View Full Version : Refrigeration thread
Vortex tube Refrigeration
http://fab.cba.mit.edu/labs/tti/ttinew/Voretxv1.html
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following copied over from another thread: (burried in thread drift...)
> The only sure source of "refrigeration" will be underground storage, i.e. a cellar. So storage temps will run mid-50s to mid 60s F.
there are a couple of peiltzer(sp?) based portable fridges out there that run on 12V w/ a car cig outlet plugin. It comes w/ a big wallwart to mate w/ it, if you want to run it off house current.
Some will hold 18 standard beverage cans (beer/pop), others will just hold a 6 pack. There is no freezer. One I have gets down to 48deg and stays there, but it can take 12 hours to go from room temp to 48 deg. Temp is not ajustable. Shop arround - prices vary for the same unit.
They run in the $50 - $100 range - shop arround. You could probably make something better if you bought the peltzier(s) and built an insulated box arround them. Add a temp guage and a rheastat to control temp.
That alt energy co in Boulder colo had kits and referbs for high efficency and alt energy fridges, washers, etc...
nice thing about peltzier's is they generate heat to - so if you need to culture something...
-t
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FERD:
There are also propane fueled (no compressor) coolers that use a small flame to heat freon (or whatever) to expand/condense via convection - these are used in (for example) RV's, and the reason that people have to level their RV's (the flame has a relatively small aperture to burn in).
There are also completely solar powered electric ice chests and freezers, and HomePower magazine had an article earlier this year (I think) on a completely solar no moving parts closed loop convective cooling system. http://www.homepower.com/files/solarice.pdf
Finally, if you live in a cold climate, you can make ice blocks in the winter time (take a plastic trash bag and line a cardboard box. Fill with water, let freeze. Remove ice and bag from box, place ice in 'icehouse' (very highly insulated structure). Repeat box / bag / water / freeze cycle as needed).
I have a very old (now, like 15 years old) 12 v icebox like you mention. It does take quite a long time to cool down (it helps if you pre-chill it with blue ice or something) but mine at least will get down around freezing.
Interesting idea about using one as an incubator. They don't really get that hot, and controling the temp would be easy. Plus, it's a handy size, and could work off of a small solar array (one or two roll-up panels?) and a small gelcell battery (for at night). Hmmmmm
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The medtech CD has a document in /medlab/equipment called "how to look after a fridge" about these type of units. Repair and maintenence type material.
-t
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Somewhere on the board we also have info on evaporative cooling - clay pot and sand and maybe a bit on swamp coolers... I'll see if I can find that and link stuff here.
-t
source TB2K:
I'm looking for alternatives that can provide enough ice to either keep things frozen, or can provide enough cooling directly to preserve food/medicine indefinitely. It can work in cycles, as long as the refrigeration produced can last the time between cycles.
I'll post a few things I've found below:
- Ammonia/water cycle "icyballs" are interesting. Heat em up for a few hours, refrigeration for the remaining 20-something hours a day.
http://www.ggw.org/~cac/IcyBall/HomeBuilt/HomeBuilt.html
http://www.ggw.org/~cac/IcyBall/crosley_icyball.html
- A salt / ammonia cycle (PDF) does pretty much the same thing as an icyball, can be solar-powered. A bit large for the solar powered version as above, but it makes about 10 pounds of ice a day. Fire-heated ones can do the same thing and are generally constructed like an icyball.
http://www.homepower.com/files/solarice.pdf?search=ammonia
- Electric, that is, your standard deep freeze run from an inverter/gen set.
- Manual compressor driven refrigeration. As I repair car A/C systems for a living, this is the area I can experiment with the easiest, so I'll waffle on here for a bit
Car A/C's are huge. A car airconditioner, transplanted to your house, could easily keep half your house cool. They're rated in a pleasingly archaic term called "tons". That's "tons of ice melted in a 24 hour period to get the same cooling effect". An average Car A/C will be rated at 2 - 2.5 tons. Can you see where I'm heading here? You don't need 2 tons of ice every day for your average icebox. Which means that you should be able to power that honking great big a/c compressor via human means to generate a smaller quantity of ice as needed. My gut feel is half an hour of pedalling = hunk of ice sufficient to last the day out.
So, that's what I'm going to construct. A pedal-powered icemaker. I've crunched the numbers and generally everything seems plausible enough to try it out .
Goals :
- To be human-powered only throughout. No electric cooling fans/pumps/etc.
- Constructed out of scrap automotive parts.... probably with new pipework for convenience though.
- Run on a 80/20 propane/butane gas mix (about the same refrigerant capacity as R12 was). It's conveniently the same mix that portable camping stoves use .
- Able to freeze 2kg (5 pounds) of water in less than half an hour of moderate (er, not heart attack inducing) pedalling.
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I got a little freezer from walmart. It's a small chest type and it only takes three amps but it holds a lot. It is probably about waist high by about two by three feet. I can run it and freeze it from being thawed out using a 600 watt inverter and I have used a battery as small as a lawn tractor. It works real well when our electric goes out and it's a cheap way to go.
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Mother Earth News...
...in it's heyday (Sept-Oct 1975) did a few short articles about the "wood burning refrigerator." The theory the author expounded on ammonia absorption was solid but turning theory into practice was more than a bit weak or more accurately non-existant.
http://www.motherearthnews.com/library/1975_September_October/The_Incredible_Wood_Burning_Refrigerator__Is_Now_U nder_Development_
Old MEN was/is still a wealth of information on a lot of alternate energy topics but sometimes their sales pitch went beyond their product.
Frankly, I have my doubts about a "pedal powered" refrigerator. A human being on a bicycle can continuously produce only about 100 watts maximum (or perhaps a bit more if you're an Olympic caliber bicyclist.) 100 watts is only about 1/8th of a horsepower.
If memory serves, automotive air conditioners while in service steal from the engine about 5 to 10 horsepower - those old 40 hp diesel rabbits with air conditioning were seriously challenged acceleration wise. And with pedalpower/mechanical refrigeration you still have the COP (coefficient of performance) factors of refrigeration cycles generally to get past.
You might do better to get a small "dorm size" refrigerator. The Sanyo where I work is rated at 112 watts and I expect it is actually "on" only about a third to a half of the time. This is a pedal power electrical load you could keep up with if you use a battery/inverter. Also, if you insulate the exterior of the dorm size refrigerator better, you could increase your chances of continuing success.
Pedalpower might also work for "Thermionic" refrigeration (seebeck effect etc.) Those Coleman coolers that use this method for a sort of weak kneed beer cooler are real and do work. Kinda. Too bad they can't freeze ice.
I have the ultimate respect for Homepower magazine. But the early Homepower magazines had a lot more "homebrew" than today's magazine to include a lot of refrigeration comparisons - mostly considering Sunfrost refrigerators coupled to PV panels. It's almost too bad that Homepower is now "grown up" and becoming more mainstream. Get yourself the Homepower archive CDs, namely Solar 2, Solar 3, Solar 4, etc. for more detail on this.
But regarding the change in Homepower Magazine, there's a lot more options/sources for alternate energy equipment than there was in the 1970s. And conversely, less people who want to "experiment."
Market driven I guess.
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Ok , I'll post the math here. I'm using metric units, because It's Just Simpler :
To freeze 1kg of water, you need to remove 334kJ of heat, plus a bit more to bring it from room temperature to zero degrees first (4kJ/kg per degree C above zero).
Now, 1 watt is equivalent to a Joule per second.
So that's 334000 joules to be moved from the water to (somewhere else), in my time limit of 1800 seconds (half an hour) to freeze 1kg. That's about 185 watts continuous in that time frame. Double that for my desired amount of 2kg.
Now, from a random medical report on the web :
A fit 25-year-old man can generate 650 watts while bicycling for a few seconds and can maintain a power of 400 watts while bicycling for 1 minute, 230 watts while bicycling for 10 minutes, and 175 watts while bicycling for 30 minutes. He is able to reach 275 watts in a progressive incremental (increasing at 16.7 watts per minute) test to capacity; this power represents peak exercise and is the power at which maximal oxygen consumption (3.3 liters per minute) is measured. To put these figures in perspective, brisk walking represents an output of approximately 50 watts of power and an oxygen intake of 0.8 liters per minute.
So, one could almost do it by pedal power alone. But wait! We're forgetting the COP of the refrigeration system. Again, general research has it that a hydrocarbon refrigerant system(1) is good for a COP of 4 to 5. I'll reduce that for frictional and pumping losses in running an (likely worn) automotive compressor at low speed. I intend to use a large barrel of water as a heatsink for the condensor, which will also improve the COP as opposed to an air-cooled setup. You'll also end up with warm water at the end of it. (eg, 10L at 25 degrees C, will end up at 35 degrees C. A bit more ice making and you can have a warm shower afterwards ) I'll make it worst case a COP of 3.
So, with a COP of 3 and the need to shuffle 360 watts from here to there for half an hour gives you 120 watts of input energy. That's a fair bit of pedalling, to be sure. But it's not heart-attack inducing (for me, anyway), and you can always pedal slower and extend the cooling time. And of course, if you have any other supply of rotational energy (engines, waterwheels, er, small children) you can adapt it to suit.
http://www.es-refrigerants.com/reports/docs/COMPARATIVE%20PERFORMANCE%20OF%20HYDROCARBON%20REF RIGERANTS.pdf
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I've thought about the ice problem somewhat myself. I like Peltier Junctions(used on the Coleman fridge) The problem, as you might know, is that those junctions only allow a temp differential of about 40 F.
So in order to get down to a freeze we have to bring the surrounding temp down to around 60F to give us a good solid 25F for our freezer.
Since the mean ground temp is around 55F we would have to either bury our fridge (essentially a root cellar) or run a length of pipe under the ground. (About 50 to 100 feet for our fridge)
The other thing is to make the fridge small, say a one foot cube highly insulated.
I like the idea of peddle power but What I would do is combine it with batteries. That is, charge the batteries over a longer period (peddle power or solar) then use the batteries with peddle power to get your ice.
I did build a peddle power bike to see what I could generate. I made the alternator out of NdFeB magnets, three phase brushless and I can generate about 80 to 100 watt hours into a resistance load on an old exersize bike with a chain drive to the alternator. I can easily generate 40 or 50 watt hours without to much sweat but I'm a bicyclist, although I'm also over 60 now, so I don't have the juice of you younger guys!
Just some ideas.
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Funny, I've been researching ways to have a refrigeration, including DC powered and propane powered. For DC, I've been thnking about Coleman's Thermoelectric Cooler or Engel's Portable Fridge/Freezer/Warmer, both powered with a cigarette lighter adapter. The Engle unit is more flexible but pricier than the Coleman which just keeps things cool.
http://www.coleman.com/coleman/search/SearchResults.asp
http://www.compactappliance.com/xq/JSP.detailmain/Engel_14_Qt__Portable_Fridge___Freezer_with_Warmer _Function/itemID.8874/itemType.PRODUCT/iMainCat.28/iSubCat.62/iProductID.8874/qx/shopping/product/MHFD015ED.htm?mtcCampaign=1494
For a power source I was thnking about the foot-powered Weza Freeplay. Create your own store of power and use it to cool or freeze things and to power other DC gadgets.
http://www.ccrane.com/more-categories/alternative-power/freeplay-freecharge-weza-portable-energy-source.aspx
I don't think I'd personally need a freezer, and, since everything I will be cooking in an emergency situation, will be consumable within a day, I don't think I will need a fridge either, but it might be nice to have. So I'm currently debating. These DC coolers are also useful on long road trips, which I do twice a year, so I'm leaning on getting the Engel.
I found a cooler than uses AC/DC and propane @ 0.55 liters of propane per 24 hours of cooling, which comes to 32 days for a 20 lb. propane cylinder. That's good for short-term emergencies, but for any Katrina-type or large EQ scenarios, I would want something that can be sustained longer-term.
http://www.lpappliances.com/RC3000.html
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Muscle power:
I remember an old rule: 1/8 HP is what men can do for a longer period.
That makes it about 100 Watts at 100% efficiency.
But I think "guy I" was looking for converting stored energy from somewhere else than body fat.
Or he didn't see that the only way to get BTUs extracted is by energy conversion.
reply: Don't forget, there's a heat pump involved that is more than 100% efficient.
You put in 100 watts , you get to transfer more than 100 watts from one place to another. In the case of a compressor driven system , it's about 3 or 4 hundred percent efficient.
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I heard a report this morning that 1.8 billion people in the world don't even have electricity.....Maybe it's just a convience that the rest of us could do without.....
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We use a "portable" ice maker. I say "portable" but it weights 46 lbs. It's actually a counter-top ice maker. It cost $179.00 on sale, not iincluding the $30.00 rebate). We bought it at Home Depot. It drops its first load of ice after 20 minutes. And every 20 minutes after that. Supposed to produce 30 or so lbs of ice per day. It only uses 200 watts, so we can run it off the generator.
Its much faster than the frig ice-maker, which died a couple of weeks after we bought this puppy. It probably died of embarrassment.
Here's a link to one just like ours, except ours is silver(colored).
http://www.directron.com/mcim30tw.html
http://medtech.syrene.net/forum/showthread.php?t=1057
making a mini-rootseller (hole in ground covered w/ sod, on platform within hole, well seperated from bottom). Or - the shaded outer bank of a stream - in a waterproof container, of course. another possibility is using amonium nitrate and water. this is supposed to produce an endothermic reaction (pulls in heat - gets cold). It can be evaporated to recover the ammonium nitrate. I'm not sure how practical this would be - how mutch water, how mutch AN, how long for the AN to evaporate and all in praportion to an insulated container. It seems feasable. Evaporation time could be reduced by taking advantage of waste heat from cooking, etc., thus making this a theoreticaly viable mobile solution. But packing water is heavy, especially if it's not for drinking.
more thoughts - one place I lived, a cabin, had a "window refrigerator" - basically a box built out the back of a window with a shelf that was an efficient refrigerator during the winter. The window was the refrigerator door. convection is an effective way of cooling things and can be produced using solar chiminies to pull air. evaporation is also effective, and is the basis of the swamp cooler - a widely used design. Other solvents evaporate faster and are more efficient for cooling but are likely to be in short supply. I have seen reference to a small scale refinary, taking waste gasses of wood and seperating them into common solvents - acetone, etc. have never seen details on how to do it on a small scale though. Some method of solvent recovery would make this possible, albiet, not easily.
I've seen and thought about those 12V refrigerators. they are usually based on a piece of electronic equipment that converts heat - the name of which escapes me at the moment. Like natural methods, they are slow to cool. They also tend to be expensive, though i've seen some attractive prices on a unit that exactly fits a 6 pack. might be worth taking a few apart and building a better fridge from the parts. the insulation and durability could certainly be improved. dean ings "pulling through" talks about turning a bike, a bike generator and some venarian blinds into a wind generator for a 12 V system... as well as lots of other interesting stuff.
on a related note - inverting a flower pot (MUST BE DRY! - like river stones, they will explode if they have any absorbed moisture) over a stove burner creates a kind of solar chimney, but the pot itself heats up and stores heat that it transfers to the passing air, causing a general heating effect in the area. to seal out cold - dunk rags in water and seal in windows. it will freeze and creat an airtight fit arround the frame.
OK - I do remember seeing this one really neat house design. think it was an A frame, but it might have been a pyramid. Anyway, the oven/stove and furnace were all the same. they were in the basement and surrounded by thermal mass. the building also took advantage of solar heat, with one whole wall glazing and a greenhouse in that side of the house. One could take this farther and use hydroponics for waste water filtering, etc. But it was a good example of a home that produced rather than used.
hope some of that helped....
-t
don't even get me started on superinsulation and heating dwellings w/ body heat alone, or thermal mass, or.... spent too mutch time on this thread allready.
http://medtech.syrene.net/forum/showthread.php?t=1109
Wind-electric icemaking project: Analysis and dynamometer testing. Volume 1
Creators/
Authors Holz, R.; Gervorgian, V.; Drouilhet, S.; Muljadi, E.
Publication Date 1998 Jul 01
Description/
Abstract The wind/hybrid systems group at the National Renewable Energy Laboratory has been researching the most practical and cost-effective methods for producing ice from off-grid wind-electric power systems. The first phase of the project, conducted in 1993--1994, included full-scale dynamometer and field testing of two different electric ice makers directly connected to a permanent magnet alternator. The results of that phase were encouraging and the second phase of the project was launched in which steady-state and dynamic numerical models of these systems were developed and experimentally validated. The third phase of the project was the dynamometer testing of the North Star ice maker, which is powered by a 12-kilowatt Bergey Windpower Company, Inc., alternator. This report describes both the second and third project phases. Also included are detailed economic analyses and a discussion of the future prospects of wind-electric ice-making systems. The main report is contained in Volume 1. Volume 2 consists of the report appendices, which include the actual computer programs used in the analysis and the detailed test results.
OSTI ID 631212
Report Numbers NREL/TP--500-24010-Vol.1
Other ID Numbers ON: DE98003849
Document Type Technical Report
Research Organization National Renewable Energy Lab., National Wind Technology Center, Golden, CO (United States)
http://www.osti.gov/gpo/servlets/purl/631212-B6Pvoo/webviewable/
(downloadable pdf document)
12/24/110v fridges and freezers:
http://www.sunfrost.com/
-t
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