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Old 22-09-2010, 12:42   #1
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Thermodynamics: Better to Stuff a Fridge ?

Hi Folks,

The fridge here on Sea Life is not the million dollar lickety-split jobbie that I would like. Its far too large. Thus causing a number of cubic feet of air to be cooled.

What would be better to do with the extra space? I already have foam restricting some space but between provisioning trips what to do with the increasing space to make it most economical.

1) Fill extra space with dense liquid like water?
2) Leave the space open and leave the air to stay as cool as possible?



Thanks for your thoughts,


Mark
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Old 22-09-2010, 12:50   #2
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Quote:
Originally Posted by MarkJ View Post
Hi Folks,

The fridge here on Sea Life is not the million dollar lickety-split jobbie that I would like. Its far too large. Thus causing a number of cubic feet of air to be cooled.

What would be better to do with the extra space? I already have foam restricting some space but between provisioning trips what to do with the increasing space to make it most economical.

1) Fill extra space with dense liquid like water?
2) Leave the space open and leave the air to stay as cool as possible?



Thanks for your thoughts,


Mark
It is common knowledge (among the experts) that keeping a refer full is more eco.
It's like a solid block of ice compared to a bag of party ice per pound. The party ice will cool faster but the block will last longer. Other cold masses in a confined space will help each other stay cold. Open a door on an empty refer and there goes all the cool.

I have a freezer and an ice box. In the freezer I keep quart bottles of water (frozen) to take up the extra space. If I need more space, I put one or two in the ice box.
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Old 22-09-2010, 12:51   #3
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hmmm. a dense liquid LIKE water

Quote:
Originally Posted by MarkJ View Post
1) Fill extra space with dense liquid like water?
Let me see if I've got this straight. You want our endorsement, under the guise of thermodynamics, for a scheme to fill "extra space," ahem, "with a dense liquid like water" (emphasis added.)

hmmm. what would the thermodynamic properties be of a liquid roughly equating water's density? Would it be carbonated, for example? Would it produce a lovely head of foam when poured into a frosty mug? Would it contain just enough antifreeze to produce a mild buzz in the afternoon? If you wrote a poem about it, would it rhyme with "deer"?

I don't know, Mark. This is a tough question.
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Old 22-09-2010, 13:01   #4
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Let me see if I've got this straight. You want our endorsement, under the guise of thermodynamics, for a scheme to fill "extra space," ahem, "with a dense liquid like water" (emphasis added.)

hmmm. what would the thermodynamic properties of a liquid roughly equating water's density? Would it be carbonated, for example? Would it produce a lovely head of foam when poured into a frosty mug? Would it contain just enough antifreeze to produce a mild buzz in the afternoon? If you wrote a poem about it, would it rhyme with "deer"?

I don't know, Mark. This is a tough question.
Don't worry Mark, I'll be your scientific enabler.

Adding water-ish substances to fill the "gaps" will increase the heat capacity inside your fridge. This means that if you're opening and closing the refrigerator often, it will take more energy to raise the temperature (granted it will take more energy to initially cool...which is why you buy your beer cold!).
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Old 22-09-2010, 13:04   #5
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which is why you buy your beer cold!).
Well, that's sump'n like I said.
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Old 22-09-2010, 13:22   #6
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"with a dense liquid like water" (emphasis added.)
Water is a scarce natural resource and should never be wasted. I conserve water to the utmost of my ability. I am proud of my Eco-Greeness. I was, actually, thinking of a water substitue that does happen to include some alcohol - but only because of the thermodynamic properties of Alcohol. I also find it on a far lower level conservation wise than water and don't mind sloshing it about.



Thanks Del
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Old 22-09-2010, 13:36   #7
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I like my rum cold......most folks do, that's why they drink it "on the rocks". Almost any liquid that is consumed cold cold be stored in a fridge as "ballast" in order to help keep the box cold.
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Old 22-09-2010, 13:46   #8
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I'd say stash your home brew there - unless you've drunk it already!

Seriously - our plan (and we do still need to test it) is to freeze bottles of water, and stick them in the empty fridge space. Then stick beer in the empty freezer space. The fridge and freezer should both run off solar power.
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Old 22-09-2010, 14:46   #9
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Mark--

Where is the evaporator plate on your frige?

On our boat it is in the upper rear (outboard) side of the unit. We have a "blanket" made of Reflectix that covers the top of the evaporator plate and can be unrolled and tucked over the contents of the 'frige, effectively, reducing the volume needing cooling as the contents are used up. With this, when one opens the top of the 'frige, the air above the blanket is cooler than the ambient air in the rest of the yacht but not as cold as the air and contents beneath the blanket and our running time is reduced accordingly.

FWIW...
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Old 22-09-2010, 18:05   #10
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I have my doubts that a full fridge is any better than one nearer to being empty. Heat loss is a function of the temperature difference between the the two surfaces inside thefridge and outside the fridge times the conductance (1/Rfactor) . I doubt there is much radiated heat but there oculd be leakage due to poor gasketing.

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Old 22-09-2010, 18:16   #11
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What's inside is insignificant compared to losses thru the walls. You want to reduce the interior (or exterior) surface area while increasing the insulation. You can do this by adding foam sheets and sealing them really well. Much more on the bottom than on the sides, even less on the top.

As a wild guess, you might add 3 inches on the bottom and 2 on the sides. Use Polystyrene Blue-board. Finish it with some nice 0.25" PVC foam-cored board. 5200 the seams.

And delete the drain if there is one. Seal it up. They are exceedingly lossy. Pump the water out.
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Old 22-09-2010, 19:37   #12
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This summer I laid a sheet of 1/2 inch neoprene (what wetsuits are made of) over the top of my refridge. It eliminated air infiltration from the cracks around the edges of the two doors and insulates also. Not only that but it provided about a square yard of non skid surface on the counter which I didnt think of before I did it but which turned out to be very handy. It reduced my energy draw noticeably - worth doing if you have an old wetsuit to cut up or you can get sheet neoprene on line by using google.
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Old 22-09-2010, 20:25   #13
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Awh! A nay sayer..........

Quote:
Originally Posted by foggysail View Post
I have my doubts that a full fridge is any better than one nearer to being empty. Heat loss is a function of the temperature difference between the the two surfaces inside thefridge and outside the fridge times the conductance (1/Rfactor) . I doubt there is much radiated heat but there oculd be leakage due to poor gasketing.

Foggy
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A full refrigerator retains cold better than an empty one. If your refrigerator is nearly empty, store water-filled containers inside. The mass of cold items will enable the refrigerator to recover more quickly after the door has been opened. On the other hand, don't overfill it, since that will interfere with the circulation of cold air inside.
Refrigerators & Freezers - Energy Choices at the Home

Here are a few facts for you.
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Old 22-09-2010, 20:51   #14
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The loss of cold (or heat gain) is a function of the total insolation of the box (the inverse of insUlation or R value.
The difference in an empty box and a full one (static load no opening or closing and uniformly cold interior) is that a full box cycles less often. The total run time is very similar, but when a refrigeration cycle starts, it's not being efficiently cooled for the first minute or so. As a result, when it's empty it starts and stops a lot more often, thereby wasting a lot of energy in the first minute of startup per unit of time.

Think city driving vs highway driving...

Richard Kollman will probably agree with me.
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Old 22-09-2010, 21:27   #15
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The loss of cold (or heat gain) is a function of the total insolation of the box (the inverse of insUlation or R value.
FYI:

insolation - incident solar radiation

A solar energy term. But I know what you mean: take two beers out at a time.
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