Controlling wood boiler and a gas boiler - RAM

Richard Miller_2

I have a job with a wood fired boiler with a gas boiler for back-up. They inject into a primary loop. Out of the primary loop I have a DHW zone, a high temp BB zone, and an injection loop into 3 RFH zones. This injection is controlled with a tekmar 356 with outdoor reset. All zones are controlled by a self built relay panel.

Any ideas on how to control the boilers? I want to only bring on the gas boiler if the wood boiler is down... I don't want them both running at the same time. Wood boiler goes into a heat exchanger and will be on continious circ. So if it drops out and goes to gas, then HO fires wood back up I need it to switch back automatically.

It is my first time with wood boiler. I have 2-staged gas and/or electric but this is not really 2-staging.

Ideas please?

Thanks

Richard Miller

Terry

what i've used

I had a similar application whereas I used a Tekmar #150 Setpoint Control with the 071 sensor located on the discharge of the wood boiler.
If the Solid Fuel Boiler was fired, the 150 (which is set to Bang-Bang Mode, Heating)would sense the hot water and the NC contacts would open, shutting down circuit to gas-fired.
Once the Solid Fuel unit cooled, the 150 will close NC contacts (which switch on the gas-fired cicuit).

The same could probably be done with a regular aquastat (open on rise). Sense Temp @ Solid Fuel discharge and break gas-fired circuit if water is hot @ solid fuel.

Hope this helps

Terry

Richard Miller_2

thanks... I was thinking along the lines of an aquastat but like the tekmar idea too.

Terry

150 vs aqua

Nice feature on the #150 is that is has BOTH NC & NO contacts incase you need to switch on/off devices @ both ends (on solid & gas units)

hr

A solar differential control

works well for me. I like the Goldline brand, lot of adjustment and reasonably priced.

Bascially it brings on the gas when the temperature at the wood falls below the temperature you set.

Thre differential is also adjustable, and a digital display is available as an option.

Graingers has them in their catalog still. Find them online, also at Graingers.

hot rod

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Mark_2

Richard....


...I would suggest a 155 and two Relays coming of the Boiler Contacts on the 356. the 155 will check the water temperature in the wood boiler and if it is hotter than your system loop, it will cut out the Gas Boiler and use the Wood Boilers heat available. If the wood boiler is cold, the Gas Boiler would be fired. If you never want both boilers on at the same time, it would be nonsense to go with a two stage boiler control. Let me know, or send me an email if I can do something for you.

Check out the attached example, showing a different system control though! This is something I used on another, but similar job.

Regards,
Mike