Discussion:
Cold retention
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j***@gmail.com
2020-06-05 16:06:22 UTC
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An empty or nearly empty refrigerator will have a continually running motor/compressor. To reduce the running time, I need to stock the refrigerator with something that will retain the cold and reduce the running time. I could possibly use bottled water as it will not spoil like food would.

Does anyone know what would be best material to place in the refrigerator to achieve this? Is water the answer?
dlzc
2020-06-05 16:32:50 UTC
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Post by j***@gmail.com
An empty or nearly empty refrigerator will have a
continually running motor/compressor.
Not unless it is near failure, has lost most of its coolant, blown the seals out of its compressor, has a crud covered condensor coil, or the unit is sitting in a very hot space.
Post by j***@gmail.com
To reduce the running time, I need to stock the
refrigerator with something that will retain the
cold and reduce the running time.
Unlikely to yield the desired result. Keep the damned door closed.
Post by j***@gmail.com
I could possibly use bottled water as it will
not spoil like food would.
Would initially require the compressor to run longer, to cool down the water.
Post by j***@gmail.com
Does anyone know what would be best material
to place in the refrigerator to achieve this?
Is water the answer?
It is but it is not the best answer.

Essentially "beanbags", with styrofoam pellets will take up the dead space, so that when you open the door it does not "spill out" onto the floor. The cold air is a "fluid" separate from outside air, much denser (lower temp, lower water vapor), and spills onto the floor each time the door is opened.

Alternates might be to get one of those refrigerators that have small doors in the middle of the bigger door where you keep the common drinks. And chest freezers where you reach down into the freezer, with the door on top.

David A. Smith
j***@gmail.com
2020-06-05 19:45:38 UTC
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The refrigeration experts told me that an empty refrigerator with warm surrounding ambient temperatures will almost always run. With cold absorbing food in the refrigerator, the motor will come on just to restore the set temperature. This has nothing to do with opening doors or cold air flowing out. It is just the way that refrigerators are engineered.

Again, the simple question was what contents within the refrigerator will retain the cold so that the motor/compressor will only rarely come on? The refrigerator is accessed only about once a month.
dlzc
2020-06-05 20:04:16 UTC
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Post by j***@gmail.com
The refrigeration experts told me that an empty
refrigerator with warm surrounding ambient
temperatures will almost always run.
Nope. You are taller on one side, because someone has been pulling your leg. And empty fridge cools down faster, because it has less thermal mass that got warmer, and then has to cool down.
Post by j***@gmail.com
With cold absorbing food in the refrigerator,
the motor will come on just to restore the set
temperature.
The contents ALSO absorbed heat, got warmer as the "on setpoint" was approached. So the compressor has to cool all that mass back down.
Post by j***@gmail.com
This has nothing to do with opening doors or
cold air flowing out.
... or any physics whatsoever.
Post by j***@gmail.com
It is just the way that refrigerators are
engineered.
No, it is the lying bastards that tricked you.
Post by j***@gmail.com
Again, the simple question was what contents
within the refrigerator will retain the cold
so that the motor/compressor will only rarely
come on? The refrigerator is accessed only
about once a month.
Air is the lowest mass content. Styrofoam is also low mass, because it is mostly air. The amount of time a perfectly good unit runs, is based on the heat rate coming into the box, and the total mass that has to be cooled down. Increase the mass to be cooled, and you make the unit come on longer, if less often.

I know you don't want to believe me, but I am not lying to you. Draw a free body diagram, show heat coming in...

David A. Smith
Martin Brown
2020-06-06 12:14:25 UTC
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Post by j***@gmail.com
The refrigeration experts told me that an empty refrigerator with
warm surrounding ambient temperatures will almost always run. With
cold absorbing food in the refrigerator, the motor will come on just
to restore the set temperature. This has nothing to do with opening
doors or cold air flowing out. It is just the way that refrigerators
are engineered.
That isn't correct. It is more efficient to have some thermal inertia
inside the fridge and especially freezer so that the thermal control
loop doesn't spend its time hunting. A large bottle of water should be
enough to provide the thermal inertia to keep things well behaved.

Any empty one will use more power than a moderately full one but it
shouldn't run continuously unless it is installed in one of the inner
circles of Hell or the coolant has mostly leaked out.
Post by j***@gmail.com
Again, the simple question was what contents within the refrigerator
will retain the cold so that the motor/compressor will only rarely
come on? The refrigerator is accessed only about once a month.
The largest possible thermal mass that you can put inside it then. Why
are you running a huge empty refrigerator empty in the first place?

Don't you think that buying a small well insulated fridge suited to the
intended usage might be a lot more cost effective?
--
Regards,
Martin Brown
dlzc
2020-06-06 17:19:12 UTC
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Post by j***@gmail.com
The refrigeration experts told me that an empty
refrigerator with warm surrounding ambient
temperatures will almost always run.
Let me say this differently. In a given "hour", an empty refrigerator will run say "12 minutes", starting probably "6 times", and stopping "6 times". A full refrigerator will start maybe "once" in that hour and run the full "12 minutes".

So yes, the thermal mass (water, soda, beer) will reduce the starts per hour, potentially letting the compressor last longer (each start reduces overall life of the system).

Don't worry about "most efficient". Roughly, each pound / kilogram you put in there will be equivalent. If you are worried about being inert, just use bricks, car parts, whatever makes sense in your context.

David A. Smith
o***@gmail.com
2020-06-08 01:50:58 UTC
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Post by dlzc
Post by j***@gmail.com
The refrigeration experts told me that an empty
refrigerator with warm surrounding ambient
temperatures will almost always run.
Let me say this differently. In a given "hour", an empty refrigerator will run say "12 minutes", starting probably "6 times", and stopping "6 times". A full refrigerator will start maybe "once" in that hour and run the full "12 minutes".
So yes, the thermal mass (water, soda, beer) will reduce the starts per hour, potentially letting the compressor last longer (each start reduces overall life of the system).
Don't worry about "most efficient". Roughly, each pound / kilogram you put in there will be equivalent. If you are worried about being inert, just use bricks, car parts, whatever makes sense in your context.
David A. Smith
And clean off those copper pipes that have dust on them.
If your liquids and gases are in dusty coils for three years,
please brush them. It increases the thermodynamic efficiency.

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