Hybrid Car – More Fun with Less Gas

Re: attic ventination test

register ::  Login Password  :: Lost Password?
Posted by nicksanspam on September 5, 2006, 1:39 pm
 

... and make the average attic temp only 2 F above the outdoor temp.

20 ASR50'south roof area (ft^2)
30 RSH=.2'shingle absorptivity
40 TA.7'outdoor temp (F)
50 GSA=2'shingle-outdoor conductance (Btu/h-F-ft^2)
60 TTS=TA+250*RSH/GSA'Thevenin equiv shingle temp (F)
70 RATT=4'R-value of roof (1-4 for radiant barrier)
80 KROOF=ASR/(1/GSA+RATT)'roof coefficient
90 H=8'vent height difference (feet)
100 A=8'vent area (ft^2)
110 C.6*A*SQR(H)/KROOF
120 T=TTS'initialize attic outlet temp (F)
130 TL=T'save previous temp
140 IF T<TA THEN T=2*TA-T'reflect
150 T=TTS-C*(T-TA)^.666'new attic temp (F)
160 IF ABS(T-TL)>.1 GOTO 130'iterate
170 C.6*A*SQR(H*(T-TA))'airflow (cfm)
180 PRINT C,(TA+T)/2'airflow and average attic temp (F)
190 C00'airflow estimate (cfm)
200 T=TA'average attic temp estimate (F)
210 TC=TA'average chimney temp estimate (F)
220 DT=KROOF*(TTS-T)/C'attic air temp gain (F)
230 T=TA+DT/2'average attic temp (F)
240 MA=H*.075*530/(460+T)'attic air mass (psf)
250 TAT=TA+DT'temp at top of attic (F)
260 CSUN=.9*250*32'sun into chimney (Btu/h)
270 CGAIN=CSUN-(TC-TA)*32'net chimney gain (Btu/h)
280 DTC=CGAIN/C'chimney air temp gain (F)
290 TC=TAT+DTC/2'average chimney temp (F)
300 MC=H*.075*530/(460+TC)'chimney air mass (psf)
310 MB=MA+MC'total bouyant air mass (psf)
320 MO=2*H*.075*530/(460+TA)'outdoor air mass (psf)
330 DP=MO-MB'bouyancy force (psf)
340 C75*A*SQR(DP)'airflow (cfm)
350 IF ABS(C-CL)>.1 THEN CL=C:GOTO 220'iterate
360 PRINT C,T,TC

airflow     attic temp   chimney temp
(cfm)       (F)          (F)

1518.035    100.8667                    H = 8' vent height difference

1496.56     94.82298     99.28098       H = 8' + 2'x4'x8' solar chimney

Nick


This Thread
Bookmark this thread:
 
 
 
 
 
 
  •  
  • Subject
  • Author
  • Date
please rate this thread