Alternative Power sources - Re: Rod Speed: Chest refrigerator article

Author

Re: Rod Speed: Chest refrigerator article

nicksanspam@ece.villanova.edu

2005-07-24, 9:05 pm

<me@privacy.net> 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

Rod Speed

2005-07-24, 9:05 pm

nicksanspam@ece.villanova.edu wrote:
> <me@privacy.net> wrote:
>
>
> http://tinyurl.com/cay4t
>
>
> 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:
>
>
> It might have a COP of 3.
>
>
> Sure.
>
>
> About 38 kWh/year, worth about $3.80 :-)
>
>
> Or 1054, with a COP of 3.
>
>
> 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
> :-)
>
>
> You might enjoy looking up "COP."
>
>
> And 1054/35 = 30.
>
>
> 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.

I have a thing which is essentially a plastic sphere with the lid as
part of the sphere for the lettuce. You put a small amount of water
in the bottom. By far the best approach for lettuce and costs peanuts.

> 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 :-)

Logan Shaw

2005-07-24, 9:05 pm

nicksanspam@ece.villanova.edu wrote:
> <me@privacy.net> wrote:

[color=darkred]
> 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.

I don't really see how that's relevant. If you put something warm
in the fridge, an amount equal to its mass times the temperature
difference (between its initial temperature and the temperature
inside the fridge) is the heat that will be pumped out. It doesn't
matter whether this heat is transferred in one millisecond or six
hours -- it's still the same amount of heat and requires the same
amount of energy to pump, right?

- Logan

nicksanspam@ece.villanova.edu

2005-07-24, 9:05 pm

Logan Shaw <lshaw-usenet@austin.rr.com> wrote:

>
>
>I don't really see how that's relevant. If you put something warm
>in the fridge, an amount equal to its mass times the temperature
>difference (between its initial temperature and the temperature
>inside the fridge) is the heat that will be pumped out. It doesn't
>matter whether this heat is transferred in one millisecond or six
>hours -- it's still the same amount of heat and requires the same
>amount of energy to pump, right?

Right, but this was directed at people who said a fridge with a small
cooling capacity could be dangerous, since a warm pot of soup might
take a long time to cool, during which time bacteria could multiply
to an unsafe level. Rather moot, since the standard freezer described
on the web site had ample capacity, even tho it only turned on for 90
seconds per hour.

Nick

Dave

2005-07-24, 9:05 pm

<
Another consideration that I would caution members about is that one of our
staff had a premature failure of a 12/24 volt Danfoss compressor driven
freezer run as a fridge because some of the internal tubing corroded at
warmer than freezing temperatures!

OzDave
www.rpc.com.au

stu

2005-07-24, 9:06 pm

<no_child_left_unleashed@yahoo.com.sg> wrote in message
news:1122038422.917774.167660@o13g2000cwo.googlegroups.com...
> Dave wrote:
driven[color=darkred]
>
>
> was that etiology verified? it doesn't seem logical that the
> tubing was
> designed to be corrosion free at 0 F, but not at 35 F
>
> for a given refrigerant, at a given vapor pressure inside the
> evaporator,
> boiling always occurs at the same temperature. temperature in the
> *compartment* depends upon how much refrigerant is allowed to
> boil, as
> controlled by a thermostat... the tubing doesn't know what the
> temp is in
> the box.

I have a theory, could it be that you can make the evaporator out of steel
in the freezer(where it will be covered in ice most of the time), but not in
the fridge because it would rust, being covered with water all the time??

Dave

2005-07-24, 9:06 pm

>> > freezer run as a fridge because some of the internal tubing corroded at
> I have a theory, could it be that you can make the evaporator out of steel
> in the freezer(where it will be covered in ice most of the time), but not
> in
> the fridge because it would rust, being covered with water all the time??
>
I'll try & find out tomorrow what corroded & brand of freezer. It did
happen several years ago- perhaps it is not an issue with most brands?

OzDave

L0Slung

2005-07-24, 9:06 pm

On Sun, 24 Jul 2005 14:36:57 +1000, "stu"
<noone@nowhere.com> wrote:

snip

>
>I have a theory, could it be that you can make the evaporator out of steel
>in the freezer(where it will be covered in ice most of the time), but not in
>the fridge because it would rust, being covered with water all the time??
>
...tis no theory.
The K1W1s perfected the american concept of PPO
with their version of steel wrapped evaps in the
'80's.
See Fisher Pykel.
The Italians had a go too. Not as successful as
their efforts did last the full 5 years,
usually<g>

--
PPO = Planned Plant Obsolescence

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