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re: most efficient refrigerator
29 jan 2004
daestrom  wrote:

>> >> >> >...a 'full' unit has less free air to 'spill'.  which is why a unit
>> >> >> >that is full or nearly so runs more economically than an empty.
>>
>> i'm questioning that. have you ever seen a serious study that says a full
>> fridge uses less energy than an empty one? how much less?...

would you have any evidence for this article of faith?

>i'd like to see the lbl cite.

http://enews.lbl.gov/science-articles/archive/energy-myths3.html and
http://enduse.lbl.gov/info/lbnl-45862.pdf

>> >> >...if you open the door to fetch something then close it, the total
>> >> >amount of water vapor let into the 'full' one is less...
>> >>
>> >> that could be true of a chest freezer, but air flows continuously when
>> >> a fridge door is open, and the driving force is the temp diff...
>> >>
>> >> >in both, the water vapor that gets in will eventually be condensed.
>> >>
>> >> imo, "the" water vapor would be condensed very quickly, while the door
>> >> is still open and the air is still flowing.
>>
>> please note the continuously flowing air, vs a one-time slug replacement.

and the enormous condensation heat transfer coefficient.

>> >the point of what i posted was that if you compare the energy usage of
>> >two identical freezers, with one 'empty' and one 'full', the 'full' one
>> >uses less energy.
>>
>> do you have any proof of this claim? to me, basic science teaches
>> the reverse.
>
>your 'basic science' does not teach the reverse.  you just think it does. 

that's one opinion :-)

>i have pointed out that your natural convection flow formula calculation is
>poorly applied here.

agreed. as you say, it seems to underestimate airflow. 

>have you compared the area of the entire inside surface of an 'empty'
>(three walls, floor and ceiling) with the 'face' (equivalent to the back
>wall in area) of a stocked fridge?

less, imo, so it's a less-efficient heat exchanger.

>the multiple surfaces of food stocks are close together, sometimes touching.
>those food items that aren't touching form channels with a high hydraulic
>diameter resulting in laminar conditions and much lower flow.

oh dear. got any numbers?

>the increased flow resistance, the poorer surface smoothness, the shorter
>vertical run before another food item obstructs/diverts the flow, are just
>some of the things your 'basic science' ignores.  to try and use the natural
>convection formula you have for such a surface and call it 'basic science'
>is a misapplication.

i disagree.

>without considering these things, you will have overestimated the flow rate
>through the multiple surface 'channels' by a wide margin.

i disagree.

>the 'empty' has one large open area in the middle so the natural convection
>formula is *close* for the three exposed walls.  but as i pointed out, this
>is still way off and not representative of actual usage.  who in their right
>mind leaves the door open long enough for steady state flow conditions to
>establish?

it seems to me that the "steady state" has less flow than the transient case.

>the 'slug' falling out of an 'empty' happens differently than your formula
>suggests, and is much larger than the 'slug' from a well-stocked unit (say
>between 5 and 10 times larger).

this reinforces my argument.

>maybe you should just do a study of your own and get back to us?

both of us seem to have some technical understanding of this situation, but
neither of us have definitive data. why on earth should anyone believe you?

nick




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