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'[EE]: refrigerator calculations -- please check me'
2008\04\30@000637 by Sean Breheny

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Hi Al,

Mostly correct I think except for one key item:

On Tue, Apr 29, 2008 at 11:07 PM, Al Shinn <spam_OUTalshinnTakeThisOuTspammindspring.com> wrote:

>  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.

50kWsec = 0.833 KWminutes=0.0138 KWhrs=0.1 cents per cooldown

Also, as you say, I doubt that all of the air fully exchanges in a
typical door opening. The thermal mass of all the other stuff in there
will do two things: 1) make it so that there is less air 2) make the
compressor have to turn on and off less. Other than that, it will not
change the average amount of energy needed per cooldown, as whatever
cooling effect you get from the cold food has to be recuperated by the
compressor.

Sean

2008\04\30@015608 by KPL

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>
>  50kWsec = 0.833 KWminutes=0.0138 KWhrs=0.1 cents per cooldown
>
>  Also, as you say, I doubt that all of the air fully exchanges in a
>  typical door opening. The thermal mass of all the other stuff in there
>  will do two things: 1) make it so that there is less air 2) make the
>  compressor have to turn on and off less. Other than that, it will not
>  change the average amount of energy needed per cooldown, as whatever
>  cooling effect you get from the cold food has to be recuperated by the
>  compressor.
>

So the problem is much worse for empty refrigerator?
One more reason to keep it always full of beer :)

--
KPL

2008\04\30@030043 by Apptech

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E --
     |
    \/

{Quote hidden}

    \/

> So the problem is much worse for empty refrigerator?
> One more reason to keep it always full of beer :)

Not really.
Most refrigerators would have only a small proportion
occupied by food, or beer.

A dedicated packing with bottled beer would probably not
reach 50% fill.

Cans stacked diameter to diameter can approach Pi/4 packing
~= 78% but only if the cooled space is an exact multiple of
can dimensions in all 3 dimensions.

If you close pack the cans in staggered rows max fill
increases to - ah - I knew there was a reason they discussed
packing in Chemistry all those years ago  ... aaagh ... Pi/6
x sqrt(3) =~ 90.7%. Round down somewhat as above. Probably
really lucky to get more than about 80%.

Note that the 90.69...% is optimum for an infinite sheet of
beer bo... er circles. Use a mix of bottle sizes and the
packing may be lower and will never be higher.

Store your beer in plastic bags and you could do better.

You'll be sorry ...

       http://mathworld.wolfram.com/CirclePacking.html

______

Also
If you maintain a high beer fill ratio this is liable to
promote a high churn and the penalty for cooling large delta
mass of beer is far worse than cooling the same volume of
air. Filling it with beer only works if it doesn't get
imbibed. To save  money adopt the double effective strategy
of storing only emergency beer supplies in the fridge and
drinking someone else's beer whenever possible.


       Russell




2008\04\30@033624 by Richard Prosser

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On 30/04/2008, Apptech <.....apptechKILLspamspam@spam@paradise.net.nz> wrote:
{Quote hidden}

The other trick is buy beer from the chiller and put it in the fridge
before it warms up!

RP

2008\04\30@053311 by KPL
picon face
So, there is one thing that our environmentalists should do now. Beer
cans must become rectangular, in the name of global warming/energy
saving this should be easy:)


>  Cans stacked diameter to diameter can approach Pi/4 packing
>  ~= 78% but only if the cooled space is an exact multiple of
>  can dimensions in all 3 dimensions.
>


--
KPL

2008\04\30@100247 by Apptech

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> So, there is one thing that our environmentalists should
> do now. Beer
> cans must become rectangular, in the name of global
> warming/energy
> saving this should be easy:)

Plus - beer must no longer involve CO2 in its production or
bottling.

If beer drinkers swapped to drinking wine from rectangular
cardboard casks it would help. But you would always have to
drink a complete cask of wine once it was taken out of the
fridge.

De Bono would suggest fridges with flexible walls.



       R

2008\04\30@165754 by Al Shinn

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Thanks to all. So a mere factor of 1000 error! Bah! I went over those
calculations at least three times. I guess I had been opening and
closing the door for beer too much or something last night - at least
now I don't have to feel guilty about getting more beer out.

 Someone said that if the cans are different sizes then the packing
density will be even worse but that's not quite true if one has really
skinny cans that fit in the spaces between the big cans and then an even
more tiny set to fit in those spaces and etc. That's why concrete has
rocks, gravel, and sand.

I think it may have been Russell that said a major loss is through the
insulation, so why not have refrigerator blankets like the water heater
blankets?


> 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.


50kWsec = 0.833 KWminutes=0.0138 KWhrs=0.1 cents per cooldown
--

Looking forward,
Al Shinn



'[EE]: refrigerator calculations -- please check me'
2008\05\01@042435 by Alan B. Pearce
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>I think it may have been Russell that said a major loss is through
>the insulation, so why not have refrigerator blankets like the
>water heater blankets?

<VBG> I can imagine the law suits that result when people wrap them around
the radiator pipes at the rear  ...

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