|
Post by peterberg on Jan 11, 2016 1:53:04 GMT -8
The flue is made from cardboard which was used to mold the cob without straw. Inside the flue it isn't perfectly smooth because where I connected different cardboard tubes there is a rough area. Do I understand correctly the cardboard flue is still in there? If positive, there won't be any heat transfer from the cardboard to the cob. In case the tubes aren't in there anymore, is the cob dried out thoroughly? Fifty percent of the times the stove isn't running well it has something to do with the transition from the barrel to the flue. The cross section area of this plenum should be much wider than the flue, 150% as the minimum.
|
|
|
Post by daniel on Jan 11, 2016 1:56:05 GMT -8
Dustin, I am curious how it would behave without the flue directly to the chimney
|
|
|
Post by dustinmattison on Jan 11, 2016 14:57:57 GMT -8
The flue is made from cardboard which was used to mold the cob without straw. Inside the flue it isn't perfectly smooth because where I connected different cardboard tubes there is a rough area. Do I understand correctly the cardboard flue is still in there? If positive, there won't be any heat transfer from the cardboard to the cob. In case the tubes aren't in there anymore, is the cob dried out thoroughly? Fifty percent of the times the stove isn't running well it has something to do with the transition from the barrel to the flue. The cross section area of this plenum should be much wider than the flue, 150% as the minimum. peterberg Yes, the cardboard flue is still in there. Originally I was thinking of burning it out but I never did that. The cob is probably 80% dry by now. So that is one problem. Then there is the cross section area of the plenum from barrel to flue. I don't think it is 150%. I was trying to figure out how to build it structurally sound, with rocks and cob with a cover on top, so I didn't make it really big. When you say 150% do you mean 1.5 times bigger than 8 inches (since the flue is 8 inches)? So these are 2 problems which are probably definitely causing problems. I need to test the stove direct to chimney next to rule out whether there is anything wrong with my stove. If there isn't, then I can decide what to do about the cross sectional area and the cardboard flues. Maybe I should dig it out and put half barrels in instead.
|
|
morticcio
Full Member
"The problem with internet quotes is that you can't always depend on their accuracy" - Aristotle
Posts: 371
|
Post by morticcio on Jan 12, 2016 1:40:15 GMT -8
peterberg and daniel I did another test this weekend. Not a bell, but the barrel and flue set up. I have 2 or 3 inches of space above the heat riser (the space between the heat riser and the barrel). The flue is about 25 feet long inside the bench. The bench has one 180 degree turn, one 90 degree turn, and about 3 turns which are about 50 or 60 degrees. The chimney is about 12 feet above the heat riser. But still it isn't running well. I assume there is not enough draft. In order for some draft to occur I have to open the batch box door and only fill the box about 1/4 full. Even then, there is still some smoke coming out of the p-channel. There is a lot of ash accumulation and incomplete burning. The barrel doesn't get that hot. After burning for 2 hours the room doesn't feel any warmer and the thermal mass is still cold. How do I troubleshoot this problem? 1. Am I burning the wood properly? Is there a special method for burning in a batchbox? How much should I fill it? 2. Is the flue too long with too many turns? My next test should be to exit the gasses directly to the chimney without going through the bench. If that solves the problem, then I will have to settle for not using the flue and instead put a half barrel on one side of the bench and get the benefits of a warm spot, rather than a complete warm bench. (my bench is 12 feet wide) 3. What if I installed a fan somewhere in the system? 4. Would adding more space above the heat riser help? Dustin
From your description it sounds like the system is being restricted, let alone getting an efficient burn. There could be various reasons - badly designed batchbox, wet fuel, narrow transitions, too many bends in the system etc. How do you troubleshoot the problem? Step by step...
1. For an efficient burn you need dry wood. To start a 'cold' batchbox you build a small fire at the back of the firebox, gradually adding more fuel until it is 'rocketing' - Peter has described this somewhere. The burn cycle is between 45 and 55 minutes. Avoid opening the door. If you need to add more fuel wait until the batchbox is at the glowing ember stage. At the end of the burn cycle the inside of the batchbox will be soot free. On my cast refractory it was a clean bright white. You only need to fill the batchbox 2/3 or 3/4 full.
2. Yes please try running the batchbox with the gasses exiting directly to the chimney. To be honest you should've done this to start with. Make sure the batchbox burns clean, as described above. If it does, only then start adding a bell or bench. If it then coughs and splutters you can identify what is causing the problem.
3. You should not need a fan
4. More space above the riser is an option you can play with once you know the batchbox is running efficiently.
|
|
|
Post by dustinmattison on Jan 12, 2016 2:02:22 GMT -8
morticcio My wood supply consists of small diameter trees and twigs I gather from the forest. I live in a humid damp climate. I don't know if the wood is completely dry, but it is all I have right now. I will test this weekend. Also, my batchbox door is not completely air tight. Is this a big problem? It is a sliding iron door, but the smoking I experienced doesn't really come out of the door cracks, but the p-channel. There are also a few leaks around the box because I haven't been able to completely cob over everything. Dustin
|
|
|
Post by daniel on Jan 12, 2016 2:24:09 GMT -8
Dustin, it is pretty clear to me that the heater does not have good draft for some or all of the reasons described previously. If the engine of the heater (firebox) works (by connecting it directly to the chimney with a bypass tube ) than you know it is drafting and able to burn. The draft pulls all of the smoke from everywhere, the door is not suppose to be airtight since it will not pull air from outside and you can not achieve combustion. The fact that there is smoke coming back through the P-channel it means to me that you draft is as bad as it gets. I never had smoke from the P-channel back. One more thing that comes to mind is if you test this outside in the cold, the very cold air from the outside will it also affects the combustion. Tell me what happens when you connected it directly and we go from there
|
|
|
Post by peterberg on Jan 12, 2016 2:24:21 GMT -8
When you say 150% do you mean 1.5 times bigger than 8 inches (since the flue is 8 inches)? When it is as wide as an 8", about 50 sq in, that would be good. What matters complicate is the 6" system size and the 8" flue size. The gases are streaming slower there as compared to in a 6" flue, so in total the heat extraction should be more. But the cardboard tubes should cancel that effect out. Enfin, I think Morti is right, there's some restriction somewhere but it's hard to pinpoint where.
|
|
morticcio
Full Member
"The problem with internet quotes is that you can't always depend on their accuracy" - Aristotle
Posts: 371
|
Post by morticcio on Jan 12, 2016 2:55:29 GMT -8
If your wood isn't dry then this is an issue. Fuel quality is essential in any appliance - vehicle/stove/furnace. You wouldn't put contaminated diesel in your truck and expect it to run well!
If you look at all the batchbox stoves that 'work' they all have airtight doors. Why? Because you need to be able to control the amount of air entering the stove by the sliding primary air vents/flaps and secondary air vent/flap on the P-channel. If your door is not air tight around the edge then you are unable to do this. In my opinion it is a big problem. I don't think the sliding door is a good design unless it sits between two fireproof rope seals.
Leaks around the box will not help!
The best advice I can give anyone building a batchbox is that it needs to be engineered not cobbled together. By that I mean for a batchbox to work efficiently, and carry on working efficiently, you need to have built it within the published tolerances and using correct materials.
|
|