Behmor exhaust modification

Discuss roast levels and profiles for espresso, equipment for roasting coffee.
looking_afar
Posts: 4
Joined: 9 years ago

#1: Post by looking_afar »

I've been roasting a lot on my Behmor (I've roasted more than 70 kgs), and since I've been roasting indoors, the smell and the smoke became a real problem. My idea was to improve Behmor's vent system and to get the smoke out of my balcony.

Here is what I came up with:



I took away the diffuser and connected the tube directly to Behmor using it's own screws.


This is a standard 100mm aluminium vent tube, used to pump the air out of the kitchen. I've also attached a standard vent fan to the tube.


Obviously, the connection could have been made better and the tube could have been smaller, but I wanted to test the idea before doing something expensive and this was cheap enough solution to try.

The results I've got after assembling this monstrosity were quite interesting.

Firstly, this mod greatly reduced the amount of smoke (and smell) that were leaking in the air.

Secondly, since the fan is quite powerfull, keeping it always at high speed sucks a lot of air out of the roaster, which prevents it from heating the beans well. But it also could be used to slow down the roast, which I ended up doing after some testing. Basically, I either turn the fan on for a few seconds every 10-15 sec after the first crack started or just leave it working. Since the heating elements still heat the beans despite great airflow, it's quite difficult to stall the roast even with this powerfull fan. I became close to baking beans (the snaps became very quiet) only once during winter when the air was quite cold and I kept the fan working for about 30 second after the 1t crack started.
Being lazy, I still haven't bought the dimmer to control the fan speed, which I should've done a long time ago.

There are some problems with this mod, though, which are worth mentioning.

Actually, the diffuser in Behmor is used not only to diffuse the hot air, but also to reduce the airflow. The turbine inside the roaster (which turns on after 2/3 of the roast when the afterburner kicks in) is quite powerfull and removing the diffuser will increase the airflow a little bit. But since the vent tube is quite big and long enough, it reduces the airflow quite a bit which leads to higher internal temp reading (when you press P1 during roasting, it displays unconverted internal temp reading from the thermocouple). So, for example, if before the mode 1t crack with a 300g batch started near 1.17 P1 reading, after modding it starts near 1.25. Unfortunately, I haven't noticed whether P2 temp reading changed (which displays exhaust temp). My guess is that it didn't change much.

The second problem which this mod led to is that because of the size of the tube, some air is pushed out of the side panel (where the cooler is) insted of going into the tube. So, ideally, there should be a fan in the tube always (or almost always) running at very very low speed to help suck the air out of the Behmor's exhaust.
Also, when you hit the cool button and turn the vent fan on, it does not suck all the air that cooling turbine pushes inside the roaster, so some smoke still ends up going through the Behmor's door. I think that either the fan should be more powerful or the exhaust hole inside the roaster (where the second cooler is located) should be covered somehow.

Since the mod modifies the amount of air that goes through the afterburner, I think it can affect it's work and even burn it out. I did notice an increase in smoke after installing the mod, but I did run an empty 1/4 cycle with the vent fan working 2/3 of the cycle once, so it could affect the afterburner somehow, I don't know. So if you are going to do something similar, beware.

Unfortunately, I don't have a thermocouple to connect to my PC and share some profiles with temp reading. I am waiting for my Center 302 to arrive, so maybe I could do some data logging with Artisan then.

ira
Team HB
Posts: 5497
Joined: 16 years ago

#2: Post by ira »

That tube is about 5 or 10 times the cross sectional area of the exhaust from the Behmor so it should not be a restriction unless it's really long. I do notice that it goes down and you're pushing hot air which want's to rise, possible causing back pressure. Also, if the fan your using is turned off it might also cause back pressure. Try making sure the exhaust tube is sloping up the whole way from the roaster to the end and try getting rid of the fan. You might find it works a lot better that way. Of course I might be wrong. Smoke coming out of the right side panel would seem to imply there is quite a severe restriction in your ducting.

Ira