[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
GBlist: re: Hemp Insulation ?
on Jun 13 1997
sullivan@crest.org (Bruce Sullivan) wrote:
[snipped & pasted]
> ... insulation and other building materials out of hemp fiber.
> ...can mineralized with lime or cement or used "raw."
> loose fill material... density is 110 Kg/m3 and the thermal
> conductivity is 0.048 W/m K.
> another density is 350-500 Kg/m3 and the thermal conductivity is 0.13
> W/m K.
> What's the general impression of this product?
Hello Bruce and HempHeads;
The Perfesser (no disrespect intended) tells us that the Imperial-SIU
conversion factor for conductance is "Imperial x 5.673"... and the
SwampPhysicist (non-relativistic) tells us that "Imperial x 6.938" is the
way to go (for conductivity).
And then Bruce takes the conversion factor for conductance and uses it to
come up with R-44 and then utters "What the &^$#*% is this ?? "
=== * ===
The IHVE Guide (a UK equivalent of the ASHRAE HoF ?) and "Moisture in
Building Construction" both list Imperial-SIU conversion factor for Thermal
ConductANCE as being:
British or Common Unit Factor SI Unit
======================= ======= ========
Btu x 5.678 = W
----- -------
hr*ft^2*degF m^2*degC
The IHVE Guide also lists the conversion factor for Thermal ConductIVITY as
being:
British or Common Unit Factor SI Unit
======================= ======= ========
Btu * inch x 0.1442 = W
----------- ------
hr*ft^2* degF m*degC
(As you can see, SwampGuy was correct and that he wasn't really snoozing
through physics class and that the Perfesser was also correct).
It may be helpful to note that the SI Units (above) are actually:
Watts * metre
-----------------
metres^2 * degC (ie some of the "metres" cancel out)
From what Bruce posted, it appears from the units that it is the
conductIVITY values that the company supplied and as such, for the loose
fill material:
Thermal 0.048 W/m*K.
Conductivity = --------- = 0.332 Btu*inch/hr*ft^2*degF
0.1442
and
Thermal = 1 / 0.332 = R-3 per inch
Resistivity
And for the high density stuff, R-1.1 per inch.
(Just like SwampGuy surmised.)
Hence, to achieve a thermal conductANCE of 0.023 Btu/hr*ft^2*degF ( or
thermal resistance of R-44) one would need 14.67 inches of the low density
stuff. Boy, can I read and do arithmetic or what ? Eh ?
=== * ===
Considering that hemp insulation (not unlike straw) is primarily cellulose
with trapped insulating air pockets, the above values seem reasonable as
they are comparable to the values for the thermal resistivity of Straw
Bales which the esteemed (cough, cough) Joe McCabe determined in his lab
tests.( and whose thesis outlining the tests is posted on the CREST
website).
General impressions ? IMO, hemp would certainly be preferable to
fibreglass as a Green insulation material ...but less desirable than dense-
pack cellulose (or even Straw Bales or other _waste_ fibres for that
matter).
Is (legal) hemp grown for any other purpose than its fibre ?
Unlike cereal grains from which straw is derived, I don't think that the
land devoted to growing (legal) hemp produces any (legal) food (other than
those hemp seed ball treats). Then again, I know nothing about (legal)
hemp.
I can't think of any compelling reasons to take increasingly scarce, arable
land + water and devote it to growing a cellulosic insulation product(hemp)
when there are other sources of _waste_ cellulosic fibre waiting to be
utilised. Then again, I'm biased towards Bales.
--
Rob Tom
---------- * ------------
be417@FreeNet.Carleton.ca
Kanata, Ontario, Canada
______________________________________________________________________
This greenbuilding dialogue is sponsored by CREST <www.crest.org>
Environmental Building News <www.ebuild.com> and Oikos <www.oikos.com>
For instructions send e-mail to greenbuilding-request@crest.org.
______________________________________________________________________