Thermal resistance of plywood

Jim Thompson · Aug 1, 2009

Several years ago, as an aside to another thermal question, I asked...

"Brings to mind a thing I've been pondering... what's the thermal
resistance of 3/4" plywood ?

"

Never saw a response.

More specifically, a closed plywood box, inside dimensions of 8" x 11"
x 18".

Outside ambient of around 77°.

How many watts of dissipation inside of box to raise interior air
temperature to 95°F? (I might use a fan to circulate the air.)

If I made one wall of the box 1/8" glass (8" x 18" side), how much
change?

...Jim Thompson
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Archimedes' Lever · Aug 1, 2009

Several years ago, as an aside to another thermal question, I asked...

"Brings to mind a thing I've been pondering... what's the thermal
resistance of 3/4" plywood ?"

Never saw a response.

More specifically, a closed plywood box, inside dimensions of 8" x 11"
x 18".

Outside ambient of around 77°.

How many watts of dissipation inside of box to raise interior air
temperature to 95°F? (I might use a fan to circulate the air.)

If I made one wall of the box 1/8" glass (8" x 18" side), how much
change?

...Jim Thompson

It is called R factor.

There are exterior panels that are made specifically for this purpose.
The best in the world are made from hemp fiber in a country that grows
thousands of acres of non-drug hemp strains because the fiber is very
strong (the strongest plant fiber) The best exterior home construction
panels are hemp.

They also mean that:

"No pine tree forests were cleared in the making of these homes".

America is stupid sometimes. Hemp laws are one such example.

Archimedes' Lever · Aug 2, 2009

Engineers call it "thermal conductivity."

John

What do you think the "R factor" value is based on?

We call it science regardless of the discipline.

Jim Thompson · Aug 2, 2009

R value is defined here:

http://www.sizes.com/units/rvalue.htm

For 3/4" the R value appears to be 0.93 delta °F x ft^2 x hour/Btu

This page:

http://hyperphysics.phy-astr.gsu.edu/Hbase/tables/rvalue.html

Has 0.125" single pane glass with an R value of 0.89. So your plywood
and glass are pretty close to even.

I'll leave the units conversion up to you for actual values.

Paul Keinanen · Aug 2, 2009

Milli-Kelvin?? Yes, that is a useable unit but isn't watts per
Kelvin a bit more practical and conventional?

In case that this is not a troll, look at it (using a fixed width font
like Courier New):

W
0.13 ----------
m K

Paul

Son of a Sea Cook · Aug 2, 2009

Milli-Kelvin?? Yes, that is a useable unit but isn't watts per
Kelvin a bit more practical and conventional?

Idiot. NOTHING "milli" uses a capital M. It was also inappropriate to
be the first word in your non-sentence, if not for that reason alone.

Perhaps "Are you saying milli-Kelvin?"

Don Klipstein · Aug 2, 2009

Several years ago, as an aside to another thermal question, I asked...

"Brings to mind a thing I've been pondering... what's the thermal
resistance of 3/4" plywood ?"

Never saw a response.

More specifically, a closed plywood box, inside dimensions of 8" x 11"
x 18".

I have some liking to page 1572 of the 43rd edition of the "CRC
Handbook", "Thermal Conductivity of Wood Across the Grain at Various
Moisture Content Values".

The moisture content values vary mainly with type of wood tested, mostly
from 9 to 14 %. Thermal conductivity in BTU/hour through 1 inch thickness
of 1 square foot with 1 degree F temperature difference has 90% of figures
in the range of .73 to 1.39, and I would like to say as a result
moderately-conservatively .8, more-usual .9.

This box, with inside surface area (assuming above dimensions are
external) of 6 * 6.5 * 9.5 * 16.5 /12^3) about 3.54 square feet, with 3/4
inch thickness, has thermal resistance (within itself, as opposed to
thermal resistance of adjacent air) of maybe 3/4 divided by 3.54 divided
by .8-.9 watts/F, or roughly (give or take) 1/4 degree F per watt.

Outside ambient of around 77°.

How many watts of dissipation inside of box to raise interior air
temperature to 95°F? (I might use a fan to circulate the air.)

If I made one wall of the box 1/8" glass (8" x 18" side), how much
change?

Thermal resistance drops bigtime, to extent where I consider likely the
thermal resistance of the air inside and just outside the box.

I know someone who, at my advice, did an experiment measuring
temperature of a metal-cased device in open air and in a "largish
shoebox", with readings taken over time to verify temperature
stabilization. As best as I remember at this moment, the "largish
shoebox" including air stagnated near its inside and outside surfaces
had thermal resistance around 2-2.5 degrees F per watt, probably closer to
2 - apparently mostly from impairing convection of air around the device
that was tested. The device being tested had overall dimensions close to
those of a "double thickness cigarette pack".

- Don Klipstein ([email protected])

Archimedes' Lever · Aug 2, 2009

m = meter.

John

Larkin = dope.

Richard Cranium · Aug 2, 2009

On Sun, 02 Aug 2009 03:04:14 -0700, Archimedes' Lever

Larkin = dope.

Archie = Celibate asshole

Archimedes' Lever · Aug 2, 2009

It's better expressed as w/m-K or even w * m^-1 * k^-1

Better is the wrong word. PROPER is the right word.

Placing it right next to the K makes it a "milli" prefix in ALL
circles. So if it is not written right, it will not get read right. It
has nothing to do with what someone "thinks".

Artemus · Aug 2, 2009

"Jim Thompson" wrote

"Brings to mind a thing I've been pondering... what's the thermal
resistance of 3/4" plywood ?"

Never saw a response.

I hope you can see this post as I've never gotten any acknowledgement on any other
post I've made in this group.

From: http://www.performancepanels.com/?content=app_pp_atr_therm
For most practical purposes it is neither necessary nor feasible to determine the
actual species makeup of the plywood panel. For determining the overall coefficient
of heat transmission (U value) of a construction assembly, APA publications use k =
0.80 for softwood, as listed by the American Society of Heating, Refrigerating and
Air Conditioning Engineers (ASHRAE). Use of this single value simplifies
computations, and produces only insignificant differences in resulting design heat
losses.

The table below shows thermal resistance, R, for several plywood panel thicknesses,
based on k = 0.80. Thermal resistance represents the ability of the material to
retard heat flow and is the reciprocal of k, adjusted for actual material thickness.
(for a 3/4" panel R = 0.94)

The definitive authority on wood properties is R. Bruce Hoadley and his book,
"Understanding wood: a craftsman's guide to wood technology", is considered by many
to be the holy bible on wood properties.

I hope this helps.
Art

Don Klipstein · Aug 2, 2009

Better is the wrong word. PROPER is the right word.

Placing it right next to the K makes it a "milli" prefix in ALL
circles. So if it is not written right, it will not get read right.

Except by those who know enough physics to know what units of heat
conductivity are - power per (area cubed * temperature difference / linear
distance), which simplifies to power per (linear distance unit *
temperature difference). People who know this and metric units as used in
physics are familiar with watts per meter-kelvin and recognize that w/mK
stated as a unit of thermal conductivity meant this.

It appears to me that you went quite a ways on a spelling flame.

- Don Klipstein ([email protected])

Archimedes' Lever · Aug 3, 2009

Except by those who know enough physics to know what units of heat
conductivity are - power per (area cubed * temperature difference / linear
distance),

Except that ANYONE that does know such a thing would also know how to
express it properly, DIPSHITS!

So... IMPROPERLY expressed means invalid at the start. Stop trying to
attack those that 'read' it. Put the fucking blame where it fucking
belongs, dumbfuck.

Lower case m in front of a figure that represents a unit of measure,
ALWAYS means milli.

Without the dash, your shit is weak. Learn to express it right.
Doesn't matter what ANYONE's familiarity with ANY segment of physics is.

You do not pull that dumb ASSumption crap just like you do not top
post.

Those that know enough physics know how to express a fucking formula
without fucking it up royally.

Jim Thompson · Aug 3, 2009

Meters makes less sense; thermal conductivity might be in terms of
such-and-such per square.
Seems a little more specificity is needed.

nospam · Aug 3, 2009

Robert Baer said:
Meters makes less sense; thermal conductivity might be in terms of
such-and-such per square.

Thermal conductivity is proportional to area (m^2) and inversely
proportional to thickness (m) which leaves you with just m.

0.13 W/mK is 0.13 W/K across a 1m cube.

--

Jim Thompson · Aug 3, 2009

I very much doubt that any pine tree forests were cleared in the making
of my home or shop -- here in western Oregon it's all Doug Fir.

Environmentalists are so dippy sometimes.

GregS · Aug 3, 2009

Perhaps,but that will cut no ice when shopping for thermal insulation
panels at Home Depot or Lowes.

I learned R-1 = 1 inch of dry wood.
R-12 = 12 inches of wood.
Plywood has glue so its less.

I learned in my basement, I used two sheets of foil/foam/foil and I get
a lot more insulation than what the stuff specifies. It about 3/16 inch
thick. On a cinderblock wall, which itself is R 3.5, I lay a sheet against the wall.
Out from the wall about 1 inch I put another layer of the foiled sheet.
Its almost as good as 2 inches of fiberglass.

I am getting an insultion value of over double what the foil specifies. The foil
adds almost R1.5 for the reflective addition, but I am seeing more.

In the garage, I stapled porous aluminum on polyethelene sheeting to the joists
on the ceiling. The results are far better than the R value. You cannot feel
any radiated energy from the roof compared to before. Even in the winter
its helps insulate mostly from reflective energy. The higher the differential
the more reflective coatings play a role in heat transfer.

greg

Archimedes' Lever · Aug 4, 2009

I very much doubt that any pine tree forests were cleared in the making
of my home or shop -- here in western Oregon it's all Doug Fir.

Environmentalists are so dippy sometimes.

I'm sorry, but the only 2x4s in MOST of the nation are PINE.

Pine is the predominate construction media in the US.

Pine grows at a wide spacing, at two feet per year. Hemp grows, even
tightly spaced, at two feet per month.

An acre of hemp can produce far more material than an acre of ANY tree
species.

The fibers are also more manageable, and there are other products that
can be derived as well.

Rich Grise · Aug 4, 2009

Excellent question; i do not know - but the manufacturers data sheet
should disclose that.
Also, there are (web) sites that give thermal conductivity and
R-values for a large group of different materials from cement to steel
(and may include plywood; do not remember since it was over a year ago
and only looked one and bypassed plywood if it was listed).

http://www.sizes.com/units/rvalue.htm
http://www.allwallsystem.com/design/RValueTable.html
etc.:
http://www.google.com/search?hl=en&q=R-value+of+plywood

Hope This Helps!
Rich

Archimedes' Lever · Aug 4, 2009

NymNoNuts is dippy 100% of the time.

You're a goddamned retard as usual, Thompson. You don't even know what
he was talking about.

You are as clueless as it gets every time you jack off and enter a
thread you only partially participate in.

You are about as stupid as it fucking get, you retarded motherfucker.

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Thermal resistance of plywood

Thermal resistance of plywood

Jim Thompson

Archimedes' Lever

Archimedes' Lever

Jim Thompson

Paul Keinanen

Son of a Sea Cook

Don Klipstein

Archimedes' Lever

Richard Cranium

Archimedes' Lever

Artemus

Don Klipstein

Archimedes' Lever

Jim Thompson

nospam

Jim Thompson

GregS

Archimedes' Lever

Rich Grise

Archimedes' Lever

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