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Default polyiso vs styrofoam

Duane C. Johnson wrote:

daestrom wrote:

If there's 'no air gap' then the emissivity of the
foil becomes pretty much irrelevant.


I agree.

Nick, can you give us citations pro or con?


Table 2 on page 22.2 of the 1993 ASHRAE HOF covers air gaps down to 0.5",
with a footnote a: ... Thermal resistance R = 1/C, where C = Hc + EeffHr,
Hc is the conduction- convective coefficient, EeffHr is the radiation
coefficient ~ 0.00686Eeff[(Tm+460)/100]^3, and Tm is the mean temp of
the air space... For extrapolation from Table 2 to air spaces less than
0.5 inches (as in insulating window glass), assume Hc = 0.159(L+0.0016Tm)/L,
where L is the air space thickness in inches and Hc is heat transfer
through the air space only.

So, the surface conductance is the sum of its radiation conductance
EeffHr and Hc, which becomes a lot larger than EffHr as L decreases.
For instance, with Eeff = 0.05 (1 foil) at 50 F, EffHr = 0.0455 (R22 :-),
but Hc = 0.159(L+0.08)/L, ie 0.17 (R5.8) for L = 1", 0.29 (R3.5) for 0.1",
1.43 (R0.7) for 0.01", and 12.9 (R0.08) for L = 0.001".

L Hc EffHr U = Hc+EffHr R = 1/U

1" 0.17 0.0455 0.2155 4.6
0.1" 0.29 0.0455 0.3317 3.0 (surprisingly large)
0.01" 1.43 0.0455 1.4755 0.7
0.001" 12.90 0.0455 12.9455 0.1

Each foil can count, on double-foil foamboard, but 2 facing foils with
an air gap only reduce the combined emissivity from 0.05 to 0.03 (1/Eff
= 1/E1+1/E2-1) OTOH, 2 foils may retain inert gas longer than 1 foil.

Notes b and c say

Values apply for ideal conditions, ie air spaces of uniform thickness
bounded by plane, smooth, parallel surfaces with no air leakage from
the space... Thermal resistance values of multiple air spaces must be
based on careful estimates of mean temp differences for each space.

A single resistance value cannot account for multiple air spaces; each
space requires a separate resitance calculation that applies only for
the established boundary conditions. Resistance of horizontal spaces with
heat flow downward are sustantially independent of temp diff [and large,
eg R8.17 for e = 0.05 with 3.5" and a 50 F mean and 30 F temp diff.]

Nick

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Solar Flare
 
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Default polyiso vs styrofoam

Fibregalss is not a great insulation. However air is a
good insulaltion when you stop it from transmitting
heat by convection. Fibreglass woll makes "trapped air"
a good insulation.

The foil people state an air gap is needed to reflect
the radiant heat. If in contact it is still a metal to
conduct the heat very well.

"Duane C. Johnson" wrote in message
...
I understand there is an associated R value

associated with
air gaps. However, I would have assumed that the R

value of
of conventional insulation, say fiber glass, would

have been
better than that of an air gap. At least for gaps

that were
greater than the separation of the fibers.

What I understood was that the foil on foil backed

insulation
had a different function. It was to "Reflect" infra

red
radiation. This reflector can be behind sheet rock

which is
able to transmit the infra red back to the source.

Duane

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Default polyiso vs styrofoam

Duane C. Johnson wrote:

I understand there is an associated R value associated with air gaps.


Sure...

However, I would have assumed that the R value of conventional
insulation, say fiber glass, would have been better than that
of an air gap.


Add the air gap's R-value to the insulation's R-value.

What I understood was that the foil on foil backed insulation
had a different function. It was to "Reflect" infra red
radiation. This reflector can be behind sheet rock which is
able to transmit the infra red back to the source.


It could do that, with an air gap bgetween the foil and the sheet rock,
but the foil won't do much if it touches the sheet rock, except to act
as a vapor barrier.

Nick

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Default polyiso vs styrofoam

Jeff Thies wrote:

Add the air gap's R-value to the insulation's R-value.


As long as we're talking about insulation, I've been trying to figure
out the radiation from the insulation and am not getting far.

From a EffHr 0.0455 (for that .05 foil Eff)


That's a radiation conductance.

Thermal resistance R = 1/C, where C = Hc + EeffHr.


Which you add to the convection conductance, which typically brings
the combined R-value of the foil down to something between 1 and 10.

It appears to me that the max effective R value would be 22...


For the foil radiation alone. But you have to add the convective
conductance Hc for the foil to its radiation conductance EeffHr.
Then take the reciprocal, then add the insulation's R-value.

It would seem that the radiation from the insulation would mean
these high R blankets would have diminishing returns.


No. Add the insulation's R-value to the foil's R-value...

It also seems that a foil barrier on the ambient side of the insulation
would be very valuable.


It's valuable on either side, but people don't like foil walls,
and the foil would weather badly outdoors, and wind would raise
its convection loss.

Nick



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daestrom
 
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Default polyiso vs styrofoam


"Jeff Thies" wrote in message
nk.net...
wrote:
Duane C. Johnson wrote:


I understand there is an associated R value associated with air gaps.



Sure...


However, I would have assumed that the R value of conventional
insulation, say fiber glass, would have been better than that
of an air gap.



Add the air gap's R-value to the insulation's R-value.


As long as we're talking about insulation, I've been trying to figure out
the radiation from the insulation and am not getting far.

From a EffHr 0.0455 (for that .05 foil Eff) and:

Thermal resistance R = 1/C, where C = Hc + EeffHr.

It appears to me that the max effective R value would be 22, and that
for an infinitely thick blanket with a foil outer barrier. It would seem
that the radiation from the insulation would mean these high R blankets
would have diminishing returns.


Well, the law of diminishing returns certainly applies to any insulation
project. But you can certainly insulate with higher effective R values than
22. Don't see what you're getting at there. One foot thick fibreglass can
give you about R-38, irrespective of the coatings or any 'facing' such as
drywall or OSB over it.

Remember, a higher R-value *behind* the foil surface makes the foil surface
temperature closer to the ambient temperature. And that reduces radiant
losses as well.


It also seems that a foil barrier on the ambient side of the insulation
would be very valuable.

But things are not done this way, what have I misunderstood?


As far as a foil barrier on the ambient side, it isn't really all that
valuable in most circumstances. Yes, it would certainly reduce the heat
gain from direct sunlight, and reduce radiant heat loss. But if you look at
how much heat is lost to the environment due to simple convection, you will
realize that even if radiant heat losses were cut to zero, it wouldn't
reduce the total heat losses by a significant percentage in most cases. You
won't get a lot of improvement for the 'buck'. And a lot of folks don't
like the idea of living in an aluminum foil sided house.

Radiant losses can be a big issue if the temperature difference is large
and/or you've already taken steps to reduce the other forms of heat loss
(conduction/convection). Or if your goal is to reduce absorption from the
sun.

daestrom


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Dennis
 
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Default polyiso vs styrofoam

I'm not on usenet and don't know how to post there, but I read your =
posts frequently...


If you can read usenet posts, you can probably post yourself...
Might be worth learning how.


OK. Looks like I got it figured out.

Now as far as window insulation goes, what about packing peanuts
between the panes?

Dennis

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Default polyiso vs styrofoam

Dennis wrote:

If you can read usenet posts, you can probably post yourself...
Might be worth learning how.


OK. Looks like I got it figured out.


Congratulations!

Now as far as window insulation goes, what about packing peanuts
between the panes?


Sounds rather permanent. The Zomeworks Beadwall system moved small
styrofoam beads into and out of a window cavity with a vacuum cleaner.
It worked well, but the beads required lots of storage space and they
wouldn't flow well through fittings, so each window cavity required
a separate store and vacuum cleaner. And the multiple vacs required
an electrical sequencer to avoid blowing fuses.

"Replacement foam insulation" (filling the space between two glazings
with soap bubble foam at night) seems more practical. It's being applied
to greenhouses now. In one system, a shop vac pushes air through a 100'x2"
pipe with some holes in a 10% detergent solution near the ground, making
bubbles rise to the top of a 100' long quonset-shaped greenhouse. When
the bubbles reach the top, the vac automatically turns off until they
recede, then starts again for a few seconds every hour or so to replenish
them during the night. The bubble system turns off at dawn and a small
blower inflates the space between the 2 plastic glazings with air.

Nick

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Anthony Matonak
 
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Default polyiso vs styrofoam

wrote:
Dennis wrote:

Now as far as window insulation goes, what about packing peanuts
between the panes?


Sounds rather permanent. The Zomeworks Beadwall system moved small
styrofoam beads into and out of a window cavity with a vacuum cleaner.

....

As I recall, I've heard reports that there were other issues with
the beadwall system. For instance, the foam beads would break down
over time.

"Replacement foam insulation" (filling the space between two glazings
with soap bubble foam at night) seems more practical.


This might be fine for a greenhouse but I question it's usefullness
in a house. For instance, how clear and streak free are the windows
when the foam goes away? How do you insure that the window cavities
are sealed well enough that they don't ever leak in some hard to
detect fashion and cause damage to the structure? With a bubble foam
system, how do you design the windows so that they can open?

How about this for a possible solution. There are double pane windows
being sold now that have window shades or blinds inbetween the panes.
Mostly, this means that they never get dusty and you won't find the
cat has hung himself from them. Air is a pretty good insulator except
when there is some kind of circulation going on. A cellular shade
could be produced using thin mylar or paper such that it folds up
into a small space at the top or bottom of the window cavity and yet
can unfold to fill the entire space with small air-filled pockets.
One or more layers of aluminum coatings could be added as well to
help cut down on radiant loss.

Anthony
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Default polyiso vs styrofoam

Anthony Matonak wrote:

... I've heard reports that there were other issues with
the beadwall system. For instance, the foam beads would
break down over time.


Not exactly. They tended to clump if never cycled.
IIRC, cycling once a month would fix that.

"Replacement foam insulation" (filling the space between two glazings
with soap bubble foam at night) seems more practical.


... I question it's usefullness in a house. For instance, how clear and
streak free are the windows when the foam goes away?


Moreso than my $500 500 ft^2 cloudy plastic film sunspace :-)

How do you insure that the window cavities are sealed well enough that
they don't ever leak in some hard to detect fashion and cause damage to
the structure?


I'd probably make the "windows" with 2 layers of 0.020" clear polycarbonate
from a 48" roll, over plastic 2x4s, with lots of silicone caulk.

... how do you design the windows so that they can open?


You don't. A few plain windows might do that.

How about this for a possible solution. There are double pane windows
being sold now that have window shades or blinds inbetween the panes.
Mostly, this means that they never get dusty and you won't find the
cat has hung himself from them. Air is a pretty good insulator except
when there is some kind of circulation going on.


Even tiny circulations.

A cellular shade could be produced using thin mylar or paper such that
it folds up into a small space at the top or bottom of the window cavity
and yet can unfold to fill the entire space with small air-filled pockets.


It could be...

One or more layers of aluminum coatings could be added as well to
help cut down on radiant loss.


Good idea. Scheme 18.7 on page 168 of Bill Shurcliff's 1980 Brick House book
"Thermal Shutters and Shades" describes 5 sheets of metallized Mylar with
springy spacers that unfold when it's rolled down. Scheme 18.8 on page 170
describes an interesting self-inflating Mylar shade. Alas, these are no longer
being made. Perhaps they can be recreated with an iron or a $118 -RS1 hot
roller for plastic film seam-sealing from Hillas at (800) 952 7274.

Symphony "energy track" shades with tracks on each side to reduce air leaks
are fairly expensive and low performing. They (877) 966-3689 say their room
darkening shade has a R-value of 3.2, when used with an R1.8 window :-) This
increases to R4.8 with side tracks. A 3'x6' shade costs $170 with the tracks.

Tiny cold soap bubbles can have the same R-value as fiberglass. A 6" window
might transmit 80% of the sun during the day and become an R20 wall at night.

Nick



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Dennis
 
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Default polyiso vs styrofoam

Now as far as window insulation goes, what about packing peanuts
between the panes?



Sounds rather permanent.


I was considering this as a seasonal plan. Fill the space between a
double sash window and storm window on the north wall with packing
peanuts in the fall and remove in spring. I could then throw them away
or keep them for next season. There is also the stationary half of my
patio door, (hinged french door), that has a cavity of 35" x 78" x 4".

Cost: $0.00, if using used packing peanuts that currently go to
landfill. Convincing wife to agree, priceless.

Dennis

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Anthony Matonak
 
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Default polyiso vs styrofoam

Dennis wrote:
....
I was considering this as a seasonal plan. Fill the space between a
double sash window and storm window on the north wall with packing
peanuts in the fall and remove in spring. I could then throw them away
or keep them for next season. There is also the stationary half of my
patio door, (hinged french door), that has a cavity of 35" x 78" x 4".

Cost: $0.00, if using used packing peanuts that currently go to
landfill. Convincing wife to agree, priceless.


I think there might also be fire issues with packing peanuts.
Not like they are going to spontaneously combust but if they
ever did catch a spark they would burn intensely and produce
lots of toxic smoke.

Anthony
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Dennis
 
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Default polyiso vs styrofoam

Anthony Matonak wrote

I think there might also be fire issues with packing peanuts.
Not like they are going to spontaneously combust but if they
ever did catch a spark they would burn intensely and produce
lots of toxic smoke.


How is this any different than the foam board that completely surrounds
my house now? Isn't glass fire resistant? How will this spark get
into the cavity? My carpeting is completely exposed and far more
susceptible to catching a spark, which would yield large amounts of
poisionous gas, than a window space filled with packing peanuts.

I was mostly curious to see if anyone actually tried this and what the
result was. I think I will give it a try in one window unless someone
knows of any real concerns that could damage my home.

Dennis

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Dennis
 
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Default polyiso vs styrofoam

Anthony Matonak wrote

I think there might also be fire issues with packing peanuts.
Not like they are going to spontaneously combust but if they
ever did catch a spark they would burn intensely and produce
lots of toxic smoke.


How is this any different than the foam board that completely surrounds
my house now? Isn't glass fire resistant? How will this spark get
into the cavity? My carpeting is completely exposed and far more
susceptible to catching a spark, which would yield large amounts of
poisionous gas, than a window space filled with packing peanuts.

I was mostly curious to see if anyone actually tried this and what the
result was. I think I will give it a try in one window unless someone
knows of any real concerns that could damage my home.

Dennis

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Jeff Thies
 
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Default polyiso vs styrofoam

wrote:
Duane C. Johnson wrote:


daestrom wrote:


If there's 'no air gap' then the emissivity of the
foil becomes pretty much irrelevant.



I agree.


Nick, can you give us citations pro or con?



Table 2 on page 22.2 of the 1993 ASHRAE HOF covers air gaps down to 0.5",
with a footnote a: ... Thermal resistance R = 1/C, where C = Hc + EeffHr,


This is a bit offtrack, but about attic insulation...

From your calculations of a typical EeffHr (radiation coefficient) of
..04555 this would give a maximum effective R value of 22 no matter how
thick the insulation. Thicker would get you closer to it but there are
diminishing returns.

Also, not knowing the Eeff of a paper barrier, it would certainly be
higher than .05


Hc is the conduction- convective coefficient, EeffHr is the radiation
coefficient ~ 0.00686Eeff[(Tm+460)/100]^3, and Tm is the mean temp of
the air space... For extrapolation from Table 2 to air spaces less than
0.5 inches (as in insulating window glass), assume Hc = 0.159(L+0.0016Tm)/L,
where L is the air space thickness in inches and Hc is heat transfer
through the air space only.

So, the surface conductance is the sum of its radiation conductance
EeffHr and Hc, which becomes a lot larger than EffHr as L decreases.
For instance, with Eeff = 0.05 (1 foil) at 50 F, EffHr = 0.0455 (R22 :-),
but Hc = 0.159(L+0.08)/L, ie 0.17 (R5.8) for L = 1", 0.29 (R3.5) for 0.1",
1.43 (R0.7) for 0.01", and 12.9 (R0.08) for L = 0.001".

L Hc EffHr U = Hc+EffHr R = 1/U

1" 0.17 0.0455 0.2155 4.6
0.1" 0.29 0.0455 0.3317 3.0 (surprisingly large)
0.01" 1.43 0.0455 1.4755 0.7
0.001" 12.90 0.0455 12.9455 0.1

Each foil can count, on double-foil foamboard, but 2 facing foils with
an air gap only reduce the combined emissivity from 0.05 to 0.03 (1/Eff
= 1/E1+1/E2-1) OTOH, 2 foils may retain inert gas longer than 1 foil.

Notes b and c say

Values apply for ideal conditions, ie air spaces of uniform thickness
bounded by plane, smooth, parallel surfaces with no air leakage from
the space... Thermal resistance values of multiple air spaces must be
based on careful estimates of mean temp differences for each space.

A single resistance value cannot account for multiple air spaces; each
space requires a separate resitance calculation that applies only for
the established boundary conditions. Resistance of horizontal spaces with
heat flow downward are sustantially independent of temp diff [and large,
eg R8.17 for e = 0.05 with 3.5" and a 50 F mean and 30 F temp diff.]

Nick




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Default polyiso vs styrofoam

Jeff Thies wrote:

Table 2 on page 22.2 of the 1993 ASHRAE HOF covers air gaps down to 0.5",
with a footnote a: ... Thermal resistance R = 1/C, where C = Hc + EeffHr,


From your calculations of a typical EeffHr (radiation coefficient) of
.04555 this would give a maximum effective R value of 22 no matter how
thick the insulation. Thicker would get you closer to it but there are
diminishing returns.


No. Add Hc to EeffHr and take the reciprocal to find the R above, for
the foil only. THEN ADD THAT TO THE R-VALUE OF THE INSULATION ITSELF.

Nick

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Jeff Thies
 
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Default polyiso vs styrofoam

Thanks Nick,

That was an old draft and I didn't mean to send it, you had answered
this days ago...

Cheers,
Jeff


Table 2 on page 22.2 of the 1993 ASHRAE HOF covers air gaps down to 0.5",
with a footnote a: ... Thermal resistance R = 1/C, where C = Hc + EeffHr,


From your calculations of a typical EeffHr (radiation coefficient) of


.04555 this would give a maximum effective R value of 22 no matter how
thick the insulation. Thicker would get you closer to it but there are
diminishing returns.



No. Add Hc to EeffHr and take the reciprocal to find the R above, for
the foil only. THEN ADD THAT TO THE R-VALUE OF THE INSULATION ITSELF.

Nick

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Cathy Strong
 
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Default polyiso vs styrofoam

Dennis wrote:
I'm not on usenet and don't know how to post there, but I read your =
posts frequently...



If you can read usenet posts, you can probably post yourself...
Might be worth learning how.



OK. Looks like I got it figured out.

Now as far as window insulation goes, what about packing peanuts
between the panes?

Dennis

Bad Idea! The glass will shatter for sure when the elephants get
in there.
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