Consider a no-loss stack if possible.

The pictures I have seen of those assume the exhaust is exiting a horizontal roof, whereas my exhaust is going out vertically through a wall. Will this work for a vertical as opposed to a horizontal exit?

Thanks,

ken

I tried to roast a 1lb sample this morning and in mid-roast I lost control of the roast. The wind apparently shifted outside and the result was I could no longer figure out how much heat to apply to allow a steady rise in temperature without risking having the burner blow out. The result was a very irregular roast that I'm assuming is bad. I stopped roasting at that point.

I called the guy who installed the roaster for me (a gas appliance guy) and he suggested I call a specific local HVAC shop he turns to when he is confronted with difficult exhaust issues. He said they would come over to my house with a truck with the capability of bending sheet metal from the truck, making whatever modifications were needed on the spot without the need to go back to the shop. I expect to get this problem resolved this week, after which the roaster hopefully will live up to its specs and be able to roast any batch size desired between 6 oz and 1kg.

ken

Ken,

In theory the no-loss should work vertically but this may not solve your issues since wind seems to be blowing into your exhaust and creating the back pressure. A wind shield seems to be what is needed to protect the termination of your exhaust from the wind.

Hi Rob,

I think there are two issues. Issue number one is that the two elbows and length of hose make too much demands on the cyclone fan to overcome. In the best of circumstances, with a draft upwards on the ducting (mostly from heat building up from the roaster), the roaster is workable however does not evacuate chaff very well and is especially marginal for 1lb roasts where the trapped heat overwhelms the greens mass. When there is little or no draft from the ducting the roast becomes uncontrollable.

The wind is a second issue which makes the first issue worse (as it did this morning). The best solution is probably going to be to drill a second hole near the roaster and go outside directly with the ducting a much shorter run and with only one elbow. A wind shield on the end cap may help as well. I will probably need to use more heat input to roast after making this change, but I have a lot of heat potential available.

The tip off is that the evacuation of chaff is sub-par as presently configured.

Thanks,

ken

Room air pressure might be a factor too. A roaster in the next town has that problem sometimes when conditions are right, door and windows open or closed, as well as the exhaust pressure/winds/temp. issues. Even flue temp. can effect flow. Very much like keeping a good balance in a pellet stove for proper burn.

I looked at the exit location of the chaff cyclone and was a bit surprised that it has a side way exit. I forgot where I read it or from physics books regarding laminar flow, generally each bend reduces efficiency by about 30%.

The no-loss stack has to exit vertically. There is no cap to reduce back pressure. If the no-loss stack exit is placed horizontally, birds may nest in the opening.

Since you are having an HVAC professional over, also consider measuring the pressure or/and air speed with his/her instrument. Use these measurement and install a magnehelic or air speed gauge, about $USD100. This will be a much more precise measurement to control damper opening.

The sideways exit from the cyclone is a non-issue, if the point made was that this represents "the first bend." At the top of the cyclone is a squirrel cage fan, and with a squirrel cage fan the exit will be off the side if the fan is located on top (as it is here). Depending on where the roaster was located, one might be able to go straight out through a window or a wall, and there would be no bends.

I think that the force of the fan can handle a limited distance and ONE right angle bend. It might even be able to handle a short distance and TWO right angle bends. What it can't handle is the two bends and several feet of vertically pointed exhaust ducting.

I think I will end up with a single bend and then a straight shot out the wall. The piping will measure a foot or two, plus the one right angle bend. With that set up, the only issue that might present itself would be that the fan could then be too powerful for the system and could suck heat out of the roaster when the damper is set to go (primarily) through the drum. Some type of wind protection on the cap might be useful. I think that will not be an issue in my case as there is ample reserve heat capacity for roasting that I am not using.

ken

I had a very nice surprise this morning, I have just over 7" wc on my roasters gauge this morning. I did 3 roasts last night and was still only getting 5.2" wc, this morning I had some heater issues with my second floor furnace and low pressure to my gas stove top so I went to check the roaster and it had very low pressure. I then got the furnace to fire up and the stove burners returned to normal and now I have more pressure at the roaster then needed, I hope it stays this way, LOL. No evidence of the gas company being around (14" of snow last 20hrs and no tracks to my meter) so I have no idea what changed but it is a great start to the day. Time to see if this extra pressure let's me do 1kg with more control.

An HVAC/Sheet Metal company is coming out tomorrow afternoon to re-do my exhaust ducting. They had sent someone out previously to have a look at it and we discussed options in some detail. I also called Diedrich but they were not of much help. Diedrich tech support did confirm that my described "symptoms" of trouble doing small batches due to excessive heat, trouble with keeping the burner lit, and difficulty evacuating chaff during the roast were all highly suggestive of inadequate airflow through the roaster consistent with too much resistance in the exhaust ducting. As to what to do about it, they deferred to the local people helping me with this issue saying that airflow engineering was not their field . . . . .

After some discussion the HVAC company and I agreed that we could easily convert a situation with too little airflow into one with too much airflow; the cyclone of the roaster has a very powerful fan, and simply going straight out the wall as I had originally proposed would probably suck too much heat out of the roaster, creating the opposite problem to what I have now. So, we are going to tidy up the exhaust run by eliminating one elbow and softening the other one, plus will use double walled aluminum pipe. The aluminum inner pipe will heat up quickly and create a draft going outwards, whereas the current SS Armadillo hose takes forever to heat up, plus has an irregular shape. Finally, the termination cap outside will be a wind resistant one where the open surface spins around out of the wind, whatever direction it is coming from. There is no practical way to vent upwards out the roof as the roof is a flat one (with a membrane) and it would have to go up two stories. Anything going up alongside the house would be very ugly.

Unfortunately, this is going to have to be a trial and error fix, although I think the likelihood of success is very high.

ken