Without checking the figures - anyone with a refrigerator 
who also pays the power bill will be able to tell you that 
you must have made a substantial error somewhere. If you 
match the above two tests tell yourself :-).

I posted a Sunpower Stirling refrigerator material after the 
start of the chest fridge thread that gave some "real world" 
figures for door openings, food insertion etc. AFAIR a 
reasonably significant number of door openings still fell 
below the typical food cooling losses and the insulation 
losses predominated for typical fridges.

Sanity check: Air has about 1000+ time sless mass than food 
and similar thermal mass. For a say 200 litre fridge cooling 
ALL the air is going to be less expensive than say cooling 
200 grams of food. In fact the figures are better than that.

Let's try with your data

1 J/g/K
= 1 J/l/K
say 30K cooling.
Say 200l
Say $0.1/kWh.

200 litre x 1J x 30k = 6000 Joule.
=  6 kW.sec = 6/3600 = 1/600th kWhour
x $0.1 = 1/6000 $

~= 0.016 cents.
20% efficiency takes that to ~~ 0.1 cents/opening.


E&OE


        Russell


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