Heater cast batchbox 18 cm, bell, bench

[peterberg]

Dec 8, 2017 2:25:21 GMT -8 grga said:

Peter some time ago you advice to modify floor channel so to bent the 45 degree part closest to the port vertically - to prevent it begin to close to the port.

 I was thinking if I could simply cut it as shown in the image. That way its corners will not be too close to the port and it will still cover the floor channel and direct air in the port...

Funny, the channel specifically made for the workshop in Mallorca was done like that. The metal worker misinterpreted the drawing and did it exactly like you suggest. It did work without a hiccup so I think you could do it as you proposed, no problem as far as I see it.

[grga]

Thank you for advices Peter. My heater gets much wormer now, obviously bricks have dried a bit. I am at cca half the load now. I am a bit scared to go to fast, so I prefer to make a longer modest fire in it over the whole day. I did get one small crack in the batchbox cast when I make half a load from cold start to fast - obviously the core was not dry enough or get moisture from the bricks while building... Other than that it burns like crazy.

[grga]

I have notice long a few meters white smoke from chimney at full burn. also when i check the chimney there is a condensation first half of the burn. I did not measure the flue temperature yet only try it by hand it it doeos not feel hot, only warm probably cca. 40. or 50C. With open baypass the condensation does not hapen. My ISA is arround 8.1m2 for 18 cm batch.

Should I lower ISA or should i wait a while for the heater to fully dry, now is 3 weeks operating by 1 daily full burn. I have no problems starting the heater with bypass closed, draw seems fine but i get the feeling that I need to have air opened more than 64cm2 during all the burn to hear more rocket sound.

[peterberg]

I'd think the heater isn't fully dried yet. Condensation in the flue during first part of the burn is unavoidable since the process of combustion produces water, much the same as with natural gas.

The air inlet need more opening when draft is low to get enough volume of air in. Which means the inlet can be smaller with high draft, caused by high winds or a hotter chimney stack. The whole of the design, bell and all is geared to a quite low chimney temperature when running twice a day or more during the depth of winter.

So in the shoulder seasons (fall and spring) the chimney temp won't rise above 80 ºC while in Januari it could be 120 ºC. This is what I view as a good range without draft problems. My own heater is tuned like that, but then, mine is without a bypass so you shouldn't have any trouble to keep the exhaust level above condensation on average.

Buy a simple thermometer and monitor the temperature is all I can say.

[grga]

I will try with termometer today and report it.  Unfortunately I can only measure main (lowest part of the bell) flue temperature, the chimney entry from bypass I can not reach...


So I guess that I can preheat chimney first by using bypass (cca 10 minutes) and there will be now condensation. Then I close the bypass and the bell will lower the temperatures and condensation can still happen in the chimney maybee also in the bell (I need to check also this). So if I this is the case and I measure the exit temperatures much below 80 degrees than I should lower ISA to have temperatures around 80C in the second half of the burn?


In shoulder season you run heater twice a day and temps are around 80C max.   What are the temperatures at the start (5 minutes from start)? How this changes if you do only one burn a day?  I can see from your testo results (http://batchrocket.eu/en/designs#floorchannel) that your heater needs at least 20 minutes to come from starting 30C to cca 80C - Do you have any condensation in the first 10 minutes of the burn or not?

[peterberg]

Dec 21, 2017 2:16:36 GMT -8 grga said:

So I guess that I can preheat chimney first by using bypass (cca 10 minutes) and there will be now condensation. Then I close the bypass and the bell will lower the temperatures and condensation can still happen in the chimney maybee also in the bell (I need to check also this). So if I this is the case and I measure the exit temperatures much below 80 degrees than I should lower ISA to have temperatures around 80C in the second half of the burn?

I mentioned 80 ºC because it's a safe figure. In fact, the temperature at the exit of the chimney should above 45 ºC to avoid condensation. But you can't measure that so I mentioned a temp that's higher than strictly required. It's a pity that you can't measure above the bypass, is it closing very tight or can you have it open a little bit?

Dec 21, 2017 2:16:36 GMT -8 grga said:

In shoulder season you run heater twice a day and temps are around 80C max.   What are the temperatures at the start (5 minutes from start)? How this changes if you do only one burn a day?  I can see from your testo results (http://batchrocket.eu/en/designs#floorchannel) that your heater needs at least 20 minutes to come from starting 30C to cca 80C - Do you have any condensation in the first 10 minutes of the burn or not?

I might have condensation in the first half of the burn or not, but that's irrelevant as long as there's more vapor exhausted than produced on average.

I can't give you temps 5 minutes from start or during the first 10 minutes because that is different for every burn. Depending on wind speed and direction, temperature difference between inside and out, temp of the heater to begin with, moisture content density and size of the fuel, you name it. Stop worrying about how it performs, just run it as much as you need to keep the house warm.

An 18 cm system could drive 7.6 m², so yours is probably a little on the large side of things. What you could do is to keep the bypass open just a crack to compensate for that oversize and go through this winter like that. In spring it's a good moment to decide whether it is time to shrink the ISA somewhat or not.

[grga]

Thanks for advices. I can open bypass just a crack (1cm or less) it is a sliding version. I intentionally want it to be a bit larger bell, however I see now that this might be a mistake. Operating it with bypass compensation does not seems to be a good thing it really sounds like a sloppy design and correcting the design error by using bypass. I hoped to use the bypass only to have smokeless starts, but I have no problems with back smoking (I do not need to open bypass) but I must use it to prevent condensation ...

[grga]

 have measured temperatures during the burn, the heater was warm from previous day the chimney has 30C. When I opened door of the heater the air moved through the door and heat the chimney sensor to 45C. Then I load and fire, it burn a bit more than 1 hour.  I supply more air than before when I had condensation in the chimney. Because I measured temperatures  I could not check if I also had condensation in the chimney (closed the chimney door with stone wool and inserted the sensor). Tomorow I will reapeat the same but modify so that I could also check for condensation...  Anyway the temperature seems fine to me?

Temperature record of the burn (4600 seconds). At first I had main door opened (1cm) and also air vent. Then I close and open the main door a few times and finally closed them at 20 minutes.  Then I have air vent fully opened and the chimney temperature at the stove exit was around 80 C. I close the air vent at 4600 seconds. The temperature in the chimney then dropped to 45C.




door image with air went

[Orange]

grga, I'm curious bout your red bricks. Did you put them in water before building? What kind of mortar you used? And is the wall strong since bricks are laid sideways?

[peterberg]

Temperature seems fine to me, well above 70 ºC within 20 minutes. No condensation fluid would be accumulating in the heater I would say.

[grga]

Dec 21, 2017 13:41:16 GMT -8 Orange said:

grga, I'm curious bout your red bricks. Did you put them in water before building? What kind of mortar you used? And is the wall strong since bricks are laid sideways?

I did put each brick into water for a few minutes. First I did mortar using 0-4mm quartz sand in proportions  sand:lime:regular_cement:clay  (cca. 2:1:0.5:1). This is good and by my opinion better than just clay and sand.

Then later I bought cheep (7 eur for 40kg) also mortar for building heaters (not in the fire zone and good up to cca 700C) Rofix 960. I found it not sticky enough. It seemed much better if I added 1/4 of tile glue (regular Portland cement and good-qulity) by this it was much easier and better to work with. I also added cca 1/6 of clay to it but I am not sure it this improves anything. 

Red bricks are fine wall seemed strong enough however you could easily brake it with heavy hammer...   you could use also just the good quality tile glue



For fire bricks (inside layer of the bell) I used mix= 3 parts fine sand, 1 part CAC, 1.5 part clay.  This is one is hard to work with, you need to be fast. Much better and easier to work with is using mortars for fire zones like Rofix 961 which is more expensive but the build is very strong - If you try to brake it apart usually you will destroy bricks first and not the mortar...

[grga]

Dec 21, 2017 13:46:27 GMT -8 peterberg said:

Temperature seems fine to me, well above 70 ºC within 20 minutes. No condensation fluid would be accumulating in the heater I would say.

I hope so also.   Like I said in this burn I tried to maximize the temperatures by supplying much more air to the stove...



What I discover in the morning are much more unburned embers. In previous runs there were also but much less.



Is this the consequence of two much wind trough the core or maybe I closed the air too soon. How to operate the heater to lower the amount of unburned coals? 

I have read that they will burn in next fire but some of them may also not as they are covered and isolated by fine ash...

[peterberg]

Dec 22, 2017 1:14:26 GMT -8 grga said:

What I discover in the morning are much more unburned embers. In previous runs there were also but much less. Is this the consequence of two much wind through the core or maybe I closed the air too soon. How to operate the heater to lower the amount of unburned coals?

You allowed more air during the burn which cools down the fire, that's one thing. Another one is the point when you close the air inlet, later means there will be less coals but more heat loss.

Dec 22, 2017 1:14:26 GMT -8 grga said:

I have read that they will burn in next fire but some of them may also not as they are covered and isolated by fine ash...

What I normally do is raking the coals a bit before loading the fuel for the next burn. By doing that most of the coals will be on top so they will burn away easier. Please look carefully during the latter part of the burn, you'll see that the old coals are burning away before there are new coals formed.

Again, stop worrying about all those things, it's just a question of getting used to another way of handling a heater. Remember, even top lighting was very strange 30 years ago but it works very well. I even had a dispute with a man from China who argued that the Chinese were lighting the fuel from below for 1000 years and now they are suddenly wrong? The answer is of course yes, because progress can and will be made.

Closing early to starve the coals and preserve energy is relatively newer but just as effective. For every burn you have the same amount of fuel, partly consisting of charcoal. And as a bonus less heat loss because the coaling phase is very short.

There's another effect I witnessed the last couple of days:
I burn quite some planks from pallets and so on. When I place those flat on an ash layer the lower half of the plank is running behind when off-gassing of the rest is already over. Caused by the insulating properties of the ash, I would say.
With a layer of coals below those planks this effect is minimized, presumably because of the lower ignition temperature of charcoal compared to the wood. So in an earlier stage there's fire under the lowest pieces of fuel burning those away in sync with the rest of the load.

[grga]

I will consider suggestions... worry less. It so interesting to observe, checking, confirming expectations and see the operation.

Its performance for now is good, with one fire a day it radiates heat the hole day.

In future days I will decorate the heater with the tiles to be a bit nicer...


And about the white oven: It is not hot enough. It can have max 150C. I will try some other modification to try to get some more out of it.

[grga]

Here is nearyl final look of the heater and image of its burn...

 



I am happy by its performance.  There is still some condensation present in the chimney at first half of the burn where the exit temperatures hardly goes to 70C. But there is no condensation inside the heater. After a month of daily use I will check it again and lower some (0.4m2) of the internal ISA (cover it by isolation) to be closer to the optimal one for 18cm system.


I guess the condensation in the chimney is quite common with rocket masss heaters as they need some time to warm the exit flue over 80C and to preaheat also entire chimney over 50C....