Dual south mesh...

[nick pine]

20 S=1.714E-09'Stefan-Boltzmann constant
30 DIM E(5,5)'combined emittance matrix
40 DATA 0,0,70,70,0,1,70,70,0,1,70,70
50 DATA 0.5,0.5,70,70,0.5,0.5,70,70
60 DATA 1,1,70,70
70 'above: solar absorption, IR absorption,
80 ' screen temp, air temp south of screen
90 TAUCUM=1'initialize cumulative layer transmission fraction
100 FOR I=0 TO 5
110 READ ASUN(I),AIR(I),TS(I),TE(I)
120 TAUCUML=TAUCUM
130 TAUCUM=TAUCUM*(1-ASUN(I))'cumulative layer transmission
140 ASUN(I)=ASUN(I)*TAUCUML'absorption fraction for layer I
150 NEXT I
160 E(1,2)=1:E(2,3)=.5:E(2,4)=.25:E(2,5)=.25
170 E(3,4)=.25:E(3,5)=.25:E(4,5)=.5
180 FOR I=1 TO 4
190 FOR J=I TO 5
200 E(J,I)=E(I,J)
210 NEXT J
220 NEXT I
230 TA=34'ambient temp (F)
240 SUN=.91^2*1000/6'sun through glazing (Btu/ft^2-h)
250 TR=70'air heater inlet temp (F)
260 CFM=1.2'airflow/ft^2
270 C=10'relaxation damping cap
280 FOR I=1 TO 499'relaxation iterations
290 FOR L=1 TO 5'mesh layer
300 GA=(TE(L-1)-TS(L))/(2/3+1/CFM)'layer air gain
310 GR=0'initialize rad gain
320 FOR K=1 TO 5
330 GR=GR+E(K,L)*S*((TS(K)+460)^4-(TS(L)+460)^4)
340 NEXT K
350 IF L=1 THEN GFLOW=(TA-TS(1))/1 ELSE GFLOW = 0
360 GFLOW=GFLOW+ASUN(L)*SUN+GA+GR'heatflow into layer
370 TS(L)=TS(L)+GFLOW/C'new layer temp
380 TE(L)=TE(L-1)-GA/CFM'air temp leaving layer
390 NEXT L
400 NEXT I
410 T1R=INT(TS(1)+.5)'round to print
420 T2R=INT(TS(2)+.5)'round to print
430 TS1R=INT(TS(3)+.5)'round to print
440 TS2R=INT(TS(4)+.5)'round to print
450 TBR=INT(TS(5)+.5)'round to print
460 T12R=INT(TE(1)+.5)'round to print
470 T2S1R=INT(TE(2)+.5)'round to print
480 TS12R=INT(TE(3)+.5)'round to print
490 TS2BR=INT(TE(4)+.5)'round to print
500 TOUTR=INT(TE(5)+.5)'round to print
510 PRINT "998'";T1R;T12R;T2R;T2S1R;TS1R;TS12R;TS2R;TS2BR;TBR;TOUTR
520 EFF=100*6*(TE(5)-TR)*CFM*60/55/1000'solar collection efficiency
(%)
530 LEFF=100*(1000-6*(TS(1)-TA))/1000'glazing-loss-based efficiency
(%)
540 PRINT "999'";EFF;LEFF

T1 air T2 air Ts1 air Ts2 air Tb air

73 72 109 93 154 127 156 143 160 152

64.62651 76.43108

This looks good, with 2 layers of IR greenhouse film and 2 layers of
50% black greenhouse shadecloth. A single layer of R1 film with 70 F
air indoors and 34 F air outdoors and no radiation loss would have a
collector efficiency of 100(1000-6h(70-34))/1000 = 78.4%.

But why don't the 2 efficiencies above match?

Nolt's Produce Supplies in Leola, PA sells $199 24'x100' rolls of
Tufflite IR greenhouse film with 92% visible light transmission and
21% thermicity (IR transmission.)

Nick

Hmm. The sunspace web site seems to be write-only today.