Towards a better tinyhouse

Inventing to freedom?

Fresh Vegetable preservation chamber

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This post was spurred by the latest post on Tinyhouseblog, by Walt Barrett, in which he mentions that he is always looking for new ways to store fresh food.

This has relatively little to do with tinyhouses, but I figure I’ll say it anyway.

Okay, it starts with Modified atmosphere packaging. Once you read up about it a bit you can see the theory.

Okay, now let’s use that general idea for a small container to store veggies in. The obvious problem is that every time you opened the lid of the container, oxygen would get in. So you need a way to ge the oxygen back out again. There are so-called molecular sieve concentrators, also called pressure swing adsorption (PSA), units which can remove something like 96% I think of the oxygen. They are used for producing high o2 concentration gas flows oxygen in those “oxygen generators” for use by individuals with impaired lung function, but obviously the effluent from such units is very poor in o2.
These units look expensive at first, but I have seen cheap ones available for $150 each direct from the Mfgrs. Also, these units are far bigger than we need, producing far more gas than we need. A smaller unit could be much cheaper.

There are also membrane based ones, which do not concentrate as much in a single pass, but could be used with multiple passes to achieve o2 poor air. Another would be a mini air condenser. Yes, condense the air. I forget what the process is called, but if you take a compessor and a counterflow heat exchanger, and an expansion valve, compressed air goes thought a coil that allows the heat of compression to escape, then in one way thought the heat exchanger, then expands, cooling down greatly, then back though the heat exchanger. This is the key part, it cools the air which is now headed to the expansion valve. Now that batch of air is quite cold by the time it gets to the expansion valve, then it cools even more when it expands. Repeat. Eventually the air is so cold the o2 condenses out. You can buy units that do this, some have an expander to improve efficiency, but that increases cost and complexity. The are also very big. There are ways of doing something much like multi effect distillation too, to increase energy efficiency and reduce the required size of compressor.

One problem is that most of the water vapor must be removed form the compressed air or it freezes to the heat exchanger, but that can be done with vapor permeable membranes like used in every air compressor.

Another way is to burn something, using up the o2, but then you need a fuel source…

Anyway, this could be a nice addition to a tinyhouse kitchen, offering fresher vegetables with less shopping. The container could be the crisper drawer in the fridge.

Lastly another way might be to use microbes that consume the o2, just add some sugar or something to a container with harmless microbes like yeast, and bubble air through the water. They use up most of the o2 pretty fast, but they can’t take it all. You could try to prevent them from escaping using the sort of plastic filter membranes used in sterilizing filters. You can buy mini sterilizing filters, I remember seeing some for sale for use with brewing equipment the “wort aerators” for aerating wort and wine. You could make this at home.

Those veggie washing machines I posted about (ultrasonic) could help too, they kill much of the bacteria that cause spoilage with O3.

Hey, Walt, if you see this, I remember seeing a “vortex-based” (spray nozzles built in to the side of the circular wash basin, they operate on the same idea (assuming they are designed correctly) as the commercial vegetable washing machines, using water jets) veggie washer from China for ~$99 with ozone or a similar site while I was searching for veggie washers. That sounds like better bang for the buck than the ultrasonic ones, $350, a piece. I wonder if that would be something to add to your product offerings? It said it made veggies last for an extra 3 days due to the ozonation step, which I can believe. I have read that these things sometimes produce excessive ozone, though, so that might be something to check before diving in.

Edit:
I just realized if you had a chest fridge, like a converted chest freezer being used as a fridge, you might do the modified atmosphere thing for the whole fridge. That could be neat. but you would have to be careful for safety reasons, you would need some way to verify that the atmosphere is what you think it is, or you might get accustomed to stuff keeping for longer than it does in a normal fridge, then your atmosphere modifying mechanism malfunctions, and you store something for too long and get sick or something. With vegetables this is not a problem because pathogenic bacteria don’t really grow on veggies (they need something with a bit of protein in it) (though they can still get onto veggies of course).

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Written by gregor

November 11, 2010 at 15:52

Posted in Uncategorized

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