Ducting & set up for a Cormorant

Discuss roast levels and profiles for espresso, equipment for roasting coffee.
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#1: Post by NH »

I'm on the waitlist for a Cormorant, should come up sometime in Feb 2023. I'm brand new to coffee roasting but like to fiddle a bit with things. I don't worry too much about a perfect cup of coffee and generally enjoy the process far more than the outcome.

I've been watching my buddy roast on his Cormorant to get an idea of what it entails. While it's probably a little more advanced than I can handle well right now, I'm happy to grow into it.

Have been thinking about where I'm going to put the machine and have settled on the mud room. It has a door out to a covered porch and used to have the exhaust duct for our old water heater (out through the ceiling and straight out of the roof) before we got a tankless.

One of the questions I had was about getting all the exhaust out of the roaster and out of the room.

In my case, that'll be up through a duct through the ceiling. This means 1 right angle and then about 8, maybe 9' including punching through the roof. A secondary exhaust fan seemed like the right way to go about it, with a bell hood positioned over a right angle exhaust coming out of the roaster and a filter between hood & fan.

I wanted to know what size exhaust fan to look at, so I picked up a DAFM3B and measured the CFM on my buddy's machine at a few different settings. I thought this forum might find the measurements useful.

Here it is as we're warming up the roaster.

The 30 second average I pulled was 37, but we saw variations up to 10 CFM more.

Here's the roaster fan on full blast, flower open, just at the drop:

It quickly went down to ~77 CFM after that during cooling.

Hope you find this useful!

Rock on,
Through hard work, victory!


#2: Post by Milligan »

I did not like the accordion tubing that is provided. It would be very difficult to clean and I imagined it would be inconsistent if it was ever bumped or moved. As you found, changing the layout could dramatically affect your roast profiles. Not something I wanted to mess with when moving the machine or disassembling for cleaning.

I switched over to hard pipe. I found everything needed for around $10.

I set up a little board that can be removed from the window in under a minute. I wanted a non-destructive way to vent and this worked out well.

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#3: Post by hankua »

Your idea sounds pretty good, either 3" or 4" with an inline fan from amazon. Mounting the fan near the ceiling rafters would probably work better. A rain cap on top, the only issue I could see are possible wind gusts; one reason to get the fan closer to the roof. I'd start out with a basic no-frill inline fan, and not worry about CMF.

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NH (original poster)

#4: Post by NH (original poster) »

Right on, thanks! Assuming the converter from the oval exhaust to round pipe was something standard?
Through hard work, victory!

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NH (original poster)

#5: Post by NH (original poster) »

Got the Cormorant in and wanted to satisfy a curiosity about rigid vs flexible duct. Did a quick video which you can see below. If you're a numbers type, here are the 1 minute test results from 16" of each type of duct Happy to test out other variations if that's of interest.
๐‘๐ข๐ ๐ข๐ (๐ฌ๐ฆ๐จ๐จ๐ญ๐ก)
Avg 58.9 cfm
Min 55.0 cfm
Max 61.8

๐…๐ฅ๐ž๐ฑ๐ข๐›๐ฅ๐ž (๐œ๐จ๐ซ๐ซ๐ฎ๐ ๐š๐ญ๐ž๐), ~๐Ÿ•๐Ÿ“% ๐š๐ฌ ๐ฆ๐ฎ๐œ๐ก ๐š๐ข๐ซ ๐ฆ๐จ๐ฏ๐ž๐
Avg 44.3 cfm
Min 43.8 cfm
Max 44.6 cfm
Through hard work, victory!

Capuchin Monk

#6: Post by Capuchin Monk »

Of course the shape of surface makes a difference in wind velocity. So do bends & curves of duct. Have you seen the Mythbusters episode which they did the air resistance comparison of smooth surface vs golf ball surface? They tried it on a car traveling at # MPH and it did make a difference. :idea:

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NH (original poster)

#7: Post by NH (original poster) »

Oooh, I haven't seen that one. Yeah, I should have pointed out that shape of surface has an effect here. My main takeaway was that you just can't use all the air you've got available if you're running with flex duct. I didn't think the difference would be so drastic though; 75% of air at just 16".
Through hard work, victory!

Capuchin Monk

#8: Post by Capuchin Monk »

NH wrote:Oooh, I haven't seen that one.
Here it is.
I didn't think the difference would be so drastic though; 75% of air at just 16".
There will be less resistance if the flex duct is stretched (pulled) out so that the internal surface shape is closer to straight. Interesting thing is, larger diameter of duct doesn't increase exhaust flow efficiency linearly. I've seen a hot rod car show which they measured the CFM of exhaust headers of increasing diameter. At about 3" diameter, it was less efficient than 2.5" diameter. Given that those are for exhaust of much higher temp and velocity so they may not apply to coffee roaster exhaust but never the less, it was an interesting data. The host of that show said, bigger isn't necessarily better and the co-host said, tell that to your girlfriend.


#9: Post by Grant »

Moving air has interia. When the diameter increases beyond a certain point, you lose that inertia (or make it less efficient). That said, it can be a good thing OR a bad thing depending on your application.

For example, in vehicles, some air intake designs use the inertia of moving intake air to "ram" more air into the cylinder, therefore getting more combustion.

The other thing to consider is that a long vertical exhaust pipe filled with hot air will also create a pull on intake air from the bottom end independent of the fan...this may be desirable...or not. You may want ONLY the machine/fans to control the airflow, not introduce another factor? Perhaps it could remove heat from the roaster you do not want to happen?


#10: Post by Milligan »

Thanks for testing those two pipes. The inconsistency of the flex was my biggest concern. Too many variables. Pulling it taut can help but then you get into: how tight? I moved it, is it as tight as last time? Does it relax over time, if so how much? Is the bend I need the exact same angle as last time? On and on. Too much that can influence the roast. A rigid pipe is not only cheap but maintains its shape and is easy to clean out. Not to mention the better flow if needed. The more variables we can control for the better when roasting.