barometric damper/outside combustion air on gasifier?

[pybyr]

In the recent other thread about putting examples of gasifiers on YouTube, when I looked at Hansson's from Scandanavia, I noticed he had a second video, and it appears to depict a chimney draft regulator/ barometric damper installed in connection with his gasifier.
See:
http://www.youtube.com/watch?v=cEycuK_9Zb4

From prior projects I have done, it's always been my understanding that USA codes and practices say that a barometric stack damper is a total no-no with any solid fuel appliance.

I happen to live in the relative boonies where "the only mandatory code is my own judgment" so I do not have any official worries, although I do like to design and construct carefully and conservatively, especially when it comes to anything relating to fire or exhaust.

But Hansson's video has me curious. I know that the basic goal of a barometric damper is to avoid situations where there's too much draft "pull" from the chimney in a way that would draw the combustion through the heat exchangers more rapidly than the heat can be efficiently extracted. It makes sense to me that this could be advantageous with a gasifier just like on an oil burner.

Any thoughts on whether it's sensible to consider a barometric stack draft control on a gasifier?

While I'm asking about such things, I also have been wondering about pros and cons of rigging an outdoor combustion air supply to feed the blower fan on a gasifier. I know that many of the more modern high efficiency fossil-fueled heating devices are designed and installed this way, so that combustion air can be obtained without creating negative pressure in the conditioned space, wich would then draw in drafts of cold air elsewhere. As far as I know, none of the gasifiers are built with this "outside air" included, but from looking at a couple of them, it doesn't look like it'd be rocket science to adapt or fabricate an arrangement by which the blower could draw from a pipe to the outdoors, rather than drawing from the "room" around the unit. This crossed my mind in connection with the stack damper, as my understanding is that "outside air" arrangements also decrease the variations in chimney draft (because both intake and exhaust are coming from outdoors)

Thanks all for any input

Trevor

 

[pybyr]

yeah, that, plus risk of spillage of combustion products, is why I thought they were such a no-no on any wood appliance, until I saw the one shown in Hansson's video. A gasifier, run properly, should have almost nothing to create a chimney fire, but???

 

[2.beans]

i use a barometric damper on my seton boiler. definitely helped my draft issues, and wood consumption. also it does let a chimney fire rip.

 

[WRVERMONT]

One possible downside to a outside air supply could be that this air would on occasion be very cold, thus not aiding proper combustion. This may not be much of an issue with some set-ups.

 

[jebatty]

A gasifier should be able to be setup so as not to need a barometric damper (in addition to other reasons not to use one). It took me quite awhile last fall to accomplish that, through experimentation, with my Tarm. Combo of factors, including 27' chimney, apparent very good roof/surrounding area conditions for good draft, and burning dry pine. I was able to adjust the forced air fan damper control to bring the temp down, and then added the home-made chain turbulators which got me to a good range, given my conditions (400-500 generally). I also put in a draft fan speed control, but now generally do not use it as other adjustments result in proper draft.

I briefly used a barometric damper in this process, and while I cannot say that it did not help, its operation with the gasifier was a little unpredictable. Also, I just couldn't see sending inside air up the chimney and loosing that heat.

 

[RubyDoo]

The Caddy EPA (hot air gasifier) I just installed REQUIRES a barometric damper. Notably it has no draft blower, using passive draft only.

Remember that your house has to be pretty tight to make combustion air supply an issue. That's why I am adding a wood burner now in my huge leaky old farmhouse ... I can burn a bunch of wood but I can't afford to replace all the windows yet! Assuming your house is tight, you could avoid the incoming combustion air from stealing house BTUs by emptying its duct close to the furnace intake without connecting it, and dampering or arranging the ductwork to only allow cold air inflow when the room has negative pressure. I have seen diagrams where the ductwork has a trap-like bend to stop the cold air, and others where the intake dumps into a box which holds the cold air like those open freezers at the grocery store.

And to complicate the question, where do whole-house air exchangers fit in the picture? These are those wonders that swap inside air for outside air constantly while recapturing the BTUs in the transfer. When a furnace (or vent hood or bathroom fan or whatever) runs, do they take in more air than they expel? Many new tight homes have these, and some communities now require them in new construction. If you have one, then combustion air source seems moot.

Good luck playing with fire!

 

[pybyr]

I confirmed with Econoburn's tech dept. today that they definitely and strongly recommend use of a swinging-type barometric damper.

Like Jim, I don't like the aspect of the damper's sending heat up the chimney, especially when the gasifier is done with the burn; still thinking of whether a motored damper between the barometric damper and the main flue pipe, with appropriate switches/interlocks, might help with that- but also not sure it's worth the cost and complexity.

On Split & Conquer's other questions about the air:air heat exchangers for modern "tight" houses, well, I, too, have an old farmhouse, and although I've done a lot to insulate and tighten it up compared to how I found it (when winter winds blew, you could distinctly see signs of a breeze indoors), I am nowhere near the risk of "too tight" - so not a candidate for one of those units. But my folks super-energy-star rated house has one of those air:air heat/ air exchange units. As far as I can tell, it does not have any "active" means of ramping up when something in the house (like a bathroom or range fan) expels air, but it seems to me that extra air will inherently be drawn in through the exchanger's outside intake, just because of pressure differentials.

 

[jebatty]

I don’t like the aspect of the damper’s sending heat up the chimney, especially when the gasifier is done with the burn; still thinking of whether a motored damper ...

You shouldn't have a problem when the burn is done. The damper will control air during the burn, likely admitting air to reduce draft to slow down high burns, and likely doing little towards the end of a burn. The damper is normally closed, and opens only based on burn conditions.

 

[DaveBP]

I, too, was tempted to plan a closed combustion duct coupled to the draft inducer fan on my Tarm. On closer inspection and with a little thought (little goes a long way) I came to the conclusion that the air intake path through the slots in the cabinet help cool the control panel instruments and it would be more prudent to simply duct in outside air adjacent to the air intake slots in the cabinet and call that close enough. My house is still under construction and it will be tight enough to need outside air brought in but I don't want to do any research on the temp limits of the control panel.