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julian
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« on: January 21, 2012, 05:42:11 PM » |
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My partner is used to an oil fired aga, and has expressed concerns over cooking on a solid fuel rayburn due to fluctuations in temperature.
We dont (yet) have a rayburn, but ive been wondering how closely the oven temp follows the air supply, and if that could be automated at all?
(im thinking a thermocouple / PID setup, and then some way to adjust a velve from the output)
Does this sound in any way feasible, or are there just too many factors involved?
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guydewdney
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« Reply #1 on: January 21, 2012, 05:48:47 PM » |
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I have a woodwarm that has a thermo-controlled air supply- its basiclly a big bi metallic strip and a big 2" washer over a hole. Its useless at temp regulation.
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julian
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« Reply #2 on: January 21, 2012, 05:53:47 PM » |
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I have a woodwarm that has a thermo-controlled air supply- its basiclly a big bi metallic strip and a big 2" washer over a hole. Its useless at temp regulation.
Do you think that the concept is inherently flawed, or just that it has been poorly implamented in your device? |
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Justme
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« Reply #3 on: January 21, 2012, 06:21:18 PM » |
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Two issues.
1, the lead time between to hot & to cold is too large or the lag between adjustments & resultant temp changes. In use you need to turn it down before it gets to hot & up before it gets to cold.
2, the temp you want to monitor is in the oven & the control needs to be in the fire box. Bimetallic strips would be a pain to set up to cover that distance.
Solid fuel Rayburns need attention & experience to master.
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Navitron solar thermal system
30 x 58mm panel 259L TS
1200watts solar 120vdc
FX80 Solar controller
Victron 12v 3000w 120a
200w (250w peak) 12v turbine as a tester
6kva genny
6 x 2v cells 1550amp/h 5C
24 x 2v cells 700amp/h 5C
Total bank 4350 amp/h @12v
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guydewdney
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« Reply #4 on: January 21, 2012, 06:28:04 PM » |
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i think - as above - that it needs prediction, not reaction.
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clivejo
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« Reply #5 on: January 21, 2012, 06:40:32 PM » |
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I second that. Control requires an experienced person who learns by trial and error! Its surprising how well it can be controlled and how well it cooks things!
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julian
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« Reply #6 on: January 21, 2012, 07:00:23 PM » |
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i think - as above - that it needs prediction, not reaction.
I was thinking somthing along the lines of a thermocouple, possibly, in the flue gas - but not necisarily in the oven. PID control units can have their output curves adjusted. Theyre not simply on/off thermostats (although how their output would control a valve sensibly, im not yet sure of!) Im not actually thinking about an up/down temp control at all, but a leveller - making minute adjustments to keep the oven stable. If that worked, then it may be possible to add a 'refuel' buzzer - for when the temperature stops responding to the air flow. I know from most of my life with a log burner that its not real simple, but im also thinking that somthing may be possible? Do you really think not? |
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clivejo
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« Reply #7 on: January 21, 2012, 07:20:55 PM » |
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They take a long time to get up to temperature. The flue gases alone would not be a great indication. For example we have to burn at full blast until the oven temperature comes up. Then close down the air and dampers to keep the temperature levelled. Not sure how such a system would work  |
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Justme
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« Reply #8 on: January 21, 2012, 08:24:19 PM » |
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Thats a good point.
Its not just the air in that needs attention.
How will you adjust the baffle & damper?
How will you alter the adjustment profile when its windy outside so you need more damper & baffle action in relation to the air control?
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Logged
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Navitron solar thermal system
30 x 58mm panel 259L TS
1200watts solar 120vdc
FX80 Solar controller
Victron 12v 3000w 120a
200w (250w peak) 12v turbine as a tester
6kva genny
6 x 2v cells 1550amp/h 5C
24 x 2v cells 700amp/h 5C
Total bank 4350 amp/h @12v
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Baz
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« Reply #9 on: January 21, 2012, 08:42:10 PM » |
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I expect they work better on coal as each fuel cycle is more predictable. Rather than Rayburn do the woodburners from wooded regions of Europe work better?
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clivejo
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« Reply #10 on: January 21, 2012, 08:47:39 PM » |
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I expect they work better on coal as each fuel cycle is more predictable. Rather than Rayburn do the woodburners from wooded regions of Europe work better?
To be honest Id be nervous of burning coal in our Rayburn, coal burns very hot, maybe too hot for cooking etc. A bucket of peat tends to keep it ticking over nicely. |
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Brian H
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Posts: 57
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« Reply #11 on: January 22, 2012, 10:43:45 AM » |
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Since changing over to a Rayburn from the old Bosky(Italian) in december, we haven't run it as cooker only, running it in heating mode. But our observation has been that the oven temperature is a lot more stable than the old Bosky, and seems to be a lot easier to use.
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AndySussex
Jr. Member
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Posts: 80
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« Reply #12 on: January 23, 2012, 09:08:22 AM » |
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I think SF Rayburns are good for long slow cooking as you can sustain a high temp quite easily with practice but not really go up or down by 10-20 degrees with any ease...
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julian
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« Reply #13 on: January 23, 2012, 10:09:09 AM » |
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I think SF Rayburns are good for long slow cooking as you can sustain a high temp quite easily with practice but not really go up or down by 10-20 degrees with any ease...
Whenever rayburns and temperature are mentioned, many people seem to assume that i *want* to be able to alter the temperature! Im *NOT* wanting to alter the temperature. Im wanting to STABLAISE it : ) An oil fired aga runs at the same temp all the time, day in, day out. Sure, there is a thermostat, but its for long term setting. Im not interested in getting adjustment over the running temp at all - im wanting to keep it as stable as possible. |
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billt
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« Reply #14 on: January 23, 2012, 10:18:08 AM » |
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Coal fired Rayburns are inherently pretty stable. Large thermal mass and a reasonably constant burn rate. You just have to get the hang of adjusting the air inlet spin wheel and the flue damper to get the temperature that you want.
Ours maintains between 160 and 180 C for hours, probably days. The temp can drop a bit when you refuel, bit if your running it on low heat you'll only need to do that twice a day.
Higher temperatures are a bit trickier as you have to allow for the time taken to heat up, and more frequent refuelling.
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