h a l f b a k e r yThe word "How?" springs to mind at this point.
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1. Freezing: At night time (low cost off peak electric
power) freeze clean water to create ice, stored in a
heat-
insulated box.
2. Salting: In daytime, automatically add ice to water,
lowering its temperature to minus 18 degrees Celsius .
(See link)
3. Cooling: When cooling needed, pass
coolant through
salt
and ice, leading it to the air blowers going through a
heat
exchanger.
4. Recycling: During the day remove brine periodically to
a
closed but not heat insulated solar evaporator, where it
is
dripped into air, heated by solar power.
4a. The salt will be reused,
4b. and the damp air will be cooled in the evening in an
artificial dew system, retrieving the water to be frozen
again.
[edit] my improved idea in the annotation:
No water turned to ice, but rather use the humidity from
the air for creating ice. (Like an air conditioner with too
little Freon. )
Evaporate the water to retrieve the salt, letting it out to
ambient air (with fans and under the sun)
So it doesn't use water (an expensive resource in my
place, soon to be rare and expensive everywhere) and it
uses the sun in its most effective way (evaporation and
heat). This is extremely efficient and should be very
cheap too.
ice and salt cooler
http://www.youtube....watch?v=O7TvEIA0Ln4
[pashute, Jun 21 2013]
Not this
http://news.cnet.co...ks-to-slash-energy/
Or at least I think its talking about something different [pashute, Jun 21 2013]
Ice Bear
http://www.ice-ener...ergy-storage-system
Much simpler solution gets you within a few deg C of your solution. [scad mientist, Jun 24 2013]
canteen
http://www.hagorsho...rce/c1409/17864.php
[pashute, Jul 01 2013]
Ice Bear (scad mientist's link)
https://www.energy....bear-storage-module
live link [pashute, Dec 08 2020]
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OK, better yet. No water turned to ice, but rather
use the humidity from the air for creating ice. (Like
an air conditioner with too little Freon. ) |
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Evaporate the water to retrieve the salt, letting it
out to ambient air (with fans and under the sun) |
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Use the evaporation to pre-cool the coolant, before
passing through the ice! |
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First time I get no remarks. First time I get only
pastry. "Where did we go right?" (the mouse that
roared) |
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I've thought about this enough before to know that it's not going to be super-economical. |
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You don't get to extract more heat by adding salt. (What you do get is the ability to reach lower temperatures). The cost of that is the need to regenerate concentrated salt, which is energetically expensive. |
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If you don't need temperatures below zero, you're better off in every way keeping salt out of the equation. |
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If you do need temperatures below zero, then your step 3 seems longwinded. Better cooling efficiency is generally obtained by minimising the number of transfer stages, to get your heat sink as close to the target as possible. e.g. ice-cream making - salt/ice mixture and cream are separated only by the container wall.
And the efficiency is still killed by salt recycling. |
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Isn't a regular refrigerator better than this because it continually uses the same few pounds of refrigerant? If you want to collect energy at night and use that energy to power your AC during the day you could just store it with a giant flywheel. |
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What [Loris] said, but also, since you're using a standard heat pump in step 1, why not just turn the temperature down a few notches so you can freeze salt water (or any other liquid with a freezing temperature that is useful for your application)? |
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That way you don't have to go through the process of raising the melted salt water from <0 deg C to above 100 deg C using solar energy, then cool to ambient (say 25 deg C) temperature during the first half of the night, so the freezer can work extra hard to lower the temperature from 24 deg C down to freezing. If you just keep the whole mixture constantly at -2 deg C (or whatever the freezing temp is for the salinity of your solution), then you can store cold during the night (using low cost electricity and a heatsink exposed to the cold night sky), and use the cold during the day. |
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Of course I'm sure my simple alternative has already been baked... Yup, see link for Ice Bear. It doesn't use salt water, but I'm not sure how much that adds: just 2 degrees at the cost of much worse corrosion issues. |
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[scad] That was my first thought, but it doesn't take
advantage of two different forms of cheap energy
(night time electricity, daytime solar). |
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OK, edited the entry according to my first anno. I
think it answers all the other questions. OK not
"efficient" energetic wise, but overall system wise. |
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I mean, using ambient humidity to create the ice,
and the sun to evaporate the water in the brine, is
an efficient use of resources. |
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Okay, I see the idea is to use solar power in addition to night time electricity, but my sense of the original idea is that the solar step would end up causing it to use more electricity at night to get the same amount of cooling than is you omitted the solar steps altogether. I could be wrong on that, but we'd need to see how much more heat the ice can absorb when comined with salt vs, how much heat needs to be removed from the water at ambient temperature to get it back down near freezing temperature. |
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If I understand the edited idea, the water is evaporating into some large store of air during the day, then at night it condenses and turns to ice on coils of the heat pump. So now, not only does the heat pump have to cool water from ambient to freezing, it first has to absorb the heat required to condense the water vapor as well. i thkn you were better off before. |
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I'd refer you to an Einstein Refrigerator, but that only works during the day using solar power. It seems you are looking for some cooling cycle that takes advantage of alternate periods of free heat and inexpensive electrical energy. That would be rather neat, but even if this solution you propose does work, you still have a standard heat pump using freon or whatever, plus the completely separate system using water and ice. I'd rather just use an Einstein refrigerator supplemented by an Ice Bear. |
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I'm not sure I get the idea. |
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Are you saying that if you add salt to 0C ice you'll end up with -18C ice ? Cool... what does that do to its heat capacity ? |
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(and a bit off topic, does anybody know how efficient an Einstein Szilard fridge is ? "not as efficient as a compressor" and "could be quadrupled" is the best 10 pages of Google can do) |
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Scad, No. The idea now is simple: |
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Cooling saltwater down from zero to minus 18
Celsius is extremely expensive. So instead:
a. Ice from AMBIENT AIR. Just like it accumulates
in a faulty air-conditioner with too little gas. I
freeze distilled water from ambient air to zero.
b. Then during the daytime spray salt on the ice
lowering the temperatures to minus 18 C.
c. During or after usage, when heat is being
absorbed by the ice and salt turning it into brine,
at the heat of day, this brine is sent out to an
evaporator. The salt is kept for reuse. The water is
evaporated OUT of the system, while cooling it
considerably. This evaporated water is not re-
used. It is lost to the environment. |
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This (sage c, above zero degrees cooling) is similar
to covering a
water bottle with a wet dark colored rag and
putting it in the sun. |
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So their are three cooling stages:
a. Ice from humidity (at 0 C, during night time)
b. pre-cooling by evaporation (during operation).
c. Freezing by salt (during operation) |
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Salt is recycled. Water is taken from ambient air
and returned to it. |
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//covering a water bottle with a wet dark colored rag and putting it in the sun// |
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Surely that's bogus, in that it would be even cooler in the shade. The 'explanation' is that the sun's heat makes the water evaporate faster which in turn increases the cooling, but that's like saying that putting on the brakes makes my bike go faster because it makes me pedal harder. |
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Every time I was in army marches in the desert, that's
at least once a day, during 4 years of the regular
army, and more than a month almost every year till a
few years ago, I would wet my canteen on my belt. |
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If I forgot it in the (hot) shade it would be warm and
taste terrible. If it was out in the sun it would dry
out quickly, and the water would be "ice cold". |
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I'll have to take your word for it, but it seems counter-intuitive. Could it be that the air in the shady area was relatively still and humid? |
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It may or may not be relevant that army canteens' carrying cases are rather thick blankets of cloth. |
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I meant water bottle. See link |
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spider, presumably your in the northern hemisphere,
and its sunny at some time today. try it out: take a
wet cloth and put it on a bottle inside your house in
the shade. Take another wet cloth and put it on a
bottle in the sun. |
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Wait 25 minutes and check the temperatures. |
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// spider, presumably your in the northern hemisphere, and its sunny at some time today. try it out: take a wet cloth and put it on a bottle inside your house in the shade. Take another wet cloth and put it on a bottle in the sun. // |
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Unfair test. As spidermother points out, humidity and wind will differ. |
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take two identical wet cloth-wrapped bottles and put them both outside in the sun. Also put up a shade so that one is covered but not protected from any wind.
Check temperatures after 25 mins.
To be thorough, repeat experiment putting the bottles inside your house - adjacent but with one in direct sunlight from a window. |
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