Another Wood Boiler Piping Setup

Paul Rohrs_4

Depending on the make of the wood boiler, it is PROBABLY an open system that would need to be isolated with a (Brazed Plate) heat exchanger between the wood boiler and the buffer tank which would then require another pump.


Regards,

PR

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Kevin_30

Take a look at this one.

Constantin

I don't like it...

... but then again I'm an engineer. The present setup is flawed IMO by the fact that the TRVs can stop all flow from the boiler to the buffer tank. If the buffer tank is intended to heat hot water for the house (as it appears to), then there is no way for it to accomplish that when the the TRVs are satified... no flow = no heat transfer.

Constantin

I don't like it...

... but then again I'm an engineer homeowner and things ought to be complicated! :-P

The present setup is flawed IMO by the fact that the TRVs can stop all flow from the boiler to the buffer tank. If the buffer tank is intended to heat hot water for the house (as it appears to), then there is no way for it to accomplish that when the the TRVs are satisfied... no flow = no heat transfer.

Have a look and a laugh with the stuff I cobbled together in my pre-coffee state this morning. Admittedly, it is more complicated than what you had in mind, but it ought to allow you to run the panel rads w/o issues, heat the IDWH, etc.

I presume that the buffer tank is large to really take advantage of the wood burning operation. Here, I have it act as the primary loop for the heating/hot water system. You'd have to hook up some differential controllers (like Goldline) to activate the pumps going from/to the IDWH and the Wood boiler while the panel rad pump could be run constantly or with the help of a thermostat.

If you want to eke out some efficiency points, you could put the panel rad loop on a 4-way or somesuch to make it cooler. The TRVs can handle pretty much any incoming heat, but the line losses will be lower if the loop temperatures are lower. Also note the addition of a PAB valve to bypass the panel rads if all TRVs are shut. That'll keep the circulator happy.

Kevin_30

Hi Paul,

no, this is a pressurised wood gasification boiler. So, no heat exchanger needed. Thanks though.

Kevin_30

Hi Constantin

Sorry, I left out some basic components such as a PAB so that if all the TRV's are closed, there will still be a constant flow thru the buffer tank. I like your setup but it does involve an extra circ and indirect tank. I am still not 100% sure how I want to pipe yet, still thinking. However, if I chose my last setup, how much heat loss do you think there would be from the unfired wood boiler? (thru the chimney)

Constantin

.. sorry, no idea...

... as I'm not an installer of these things, I have no idea whether or not they allow flue gases to exit the boiler when it's not in use. I would suspect less than 10% based on the little equipment AFUE data I see out there (difference between low-eff atmospheric vs. powered non-condensing equipment).

On many atmospheric gas boilers, flue dampers are offered as an extra to reduce stand-by losses. During the last energy crisis even some oil-based equipment was apparently retrofit with automatic flue dampers before people had to deal with the attendant corrosion/combustion/etc. issues.

If the boiler depends on a blower to get the combustion process going, then the chimney losses may be relatively low. In that case, it may not make a lot of sense to have a buffer tank - if the thermal mass of the boiler is sufficient on its own.

If you compare the heat loss and IDWH needs to the thermal capacity of the boiler (in BTUs), you can establish pretty quickly how often the boiler has to come on in a given day to supply the buffer tank. If your client wants to deal with few refills per evening, a large buffer tank may be required in addition to the boiler.

My boiler has a large water jacket, which makes it relatively efficient even though the single-stage burner is way oversized most of the time.