On Saturday, April 12, 2014 10:46:34 AM UTC-4, nestork wrote:
> trader_4;3221641 Wrote:
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> >
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> > IDK on what basis you can conclude that the humidity is going
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> > to be 100% leaving the evaporator. Not that it matters that much.
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> >
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>
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> Well, imagine the air isn't moving.
But the air *is* moving across the evaporator.
If you have room temperature air,
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> and you cool that air down to -60 deg F, then at some point during the
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> cooling process you'll go below the dew point and moisture will
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> precipitate out of that air. From then on, as you continue cooling the
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> air, moisture will precipitate out of the air and the air will remain at
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> a relative humidity of 100%.
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>
Sure if it's air that's just sitting around and it has time to reach
a steady state. But this air is moving past the chilled coils. If you
applied your reasoning to a home central AC system, then the air that's
leaving the unit at about 55F should be 100% humidity. Do the math.
If that air was indeed 100% humidity, even when it warmed up inside
the house, the humidity would still be way too high to be comfortable.
It's not going to go from 100% to 40% or 50%, ie a comfortable range,
by just warming up 15F.
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> >
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> > But he's not keeping it at freezer temps, he's keeping it at
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> > 50F. The evaporator coils will be constantly defrosting themselves.
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> > The coils will get cold for a short time, only long enough to drop the
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> > temp of the unit back to 50F, then turn off. They will then warm up
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> > and melt. Its going to have a very short on duty cycle compared
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> > to it's off time. The real problem I see there is that he may need
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> > some way of getting rid of the condensate, as the freezer system
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> > may not be able to handle it.
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> >
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> No, the cold control in a fridge works just like the thermostat in an
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> oven.
No what?
It doesn't shut the compressor down when the set temperature is
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> reached because then, the fridge will be spending all of it's time ABOVE
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> that set temperature. When you set an oven to 350 deg. F, the oven
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> bake and/or broil elements don't shut off at 350 deg. F. Typically with
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> the old oil filled capillaries, the oven bake and broil elements will
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> shut off at 362 deg F and go back on again at about 338 deg F so that
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> you have a 25 degree hysterisis that gives you an AVERAGE temperature of
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> 350 deg. F.
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>
Which is irrelevant. If I set my fridge and freezer at say 37F/0F,
it stays pretty damn close to those numbers, when the door is left
closed. So what if it goes up or down 2 or 3 degrees? It doesn't
change the fact that to maintain 55F inside, a fridge isn't going to
run much at all, unless it's in a garage or someplace where it's 90F.
Put it in a house where it's 70F or a basement where it's 65F and
it's not going to run enough to keep the coils frozen. It will run
for a few minutes, shut off, and any ice on the coils is going to have
a long time to melt at 55F.
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> A fridge's cold control will do the same thing, but I'm just not sure of
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> the temperature range. But, suffice it to say that there's a hysterisis
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> built into cold controls to control the temperature so that the AVERAGE
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> temperature over time is the set temperature.
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>
And the range is pretty tight too. A fridge set at 37F, with the door
closed, isn't going from 45 to 29F. To maintain 55F, it's going to run
for a few minutes and shut off.
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> The OP said it's NOT a self defrosting freezer.
Where did he say that?
So, with open
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> containers of water in that freezer, his evaporator coils are going to
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> get caked up with frost and he's going to be spending several hours
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> every 2nd or 3rd day defrosting the evaporator. It's going to be just
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> like the old manual defrost fridges, only with the frost accumulating on
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> the evaporator very much faster, which is why I'm saying the use of a
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> freezer to provide a cool humid environment won't work. A freezer will
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> only provide a cool dry environment.
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But it's *not* a freezer, because he's running it to maintain 50 - 55F.
Good grief.