential control to turn on and off various components.
Be sure to size the expansion tank to all the volume and temperature swing!
And a means to watch boiler return temperatures. both the wood and oil need 140F return temperatures. this is critical if you have a large buffer tank that you draw way down, temperature wise.

hot rod

Rob_36

Buffer Tank

What do you have for a buffer tank? Is it pressurized? Your diagram shows the return to the tank going to the bottom and running across. Is that accurate? Is the horizontal run like a manifold with multiple outlets?

When you charge the buffer tank you would run both (wood and tank) pumps?

Thanks, Rob.

hot_rod

I used a 500 gallon

retired LP tank. It is a pressurized tank. I built a dip tube with a curve to better mix the tank.

I used a setpoint control that fires the bufffer tank circ when the primary loop hits 140F. 20 degree delta t. My boiler has a protection feature built in that stops the boiler circ until the boiler reaches 140. simple but effective. ideally a delta T circ would be more efficient.

I'd like to upgrade the system with all ECM circs for more control and less power consumption. Be nice to run it off a battery bank in the event of an extended power outage. a few ECMs would slash my circ power consumption.

I'd like to find a more intergrated control instead of the multiple pieces I have. Be nice to leverage a 60 degree delta t from the tank.

I would also like to dump some solar into the tank.

The "ideal" control logic still eludes me. tekmar did send me some possibilities. Still multiple controls.

A clever fellow, like Kal could probably build and program a PLC control to do everything just perfectly. That's a little beyond my control knowledge.

The HBX folks sent me a demo HBX 1000 control that may be an option. I'll try it out this season.

hot rod

Joe Billow_6

Hotrod,

I know a really good PLC guy he would jump at the chance to do something like this. How do you do the circle primary piping? It looks really cool.

mtfallsmikey

Hey Rob:

don't know your location, but am curious as to which dealer you got yours from, and are you installing indoors or in a building outside?

Rob_36

I'm in central PA. Bought the boiler from New Horizon in Sutton, WV. It's similar to the EKO line. Installation is indoors (basement).

Do you own or have you installed gasification boilers?

mtfallsmikey

Rob:

No, I have not installed any gasification boilers, but installed a bunch of 1st gen. wood boilers back in the '70's...what junk they were! I'm looking to do this next year, but am starting to plan now.

Rob_36

Nice

Nice tank and I agree with Joe, the primary loop looks sharp. I see some blue insulation board. Do you surround the tank with it?

I was a little suprised there wasn't a more direct answer to the controls. This type of system didn't seem that uncommon. I'm still hopeful that I can work with tekmar and come up with something that will work nicely with the current tn4 422.