Buffer Tank Piping

Unknown

would a simple flow control be simpler/more reliable than a completely passive piping detail?

Eric Johnson

Buffer Tank Piping

I was looking at another guy's wood gasification boiler buffer tank design recently. It's a nonpressurized tank with copper coil heat exchangers immersed in the tank. When the hx supplies and returns come out of this tank, they hook straight down for about 2 or 3 feet before going back up to the supply and returns from the boiler. It's a U-shaped route. He says this is to prevent thermosiphoning.

Pardon my ignorance, but I don't really know what thermosiphoning is, although I gather it involves hot water convecting or otherwise moving where you don't want it to go.

If that's the case, wouldn't a simple flow control solve that problem?

Eric Johnson

I don't know.

Let me rephrase the question: I'm about ready to pipe my own tank up. Since I already have flow controls on the lines going into the hx units, do I need the fancy piping scheme?

Are you suggesting that it's a more reliable way to get the job done?

Unknown

depends on the flow control I suppose. Thermosiphoning can be slow enough not to trigger a swing check's action, for example. A spring check induces resistance you don't need but might be adequate.

You can be pretty sure pipe isn't going to stick open or closed though, so I'd call it pretty reliable long-term.

Eric Johnson

What I have

Is one of those standard red cast-iron flow controls on the 1" line and a circulator with an integral flow control on the 3/4-inch line.

Sounds to me like you recommend the low-tech approach.

Unknown

Well, you can't flow-check in both directions. Thermosiphoning, on the other hand, will go in any direction it can. If you have two pipes rising out of your stored heat, either one can thermosiphon.

So the heat trap method is passive (can't fail), simple, cheap, and works in both directions... I would endorse it if thermosiphoning is a concern, yes.

Eric Johnson

Thanks for your help, Rob.