I hope this IS EE?? but some may see it as [GW] politics?

Some time ago it was mentioned that opening the door on a fridge was a 
major energy expense. That seemed somehow wrong to me so I finally did 
some calculations but I frequently mess such stuff up so I am asking for 
a reality check from the rest of us.

The data:
sp heat of air  1 J/(gram degK)  - (wikipedia)
density air .0745lb/cuft -  (don't remember wherefrom)  = 33 g /cuft 
(how's that for mixed units? :-)  )

calcs:
so we get 33 J/cu ft deg C   = 33Wsec / cuft deg C

my fridge is about 12 cuft  (33" x 23" x 26") so I get  396 Wsec/deg C,
drop the temp from 25 to 0C gives 25 x 396 = 9900 Wsec per cool down
lets make up, say, 20% efficient gives 49,500Wsec  ~~50,000Wsec
so, 50kWsec/60= 833 KWmin = 13.8 KWhr  at $.10/KWHr = $1.38 / cooldown
Can this be so?  I'm never gonna open that sucker again as long as I 
live!! At least not till I need the next cold beer.


Of course not all the air escapes when you get the milk out, and there 
IS other stuff in there taking up volume, and etc but still...

So the guy that converted his chest freezer DID have a valid point 
(unless my calculations are messed up) I am still quite skeptical as I 
doubt that the fridge uses a KW (can't find that spec on any of the 
labels?) when running but even if it does, I doubt that it takes 13 hrs 
to cool down.

So we could save KWHrs (= $$) by putting in little clear doors for each 
shelf so only the level you are accessing is air exchanged??
-- 

Looking forward,
Al Shinn


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