wrote:

Here's one way to estimate the R-value of a radiant barrier based on the air
gap and the emissivities and surface temps and the direction of heatflow from
http://www.reflectixinc.com/pdf/RIMA_Handbook.pdf

Nick,

How does this work out for the double bubble?

URL: http://www.blueridgecompany.com/radi...ic/189#pricing

It seems to me there are two ways to go for the underfloor insulation
for staple up radiant.

One is foil backed fiberglass insulation with an airspace. That is hard
to find! The other would be double bubble stapled on the joists. It
seems to me that would minimize heat loss through the joists themselves
as they would be uninsulated elsewise. Any thoughts?

Jeff

10 SCREEN 9:KEY OFFIM HC(18,6)
20 DATA 0.359,0.184,0.126,0.097,0.080,0.068
30 DATA 0.361,0.187,0.129,0.100,0.082,0.072
40 DATA 0.363,0.189,0.131,0.101,0.085,0.075
50 DATA 0.364,0.190,0.132,0.103,0.087,0.078
60 DATA 0.365,0.191,0.133,0.105,0.090,0.081
70 DATA 0.366,0.192,0.134,0.106,0.092,0.082
80 DATA 0.360,0.204,0.169,0.179,0.185,0.189
90 DATA 0.366,0.267,0.223,0.233,0.238,0.241
100 DATA 0.373,0.247,0.261,0.271,0.275,0.276
110 DATA 0.380,0.270,0.292,0.301,0.303,0.303
120 DATA 0.387,0.296,0.317,0.325,0.327,0.326
130 DATA 0.394,0.319,0.339,0.347,0.347,0.345
140 DATA 0.381,0.312,0.295,0.284,0.275,0.268
150 DATA 0.429,0.381,0.360,0.346,0.336,0.328
160 DATA 0.472,0.428,0.405,0.389,0.377,0.368
170 DATA 0.511,0.465,0.440,0.423,0.410,0.400
180 DATA 0.545,0.496,0.469,0.451,0.437,0.426
190 DATA 0.574,0.523,0.494,0.475,0.460,0.449
200 FOR I=1 TO 18'read data table
210 FOR J=1 TO 6
220 READ HC(I,J)
230 NEXT:NEXT
240 T1=105'temperature of surface 1 (F)
250 E1=.03'emissivity of surface 1
260 T2=75'temperature of surface 2 (F)
270 E2=.8'emissivity of surface 2
280 L=2'air gap (valid range: 0.5-3")
290 LI=INT(2*L+.5)'length table index
300 HF=0'heatflow 0-down,1-sideways,2-up
310 E=1/(1/E1+1/E2-1)'effective emittance
320 TM=(T1+T2)/2'mean temp (F)
330 DT=ABS(T1-T2)'temp diff (valid range: 5-30 F)
340 DTI=INT(DT/5+.5+6*HF)'temp diff table index
350 HR=.00686*((TM+459.7)/100)^3'radiant conductance
360 R=1/(E*HR+HC(DTI,LI))'US R-value (ft^2-F-h/Btu)
370 PRINT T1,E1,T2,E2
380 PRINT L,HF,R

T1 (F) E1 T2 (F) E2

105 .03 75 .8

gap heatflow US R-value

2" 0 (down) 7.146456

With more than one space in series (eg double-foil foamboard spaced away
from a basement wall), we can't just add R-values. We only know the overall
temp diff, so we have to iterate to find a solution. It's no surprise that
the FTC prohibits makers from advertising R-values for radiant barriers
to avoid confusing the public.

Nick