R-values of reflective insulation materials

Apr 28, 2008 12 Replies
N

Adapted from "Prediction of the thermal performance of single and multi-airspace reflective insulation materials" by Andre O. Desjarlais and David W. Yarbrough, from ASTM STP 1116--Insulation Materials, Testing and Applications, Ronald S. Graves and Donald C. Wysocki, editors, 2nd volume, October 1991, pp 24-43:


20 DATA 2.5,5.09,7.5,1.4959,-0.608,6.359e-2,6.5572e-3,2.7129e-4
30 DATA 3.5,4.68,7.82,-1.3771,.2989,5.93e-3,1.2676e-3,8.7056e-2
40 DATA 2.5,4.35,7.2,-2.2234,0.6784,-3.028e-2,1.6481e-3,2.3528e-2
50 DATA 0,0,0,0,0,0,0,0
60 DATA 2.5,3.49,6.8,-.862,.2912,-3.863e-4,.16645,-1.397e-2
70 DATA 2.5,4.14,6.9,-.3,.0381,2.409e-2,1.5679e-2,-3.4369e-2
80 FOR I=0 TO 5
90 READ GR0(I),GR1(I),GR2(I),A(I),B(I),C(I),A2(I),A3(I)
100 NEXT I
110 DIR=0'heatflow direction
120 IF DIR=-1 THEN DIR$="down"
130 IF DIR=0 THEN DIR$="horiz"
140 IF DIR=1 THEN DIR$="up"
150 DIAG=0'0 for up or down, 1 for diagonal heatflow
160 IF DIAG=0 THEN DIAG$="no" ELSE DIAG$="yes"
170 I=2*DIR+DIAG+2'index (0-5, skipping 3)
180 T1=30'surface 1 temp (F)
190 T2=70'surface 2 temp (F)
200 DT=ABS(T2-T1)'temp diff
210 TBAR=(T1+T2)/2'mean temp
220 HR=.00686*((TBAR+460)/100)^3'radiation conductance (Btu/h-F-ft^2)
230 E1=.05'surface 1 emittance
240 E2=.05'surface 2 emittance
250 E=1/(1/E1+1/E2-1)'effective emittance
260 L=3.5'airspace width (inches)
270 LGR=LOG(DT*L^3)/LOG(10)+3.4146-.004359*TBAR+3.6441E-06*TBAR^2'log10 Grashof
280 IF LGR=LOG(GR1(I))/LOG(10) THEN LNU=A(I)+B(I)*LGR+C(I)*LGR^2:GOTO 320'eq 5
300 LNU=A2(I)*(LGR-LOG(GR0(I))/LOG(10))^2
310 LNU=LNU+A3(I)*(LGR-LOG(GR0(I))/LOG(10))^3'equation 6
320 NU=10^LNU'Nusselt number
330 K=.0003053*TBAR+.1575'air conductivity (Btu-in/F-ft^2-F)
340 HC=K*NU/L'convection conductance
350 R=1/(E*HR+HC)'US R-value (ft^2-F-h/Btu)
360 PRINT "gap (in):",L
370 PRINT "dir:",DIR$,"diag:",DIAG$
380 PRINT "T1 (F):",T1,"T2 (F):",T2
390 PRINT "Tmean (F):",TBAR,"dT (F):",DT
400 PRINT "E1:",E1,"E2:",E2
410 PRINT "Eeff:",E
420 PRINT "R-value:",R

gap (in): 3.5 dir: horiz diag: no T1 (F): 30 T2 (F): 70 Tmean (F): 50 dT (F): 40 E1: .05 E2: .05 Eeff: 2.564103E-02 R-value: 2.461726



Nick



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R

snipped-for-privacy@ece.villanova.edu wrote in news:fv4q04$ snipped-for-privacy@acadia.ece.villanova.edu:

Another rap tune?

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R

OTO

Can anyone understand what he posted, will it actualy help themselves ! No..its nickys numbers, again.

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S

What version of basic is this, looks like GWBasic or TurboBasic, something I last used about 15 - 20 years ago. Can you still get it. Have been running VB.Net last 8 years, and VB6 before that. If someone could point me in the direction of where to get a suitable windows version to run this, would be cool to try running the code.

Cheers Mike (NZ)

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J

It would be even cooler to go read a book.

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N

Yup. IIRC, gwbasic.exe is still available free from a web site and runs from a DOS prompt. BWbasic is almost identical and runs with Ubuntu linux. The new ASHRAE comfort spec also contains a gwbasic program. It's not easy to estimate the US R-value of a reflective insulation system. It varies from about 1 to 10, depending on emissivities, airspace thickness, mean temperature, temperature difference, and the direction of heatflow. The complex table in the ASHRAE HOF rarely matches real situations, but this program can help with that.

Nick

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S

wrote

Thanks for that Nick I will google somewhere to download it from. Was going to use 3 reflective air spaced layers behind a trickle solar panel array system.

Mike

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M

Try . I think that's where I got my copy a while back.

I think you'll need to run it in a DOS or CMD window (depending on which version of Windows you're running).

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N

Under what kind of glazing? Warm water vapor quickly degrades polycarbonate.

Multiple relfective airspaces require iteration to determine intermediate surface temps, as described in ASTM STP 1116. Adding individual airspace resistances does not work.

Nick

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S

snipped-for-privacy@ece.villanova.edu wrote

Yes I know, talking to people in the local plastic shop it aborbs water vapour over time and goes brittle. I wanted them to heat bend some sheets of it with folded right angle edges; cannot readily be done because of this.

Trickle panels are:

3m high x 1m width galv iron sheets, matt black powder coated on the sun side, water channels made by vertically running silicon beading spaced every 5cm down the metal sheet, laying 75u clear mylar on top of the silicon, lightly pressing before it sets to form a vapour shield. The water runs between the metal and the mylar. Each panel then sits in a wood frame with an overall cover of 1mm flat clear thick polycarbonate with uv protection.

Time will tell how long the mylar will last. The poly glazing will block the uv entering the box and hopefully stop the plastic header/bottom water pipes from falling to bits..

Was going to run multiple air spaced layers of foil faced building insulation paper (the stuff without bitumen) behind the metal panels finally the wooden ply bottom. Figured some water vapour will escape into the box , so there will be vent holes.

May make a small test panel and do some measurements with foil then non water absorbent insulation material.

Cheers Mike (NZ)

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S

Thanks have just gone and downloaded it from the above link.

Cheers Mike

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M

....and most of the time it can be completely ignored (assuming you are not working on an off the planet application)

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