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That CAN'T be true! / Re: Is a fridge most efficient empty and a freezer best kept full?
« on: 01/07/2017 20:47:59 »
According to some, they are lots of things than can influence the performance of a freezer based on its content.
See : https://www.thenakedscientists.com/forum/index.php?topic=43522.msg477756#msg477756
Some of it being true, in the end all of this has very little effect on your real life fridge or freezer, or combo.
A given appliance, in a given room, with a given number of door openings, is less efficient when empty : this is due to the fact that it runs often because it has no thermal inertia, and because the cooling system is not 100% efficient.
Thermal Inertia :
When empty, as you start the freezer, the system has to remove all the heat from almost no mass of air inside the freezer. This is quick, but as the freezer is not 100% insulated, this given "almost no mass of air" will become warmer faster than a larger mass of frozen good for a given insulation.
The freezer will need to start frequently for short runs. Is this the same as if it would start less often for longer runs? No.
Efficiency of the cooling system :
Real life heat transfer does not start right away when the compressor kick ins. The compressor needs to rebuild pressure. This takes so much energy that your fridge has to be on a separate breaker according to the current building code. So on a short run, the efficiency of the cooling system drops because of the priming period.
As you may know, a freezer transfers energy. The energy is taken from the freezer back to the ambient air where the freezer sits. In the case of an empty freezer, this will account for almost nothing, and won't really warm up the ambient air. But, your compressor, when running, releases (lots of) heat in the ambient room. As it runs often for inefficeint short runs (empty freezer, no thermal inertia), it will make the ambient air warmer, which will lead to faster loss of cold in the freezer and so on, and have the system start even more often.
A combination of an empty freezer in a poorly ventilated room, can have a significant impact on your energy bill, and you will notice the air in the room being significantly warmer.
As for a freezer / fridge combo, thermal inertia still applies, and as they have the same cooling system, using a active or passive techniques to transfer cool from freezer to fridge (forcing the cold air up or down)
Phil
See : https://www.thenakedscientists.com/forum/index.php?topic=43522.msg477756#msg477756
Some of it being true, in the end all of this has very little effect on your real life fridge or freezer, or combo.
A given appliance, in a given room, with a given number of door openings, is less efficient when empty : this is due to the fact that it runs often because it has no thermal inertia, and because the cooling system is not 100% efficient.
Thermal Inertia :
When empty, as you start the freezer, the system has to remove all the heat from almost no mass of air inside the freezer. This is quick, but as the freezer is not 100% insulated, this given "almost no mass of air" will become warmer faster than a larger mass of frozen good for a given insulation.
The freezer will need to start frequently for short runs. Is this the same as if it would start less often for longer runs? No.
Efficiency of the cooling system :
Real life heat transfer does not start right away when the compressor kick ins. The compressor needs to rebuild pressure. This takes so much energy that your fridge has to be on a separate breaker according to the current building code. So on a short run, the efficiency of the cooling system drops because of the priming period.
As you may know, a freezer transfers energy. The energy is taken from the freezer back to the ambient air where the freezer sits. In the case of an empty freezer, this will account for almost nothing, and won't really warm up the ambient air. But, your compressor, when running, releases (lots of) heat in the ambient room. As it runs often for inefficeint short runs (empty freezer, no thermal inertia), it will make the ambient air warmer, which will lead to faster loss of cold in the freezer and so on, and have the system start even more often.
A combination of an empty freezer in a poorly ventilated room, can have a significant impact on your energy bill, and you will notice the air in the room being significantly warmer.
As for a freezer / fridge combo, thermal inertia still applies, and as they have the same cooling system, using a active or passive techniques to transfer cool from freezer to fridge (forcing the cold air up or down)
Phil
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