Make-up air for roaster - Page 2

Discuss roast levels and profiles for espresso, equipment for roasting coffee.
Milligan (original poster)
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#11: Post by Milligan (original poster) »

PBJ wrote:I'm saying that you have a 2" combustion air intake for your furnace. I have a 4" intake, which is 4 times the area of yours. If your furnace works with the 2", then 4 times that area will supply enough for my roaster. Again, the combustion air intake is for resupplying oxygen that is used when gas appliances are used. It's not just replacing the air that is going out of your exhaust. It is always supplying air, not just when the burners are running.
We are talking about two different types of systems. You are talking about an older style furnace that uses interior air for combustion. My furnace is a high efficiency unit, it directly draws outside air that is closed to the house, uses it for combustion, and exhausts out. My intake is not used by anything other than the furnace, it is a closed system. Anyone with a heat pump would not have a combustion air supply either.

In the video I posted, he shows readings with different hole sizes. The passive hole needs to be sized to the roaster. In his case, he was venting using an 8in duct so he would have needed the equivalent to 3x8in passive openings to hope to get the pressure in the house within code as read by his meter. They opted for a powered unit that turns on when the vent duct turns on to reduce the hole size. In my case, I use a 4in vent duct for my cormorant. So I'd need a bare minimum of a 28" window cracked roughly 1.5". Pretty easy to do.

FWIW, my house was built in the 80's so it is plenty leaky enough for this to mostly be an unnecessary exercise. However, having the make-up air flowing across my basement room from the far window does seem to have its benefits rather than finding its way through top plate holes, window seals, recessed light openings, etc.

Milligan (original poster)
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#12: Post by Milligan (original poster) »

Capuchin Monk wrote:Passive method can work better if the intake opening and louver is very close to the exhaust hood but that would require opening up the exterior wall of kitchen area which is not feasible for most homes.
That would be a very nice solution to keep the exterior air moving across the work area instead of mixing with the interior air, much like a lab fume hood works.
Capuchin Monk wrote:Remember this post? :arrow: My 5kg USRC Roaster, I took the the plunge :wink:
I have more time this morning to discuss this. As was noted in the thread, that method doesn't work very well with my roaster which uses an atmospheric burner. The burner is not in a closed system with powered air flow. The gas flow draws air through the mixing tube to be combusted at the burner. I am not well versed enough in burner design to know how preheating the air drawn into atmospheric burners would have an effect on burner efficiency. Separating the air drawn through the mixing tube and the preheated air being drawn around the burner may be a solution but likely very hard to implement on a roaster not designed that way from the start.

I have given thought to using a heat exchanger to preheat the makeup air during the winter season to save on HVAC. Having the make up air very near the bottom of the roaster would help draw the exterior air through the unit instead of mixing with the interior air as much but would reduce consistency unless the air was somehow treated to be the same temperature and humidity year round.

Capuchin Monk
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#13: Post by Capuchin Monk »

Milligan wrote: I have given thought to using a heat exchanger to preheat the makeup air during the winter season to save on HVAC. Having the make up air very near the bottom of the roaster would help draw the exterior air through the unit instead of mixing with the interior air as much but would reduce consistency unless the air was somehow treated to be the same temperature and humidity year round.
In that older thread, I posted a link to furnace heat exchange pipes. It would help the heating efficiency of your larger roaster during winter months if the incoming air is warmed up by exhaust air via heat exchanger. Other heat exchanger may or may not be rated for the exhaust air temperature of your roaster. Something to look into when implementing it.