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Nicholas Covey
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Over in the alternative building forum we were discussing the technology of the Gaviotas community in Columbia. They apparently have made some real breakthroughs in living without grid power. One such technology is their solar refrigerator... So I started to research. There is apparently no real evidence of how this particular device works (if they really want to help the world, some plans might be useful for the rest of us  ), but I did find interesting bits and pieces of how it may work... concepts and such.

I found a few devices for sale:

http://www.energy-concepts.com/pf_isaac.html

and I found how to construct a simplistic device called an icy ball...

http://crosleyautoclub.com/IcyBall/HomeBuilt/HomeBuilt.html


So this could start some serious experimentation... let me first put on my handy dandy mad scientist glasses and call over the local hunchback, and I'm good to go

I have more, but those are the best two links. If this is interesting to anyone (COUGH... Paul) I can dig up some more.
 
paul wheaton
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I remember reading a lot about the icy ball about five years ago.  It is an interesting idea. 

I like the idea of solar fridge. 

The gaviotas fridge was solar powered (at least, I think it was), but even more important is that it was super-duper insulated. 

I like the idea of eco technology coming in degrees, as opposed to all-or-nothing.  Imagine somebody that has an interest in eco stuff, but might not be as crazy about it as I am.  If I am, say, level 8 eco-crazy - what about the folks that are more like, level 3 or 4.  They might be willing to do a couple of quick and easy things that cut their power bill.  Move gradually to super eco. 

So switching to chest type refrigeration plus four inches of excellent insulation might cut their fridge power consumption by a factor of 10 and be withing their comfort zone.  Whereas solar stuff on the roof, routed into a cold storage room might be too much.

So, here is some good info:

Start with just getting your head wrapped around common usage: http://michaelbluejay.com/electricity/refrigerators.html

So a really good fridge uses about 1kwh per day.

Now, let's add in the chest type: http://mtbest.net/chest_fridge.html



Right there - 10 times less juice.

Imagine adding in the super insulation.

 
Nicholas Covey
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I agree with your "degrees" concept. I'm not agianst anything that I can get to work with as little intervention as possible... of course Im willing to live in a plastic wrapped pole barn, buried under the ground too.

Anyhow, One thing that I've run across a few times is the concept of removing the coils and fan from the freezer/refrigerator and moving it to someplace where the heat can be utilized, or at very least be dispersed where it doesn't affect the insulated box itself.  Obviously this is outside the realm of what most of us are capable of doing ourselves, but a good HVAC man might be able to do such a conversion... in trade for fresh produce? Just a thought.
 
paul wheaton
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Once the fridge becomes super efficient, the amount of heat extracted should be less than what is put out my a dim light bulb.  Probably not worth the effort of moving the heat.
 
Susan Monroe
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I've already returned the Gaviotas book to the library, so I can't check it, but hardly looking, I found two references to the fact that... "repeated efforts to design an effective solar refrigerator never succeeded."  This one was dated 2007: http://findarticles.com/p/articles/mi_hb6376/is_/ai_n29343219

Does anyone know anything about this Earth4Energy stuff on how to build your own solar panels cheaply?
http://www.earth4energy.com/solarpanels.php

There is also the Friends of Gaviotas:  "Friends of Gaviotas was formed in 2002 as a 501(c)(3) nonprofit to facilitate initiatives such as:
•North-South research exchanges like the Gaviotas biodiesel project.
•Periodic get-togethers with Gaviotans (Paolo Lugari and others)."  http://www.friendsofgaviotas.org/Home.html

I've just signed up for their newsletter.

Sue
 
paul wheaton
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Susan Monroe wrote:
I've already returned the Gaviotas book to the library, so I can't check it, but hardly looking, I found two references to the fact that... "repeated efforts to design an effective solar refrigerator never succeeded."  This one was dated 2007: http://findarticles.com/p/articles/mi_hb6376/is_/ai_n29343219


Great link!

I hate the "Illustration Omitted" stuff. 

And ...  "repeated efforts to design an effective solar refrigerator never succeeded." is a real drag.



 
Susan Monroe
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To tell the truth, the old method of cutting chunks of ice out of the lake and storing them in a straw-insulated shed still seems to be the simplest and most cost-effective way of cooling.

Of course, if you live in TX or SoCal or AZ, where you need cool worse than anywhere.... natural ice is probably hard to find.

Still, it just seems like there should be a way to do it with solar if someone who knows something could grab onto some kind of basic idea.

Sue
 
                            
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paul wheaton wrote:
I remember reading a lot about the icy ball about five years ago.  It is an interesting idea. 


It seems the problem with the icy ball was that it tended to explode, every so often. An updated variation of it seems to be in the works (though I've not been able to find anything more recent about it): http://www.ted.com/index.php/talks/adam_grosser_and_his_sustainable_fridge.html

 
Dave Boehnlein
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A couple of comments here:

1) During an energy talk I've heard Doug Bullock refer to an ice factory where he grew up in San Luis Obispo. Apparently, the factory was located in a spot with high, near-constant winds. They had a series of radiators mounted to the roof where the wind would would blow through them and cool the refrigerant down. As it cooled it would sink inside the building make it really cold. Cold enough to make ice, apparently. According to Doug the walls were made from thick cork and they were super insulated.

When Doug visited as a kid he realized that all the electric lights were tacked onto the ceiling with exposed wires. This is because the the factory was actually build before the era of electricity. In other words, they were manufacturing ice in California with no electricity. In the 70's they were even able to make dry ice.

I've tried searching the internet, but I haven't been able to find anything.

2) Susan has struck upon one of my fantasy future scenarios! The return of the ice man! As electricity becomes more and more expensive I think we will eventually see the return of ice boxes, ice houses, and the ice man who comes around every week to deliver a block. In fact, I can talk ad nauseum about my dream of living on Lake Superior and harvesting ice with a team of sled dogs in the winter. I'd pack them away in my well insulated, subterranean ice house and deliver them with my horse and wagon. The good life!

3) Sam Bullock has a propane refrigerator that uses the exhaust heat to dry fruit. Unlike an electric fridge where the fan blows out by your feet, propane fridges blow out the back. Sam mounted a box with screens overhanging the back and Viola! we can dry 5 trays of apples in two days. It would be neat to see a similar system develop for electric fridges.

Dave
 
                                    
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1897 MORNING TRIBUNE story on new SLO Ice Factory
(note the ice was made using an ammonia based system and a gasoline powered engine)
ENTERPRISE OF OTTO TULLMANN.
HIS ICE FACTORY TURNS OUT THE BLOCKS TO PERFECTION.
Fine Mechanism Which Defies the Workings of Jack Frost.

  Yesterday afternoon a TRIBUNE representative was enabled to note the workings of the new ice factory.

  The genial and enterprising proprietor, Mr. Otto Tullmann, acted as the pilot and very kindly answered a hundred or more questions and explained the various processes through which the water of a tropical country is converted into the congealed coldness of the Arctic regions.

  The ice plant in the main is situated in the cellar, beneath Mr. Tullman’s well known place of business on Chorro street. It has been in operation several days, and the public is gradually extending its patronage and the pure crystal blocks are being sold every where to drive away the effects of old Sol’s rays, these warm summer days.

  The plant has a capacity of two and a half tons of ice every twenty four hours. The water is frozen in fifty-one corrugated iron cans arranged in a vat. Previous to turning the water into the cans from a cold storage tank, it is run through two of the most modern improved filters, each having a capacity of 300 gallons. From these filters the water flows into a big tank, and for crystal purposes, would rival the poetic charms of one of nature’s most celebrated mountain streams. From such water as this, without the slightest speck of dust, the ice produced is much purer and better than the natural ice that is shipped from some stream where tadpoles and other kindred animalculae (sic) abound. Wherever the pipes appear through which the ammonia passes for the purpose of condensing the freezing water, there is one long line of white crystals of snow.

  The engine used is one of eighteen horse power, and is in charge of that expert mechanic, John Hanna. It is a gasoline engine and the tank from which the supply of gasoline is obtained is situated in a place where it cannot in the least endanger the property in that vicinity in case of fire. The tank is placed upon two long timbers which extend out over the waters of San Luis creek. In case of a conflagration, the tank can, on a moment’s notice, be dumped into the creek. It is a safeguard which Mr. Tullmann was very careful to take. Another precaution taken deadens the noise of the exhaust pipe.

  Everything about the factory is very neat, and the machinery works to perfection. For the benefit of the TRIBUNE scribe, Mr. Tullmann had one of the big cakes of ice weighing 100 pounds, hoisted from the vat. It was a fine piece and as clear as crystal. After examination it was stored away in the cold storage vault.

  The entire plant, together with the labor of putting it in place has cost the proprietor $4200. The machinery is of the latest pattern and was manufactured by the Vulcan Iron Works of San Francisco, and was put in place by John W. Dyer, one of the company’s most trusted and expert mechanics. Mr. Dyer left yesterday to put in a cold storage plant for Baron Von Schroeder at the Eagle ranch.

  Now that San Luis Obispo has an ice factory, not a single pound of ice should be purchased outside of this city. The way to progress is to patronize home industry and Mr. Tullmann is one of our citizens who has expended his money in a new enterprise for this section of the state and he deserves all the encouragement and support which can be given him.

--from a compilation by Wilmar N. Tognazzini - http://wntog.tripod.com/97.html
 
Dave Boehnlein
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Nice find! I had no idea where to find info. I don't suppose there were any later articles, were there?

As I'm passing the story on second hand I'm not sure what the full story was. Perhaps the cold storage was wind cooled? It could also be a retrofit, but who knows? I'll try to pick Doug's brain if I remember, although he was just a kid at the time.

Thanks, Suburbman!

Dave
 
                                    
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permaculture.dave wrote:
I don't suppose there were any later articles, were there?
  . . .
Perhaps the cold storage was wind cooled?

Ammonia based cooling systems have condenser coils that must be located vertically above the other parts of the system.  These condenser coils are typically put on top of the roof and would look just like radiator coils.  During the summer months when ice would be in greatest demand, SLO has an avg nightly low of 53F.  No way are you going to be able to make any ice at those temps -- let alone 2.5 tons/day!

BTW, the refrigeration part of ammonia based cooling has no moving parts making such system extremely reliable, low maintenance, and long lasting.  Residential ammonia based refrigerators from the 30's are still running today.  Since electricity is priced on an increasing marginal scale in CA, I looked into getting a Servel ammonia based (natural gas powered) central AC to replace my old unit and discovered it was illegal to import them into CA.  (I 'm sure the electric companies had nothing to do with that... NOT!)

Good info on ammonia based (natural gas powered) cooling systems at the site below:

  http://www.gasrefrigerators.com/faq.htm


[And yes, that was the only ice factory article in the archives]


 
Dave Boehnlein
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Suburbman wrote:
Ammonia based cooling systems have condenser coils that must be located vertically above the other parts of the system.  These condenser coils are typically put on top of the roof and would look just like radiator coils.  During the summer months when ice would be in greatest demand, SLO has an avg nightly low of 53F.  No way are you going to be able to make any ice at those temps -- let alone 2.5 tons/day!


On the theoretical front, if the air temperature was 53F (min) and you had fairly steady high wind speeds, do you think you could drop the inside temp lower if you used some sort of condensation system (kind of like a swamp cooler)? If so , how cold do you think you could go?

The ammonia fridges sound quite practical. Definitely worth more research. Is there any official statement as to why they're banned?

Dave
 
                                    
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On the theoretical front, if the air temperature was 53F (min) and you had fairly steady high wind speeds, do you think you could drop the inside temp lower if you used some sort of condensation system (kind of like a swamp cooler)? If so , how cold do you think you could go?

I don't have any formal education on the subject so I'm not not qualified to comment about the theoretical aspects of your question.  I do have friends and relatives who live in the desert and they tell me that 10-12 degrees in the max cooling effect you can get from a swamp cooler -- and that's with 100+ weather and very low humidity.

The ammonia fridges sound quite practical. Definitely worth more research. Is there any official statement as to why they're banned?

Ammonia fridges are fine in CA.  Natural gas powered ammonia-based central home air conditioners are prohibited as part of a larger ban on residential combustion engine type appliances due to air quality concerns.

.
 
paul wheaton
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Heading in a non-solar direction with this thread ....

I wonder about the idea of expanding on the idea of a root cellar. 

In fact, I wonder about the idea of the oehler structure combined with the umbrella design.  You could build a root cellar for about $200 in a day or two.  And what if you have a six inch tube that runs around the soil under the umbrella.  You could have two openings for the tube that come to the outside.  And on a really cold day, you can pull the plugs out and mount fans on it to run the cold, outside air through the tubes.  Maybe run these fans for three or four days each year. 

Without this bonus, you would have a reasonably cold root cellar.  But with this bonus thing, you should have something much colder. 

Inland, you might even have a year round walk in freezer? 

Possible? 


 
Joel Hollingsworth
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Interesting little strategy to save money on refrigeration:

http://www.builditsolar.com/Projects/Conservation/chest_fridge.pdf

via hackaday.
 
paul wheaton
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Hope ya don't mind that I mashed your new thread in with an old thread that kinda touched into this stuff in the past. 



 
Joel Hollingsworth
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I don't mind this being moved here at all, though it's a lot less radical of a topic than the ones they brought up.

As to heat-driven heat pumps:

They tend to be of the absorption type, which doesn't necessarily use ammonia.  Ammonia is flammable and can be toxic, one of which is true of most every other refrigerant, except halogenated hydrocarbons.

There are also adsorption refrigerators, like the one built in Guatemala:  the working fluid is alcohol (grain alcohol for refrigerator, wood alcohol for freezer), and it is adsorbed onto activated charcoal rather than being compressed with an electric pump.  I could imagine a freon-like fluid working with the right sort of sorbant, maybe charcoal would work for it, too.

http://www.aidg.org/component/option,com_jd-wp/Itemid,34/p,1479/

The authors list this as an absorption cycle, but charcoal is a solid... 

For the icy sphere etc., what drives the ammonia to evaporate from the cold side is its desire to dissolve in water.
 
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I've been studying ice caves the last couple of months.  And I wonder about two different approaches to making your own ice cave:

1)  Using the passive annual thermal inertia concepts.  So a sort of root cellar in the hillside surrounded by 20 feet of dry soil. 

1a)  In a cold climate, have a tube that runs through the middle of the dry soil.  On days where the temp is below zero, open the tube and move air through the tube.

1b)  Hook up the air conditioner thing that can turn an insulated room into a walk in freezer.

1c)  Make the root cellar have two rooms.  The first room being a cold room that you walk through to get to the second room which is freezer.

2) If the room is shaped right .... or if there is a series of garbage can size chambers ....  I wonder if a vortex tube could be used so that whenever a breeze comes along that the air is moved just right to make for really, really cold air.

 
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Suburbman wrote:
It is a gasoline engine and the tank from which the supply of gasoline is obtained is situated in a place where it cannot in the least endanger the property in that vicinity in case of fire. The tank is placed upon two long timbers which extend out over the waters of San Luis creek. In case of a conflagration, the tank can, on a moment’s notice, be dumped into the creek. It is a safeguard which Mr. Tullmann was very careful to take.


Wow. We've come along way in the last 100 and some odd years. And to even call it a safeguard. Think burning creek.
 
Joel Hollingsworth
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paul wheaton wrote:

I wonder if a vortex tube could be used so that whenever a breeze comes along that



Vortex tubes are crazy inefficient.  Gale force winds probably would be difficult to capture for enough of a pressure differential to get a decent temperature gradient.

They're rarely practical, and were only ever widely used due to contract negotiations: Rail workers were entitled to cool water, and they couldn't work without compressed air anyway, so there was always a vortex tube on hand and there was no worry of work stopping due to a broken moving part.  A lot of fuel was wasted compressing that air, but too bad.

Wikipedia says air compressed enough to run pneumatic tools can achieve a 45 C degree drop.  Due to thermodynamics, the achievable temperature drop will decline much faster than the pressure difference used to drive the device.  A shop compressor might run 100 psi...freakishly strong wind might apply 0.1 psi.  Even if efficiency were to remain the same, this would mean a temperature drop of 0.05 C degrees for your wind-driven vortex tube.
 
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A friend and I were talking about his experiences with an ice cave from his childhood.  He's an engineer.  After college, he re-visited the ice cave and speculated that what made it cold was a vortex tube effect.  This particular cave had all the fixens:  cylindrical shape of the room, one steady wind input at the right spot and two outputs at the right spots.  Granted, not a significant proof.

I thought about taking a garbage can, insulating it, cutting the right holes and hooking a shop vac up to it to see if the temps would change. 

It does seem that if the vortex tube worked this way that we would hear about it a lot more often.  But when thinking about HOW it works, it does seem like something that is plausible:  the larger, warm air is forced to the center ....

 
Joel Hollingsworth
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Cold air is in the center.

The way my thermo professor presented it was in terms of fast molecules and slow molecules.  Faster ones can't take such tight corners.
 
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Joel Hollingsworth
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Yes, it is.

Cold air is vented from the center of the tube, and is then allowed to expand, further cooling it.

Hot air is vented from the other side of the tube, at the periphery.
 
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Therefore, at this point, I have to let go of the vortex tube as something I can wrap my head around at this point.  And because of that, I cannot speculate on how to tinker with that idea to make something larger scale. 

Bummer. 

In other news, I did find some cool stuff on "ice wells" and "ice houses":

http://www.london-footprints.co.uk/articehse.htm

http://hampsteadheath.net/the_ice_house.html

http://gadsbys.home.att.net/icewell.htm

http://www.icehouses.co.uk/brighton.htm

Which makes me think that the house of soil thing could be tweaked to be an excellent ice house.


 
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I love the ice well idea,  but I'm not so keen on the chore of pounding chunks of ice into one solid slug...or having it delivered, for that matter.

Better, I think, to add liquid water in late autumn and extract heat through the winter.  Passive ammonia-filled radiators of the sort used on the Trans Alaska Pipeline might be appropriate, as long as there were a few hard freezes each year.
 
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My thinking from above is to focus on 1, 1a and 1c.

An underground stucture surrounded by 20 feet of dry soil.  Further, there is a tube running about 10 feet from the walls within the "20 feet of dry soil".

Normally, the tube is plugged.  On days where the temp is below 10 degrees, the tube is unplugged and air is encouraged to pass through (maybe a fan - maybe something that doesn't use energy).

No chopping of ice.  No hauling. 
 
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paul wheaton wrote:
  On days where the temp is below 10 degrees, the tube is unplugged and air is encouraged to pass through (maybe a fan - maybe something that doesn't use energy).


NH4 is nice stuff for this.  Depending on how much space you give it, you can tweak the boiling point to be perfect for ice-making systems.  The Trans Alaska Pipeline system is really elegant in this regard: it's like your tube, but it automatically plugs itself, and carries heat faster when it runs.

Imagine a closed loop, with very thin tubes connecting a condenser above ground and a (cold!) boiler below ground.  If the air is colder than your ice well, the NH4 will condense in the aboveground coils and drizzle down at air temperature.  The resulting drop in pressure will cause the NH4 in the ground to boil, absorbing heat from the well.

When the air is warmer than the well, warm NH4 will accumulate in the top coils, with enough pressure to keep below-ground ammonia liquid.  This shuts down the cycle.  With no circulation, the only heat flow through them will be through still gas, or through the tube walls (which are probably stainless steel).  Daily cycles will change the pressure somewhat, but thin tubes mean everything will stay neatly arranged with warmer layers of gas on top, and colder layers below.

The heat exchangers above and below can use an aqueous working fluid (brine, antifreeze, moonshine heads/tails...) to simplify repairs, minimize the proportion of highly-skilled labor for installation, and give a little better safety.  These fluids can be circulated by convection currents.

Part of the beauty of this is that the drawbacks of a typical anhydrous ammonia sytem would be minimized, but it would still play to its usual strengths.
 
paul wheaton
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Next up in my series of crazy ideas .....

Every notice how when you use canned air it gets freaky cold?  I suppose that is from liquid air getting to be a gas ....  yes?

So, the primary ingredient we need for this next crazy idea is liquid air. 

I wonder if there could be such a thing as a ram pump for air.  And then, as the air gets very compressed, it turns to liquid.  And then as the temp drops in your freezer/fridge, you let some air out and things get colder.

Lame idea?
 
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It's a very good idea.  A multi-billion-dollar-per-year idea.  That's exactly how commercial heat pumps already work, as a matter of fact.

The canned "air" you buy in stores is actually an ozone-safe replacement for Freon, and it is exactly the same stuff used in a/c and fridge coils.  (Actual liquid air builds up crazy high pressure, and is also a tremendous fire hazard: the N2 boils off faster, leaving increasingly pure liquid oxygen.  The gas they sell has a much lower vapor pressure at room temperature, isn't flammable or oxidizing or toxic, and the new stuff doesn't eat the ozone layer either.)

The only difference is, store-bought systems run on a continuous cycle, which re-claims the gas as it boils.  A compressor liquefies it, and lets it cool back to room temperature in those coils at the back of your fridge.  This liquid is then allowed to boil inside the fridge, cooling it through the inside coils.  There isn't really a reserve of liquid, for a number of reasons: it just cycles when the thermostat says it's too warm in there.
 
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So ... canned air isn't air? 

I guess I had this crazy idea of connecting a bunch of scrap pipes together and pointing an open pipe into the wind and on a windy day the contraption gets frost on it.

No special gasses. 

But it would be a fire hazard?

Hmmmmm ..... a fridge also has at least one fan in it .... and I suspect it would have a dehumidifier too (or something that just moves the moisture out of the fridge) - true?

 
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Frost is not a fire hazard.

Concentrated oxygen is.  Try hitting a charcoal fire with compressed air, for an example.  Liquid air is hundreds of times more concentrated than even the air inside the compressor, or the air that causes spontaneous combustion with each stroke of a Diesel engine or fire piston.  And allowing the more-volatile nitrogen to boil off makes for an almost pure oxidizer. 

Canned atmospheric air would either a) last a tiny fraction as long, because it's merely compressed, not liquefied, or b) have can walls half an inch thick.    But "air" can be used figuratively, as a mentonym for "gas".

Any fan in a refrigerator is probably there to drive air over the heat-exchanger coils.  Inside, the coils are often cold enough that dew or frost forms (which is how a de-humidifier works anyway, btw...it's just another application for a heat pump), and then the problem is merely removing that water.  The freezer might run its cycle in reverse until liquid stops dripping off the coils, for example; the fridge can just make allowances for the dew to drip off of it and pool somewhere outside to evaporate.

paul wheaton wrote:
pointing an open pipe into the wind and on a windy day the contraption gets frost on it.


I'm not sure I understand.  Do you expect frost because the wind is cold and damp?  Wouldn't a net do better at that, like the kind they build to collect fog?  What is transporting heat away from the region where frost is collecting, in the contraption you had in mind?
 
paul wheaton
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I have used canned air on a fire.  And it is spectacular.  Better than using propane.  And I also tried plain compressed air which was pretty lame.

So, the liquid in canned air is liquid oxygen?

I knew about the dehumidifier.  I suspect that there is a pan to collect water somewhere that is near where the warm parts of the fridge are - that way, the water is taken out of the fridge, routed to outside the fridge where it is extra warm and the extra warm bits lead to evaporation.

The contraption I was thinking about would use ramp-pump-thinking to make some sort of super compressed air that would be used for cooling.  But now I'm beginning to think that this whole train of thought is pretty weak.
 
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Maybe not, Paul, in some areas, at least.  I think you just gave me an idea for refrigeration in that village on the AK Peninsula where I hope to end up -- high humidity much of the time, high winds, and cool temperatures even in the summer -- the record high temp there is barely into the seventies.  Some kind of a wind scoop taking cool air through pipes that run through the top (because cold falls) of a long box -- it could be a cabinet in the pantry, which will be attached to the north side of the house along with the root cellar.  I don't need a steady forty degrees for much of anything, as all our milk is made into kefir or cheese, which don't spoil as fast as milk does. 

Kathleen
 
Joel Hollingsworth
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paul wheaton wrote:
I have used canned air on a fire.  And it is spectacular.  Better than using propane.  And I also tried plain compressed air which was pretty lame.

So, the liquid in canned air is liquid oxygen?


Yikes.

Canned air cannot be liquid oxygen.  It can't even be supercritical oxygen.  The news reports would occasionally mention people dying from it if it were.  Did your fire respond like this one?

http://www.youtube.com/watch?v=TBLr_XrooLs

The stuff they give out from the stockroom here at work is a hydrofluorocarbon, not the kind of stuff I would want to put on a fire.  I imagine its effects on fire would vaguely resemble halon, so I don't imagine that's what you used.

Maybe yours is butane?  I hope so.  That would, indeed, be a better fuel than propane, and less likely to give you cancer than halocarbons.  Doesn't it say on the can, what's in it?

Thanks for setting me straight on the compressed air thing.  I was thinking of this, when I commented (the source which introduced me to this project, had mistakenly reported compressed air rather than pure oxygen):

http://www.youtube.com/watch?v=w9dskxN10N0
 
Erica Wisner
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The wind-makes-frost concept sounds a little like magical thinking to me.
Magical thinking gets my explain-er-a-tor going. 
Bear with me as I work my way toward the discrepancy I see.

Root cellars operate by using the ground's intrinsic temperature and thermal mass - about 55-58 degrees F, big - to maintain cool, but not freezing, temperatures.  In cold areas, a hole in the ground can collect cool air and get colder than 55, but thermal contact with the ground tends to keep it above freezing in most cases.  These are great storage conditions for roots, and if your cellar is dry (not moldy) then other things (pickles, krauts, jams, cheeses) can store well too.
  Trouble with piping cool air through the ground - there's a lot of thermal mass in the ground, and not much in the cool air.  If you're going to pump chill into a hole in the ground, you want it insulated.

Ice houses operate by using heavy insulation, plus the hole-in-the-ground (or chest-freezer) effect to trap the chilled air.  The chill comes from the ice itself, stored away in winter.  You'd need to mine the top first, and use layers of sawdust to protect the rest of the stores.  It operates like a giant ice chest or camp cooler.
(By the way, stored lake ice can be a health problem if used directly in food - it's safer to use it as a chiller, in a separate container from the food being chilled.)

The other "no-energy chiller" is a cold closet.  An [insulated] pantry with a back that is open to outside air, screened or vented to protect it from vermin.  This works in cold season, when you are heating your house, to provide cooler outside temperatures for your food.
  In hot season, you use a root cellar, eat the abundant fresh food and dry/preserve it for later, or use evaporative cooling (or artificial refrigeration) to keep temperatures down.

You could get colder than freezing by adding salt to ice, like an ice-cream maker.  This only works because the salt helps melt the ice faster, and going from solid to liquid soaks up a lot of energy.  It's an active process, not a passive one, and would tend to consume your ice quicker than otherwise.

Most refrigerators work by using this energy of state change, not once, but again and again.  Pipes transport a warmed gas away from the "chill zone", let it condense or compress it in a sacrificial "heat zone", then send it back into the area to be chilled, to evaporate (or expand), pulling a lot of energy away and storing it in the gas. 
  You could use a melting solid (like ice and salt) instead of an evaporating liquid (like ammonia), but it's harder to move the solid around with little pipes.  I think the main reason ammonia is popular is that it's cheap, available almost anywhere, and boils at about the right temperature to be useful to us.

  Heat of condensation and heat of evaporation are big quantities - boiling, melting, or evaporating anything soaks up a lot of energy.  Evaporative cooling (swamp coolers) use this effect, and work best in dry areas where you can evaporate a lot of water.
  A squirt of water in a stiff breeze will chill your skin, even if the water is luke-warm. 

But freezing also soaks up a lot of energy.  To bring non-frozen items to frozen status, you're requiring state-changing amounts of energy. 
  If you loaded your new chest freezer with fresh, sun-warmed produce from the garden, I bet you'd see a much longer spike in the temperature readings and energy usage.  Letting hot foods cool to room temperature before putting them in a fridge or freezer can save a lot of energy, and even be safer, provided that you cool them quickly enough.

Wind doesn't pack the same punch that boiling, condensing, or evaporating refrigerants do.  Wind can chill things via evaporation, and by stripping the "envelope" of heated air away from warm bodies.  It effectively reduces the insulative effects of still air.  And it dramatically speeds up evaporation, more so even than heat.  But as far as I know, wind chill factor is finite, reducing ambient temperatures by a certain number of degrees.  It would be weird if you could make it cumulative at ambient pressure.

  The chill in compressed air is generated by the sudden release of pressure.  That pressure was created, using lots of energy, in an industrial fridge or condenser. 
  It's not the speed the air is moving that changes its temperature.  It's the fact that it was heated up when it compressed, allowed to cool to room temperature, and will now release the same amount of heat as it decompresses, getting even colder.  The physics explanation for this involves molecules being speeded up as the walls of the condenser close in on them, slowly reaching equilibrium inside the container by transferrring heat out, then as the 'walls' are removed / expanded, the average speed (and temperature) is correspondingly reduced.  A molecule won't bounce back as fast, because the molecule it hits is also on its way out the door.

I've heard of wind-chilled, shady rocks getting cold enough to condense water in the desert (come to think of it, wasn't that from you, Paul?).  But as far as I know the only natural summer ice-maker in the desert is nightly radiant heat loss, and radiant frost.

Is there an aspect of 'wind chill' that I'm missing, one which can be exploited to produce freezing temperatures from hot, windy ones?

-Erica
 
Joel Hollingsworth
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Erica Wisner wrote:Is there an aspect of 'wind chill' that I'm missing, one which can be exploited to produce freezing temperatures from hot, windy ones?


Not that I'm aware of.  And I've studied a lot of this stuff in depth.

I was wondering what systems of thought Paul was working in.  I didn't want to use the word "magic" in case he took offense, but I thought much the same thing you did.
 
paul wheaton
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Yeah, I think when we're being goofy, "magic" is a great word.  But when we're trying to figure something out, I always thought the term "magic" reflected poorly on everybody - especially the person using the word.

I readily admit that I am fishing around for knowledge and throwing lots of goofy ideas out there in a feeble attempt to expand my knowledge. 

But hey, if this is what it takes to get the ole explain-er-a-tor going, then I'll have to do this more often!

So my thoughts weren't about evaporation as much as they were about getting pressurized air (hence the idea of some sort of ram-pump-for-air-thingy).  The idea was that a convenient breeze could be used to compress air, and .... well, it turns out to be a lame idea.  And there is now another reason why the idea sucks:  the compression generates heat!


I've heard of wind-chilled, shady rocks getting cold enough to condense water in the desert (come to think of it, wasn't that from you, Paul?).


I think I'm familiar with the idea.  A stack of rocks near a tree will water the tree a bit more than the spots that have no stack of rocks.  The idea is that the surrounding stuff is warmed by the sun, but the rocks in the middle of the pile never see the sun - and are, therefore, cooler.  Further, there is that whole thing about the average temp of the deeper soil being lower than the average air temp in the summer.  Therefore, the rocks at the middle of the pile are are cool.  And then when water laden warm air passes through, you get condensation. 

Erica,

What do you think of the idea of ....  (I'm gonna make up a word) a thermal inertia freezer?  Where you have a root cellar that has a very large umbrella keeping a large mass of dirt dry around the root cellar.  And then you have a tube (or two) running through the thermal mass - and you open that tube (and maybe encourage air to pass through) when the temp is below zero. 


 
Joel Hollingsworth
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paul wheaton wrote:
the compression generates heat!


That's actually the best part of your idea.  The compression doesn't so much generate heat, as it forces it out of the passing air.

For instance, that is how the A/C in an airplane works.  The jet engines use a series of turbines to compress air.  Compressed like that, its temperature rises, and the kinetic energy is available as heat.  Most of that heat is used to keep the fires burning in the engine, but some of it is tapped ("bleed air", they call it) and run through the wings (to defrost them in cold weather).

The air coming out of this is only slightly warm: it has lost a lot of thermal energy.  It is then allowed to expand and cool: it exits the little nozzles above your seat cooler than the outside temperature.  Or hot bleed air is used if the cabin is too cold.

Unfortunately, only supersonic planes move fast enough for effects like this to generate significant cooling through ram compression alone: turbines are necessary.  The effects of survivable wind speeds would not be very intense at all.

This isn't practical, but if you're interested in heat pumps, I'd highly recommend playing with a scrap of balloon sometime.  Fun way to teach the kids some thermo, too, if they're old enough not to choke.

Take a largish scrap of a balloon next time one breaks, and stretch it out quickly, then hold it against your cheek to feel the warmth.  In terms of entropy, this is very, very much like compressing a slug of air.  Allow it to cool to room temperature as you hold it tight.  Then let it return to its original shape, and feel how cool it becomes for a moment.  This is like allowing gas to expand.  A good portion of the heat that flowed out after you stretched it wasn't generated by the stretching, it was just concentrated, to the point that some could leave, like water out of a sponge.  That portion of the heat then flows back in when the tension is released.

 
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