re: cordwood masonry SOLAR.KnowledgePublications.com

re: cordwood masonry
13 may 1997
i wrote:

>a 12" sawdust or strawbale wall with 6" cement/sawdust walls inside and
>outside might work better with only occasional cordwood ties...

having explored this more, i still agree with myself :-) 

10 'r-value of cordwood wall             masonry air film
20 '             |                   |   resistance
30 '             |          ---zero------www-------70 f
40 '             |         |         |   rma
50 '---------------------------------|
60 '  interior   |  radial | wood    |
70 '  cordwood   |  res--> w rcr     |   wood air film
80 '  resistance |         |         |   resistance
90 '-----www---------www-------www-------www-------70 f
100 '    rci         rcm  ^    rcm   |   rca
110 '           cordwood  | rex-->   |
120 '--------------------------------|
130 '            |                   |
140 ' sawdust    |   masonry face    |   masonry air film
150 ' resistance |   resistance      |   resistance
160 '----www---------www-----------------www-------70 f
170 '    rsd         rfr             |   rma
180 for dc=4 to 24 step 4'cordwood tie diameter (inches)
190 lc=24'cordwood tie length (inches)
200 rc=1.3'cordwood tie resistivity (ft^2-f-h/btu-in)
210 sc=24'cordwood tie spacing (inches)
220 wm=4'masonry wall thickness (inches)
230 rm=.2'masonry wall resistivity (ft^2-f-h/btu-in)
240 rs=3.5'sawdust resistivity (ft^2-f-h/btu-in)
250 fca=3.14*dc^2/(4*144)'cordwood face area (ft^2)
260 rci=rc*(lc-2*wm)/fca'simple r-value of cordwood tie
270 rcm=rc*wm/2/fca'exterior cordwood resistance
280 rcr=rc*dc/4/(3.14*dc*wm/144)'radial exterior cordwood resistance
290 rca=1/2/fca'wood air film resistance @ 2 btu/hr-f-ft^2 conductivity
300 rma=1/2/(sc^2/144-fca)'masonry air film resistance
310 rex = rcm + (rcr+rma)*(rcm+rca)/(rcr+rma+rcm+rca)'exterior resistance
320 rcs = rci + 2*rex'cordwood wall section resistance
330 rsd = rs*(lc-2*wm)/(sc^2/144-fca)'sawdust resistance
340 rfr = rm*wm/(sc^2/144-fca)'masonry wall face resistance
350 rws = rsd + rfr + rma'sawdust wall section resistance
360 rw = (rcs*rws)/(rcs+rws)'wall section resistance
365 if dc >5 goto 470
370 print"interior cordwood resistance, rci =";rci
380 print"exterior cordwood resistance, rcm =";rcm
390 print"radial exterior cordwood resistance, rcr =";rcr
400 print"wood air film resistance, rca =";rca
410 print"masonry air film resistance, rma =";rma
420 print"exterior resistance, rex =";rex
430 print"cordwood wall section resistance, rcs =";rcs
440 print"sawdust resistance, rsd =";rsd
450 print"sawdust wall section resistance, rws =";rws
460 print"wall section resistance, rw =";rw
470 rvw = rw*sc^2/144'wall r-value
480 print "cordwood diameter, dc =";dc,"wall r-value, rvw =";rvw
490 next dc

interior cordwood resistance, rci = 238.4713
exterior cordwood resistance, rcm = 29.80892
radial exterior cordwood resistance, rcr = 3.726114
wood air film resistance, rca = 5.732484
masonry air film resistance, rma = .1277865
exterior resistance, rex = 33.2858
cordwood wall section resistance, rcs = 305.0429
sawdust resistance, rsd = 14.31208
sawdust wall section resistance, rws = 14.64433
wall section resistance, rw = 13.9735

cordwood diameter, dc = 4   wall r-value, rvw = 55.89399
cordwood diameter, dc = 8   wall r-value, rvw = 52.47021
cordwood diameter, dc = 12  wall r-value, rvw = 48.12962
cordwood diameter, dc = 16  wall r-value, rvw = 43.46009
cordwood diameter, dc = 20  wall r-value, rvw = 38.8077
cordwood diameter, dc = 24  wall r-value, rvw = 34.43655

the r-value of a 2'x2' section of wall containing a single cordwood tie
seems to decrease as the cordwood diameter increases from 4" (2% wood)
to 24" (78% wood)...

the r-value would be higher without any "cordwood." put some thin wood inside
and parallel with the masonry walls, and tie them together with diagonal
bailing twine? 

nick