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Refrigerator that doesn't use power - could we build this?

 
pollinator
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Saw this link here: https://www.sciencealert.com/this-clever-new-refrigerator-keeps-food-cold-without-electricity

I've been thinking lately about peak oil and energy and what ifs and it has got me thinking about replacing some important things in my life that use power with similar things that don't use power.

I've tried the evaporative clay pot-within-a-pot thing, which cools food up to 10 degrees lower than ambient temps, but I'm trying to figure out if there is a way to legitimately have refrigeration - actual fridge temps - without any sort of power being used. The above link has an example that apparently uses a small bit of solar power but I wonder if it would be possible to do something without it?

Or - my brain wants to say I remember reading something years ago about some sort of cooling system using ammonia that caused a chemical reaction with SOMETHING that made things chill or freeze. Any thoughts?
 
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Ammonia is used in many cooling systems, primarily in RVs. It is a less efficient system than a compressor based unit, but has the advantage of being powerable by thermal energy, so you can run it off propane.

I hear they are really miserable when they eventually corrode through and leave RV very malodorous...
 
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Physics says no. The reasoning being: If there was such a thing, you could create energy from it and that is not allowed.
That being said, a chest unit will not use much power. A 100W solar panel could run it, IF it wasn't for the startup current.
 
pollinator
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There's also this bit o' kit:

Coolgardie Safe - Wikipedia

Although it works on the same evaporative principle as the the Zeer pot.
 
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Hi Bethany;   I have to agree with the others. Other than the free fusion reactor in the sky there really isn't any free unlimited power... YET!
That said I've lived with various ammonia fridges (commonly called a propane fridge) for 40 plus years.  They all work , some are cheap plastic junk, some are horribly inefficient. The small ones that come in rv's are the worst. I have yet to have one rot thru, although I'm sure they do.

For the last 7-8 years we have had the best one yet.  Diamond brand, Amish built, 18 c.f.  sip's propane and freezes ice cream rock hard. (something the other older models couldn't do very well)

With a propane fridge you are still reliant on fossil fuel but it can be bulk delivered and does not need electricity.
fusion-reactor.jpg
[Thumbnail for fusion-reactor.jpg]
Free Fusion Reactor
 
pollinator
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While it obviously doesn't travel, a root cellar is an off-the grid refrigerator.
 
pollinator
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Propane refrigerators don't NEED to run on propane.  There used to be kerosene versions, too.  I know you could retrofit one to run from a small rocket stove.
 
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This comes close to one of my mental enthusiasms.  (meaning I haven't built anything yet, but I have spent a fair amount of time reading and thinking it through).  It's high on my list of "Stuff that's So Cool I have to Just Have to Build it!!!"  (I think I just heard my patient, long-suffering wife roll her eyes.)

Ammonia is the most efficient refrigerant we have, which is why the big commercial freezing systems (fish packing plants, frozen food factories)  are generally ammonia.  Some ammonia based systems are probably more efficient than others, but that is the design of the system, not the ammonia.  

Downside is that anhydrous ammonia is dangerous if you get a big leak.  I would be cautious about using an ammonia system in my home, because ammonia has a strong affinity for water. In the event of a major leak, eyes and lungs might be the nearest water (blindness, lung damage, death are possibilities).  That's why home systems don't have ammonia anymore.  Coupled with that, the druggies use anhydrous to make meth.  Local law enforcement can get pretty interested if your inquiring about ammonia.  Still, just about every farm has a big tank of anhydrous ammonia on premises for fertilizing.  This is also where druggies get their anhydrous.  (I worked with a guy whose dad delivered propane to farms.  The propane tanks were generally next to the ammonia tanks.  He said occasionally they would find a glove on the ground that contained fingers.  It seems the druggies would get to screwing around with ammonia at night, trying to steal it and it would spray out onto their gloved hand.  They would jerk the frozen glove off, not realizing their frozen fingers would snap off inside like brittle sticks.  Like I said, it's a great refrigerant!

Ammonia also reacts with zinc, copper or brass, but doesn't react with iron or steel.  

There are a lot of old designs for ammonia systems around, some using water, some using MgCl2 or CaCl2for absorbents.  There may be some other absorbents I haven't read about.  The absorbents hold way more ammonia cold as apposed to when they're hot, so when you heat the absorbent it drives off the ammonia, which cools going through thin lines that radiate heat and then condenses and collects in a spot designed for that purpose.  When you take the heat off the absorbent and it cools, it will reabsorb ammonia gas, reducing pressure which lets the pooled ammonia evaporate.  Evaporation sucks the heat out of where the area liquid ammonia was collected.  The cooling is generally cyclical (refrigerates when the ammonia is absorbing, otherwise not refrigerating).  

I wouldn't want a system in my house, but I think the risk could be reduced to acceptable levels by having the system outside and using it to cool an insulated container of antifreeze which is then circulated to cool things indoors (fridge, freezer, A/C unit if you really go crazy).  Use a heat sensor to monitor the antifreeze temperature and turn the gas on or off.

Lots of possibilities!  I've read about a portable system developed by the military that could use a wood fire to heat (no specifics given).  I've also read about a system someone developed in Africa for keeping medicine cold that had a single daily cooling cycle, (the system used the daytime heat and night time cool to cool a small, super insulated medicine box.  If you were using water to move the heat around you could use a rocket stove as the heat source.  If you had a cold water source, you could cycle back and forth, heating and cooling the absorbent, greatly increasing the number of heat cycles in an time period.

 
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There's always the freezer wofati concept.  If you're not cold enough for a freezer it should still work as a fridge...
 
D Nikolls
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Sebastian Köln wrote:Physics says no. The reasoning being: If there was such a thing, you could create energy from it and that is not allowed.
That being said, a chest unit will not use much power. A 100W solar panel could run it, IF it wasn't for the startup current.




This is by no means a magical source of free energy.

It is using the lower temperature below ground, plus the cooling effect of evaporation. Both well known..

The question is, can the method described cool adequately in a given climate..
 
pollinator
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People used to gather big blocks of ice in the winter and store them together in an insulated structure of some sort. We have a lot better insulation now so we could make it last even longer, so if you live somewhere with cold enough winters you could sort out some kind of cellar system using stored ice maybe. Even here in ohio it's rare to have it cold enough for long enough to get more than the top several inches of standing water to freeze, though.
 
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A couple of caveats: Here's an idea that does use power but shifts the load and lowers it somewhat. The company that the link is about has filed for bankruptcy just last month (12/2019), their website no longer exists. Who knows why the company failed, but the idea seemed sound.
Inhabitat article about Ice-Energy Ice Bear storage system

It is basically a powered version of an ice house, working on a small scale and daily schedule.
The A/C unit works in reverse to create a block of ice, so that when the A/C runs forwards (cooling the house) the ice is melted by the waste heat, reducing/eliminating the need for the compressor to run (the costly part of the A/C to operate).
The main benefit in a market like California, (where the company was) with high energy rates and peak pricing, is to be able to shift the load to "off-peak" times, using less expensive electricity.

Kind of like gathering ice in Winter and storing it in an ice house until summertime. It could be imagined that one could use the same technology to shift/extend solar PV collection for cooling use at night/24 hrs. a day.

 
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https://pin.it/Jr1JbAgz

I cannot find the original article but the refrigerator depicted here ran for at least 20 years.  It didn't always get to ice cream cold but it kept ice cold all year round.
 
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Bethany Dutch wrote:

I've been thinking lately about peak oil and energy and what ifs and it has got me thinking about replacing some important things in my life that use power with similar things that don't use power.

...Any thoughts?



I have a few.

While the zeer pot is a good, short term solution for regions with dry air, it doesn't work very well in places that it tends to get humid in summertime.

The best idea is to take a lesson from our homesteding forefathers before the age of powered refrigeration, and build a "root cellar".

Of course, the upcoming wofati freezer is basically a root cellar using additional designed principles to "save" the cold winter temps for mid-summer use.  One detail that I've thought a lot about in this kind of thing is a "heat pipe" network.  A heat pipe is just a pressure vessel made of threaded pipes, so that condensation of liquids in the highest portion can flow down into the lowest portion.  This uses some energy, but it's all latent energy, mostly just gravity. The bottom portion is placed inside your root cellar airspace, while the top portion is above everything and exposed to a northern sky (in the northern hemisphere, towards the nearest pole) while shaded from as much sunshine as possible.  Once the pipes are in place, the air needs to be vacuumed out and a measured amount of some kind of liquid needs to be put into that vacuum, to act as freon.  But it doesn't have to be freon; pure water works (down to about freezing, so not really good for a wofati freezer) and so does propane. And it doesn't take much propane, only a few cups probably; and it will never need more propane unless it leaks. What happens inside the pipes is, because it's not a mixed atmosphere, some of the propane will boil until the pressure "equalizes" between it's liquid and gas state. So long as there's some amount of liquid propane left across the temp range, we're fine.  But then we will quickly have a temp imbalance from top to bottom. When the top is hotter than the bottom, nothing happens except the pressure goes up some. But when the top is colder than the bottom, some magic happens.  Because pressure is related to temperature; when the top section gets cold, the pressure inside the pipe declines.  As it does so, the gas in the top will cool down until it reaches it's new dew temp (which is rising because of dropping pressures) and condenses inside the upper portion of the pipes. That condensed liquid then runs downhill until it drips into the lower section, which is hotter, and evaporates. Since gasses are lighter than liquids, the warmer gas is being pushed up the pipe as liquid flows down anytime the bottom is warmer than the top, until the liquid freezes.  In this way, so long as the vertical section of the pipe is insulated (and a shut-off value about mid-height for late spring and summer would help) any latent heat in the thermal mass will naturally convect out during winter nights without any human intervention nor energy using devices.  This method is limited to how cold your winter nights get, as well as the freezing temp of your chosen liquid, but it's very capable of moving a lot of heat under ideal conditions.
 
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I'm guessing you've already found this Absorption refrigerator about absorption refrigerators.  You'll note that the process only requires a heat source.  That's why RV fridges, for example can be "3-way" - they run on propane, or on 12V from the vehicle when the vehicle is running (they drain batteries quite impressively if they're not being charged) or from mains power from a hookup.  Generally, the gas-powered mode has a small flame, while the electric ones have a heating coil built into it.

Point being you can use any source of heat, such as solar heat or geothermal, to drive the cycle.  

As I recall it, they're also very fussy about orientation; you needed to make sure the RV was level or the fridge wouldn't work.  That's to do with one part of the cycle where the ammonia (IIRC) has to flow downhill.  If you look at the "works" at the back of those fridges, parts of it are slanted.  In a fixed installation though it just means you need to install it right to begin with.  Others have already made the point that Ammonia isn't very nice.
 
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I find absorption refrigerators an interesting application of physics.  The most common ones use a solution of ammonia, water and hydrogen.  Heat is applied causing phase changes at different places for the different fluids.  I personally find the most attractive aspect to be that aside from the fluid, there are no moving parts.  No pumps, no fans, nothing.  Only heat inducing currents in the fluid.

Unfortunately by themselves they are very inefficient.  Their main application is in RV’s because of the silent operation.  The use of pumps and compressed fluids is considerably more efficient which is why home units use Freon or similar working gas today.

However, absorption coolers really excel in applications where there is already a great deal of waste heat.  The total efficiency of an operation that uses some engine with waste heat used to drive absorption coolers is quite high which is why they get used in some commercial applications.

I suppose though that an absorption cooler could be an efficient way to utilize sunlight.  Instead of using PV for electricity to run a pump, focusing solar heat as a heat source could make these coolers attractive in hot, sunny climates.  As a bonus, they would work best during the heat of the day.

Food for thought,

Eric
 
Mike Haasl
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So for the adsorption refrigeration, what temps are required?  

And for the "heat pipe", is there a DIY way to make them?  They seem really cool.  Can they work in reverse to warm an area?  Does the part that needs to lose heat always have to be below the part that needs to take the heat?
 
Eric Hanson
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Hi Mike,

So your question is a simple question that has a highly complicated answer.

Hot water, defined as being about 200 degrees Fahrenheit can chill air about 10 degrees.  This is pretty lousy efficiency, but the higher the temperature on the heat end, the cooler the temperature on the cold end and the more efficient the process becomes.  The most efficient and effective absorption coolers run at about 850 degrees Fahrenheit.

I imagine a tiny little propane pilot light heats up nicely and really cools down.  Personally, my favorite application is in some type of solar heating technique where concentrated sunlight really heats up the hot end and cools down most efficiently during the heat of the day.  If the cool end was properly insulated (preferably underground) and provided with a cool thermal mass, then I imagine that temperatures could be maintained nice and cold throughout the day.

If I really go crazy I think I would want the hot end to be buffered with potassium nitrate solar salt to really keep the hot end hot even after sundown, and the cool end buffered by liquid ammonia which has a higher specific heat capacity than even water.  In this example the KNO3 salt and NH3 should keep the thermal engine running well past sundown and the cooled area should stay cool even after the engine quits working for the night.

I would think that converting sunlight directly to heat would be more efficient than a PV system (only about 30% efficiency right off the bat) running an electrical motor to power a compressor.

Anyhow, this is just a fun little thought experiment, but what an amazing project it could make!

Eric
 
Mike Haasl
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Time to build one Eric!  Make an insulated refrigerator box with a solar collector on top (doubles as shade for the fridge).  Adsorption refrigeration cycle to keep it cold inside.  Enough insulation to keep it cold overnight.  All made with parts from the big box hardware store.  
 
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