Martin Howard on tue 16 jul 02
My kiln room gets hot when the kiln is on.
During winter I let the heat out a little at a time to keep me warm in the
rest of pottery.
I could install a sauna, but really want the space for extra shelving:-)
But in summer, even the bit of UK summer we are now experiencing, it means
the kiln room is not usable for anything else when the kiln is on. And the
electricity bill is a little higher than I would like; up by 25% over
figures I got when I first had the kiln 3 years ago.
Has anyone on list put an outside coating of insulation around such a kiln?
It is a large front loader with metal frame and block infill.
For example, would the packages that we put around hot water tanks in the UK
be OK for this kind of job?
Martin Howard
Webbs Cottage Pottery
Woolpits Road, Great Saling
BRAINTREE, Essex CM7 5DZ
01371 850 423
martin@webbscottage.co.uk
http://www.webbscottage.co.uk
Updated 6th July 2002
Snail Scott on tue 16 jul 02
At 08:41 PM 7/16/02 +0100, you wrote:
>Has anyone on list put an outside coating of insulation around such a kiln?
>It is a large front loader with metal frame and block infill.
I think this might put a lot of stress on the frame.
The steel really ought to remain tight around the
bricks to hold everything together. Wrapping insulation
around the outside will cause the steel to get hotter
and expand more than it was designed to.
I'm assuming that the frame would have to be modified
to put insulation between the brick and the steel, so
that's probably not a good choice, either.
Maybe a vent fan for the shed would be preferable. For
venting excess heat, just a cheap box fan or two can
do wonders. Cut a hole in the wall and just plug it
in to pull air out of the shed. (You might need another
hole to let the outside air in from the other side, if
the shed's not drafty already.) In the winter, just
unplug the fan and board over the hole.
-Snail
Dave Finkelnburg on tue 16 jul 02
Friend Martin,
No, the hot water tank insulation probably isn't a good idea. Others
will doubtless make this observation also. DO NOT put any insulation on the
outside of the metal jacket. Offgas from the kiln will condense on the
metal and corrode it away, causing the kiln structure to fail.
Many have insulated such kilns by opening up the metal jacket, extending
the bands which hold the jacket together, adding some sort of
non-compressible insulation (usually board-type), and connecting the bands
again. This will save power, make the kiln fire faster if you want to go
faster, and make it cool slower if you want it to cool slower.
Regards,
Dave Finkelnburg in Idaho
From: Martin Howard
>Has anyone on list put an outside coating of insulation around such a kiln?
>It is a large front loader with metal frame and block infill.
>For example, would the packages that we put around hot water tanks in the
UK
>be OK for this kind of job?
william schran on wed 17 jul 02
Martin - I would suggest that you NEVER wrap any insulation over the
metal skin on the outside of any kiln - you are inviting disaster.
I'd recommend creating a better airflow or draft through your kiln
area using fans to bring in new air and exhausting the heated air
(not to mention fumes). Think also if you could put up a wall to
isolate the kiln area from your work area.
I work in a small basement, kiln is sitting 2 feet way from my wheel.
I have a powered exhaust vent on the kiln and a fan running behind
me. Does get a bit warmer when firing, but never hot enough to make
me uncomfortable. The cats love to lay around the kiln though.
Bill
Eleanora Eden on thu 15 aug 02
Hi Martin and all,
Determined today to use some clayart time doing more than deleting
thousands of messages. And here is something I know something about and
that something is contrary, of course and as usual, to all other comments.
Twelve or thirteen years ago we wrapped my L&L kiln with kaowool and tin
foil and wire. At the time I was told in no uncertain terms the same
mantra that all the posts responding to Martin, ie it will wreck the
stainless steel shell. Well we did it anyway because, frankly, that made
no sense to me.
Well, about 3 years ago we took all that off as the top area of kaowool had
been degrading (it is a top-loader) and, no surprise at all, the stainless
steel shell is still in perfect condition. We replaced it with a new
kaowool layer and this time we used masonry cement to make an impervious
outer shell. So my kiln looks like a little missile silo.
So, Martin, GO FOR IT!!!!!! If you want specifics let me know and maybe
Fred, who actually did it, can talk with you on the horn.
This was relatively easy to do and the fuel savings have got to be
enormous, and less heat in the studio of course. BTW I also use several lids.
And, BTW, sometimes I wonder at the myths people spout. I wonder if
anybody ever actually saw a kiln degraded by adding insulation or if
somebody's theoretical prognosis eventually became commonly accepted fact.
Eleanora
PS There was a time when I shared with open heart on this list. The
endless and sometimes nasty criticisms shoved at me cured me of that quite
a long time ago. It is too bad, I have alot to offer. Maybe the current
batch of knee-jerk critics will think one second before just tripping over
themselves to loudly proclaim I don't know what I am talking about.
At 08:41 PM 7/16/02 +0100, you wrote:
>From: Martin Howard
>Subject: Insulating the outside of an electric kiln.
>
>
>My kiln room gets hot when the kiln is on.
>During winter I let the heat out a little at a time to keep me warm in the
>rest of pottery.
>
>I could install a sauna, but really want the space for extra shelving:-)
>But in summer, even the bit of UK summer we are now experiencing, it means
>the kiln room is not usable for anything else when the kiln is on. And the
>electricity bill is a little higher than I would like; up by 25% over
>figures I got when I first had the kiln 3 years ago.
>
>Has anyone on list put an outside coating of insulation around such a kiln?
>It is a large front loader with metal frame and block infill.
>For example, would the packages that we put around hot water tanks in the UK
>be OK for this kind of job?
>
>Martin Howard
>Webbs Cottage Pottery
>Woolpits Road, Great Saling
>BRAINTREE, Essex CM7 5DZ
>01371 850 423
>martin@webbscottage.co.uk
>http://www.webbscottage.co.uk
>Updated 6th July 2002
>
>______________________________________________________________________________
>Send postings to clayart@lsv.ceramics.org
>
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at
>melpots@pclink.com.
Eleanora Eden 802 869-2003
Paradise Hill eeden@vermontel.net
Bellows Falls, VT 05101 www.eleanoraeden.com
Gavin Stairs on fri 16 aug 02
Dear Elanora,
All that advice comes from very good understanding of what is involved,
and I'm very sure that some people have had bad experiences trying just
this sort of thing.
The theory is very simple: you add insulation to the outside of a kiln,
and the hot zone moves outward. If you add enough insulation, the
temperature of the metal skin will rise well above its comfort level, and
two things will occur: the tension in the straps will relax, making it
easier for the inner bricks to shift and loosen, and the skin itself may
suffer heat damage of one sort or another.
If you have not experienced these symptoms, it is because a) your kiln is
never fired to equilibrium, and the hot zone never moves out. This
may be because you don't fire above cone 4, or some similar restriction,
and the kiln is made to fire much higher (ie., it is already well
insulated), or your firing profile is very rapid. b) your outer
insulation layer isn't very effective. In either case, I doubt you
are getting much benefit from your wrap.
It is a peculiarity of most so-called hobby kilns made for studio potters
that they never actually reach thermal equilibrium when firing to the
bisque and lower stoneware temperatures. In terms of insulation,
this means that the brick never gets as hot as the equilibrium
calculation would suggest. It also means that any outer insulation
layers are very underutilized during the firing. What they mainly
do is slow the cooling slightly, but not really in a useful way, since
the initial rapid cooling down from the peak temperature is not much
affected. It is for this reason that many of the cheaper designs
are very skimpy with the fire brick. This cuts the cost
considerably, but means that the kiln is under-designed for longer firing
cycles and higher temperatures, and it will cool rapidly even after the
brick has reached thermal equilibrium.
The warnings are directed toward these firing conditions. If you
will never suffer from the deleterious effects of the outer insulation,
then I doubt strongly that you will derive any significant benefit from
it either.
Elanora, if you are happy with your outer insulation, then I wish you
well, and I have no objection. However, your experience will not be
universally enjoyed by anyone who tries the same trick. If anyone
else wants to try it, then caveat emptor. If you understand
clearly what you are doing and what you are risking, I say go
ahead. But if you are desperately trying to reach cone 10 in an
under-designed kiln, this is not the way to proceed.
Gavin
At 12:48 PM 15/08/2002 +0100, Elanora wrote:
Twelve or thirteen years ago we
wrapped my L&L kiln with kaowool and tin
foil and wire. At the time I was told in no uncertain terms the
same
mantra that all the posts responding to Martin, ie it will wreck
the
stainless steel shell. Well we did it anyway because, frankly, that
made
no sense to me.
Well, about 3 years ago we took all that off as the top area of kaowool
had
been degrading (it is a top-loader) and, no surprise at all, the
stainless
steel shell is still in perfect condition. ...
Snail Scott on fri 16 aug 02
At 12:48 PM 8/15/02 +0100, you wrote:
>Twelve or thirteen years ago we wrapped my L&L kiln with kaowool and tin
>foil and wire. At the time I was told in no uncertain terms the same
>mantra that all the posts responding to Martin, ie it will wreck the
>stainless steel shell.
I recall that Martin has a front-loading kiln with a
welded frame and such. It was the thought of the steel
getting warmer than usual and allowing the roof bricks
to shift which was my main source of concern. Having
witnessed the corrosion of the spot-welded hose clamps
on my standard top-loader, I'm not too sure I'd want to
wrap the outside of it, either, but the structural
issues for a top-loader are much less critical, IMHO.
I'm glad to hear that your experiments with outside-
the-jacket insulation have been successful, though. I
will keep it in mind.
-Snail
Bonnie/Jeremy Hellman on fri 16 aug 02
Eleanora,
What cone are you firing to? Do you go to ^04, ^6 or ^10? I wonder if your
final firing temp would make a differences in the survival of the metal
jacket on the kiln.
Bonnie
----- Original Message -----
From: "Eleanora Eden"
To:
Sent: Thursday, August 15, 2002 7:48 AM
Subject: Re: Insulating the outside of an electric kiln.
> Hi Martin and all,
>
> Determined today to use some clayart time doing more than deleting
> thousands of messages. And here is something I know something about and
> that something is contrary, of course and as usual, to all other comments.
>
> Twelve or thirteen years ago we wrapped my L&L kiln with kaowool and tin
> foil and wire. At the time I was told in no uncertain terms the same
> mantra that all the posts responding to Martin, ie it will wreck the
> stainless steel shell. Well we did it anyway because, frankly, that made
> no sense to me.
>
> Well, about 3 years ago we took all that off as the top area of kaowool
had
> been degrading (it is a top-loader) and, no surprise at all, the stainless
> steel shell is still in perfect condition. We replaced it with a new
> kaowool layer and this time we used masonry cement to make an impervious
> outer shell. So my kiln looks like a little missile silo.
>
> So, Martin, GO FOR IT!!!!!! If you want specifics let me know and maybe
> Fred, who actually did it, can talk with you on the horn.
> This was relatively easy to do and the fuel savings have got to be
> enormous, and less heat in the studio of course. BTW I also use several
lids.
>
> And, BTW, sometimes I wonder at the myths people spout. I wonder if
> anybody ever actually saw a kiln degraded by adding insulation or if
> somebody's theoretical prognosis eventually became commonly accepted fact.
>
> Eleanora
>
> PS There was a time when I shared with open heart on this list. The
> endless and sometimes nasty criticisms shoved at me cured me of that quite
> a long time ago. It is too bad, I have alot to offer. Maybe the current
> batch of knee-jerk critics will think one second before just tripping over
> themselves to loudly proclaim I don't know what I am talking about.
>
> At 08:41 PM 7/16/02 +0100, you wrote:
> >From: Martin Howard
> >Subject: Insulating the outside of an electric kiln.
> >
> >
> >My kiln room gets hot when the kiln is on.
> >During winter I let the heat out a little at a time to keep me warm in
the
> >rest of pottery.
> >
> >I could install a sauna, but really want the space for extra shelving:-)
> >But in summer, even the bit of UK summer we are now experiencing, it
means
> >the kiln room is not usable for anything else when the kiln is on. And
the
> >electricity bill is a little higher than I would like; up by 25% over
> >figures I got when I first had the kiln 3 years ago.
> >
> >Has anyone on list put an outside coating of insulation around such a
kiln?
> >It is a large front loader with metal frame and block infill.
> >For example, would the packages that we put around hot water tanks in the
UK
> >be OK for this kind of job?
> >
> >Martin Howard
> >Webbs Cottage Pottery
> >Woolpits Road, Great Saling
> >BRAINTREE, Essex CM7 5DZ
> >01371 850 423
> >martin@webbscottage.co.uk
> >http://www.webbscottage.co.uk
> >Updated 6th July 2002
> >
>
>___________________________________________________________________________
___
> >Send postings to clayart@lsv.ceramics.org
> >
> >You may look at the archives for the list or change your subscription
> >settings from http://www.ceramics.org/clayart/
> >
> >Moderator of the list is Mel Jacobson who may be reached at
> >melpots@pclink.com.
>
>
>
> Eleanora Eden 802 869-2003
> Paradise Hill eeden@vermontel.net
> Bellows Falls, VT 05101 www.eleanoraeden.com
>
>
____________________________________________________________________________
__
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
>
Steve Mills on sun 18 aug 02
Interesting this;
According to some research done (I think) by the late Donald Shelley in
the UK, and others, there is, in layman's terms, an optimal point in the
insulation of a Kiln. Below that point the kiln is inefficient due to
excessive heat loss through the wall. At the optimal point the heat loss
is at its least, tho' there is still some. As the wall gets thicker
beyond that point the heat is effectively drawn out of the kiln by the
cooler outer layer, causing the heat to accelerate as it travels
outwards. So *theoretically* you could have so much extra insulation on
the outside that it could degrade the stainless steel jacket, though I
think the Electrics would melt long before that happened :-)
So, as I've mentioned in an earlier post, and Eleanora has demonstrated;
follow the rules of experience and take nothing for granted.
Steve
Bath
UK
In message , Eleanora Eden writes
>Hi Martin and all,
>
>Determined today to use some clayart time doing more than deleting
>thousands of messages. And here is something I know something about and
>that something is contrary, of course and as usual, to all other comments.
>
>Twelve or thirteen years ago we wrapped my L&L kiln with kaowool and tin
>foil and wire. At the time I was told in no uncertain terms the same
>mantra that all the posts responding to Martin, ie it will wreck the
>stainless steel shell. Well we did it anyway because, frankly, that made
>no sense to me.
>
>Well, about 3 years ago we took all that off as the top area of kaowool had
>been degrading (it is a top-loader) and, no surprise at all, the stainless
>steel shell is still in perfect condition. We replaced it with a new
>kaowool layer and this time we used masonry cement to make an impervious
>outer shell. So my kiln looks like a little missile silo.
>
>So, Martin, GO FOR IT!!!!!! If you want specifics let me know and maybe
>Fred, who actually did it, can talk with you on the horn.
>This was relatively easy to do and the fuel savings have got to be
>enormous, and less heat in the studio of course. BTW I also use several lids.
>
>And, BTW, sometimes I wonder at the myths people spout. I wonder if
>anybody ever actually saw a kiln degraded by adding insulation or if
>somebody's theoretical prognosis eventually became commonly accepted fact.
>
>Eleanora
>
>PS There was a time when I shared with open heart on this list. The
>endless and sometimes nasty criticisms shoved at me cured me of that quite
>a long time ago. It is too bad, I have alot to offer. Maybe the current
>batch of knee-jerk critics will think one second before just tripping over
>themselves to loudly proclaim I don't know what I am talking about.
>
>At 08:41 PM 7/16/02 +0100, you wrote:
>>From: Martin Howard
>>Subject: Insulating the outside of an electric kiln.
>>
>>
>>My kiln room gets hot when the kiln is on.
>>During winter I let the heat out a little at a time to keep me warm in the
>>rest of pottery.
>>
>>I could install a sauna, but really want the space for extra shelving:-)
>>But in summer, even the bit of UK summer we are now experiencing, it means
>>the kiln room is not usable for anything else when the kiln is on. And the
>>electricity bill is a little higher than I would like; up by 25% over
>>figures I got when I first had the kiln 3 years ago.
>>
>>Has anyone on list put an outside coating of insulation around such a kiln?
>>It is a large front loader with metal frame and block infill.
>>For example, would the packages that we put around hot water tanks in the UK
>>be OK for this kind of job?
>>
>>Martin Howard
>>Webbs Cottage Pottery
>>Woolpits Road, Great Saling
>>BRAINTREE, Essex CM7 5DZ
>>01371 850 423
>>martin@webbscottage.co.uk
>>http://www.webbscottage.co.uk
>>Updated 6th July 2002
>>
>>______________________________________________________________________________
>>Send postings to clayart@lsv.ceramics.org
>>
>>You may look at the archives for the list or change your subscription
>>settings from http://www.ceramics.org/clayart/
>>
>>Moderator of the list is Mel Jacobson who may be reached at
>>melpots@pclink.com.
>
>
>
>Eleanora Eden 802 869-2003
>Paradise Hill eeden@vermontel.net
>Bellows Falls, VT 05101 www.eleanoraeden.com
--
Steve Mills
Bath
UK
Gavin Stairs on sun 18 aug 02
At 11:59 PM 18/08/2002 +0100, Steve Mills wrote:
>According to some research done (I think) by the late Donald Shelley in
>the UK, and others, there is, in layman's terms, an optimal point in the
>insulation of a Kiln. Below that point the kiln is inefficient due to
>excessive heat loss through the wall. At the optimal point the heat loss
>is at its least, tho' there is still some. As the wall gets thicker
>beyond that point the heat is effectively drawn out of the kiln by the
>cooler outer layer, causing the heat to accelerate as it travels
>outwards.
Hi Steve,
Nice idea, but nope. There is no acceleration in heating kilns. The
transmission of heat through a wall depends on local conditions, i.e., the
temperature gradient across a bit of wall. So no amount of insulation
beyond a certain point will draw heat from the local area.
However, there is a skin effect, which has to do with the
radiation-convection-conduction of heat away from an open surface. If the
skin were particularly effective as an insulator, then it could be better
than any amount of some given insulator. For example, if the skin were a
perfect reflector. This is not usually the case, however.
There is also a heat sink effect, which may be what was being alluded to in
the work you cite. I referred in my notes to the heat capacity of a
material. If the wall of a kiln is a good heat conductor, and is connected
to an efficient heat sink like running water in sufficient quantity, then
you have a heat sink, in which the temperature will never rise above a
certain point, no matter how long you heat it. In fact, every kiln has
this characteristic. It's just that with good insulation, that temperature
is high enough not to be a problem. However, the greater the heat mass of
the wall, especially the wall close to the inside, the longer it will take
to heat the kiln to its operating point.
And finally, there is a temperature coefficient of insulation
effectiveness, which means that as the inner wall heats up past
incandescence, its effectiveness is lessened. So, as the kiln heats up, it
behaves as though the wall were becoming thinner, or as though the inner
wall were becoming transparent to heat, which is pretty close to what is
actually happening.
When people calculate optima in heat transfer, they are usually trying to
calculate the right amount of money to spend on insulation. There
certainly is a point beyond which it is uneconomic to insulate. That is
what kiln manufacturers do to decide how much insulation to put in a
kiln. In studio kilns, there has been a wide disparity in the amount of
money people have been willing to spend on insulation. In Japan, they want
a durable, well insulated kiln. That costs a lot of money. In America,
people seem less willing to spend money on insulation (and other quality
issues), so there seem to be a lot of poorly insulated kilns about. As
fuel and energy costs rise, the amount people are willing to spend on
insulation also rises.
The general idea is that the amount you spend on the next layer of
insulation should pay back its cost in energy savings over some reasonable
period. There are accounting techniques for this kind of calculation. If
you pay $100 to save $1/year, it may not be a wise investment. However, if
it saves you more than $20/per year, it begins to be attractive. You get
your money back in about 5 years.
The issue here is less about how much is good, than how it is sensible to
apply it. In general, over the structural skin is a bad idea, while
putting it under the skin is a good idea. With some kilns, this is
easy. In other designs, it is very difficult. Do as you please, but have
a think about it first.
Gavin
| |
|
