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  #1  
Old 20 June 2014, 09:06 PM
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Ponder Full refrigerators are more energy efficient?

Comment: A full fridge operate more efficiently than an empty one?

I have over the years been told by various non-technical people that the
fridge does not work well, or uses more electricity when empty -- I lately
notice the claim here;

https://shine.yahoo.com/at-home/10-r...155100804.html

However, having a science background, this make no sense to me -- sure
cold air will flow out faster if there is a lot of it, but only when you
open it -- and the air is also less expensive to cool down than say water.

Is there any actual science behind the claim of the empty fridge not being
economical?
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  #2  
Old 20 June 2014, 11:17 PM
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True, it takes more energy to cool a gallon of water than it takes to cool a gallon of air, but you only have to cool the gallon of water once, not each time the 'fridge door is opened.
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  #3  
Old 20 June 2014, 11:27 PM
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Also when people say it works better, they may mean that the temperature stays more constant, without dipping into the danger zone. Whether or not it's more energy efficient, it's better for food safety.
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Old 20 June 2014, 11:56 PM
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I suppose if you never needed to store enough food to fill up a large fridge you might be better off just getting a smaller fridge, which would in turn be more energy efficient, and then the fridge would be more full, but that's not really what the OP is arguing.
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  #5  
Old 21 June 2014, 12:52 AM
Singing in the Drizzle Singing in the Drizzle is offline
 
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On the other hand over filling will as make it less efficient. That is unless you like everything next to the vent to freeze and stuff by the door to get to warm. The fridge also needs enough room for the air to circulate in order they keep everything nearly the same temperature.
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  #6  
Old 21 June 2014, 02:27 AM
Onyx_TKD Onyx_TKD is offline
 
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I don't have any actual data on efficiency for full vs empty fridges, but I think the following factors would be important:

1. A full refrigerator has more "thermal mass," so it will heat up and cool down more slowly than an empty refrigerator. The flip side of that is that the refrigerator must remove more energy to cool the full refrigerator by the same number of degrees as it does for the empty refrigerator.

2. The refrigerator maintains its setpoints by monitoring the temperature and adjusting the compressor accordingly based on its algorithm. If the compressor has variable speed, then there is probably a most-efficient speed to run. That would be the speed it is expected to run at most frequently, not the top speed. Thus, a rapid temperature rise prompting a high compressor speed would cause the refrigerator to run less efficiently than a slow temperature rise that could be handled by a lower compressor speed.

Points 1 and 2 together would support the idea that a full fridge would be more efficient, at least for a variable-speed compressor. Not sure about a single-speed compressor that's either on or off, and those are in a lot of home fridges.

3. As Singing in the Drizzle noted, blocking the airflow by overpacking it would decrease the efficiency due to screwing up the temperature uniformity (and consequently preventing the control algorithms from working correctly).
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  #7  
Old 21 June 2014, 05:07 AM
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That's what I figured had to be the case.
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  #8  
Old 21 June 2014, 02:51 PM
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What about standing there in front of an open fridge door? Cecil says not to do it in that article, but how long does it actually take for cold air in a fridge to be replaced by room temperature air?
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  #9  
Old 21 June 2014, 06:08 PM
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The problem with the open fridge is that the heat is continually flowing into the fridge and all of its contents. If you open and then close it, the fridge only has to cool one "exchange" of air. If you leave it open, the air is circulating, so the contents are going to get considerably warmer. Now when you finally close the door, the fridge has to cool the exchanged air, plus the fridge contents that had heated up a bit.
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  #10  
Old 21 June 2014, 11:19 PM
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And with an open door, the fridge is going to be constantly trying to cool air that will be lost almost instantly.
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  #11  
Old 21 June 2014, 11:27 PM
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When the fridge is very full, the door tends to be opened longer; it takes longer to find what I want. So...you've got to account for the human factor here, too.
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  #12  
Old 24 June 2014, 11:06 PM
jimmy101_again jimmy101_again is offline
 
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Quote:
Here's the crucial factor you're overlooking: Every time you open the door to the refrigerator, you let out cold air and let in warm air--and when you shut the door, all that warm air you let in has to be cooled down. The more air space in the fridge, the more cold air that can be swapped with warm air from the kitchen.
So the key factor isn't "full" versus "empty" the key is not to open the door constantly. The actual amount of energy required to cool a couple cubic feet of air from room temperature to fridge temp is pretty small.
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