Post by permamax on Nov 25, 2012 14:31:21 GMT -8
Dear rocket scientists!
Last week I came much too close to burning down the future home of a client, and figured I could use some help on this one!!!
The question boils down to: insulation or not of the horizontal burn tunnel?
First the full picture:
The client is a 53 year old spiritual single woman, in other words not the practical/technical type at all.
She contacted me to help with overall design of transferring a small garden cabin built from a type of cement based building bricks into a sustainable living residence. My approach was to 'spiff up' the very ugly small Rumford fireplace which was in the cottage so she could have fast instant heat, as well as
installing a rocket mass heater for slow constant heat. Significantly I designed a well insulated wrap around porch/kitchen on the South and West, and 10cm styro-foam insulation on the Northern uphill and Eastern sides. The floors have also been insulated and the ceilings are now getting 20 cm hemp insulation... The new set up means the sun will be significant in heat gain, and the heavy mass core of
the old cabin functions as the thermal mass with the Rocket and Rumford to regulate it from cool to warm. The new kitchen area can be heated during winter from a wood cook stove, which also can heat water for the boiler; sharing the system with a simple solar collector set-up for kitchen/bath hot water.
...So far so good, but...
I still haven't experienced a rocket which can be 100% guaranteed not to back-fire, causing fire and smoke to get into the room...(Have you?), so due to liability I designed the rocket to go through a corner of the small cabin, bringing the burn chamber outside, but the heat riser inside. My experience from our
own rocket designed this way is that winds and down draft may be causing more frequent smoke/fire problems, however any such issues don't cause interior problems.
The core of the rocket is built according to standard design using firebricks, joined with a minimum thickness of clay mortar. We didn't insulate the part which is outside of the hole in the wall it goes through, we simply packed it all in about 5 cm of sand rich cob: on the left side (as seen from burn chamber) it is pretty exposed to the exterior, the right side is where the dilemma is: We covered the cob with a 3 cm special composite non-flammable light-weight panel as this side is integrated in the wall structure and furthermore insulated with 30 cm of perlite for the first meter; above that with stuffed straw. My understanding was that this would have same effect as insulating the chamber with
zebral; in other words not be flammable or able to accumulate heat... Well: This is where I was dead wrong!
Both the panel and the perlite got mighty hot (guessing 80-100 degrees celcius, as the cob covered right side of the burn tunnel slowly accumulated and transferred the heat; the problem first appeared about 5 hours after we stopped firing the rocket for about 7 hours.
You see, within the perlite we had a light-weight wooden wall frame element made from battens, and the heat combined with lack of oxygen caused a charcoal like burn of the batten making it severely charred and 'burning' apart at about cm above floor level 20 cm.
-I observed all of this opposite; smelling smoke, seeing it seeping up between the old cement plastered wall and the straw insulation, pulling out the straw/ tearing down the wooden construction used for mounting the interior plaster boards, getting down to the perlite while drenching it with water, slowly
excavating the hot perlite, finding the charred wood and exposing the extremely hot and steaming non- flammable panel, lastly exposing the hot and (now) steaming cobbed side of the rocket heater...
[See attached image. More photos here: picasaweb.google.com/111796347268830755973/DanaSRocket?authuser=0&authkey=Gv1sRgCJXKz7LM5sW2_wE&feat=directlink
And yes, I'm extremely grateful I was there staying overnight at the work-site and able to catch this, possibly save the whole building from burning down! (And happy that my colleague reacted fast and drove in to help me at 11PM!).
Solution?
1st. option:
As I've now experience first hand how warm the side of the burn tunnel can be, I'm very interested in keeping it exposed to the interior to heat the new kitchen when burned. It would likely require an insulated door for when there's no heat, as otherwise it's a massive cold bridge to the outside. This would eliminate any contact
with wood, no further build up of heat within a wall etc:
My concern is that I'm not aware of what the effect of this would be to the burn process within the fire chamber, will it still generate the necessary expansion, giving the 'push' necessary in this part of the rocket? (-Especially as the opposing side is exposed to the outside until it reaches the wall; above and within the wall it's insulated with perlite).
-And please; any tips as to how I make an insulated wall above the exposed side of the rocket, as I hesitate to use wood and the fireproof panels are of a flimsy character so their can't simply be screwed together and filled with perlite.
2nd option:
I'll wrap the entire burn tunnel with Ceramic Fibre Insulation Blanket (Like this: www.armstrongbrickovens.co.uk/OvenInsulation_Thermal_Blanket_Vermiculite.html ), and perlite next to that within a wall much like before, just not with wood construction near the Ceramic Fibre Insulation Blanket. This option should result in the heat only being able to escape back into the tunnel or to the exterior or interior of the rocket system.
3rd option:
I'll remake the wall to include the entire rocket to the interior, not having any fire risk from accumulated heat and gaining the radiator effect, however risking the issues with blow-back, smoke in or fire coming the wrong way... -I may add here that the rocket is connected to the same chimney as the Rumford, which reaches up above the roof.
4th option?
?
All in all, I'd really appreciate advice on this one; it's last chance and have to be made right; Naturally the client is nervous, and she flatly refuse to try to understand any concept such as thermal mass, insulation, hot, cold, push, pull, (Hrmpf!), she just want a system which simply works...
Last week I came much too close to burning down the future home of a client, and figured I could use some help on this one!!!
The question boils down to: insulation or not of the horizontal burn tunnel?
First the full picture:
The client is a 53 year old spiritual single woman, in other words not the practical/technical type at all.
She contacted me to help with overall design of transferring a small garden cabin built from a type of cement based building bricks into a sustainable living residence. My approach was to 'spiff up' the very ugly small Rumford fireplace which was in the cottage so she could have fast instant heat, as well as
installing a rocket mass heater for slow constant heat. Significantly I designed a well insulated wrap around porch/kitchen on the South and West, and 10cm styro-foam insulation on the Northern uphill and Eastern sides. The floors have also been insulated and the ceilings are now getting 20 cm hemp insulation... The new set up means the sun will be significant in heat gain, and the heavy mass core of
the old cabin functions as the thermal mass with the Rocket and Rumford to regulate it from cool to warm. The new kitchen area can be heated during winter from a wood cook stove, which also can heat water for the boiler; sharing the system with a simple solar collector set-up for kitchen/bath hot water.
...So far so good, but...
I still haven't experienced a rocket which can be 100% guaranteed not to back-fire, causing fire and smoke to get into the room...(Have you?), so due to liability I designed the rocket to go through a corner of the small cabin, bringing the burn chamber outside, but the heat riser inside. My experience from our
own rocket designed this way is that winds and down draft may be causing more frequent smoke/fire problems, however any such issues don't cause interior problems.
The core of the rocket is built according to standard design using firebricks, joined with a minimum thickness of clay mortar. We didn't insulate the part which is outside of the hole in the wall it goes through, we simply packed it all in about 5 cm of sand rich cob: on the left side (as seen from burn chamber) it is pretty exposed to the exterior, the right side is where the dilemma is: We covered the cob with a 3 cm special composite non-flammable light-weight panel as this side is integrated in the wall structure and furthermore insulated with 30 cm of perlite for the first meter; above that with stuffed straw. My understanding was that this would have same effect as insulating the chamber with
zebral; in other words not be flammable or able to accumulate heat... Well: This is where I was dead wrong!
Both the panel and the perlite got mighty hot (guessing 80-100 degrees celcius, as the cob covered right side of the burn tunnel slowly accumulated and transferred the heat; the problem first appeared about 5 hours after we stopped firing the rocket for about 7 hours.
You see, within the perlite we had a light-weight wooden wall frame element made from battens, and the heat combined with lack of oxygen caused a charcoal like burn of the batten making it severely charred and 'burning' apart at about cm above floor level 20 cm.
-I observed all of this opposite; smelling smoke, seeing it seeping up between the old cement plastered wall and the straw insulation, pulling out the straw/ tearing down the wooden construction used for mounting the interior plaster boards, getting down to the perlite while drenching it with water, slowly
excavating the hot perlite, finding the charred wood and exposing the extremely hot and steaming non- flammable panel, lastly exposing the hot and (now) steaming cobbed side of the rocket heater...
[See attached image. More photos here: picasaweb.google.com/111796347268830755973/DanaSRocket?authuser=0&authkey=Gv1sRgCJXKz7LM5sW2_wE&feat=directlink
And yes, I'm extremely grateful I was there staying overnight at the work-site and able to catch this, possibly save the whole building from burning down! (And happy that my colleague reacted fast and drove in to help me at 11PM!).
Solution?
1st. option:
As I've now experience first hand how warm the side of the burn tunnel can be, I'm very interested in keeping it exposed to the interior to heat the new kitchen when burned. It would likely require an insulated door for when there's no heat, as otherwise it's a massive cold bridge to the outside. This would eliminate any contact
with wood, no further build up of heat within a wall etc:
My concern is that I'm not aware of what the effect of this would be to the burn process within the fire chamber, will it still generate the necessary expansion, giving the 'push' necessary in this part of the rocket? (-Especially as the opposing side is exposed to the outside until it reaches the wall; above and within the wall it's insulated with perlite).
-And please; any tips as to how I make an insulated wall above the exposed side of the rocket, as I hesitate to use wood and the fireproof panels are of a flimsy character so their can't simply be screwed together and filled with perlite.
2nd option:
I'll wrap the entire burn tunnel with Ceramic Fibre Insulation Blanket (Like this: www.armstrongbrickovens.co.uk/OvenInsulation_Thermal_Blanket_Vermiculite.html ), and perlite next to that within a wall much like before, just not with wood construction near the Ceramic Fibre Insulation Blanket. This option should result in the heat only being able to escape back into the tunnel or to the exterior or interior of the rocket system.
3rd option:
I'll remake the wall to include the entire rocket to the interior, not having any fire risk from accumulated heat and gaining the radiator effect, however risking the issues with blow-back, smoke in or fire coming the wrong way... -I may add here that the rocket is connected to the same chimney as the Rumford, which reaches up above the roof.
4th option?
?All in all, I'd really appreciate advice on this one; it's last chance and have to be made right; Naturally the client is nervous, and she flatly refuse to try to understand any concept such as thermal mass, insulation, hot, cold, push, pull, (Hrmpf!), she just want a system which simply works...
