rec.crafts.metalworking removed form distribution as this thread is
off-topic there.

Rod Speed wrote:
wrote:
Odinn wrote:
On 9/18/2005 8:29 PM mumbled something
about the following:
Odinn wrote:

http://www.loghomesnetzine.com/vol2iss1/technotes.html


Sounds like these guys SELL log homes, like Enertia, who claim
their homes need NO HEAT ENERGY AT ALL (at certain times of year
:-)



...the link contains data from a test done by the National Bureau
of Standards for HUD comparing heating and cooling costs between
a log home and a standard stick frame.


This "data"? :-)

...In 1981-82, the National Institute of Standards [1] conducted
a series of tests at its facility outside of Washington DC for
the Dept. of Housing and Urban Development... over the course of
seven months using six 20' X 20' buildings that were identical
except for the construction of the exterior walls, one of which
was log...

...the log home (rated as an R-10 wall) performed as well as the
insulated wood frame house (R-12 rated wall) during the winter
heating period. The log home consumed 24% less energy during the
summer cooling period and 46% less during the transitional
spring/fall heating period...

1.) Contact: Mr. Douglas Burch, National Institute of Standards &
Technology, BR-B 320, Gaithersburg, MD, (301) 975-6433...


No one is claiming that log homes don't require heating or
cooling, only that they are not energy inefficient as would be
perceived by the R value of wood.


OK. I CLAIM log homes are "as inefficient as would be perceived by
the R-value of wood." Somebody should defend this 300-year old
physics :-)

The alleged R10 "home" above may have had less air infiltration than
the fiberglass "home," so it performed "as well" in wintertime, or
maybe the fiberglass did contain some moisture. Who knows? But that
has nothing to do with the log's R-value.

Did you even read it, or just copy it? They said they were IDENTICAL
except for the construction of the exterior walls.

That is not possible, whether they said so or not. If the
exterior dimensions are identical the log building will have
less volume inside due to the thicker walls. For a 20' by 20'
building, that could easily be a ten percent difference
in the internal volume of the buildings.

Nope, basic maths. Its only the difference between the wall
thicknesses that matters and that isnt 2' with log and drywall.

SPLORF! Do the basic math. If one building has a wall thickness
of 12" and the other has a wall thickness of 4" they cannot be
otherwise identical. If the internal dimensions are the same
they must have different external dimensions or vice versa.

Dunno where you got 2' from.

Just do the basic math and calulate the internal volume
differences assume that the 20' by 20' dimensions are
the external dimensions, which is how buildings are typically
measured.

It may be that the researchers normalized the building by internal
dimensions, but I don't see on that webpage where they
said one way or another.


And its academic anyway, they'd have got the same result
if they had ensured that the internal dimensions were identical.

They absolutely could not get the same results. This is easily
demonstrated without doing any math. Just imagine two log buildings,
one that is 20' by 20' inside, the other 20' by 20' outside.
Those will give you different results from each other, right?


The R-10 log home performed as well as an R-12 framed wall.

Yet there was no actual explanation for why. My guess would
be that the reduced surface area of the interior walls was
a major factor. But unless I do the math, that is only a guess.

And it isnt hard to do the maths and show its bull****.

But instead of doing math, you go on and spew bull****.
Clearly you won't even do arithmetic.

--

FF

wrote
Rod Speed wrote:
wrote:
Odinn wrote:
On 9/18/2005 8:29 PM mumbled
something about the following:
Odinn wrote:

http://www.loghomesnetzine.com/vol2iss1/technotes.html


Sounds like these guys SELL log homes, like Enertia, who claim
their homes need NO HEAT ENERGY AT ALL (at certain times of year
:-)



...the link contains data from a test done by the National Bureau
of Standards for HUD comparing heating and cooling costs between
a log home and a standard stick frame.


This "data"? :-)

...In 1981-82, the National Institute of Standards [1]
conducted a series of tests at its facility outside of
Washington DC for the Dept. of Housing and Urban
Development... over the course of seven months using six 20' X
20' buildings that were identical except for the construction
of the exterior walls, one of which
was log...

...the log home (rated as an R-10 wall) performed as well as
the insulated wood frame house (R-12 rated wall) during the
winter heating period. The log home consumed 24% less energy
during the summer cooling period and 46% less during the
transitional spring/fall heating period...

1.) Contact: Mr. Douglas Burch, National Institute of
Standards & Technology, BR-B 320, Gaithersburg, MD, (301)
975-6433...


No one is claiming that log homes don't require heating or
cooling, only that they are not energy inefficient as would be
perceived by the R value of wood.


OK. I CLAIM log homes are "as inefficient as would be perceived by
the R-value of wood." Somebody should defend this 300-year old
physics :-)

The alleged R10 "home" above may have had less air infiltration
than the fiberglass "home," so it performed "as well" in
wintertime, or maybe the fiberglass did contain some moisture.
Who knows? But that has nothing to do with the log's R-value.

Did you even read it, or just copy it? They said they were
IDENTICAL except for the construction of the exterior walls.

That is not possible, whether they said so or not. If the
exterior dimensions are identical the log building will have
less volume inside due to the thicker walls. For a 20' by 20'
building, that could easily be a ten percent difference
in the internal volume of the buildings.

Nope, basic maths. Its only the difference between the wall
thicknesses that matters and that isnt 2' with log and drywall.

SPLORF!

GTREWS!!!

Do the basic math.

Been there, done that.

If one building has a wall thickness of 12" and the other has
a wall thickness of 4" they cannot be otherwise identical.

Never said a word about identical, I JUST said
that the difference isnt 2' with log and drywall.

If the internal dimensions are the same they must
have different external dimensions or vice versa.

Duh.

Dunno where you got 2' from.

Your silly 10% claim.

Just do the basic math and calulate the internal volume differences
assume that the 20' by 20' dimensions are the external dimensions,
which is how buildings are typically measured.

You dont get your 10% when you do, and like I said,
it aint the internal volume that determines the heat loss
anyway, its the AREA of the walls that determines that.

It may be that the researchers normalized the building
by internal dimensions, but I don't see on that webpage
where they said one way or another.

Because it doesnt matter which way it was done.

And its academic anyway, they'd have got the same result
if they had ensured that the internal dimensions were identical.

They absolutely could not get the same results.

Wrong. Its the AREA of the walls and their R value
that determines how much heat is lost thru the walls.

This is easily demonstrated without doing any math.
Just imagine two log buildings, one that is 20' by 20'
inside, the other 20' by 20' outside. Those will give
you different results from each other, right?

Not with the HEAT LOSS being discussed they wont.

The R-10 log home performed as well as an R-12 framed wall.

Yet there was no actual explanation for why. My guess would
be that the reduced surface area of the interior walls was
a major factor. But unless I do the math, that is only a guess.

And it isnt hard to do the maths and show its bull****.

But instead of doing math, you go on and spew bull****.
Clearly you won't even do arithmetic.

I did it and doing it shows that your 10% claim is just plain wrong
and the arithmetic on the internal volume is irrelevant to the AREA
of the walls, which doesnt change. Its THAT that determines the
heat loss, not the internal volume of the house.

rec.crafts.metalworking removed from distribution as this is off-topic
there.

wrote:
Steve Spence wrote:

wrote:

Huh? Doesn't the R-value depend on thermal diffusivity and thickness?

It seems more accurate to say thermal diffusivity (1/RC) depends on R-value,

Not if the other poster, who wrote that R = t/k, where t is thickness
and k is thermal conductivity, is correct.

If so, R-value is independant of the specific heat, therefor there
is no direct correspndence between thermal diffusivity and R-value.
Two materials with the same thickness nd same R-value can have
different thermal diffusivities.


R- value isn't all that useful for comparison.

Wrong. Open your brain a bit, Steve :-) Even George Ghio admits mistakes.
Your stubbornness is giving you and alternative energy a bad reputation.

I think he's right. You really should be comparing thermal
diffussivities.

--

FF

wrote:

Doesn't the R-value depend on thermal diffusivity and thickness?

It seems more accurate to say thermal diffusivity (1/RC) depends on R-value,

Not if the other poster, who wrote that R = t/k, where t is thickness
and k is thermal conductivity, is correct.

You might enjoy looking up thermal diffusivity vs conductivity.

Nick

wrote:
wrote:

Doesn't the R-value depend on thermal diffusivity and thickness?

It seems more accurate to say thermal diffusivity (1/RC) depends on R-value,

Not if the other poster, who wrote that R = t/k, where t is thickness
and k is thermal conductivity, is correct.

You might enjoy looking up thermal diffusivity vs conductivity.


You must be trolling.

--

FF

wrote in message
oups.com...
rec.crafts.metalworking removed from distribution as this is off-topic
there.

wrote:
Steve Spence wrote:

wrote:

Huh? Doesn't the R-value depend on thermal diffusivity and thickness?

It seems more accurate to say thermal diffusivity (1/RC) depends on
R-value,

Not if the other poster, who wrote that R = t/k, where t is thickness
and k is thermal conductivity, is correct.

If so, R-value is independant of the specific heat, therefor there
is no direct correspndence between thermal diffusivity and R-value.
Two materials with the same thickness nd same R-value can have
different thermal diffusivities.


This is right on target. The 'k' is thermal conductivity of a material, not
thermal diffusivity.


R- value isn't all that useful for comparison.

Wrong. Open your brain a bit, Steve :-) Even George Ghio admits mistakes.
Your stubbornness is giving you and alternative energy a bad reputation.

I think he's right. You really should be comparing thermal
diffussivities.


If you are modeling the steady-state behavior of a wall, the thermal
diffusivity is irrelevant. A higher thermal diffusivity merely means the
wall structure reaches equilibrium temperature distribution sooner when a
new inside/outside temperature are applied.

In a passive solar system, the diffusivity of building structure can be
important for 'evening out' the diurnal temperature swings. But that gets
into the whole discussion about the use of large thermal capacitance and
whether it can be used to save energy.

daestrom

wrote:

...Doesn't the R-value depend on thermal diffusivity and thickness?

...thermal diffusivity (1/RC) depends on R-value

Not if the other poster, who wrote that R = t/k, where t is thickness
and k is thermal conductivity, is correct.

You seem to be confusing conductance and diffusivity.

R is the thermal resistance (a wall property), k is the conductivity
(a material properrty), 1/R is the conductance, (a wall property), and
1/RC is thermal diffusivity (a largely irrelevant material property,
in constantly cold weather.) Generally, words ending with "-ivity" are
bulk material properties and words ending with -ance" are properties
of a particular chunk of material.

Nick

wrote:
wrote:

...Doesn't the R-value depend on thermal diffusivity and thickness?

...thermal diffusivity (1/RC) depends on R-value

Not if the other poster, who wrote that R = t/k, where t is thickness
and k is thermal conductivity, is correct.

You seem to be confusing conductance and diffusivity.

No. I did not know the definition of R-value, speculated, and was
shown to be wrong. R-value is not a generally useful concept in
heat transer work. It is a very useful concept for builders.


R is the thermal resistance (a wall property), k is the conductivity
(a material properrty), 1/R is the conductance, (a wall property), and
1/RC is thermal diffusivity (a largely irrelevant material property,
in constantly cold weather.) Generally, words ending with "-ivity" are
bulk material properties and words ending with -ance" are properties
of a particular chunk of material.

R-value, as you note, is a wall property, it is partly
dependent on thickness. Thermal diffusivity, as you note,
is a material property, independent of the 'bulk' geometry
of the material.

Thus thermal diffusivity is independent of R-value. The
thermal diffusivity of the material does not 'know' how
thick the wall is.

For example, two walls with identical geometry can have the
same R-value but different thermal diffusivities if the
material therein has the same thermal conductivity but
different specific heats or densities.

Both R-value and thermal conductivity have a common dependency
on thermal conductivity.

It is clear that R-value is dependent on thermal conductivity,
not vice-versa. Changing the thicknes of a wall changes the
R-value while the thermal conductivity of the material in the
wall does not change despite that change in the R-value. But
changing the thermal conductivity of the material in the wall
DOES change the R-value.

--

FF

wrote:

R-value is not a generally useful concept in heat transer work.

I'd say it's very useful :-) Diffusivity seems less useful.

It is a very useful concept for builders.

It could be, but most builders seem to have little interest in heatflow.
They just look at the drawing and the building inspector and figure out
what they can get away with before they shoot themselves in the leg with
a nailgun or declare bankruptcy and leave town with pocketfuls of money.

Nick

wrote:
wrote:

R-value is not a generally useful concept in heat transer work.

I'd say it's very useful :-) Diffusivity seems less useful.

I worked in industry for several years doing, among other things,
heat transfer, and never even saw a definition for R-value at
work or in heat-transfer and solar energy utilization classes.


It is a very useful concept for builders.

It could be, but most builders seem to have little interest in heatflow.
They just look at the drawing and the building inspector and figure out
what they can get away with before they shoot themselves in the leg with
a nailgun or declare bankruptcy and leave town with pocketfuls of money.


That's what makes R-value a useful concept to them. They can
just add up the R-values to meet spec (code perhaps) and not
worry about what the actual energy losses/costs are going to be.

--

FF

wrote:

R-value is not a generally useful concept in heat transer work.

I'd say it's very useful :-) Diffusivity seems less useful.

I worked in industry for several years doing, among other things,
heat transfer, and never even saw a definition for R-value at
work or in heat-transfer and solar energy utilization classes.

You "did heat transer work" for several years and never ran into
an R-value, and then confused conductance with diffusivity? :-)

It is a very useful concept for builders.

It could be, but most builders seem to have little interest in heatflow.
They just look at the drawing and the building inspector and figure out
what they can get away with...

That's what makes R-value a useful concept to them. They can
just add up the R-values to meet spec (code perhaps) and not
worry about what the actual energy losses/costs are going to be.

They could... Then again, my brother (a mechanical engineer) bought
an expensive new house on paper in a development near Philadelphia.
When he noticed the foundation was rotated 180 degrees, ruining his
plans to add on a solarium, the builder said "Read the fine print
in the contract. It's our choice."

Then he visited after work every day as the house went up, kicking out
twisted studs which were often replaced with better studs the next day.

When he noticed carpenters building a first floor ceiling in his
2-story cathedral entrance hall, they told him that was easier.
After some negotiation, they removed the ceiling...

Time passes. The builder's corp goes bankrupt 3 months after selling
the last house, a standard practice around here. And 12 years later,
the bathroom ceiling collapses, because there's no insulation or vapor
barrier in the wall. My brother checks the rest of the walls and finds
lots of similar problems and tears out the drywall and fixes the walls.

And he discovers that all of the windows are rotting because
of insulation and vapor barrier problems, so he replaces them.

Then he finds a job in Detroit and sells the house for about the same
price as the other hundred development houses... The new owner gots
a good bargain, comparatively.

Nick

wrote:
wrote:

R-value is not a generally useful concept in heat transer work.

I'd say it's very useful :-) Diffusivity seems less useful.

I worked in industry for several years doing, among other things,
heat transfer, and never even saw a definition for R-value at
work or in heat-transfer and solar energy utilization classes.

You "did heat transer work" for several years and never ran into
an R-value, and then confused conductance with diffusivity? :-)


Yes and no, respectively. But then again, you knew that
because I had told you both befor.


It is a very useful concept for builders.

It could be, but most builders seem to have little interest in heatflow.
They just look at the drawing and the building inspector and figure out
what they can get away with...

That's what makes R-value a useful concept to them. They can
just add up the R-values to meet spec (code perhaps) and not
worry about what the actual energy losses/costs are going to be.

They could... Then again, my brother (a mechanical engineer) bought
an expensive new house on paper in a development near Philadelphia.
...

Well if he was a Civil Engineer he probably would have bought a
house on a more substantial foundation, like cement block.

--

FF