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re: rod speed: chest refrigerator article
20 jul 2005
wrote:
>here is an article i came across on a home made chest
>fridge. note that i said fridge and not freezer
http://tinyurl.com/cay4t
>to me this idea has merit... what's everyone else think?
i think it's great :-) i also imagine that self-cleaning ovens
are more efficient, since they have higher temps which require
more insulation and airtightness.
i like the digital thermostat. we might put it in series with the freezer
thermostat instead of using the latching relay to switch the full power or
try to fool the freezer stat to make it think the freezer is colder, and
leave the light bulb connected (to keep the fridge from freezing in a very
cold room, inter-alia), but those are only minor potential improvements.
in a pv house, we might make ice when the sun shines.
no_child_left_unleashed@yahoo.com.sg wrote:
>i see an issue... there is no stated heat-pumping performance...
it might have a cop of 3.
>the calculation of required heat-flow for any given situation (ie,
>ambient temp, desired interior temp, allowable number of door
>openings/day, etc, insulation supplied) is obscure, in the sense of
>seldom discussed - but actually quite simple. really requires only the
>simplest of algebra, because heat flow exactly follows ohm's law.
sure.
>the fellow says he is consuming 0.103 kilowatt-hours per day.
about 38 kwh/year, worth about $3.80 :-)
>now, 1 btu is 0.0002931 kilowatt-hours (if you have 100% conversion
>efficiency). so, in your 24 hour day, you have pumped (at theoretical
>100% efficiency) 351.4 btu from inside to outside.
or 1054, with a cop of 3.
>during that 24 hours, heat was continually leaking through the insulation,
>from the outside to the inside... you may have opened the door xx number
>of times.
say xx = 12, at 10 seconds each. this chest fridge might not lose much
cool air when the door is open, but it would still collect radiant heat
from a room. say 0.1714x10^-8((460+70)^4-(460+40)^4)12ft^2x12x10/3600
= 11.2 btu/day :-)
>just off the top of my head, let's posit that our refrigeration
>efficiency from electricity to coolth is 50%...
you might enjoy looking up "cop."
>a btu will drop a pound of water, one degree fahrenheit. a lb of water
>is approximately a pint. if the water went into the fridge at ambient
>of 75, and we want to bring it down to 40, that is a delta of 35.
>87.85 divided by 35 is 2.51
and 1054/35 = 30.
>so in a day of operation, this baby will chill down two-and-a-half
>pints of drinking water
or maybe 30, but this "transient cooling capacity" is likely irrelevant
in a home, since it ignores the fact that the rest of the cold contents
of the fridge can quickly cool newly-inserted warm food.
some people wondered how to defrost a fridge like this, but it probably
won't require defrosting, since it has no freezing compartment (it might
be nice to make a freezing compartment, as a part of fooling the freezer
stat, but that might add a lot to the power consumption.)
somebody said the inside of this fridge would be wet, but the web page
said it has a drain. it might be nice to have more humidity and less
wilting lettuce inside a fridge.
it might be fun to add insulation board around it to save more energy,
if we could find a freezer that doesn't have warm coils under the skin.
what's the minimum energy? if we cool 10 pints of water per day, that's
350 btu. add 11.2, and we get 361.2. divide by 3 to get 120.4. divide
by 3412 to get 0.035 kwh/day. multiply by 365.25 to get 12.88 kwh/year,
worth about $1.29.
this chest freezer mod comes close to that :-)
nick
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