
re: solar heat storage..
25 feb 2001
mike russon wrote:
>i am currently constructing a solar heating system using air as the
>liquid. in designing a storage bin, would it be wise to not only
>insulate the exterior of the enclosure but also line the interior using
>a heat relflective polyisocyanurate insulation to increase r value as
>well as prevent out gas problems from the wood sides?
outgassing from wood seems an unlikely problem, but the foil would add
about r3, with an airspace on both sides, from the calc below for 1"
atlas energy shield "r7.2" polyisocyanurate foamboard with and without
its 2sided foil, using equations derived from pages 4667 of kreider
and rabl's heating and cooling of buildings (mcgrawhill, 1994.)
nick
10 data 0.05,0.05,1,1'emissivities with and without foil
20 s=1.714e09'stefanboltzman constant (btu/hr^4ft^2)
30 tin=130'internal temp (f)
40 tou=70'external temp (f)
50 rb=7.2'bulk rvalue of foamboard (usft^2fh/btu)
60 for p=0 to 1'calculate heatflow with and without foil
70 read ein,eou'emissivities
80 hri=4*s*(tin+460)^3/(1/ein)'internal radiation conductance (btu/hfft^2)
90 hro=4*s*(tou+460)^3/(1/eou)'external radiation conductance (btu/hfft^2)
100 hci=.19*dtin^(1/3)'internal convection conductance (btu/hfft^2)
110 hco=.19*dtou^(1/3)'external convection conductance (btu/hfft^2)
120 ri=1/(hri+hci)'rvalue of interior surface (ft^2fh/btu)
130 ro=1/(hro+hco)'rvalue of exterior surface (ft^2fh/btu)
140 i=(tintou)/(ri+rb+ro)'heatflow from inside to outside (btu/h)
150 dtin=i*ri'interior surface temp difference (f)
160 dtou=i*ro'exterior surface temp difference (f)
170 if abs(iil)/i>.01 then il=i: goto 100'iterate to 1%
180 rt=(tintou)/i'overall rvalue (ft^2fh/btu)
190 print tin,tindtin,tou+dtou,tou,rt
200 next
inside inside outside outside overall
air (f) surface (f) surface (f) air (f) rvalue
130 119.2 81.2 70 11.4
130 125.9 75.2 70 8.5

