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a spencerator
28 feb 2005
a fridge can be a large winter load for an off-grid pv house...

nrel says the average daily november temp in massena ny is 35.3 f, with an
average daily min of 27.7. december has 20.2 f and an 11.7 min. january has
14.3 and 4.3. february has 16.5 and 6.5. march has 28.3 and a 19.1 f min. 

a 2'x2'x8' tall r20 34 f fridge in a 70 f room needs (70-34)80ft^2/r20 = 136
btu/h or 3456 btu/day of coolth, or 17,280 btu for 5 days, which might come
from at least 17280/144 = 120 pounds of ice in an outdoor box, with a large
water tray with a copper pipe in the freezer compartment, with free airflow
to the fridge below and a liquid thermosyphoning loop to move coolth in from
the box. can the loop stop working before it freezes the fridge contents? 

the ice box might be 2'x2'x8' tall, with a 55 gallon drum packed with 100
2 liter water bottles surrounded by an antifreeze solution thermosyphoning
through an old 800 btu/h-f auto radiator above with an 8' chimney above.
cold air might enter the radiator and flow out at the top of the chimney.

with 800 btu/h-f of conductance from 32 f water to outdoor air at temp t,
(32-t)800 = 3456 btu makes t = 32-3456/800 = 27.7 for 1-hour per day cooling
and t = 32-3456/1600 = 29.8 for 2-hour cooling, and so on.

the crude tmy2 (typical meteorological year) simulation below indicates
that a fridge like this could work for 241 days (2/3) of a typical year
in massena, from september 23 through may 22...

nick

this program makes a "fridge" prep file with
the month, day, hour, and dry bulb temp...

10 screen 9:key off:cls
40 line (0,0)-(639,349),,b:xdf=.073:ydf=2.92
50 for tr= 20 to 40 step 10'temp ref lines
60 line (0,349-ydf*(tr+20))-(639,349-ydf*(tr+20)):next
70 open "94725.tm2" for input as #1'nrel tmy2 file name (massena)
80 open "fridge" for output as #2
90 line input#1,s$'read header
100 city$=mid$(s$,8,25)
110 lat=val(mid$(s$,40,2))+val(mid$(s$,43,2))/60
120 lon=val(mid$(s$,48,3))+val(mid$(s$,52,2))/60
130 print#2,city$,lat,lon
140 for h=1 to 8760'hour of year
150 line input#1,s$
160 month=val(mid$(s$,4,2))'month of year (1-12)
170 day=val(mid$(s$,6,2))'day of month
180 hour=val(mid$(s$,8,2))-.5'hour of day
190 n=1+h/24'day of year (1 to 365)
200 tdb=val(mid$(s$,68,4))*.18+32'dry bulb temp (f)
230 pset(xdf*h,349-ydf*(tdb+20))
470 print#2,month;day;hour;tdb
480 if day=1 and hour=.5 then line (xdf*h,349)-(xdf*h,345)'tick months
490 next h

here's the start of the fridge file...

massena                ny    44.93334      74.85
 1  1  .5  24.98
 1  1  1.5  24.98
 1  1  2.5  24.98
 1  1  3.5  26.06
 1  1  4.5  26.06
 1  1  5.5  19.94
 1  1  6.5  15.98
 1  1  7.5  10.94
 1  1  8.5  8.959999
 1  1  9.5  6.979999
 1  1  10.5  6.979999
 1  1  11.5  6.079999
 1  1  12.5  6.079999
 1  1  13.5  6.079999
 1  1  14.5  6.979999
 1  1  15.5  6.979999
 1  1  16.5  6.079999
 1  1  17.5  1.939999
 1  1  18.5 -2.020001
 1  1  19.5 -2.920002
 1  1  20.5 -4.000002
 1  1  21.5 -4.000002
 1  1  22.5 -.9400013
 1  1  23.5 -.9400013
....

this program simulates a typical year...

10 screen 9:key off:cls
20 daystart=0'display start time (days)
30 ds=daystart*24'display start time (hours)
40 range=8760'display range (hours)
50 line (0,0)-(639,349),,b:xdf=640/range:ydf=2.69
60 for tr=-30 to 30 step 10'temp ref lines
70 line (0,349-ydf*(tr+30))-(639,349-ydf*(tr+30)):next
80 open "fridge" for input as #1:line input#1,h$
90 for h=1 to 8760'hours of typical (tmy2) year
100 input#1,month,day,hour,tdb'read fridge file
110 if tdb144*440 then ice=144*440'upper ice limit (btu)
160 if ice>0 then line (xdf*(h-ds),340)-(xdf*(h-ds),330):iceh=iceh+1'ice hours
170 if day=1 and hour=.5 then line (xdf*(h-ds),349)-(xdf*(h-ds),345)'months
180 next h
190 close #1
200 print tmin,iceh
210 end

min yearly     hours
temp (f)       with ice

-25.96         5468




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