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freezer wofati

 
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It is my impression that these convective air currents work best at angles steeper than 45 degrees.
 
paul wheaton
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I am thinking that the duct will be plugged march 1 to october 1.   The rest of the year (the cold part of the year), whenever the temp outside is colder than the mass, there is an air exchange - thus making the mass even colder.



 
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Where it comes to wofati (I am going to go there and use the acronym as a plural), I think one thing whose spirit I appreciate but that I would change would be the "freaky cheap" part, which I would swap for "fairly frugal." There are places in the design, like heat tubes, where I think it makes sense to spend a reasonable amount (still frugal) to ensure a little margin of error to its capacity. I suppose that would make it a woffati, then?

I love this idea. I would like to emphasize how much I love the elegance of the design of the self-plugging pipes in Hait's book.

Correct me if I'm wrong, but shouldn't the frost pocket "drain" you're discussing be in the same place as the intake for the cold air?

Also, is there any use for an airwell of stacked stones around the outlet to the drain? Theoretically, a shaded airwell would condense humidity out of the air and perform a first-stage cooling. If the air-well were large enough, condensation inside the stack would cool it through forced evaporation, further cooling the air passing through it. If all of this is based on the self-plugging pipe design, it would only draw in warm weather when warm air needed to leave the system.

For me, it is tempting to use some kind of thermal battery other than the surrounding soil, and I would modify the overall construction, I think.

I love the properties of brine, and the less-corrosive glycol options, in terms of thermal carrying capacity and low freezing temperature. A saturated brine solution, just sodium chloride and water, has a freezing temperature of just colder than -23 C. Having, for instance, a thick, flat tank on the ground containing such a heat transfer fluid coupled with the insulative effect of feet of earth could produce the inverse of a haybox cooker effect, whereby heat gradually leaves the system, but isn't replaced.

I would consider tiling the top of the tank in clay, or just installing a packed clay floor atop it. This could be sprayed down, in the style of Tudor Monastic Farm breweries, using a draught to employ evaporative cooling, but really only during the cooling phase, before the temperature drops below freezing.

I would also think about using any readily-available insulative resource as a layer of insulation between the top of the dry soil umbrella and the protective and waterproof layers. A foot of compressed biomass wouldn't hurt the insulative capacity of the system, or how quickly it cools initially, either.

Lastly, I was thinking about the possibility of sinking tube heat exchangers into the ground under the freezer wofati, inside the freezer structure, probably one in each corner, so as to be able to make them smaller. They would further lower the temperature under the whole system, below the ambient subterranean temperature (54 degrees, if I recall correctly). You could conceivably end up with a column of permafrost powering your earth freezer.

-CK
 
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I love this freezer concept.  Here are a few ideas to throw out there:

1.  I suspect the "U" shaped cold air tubes would move more air (if that's a good thing) if the two ends were at different heights.  Then as cold air tries to replace slightly warmer air, the warm air can rise up the steeper end of the "U" and the colder air can enter the shallower end.  

2.  I think the bigger the tubes are, the better.  If we're relying on 10F air to displace 20F air, I'm guessing there won't be a lot of pressure helping us out.

3.  Would there be an advantage to having the tubes cross through the interior of the freezer?  Their coolth would settle in the freezer and transfer to the mass.  Otherwise the tubes in the mass would cool the mass but that coolth would have to travel through the mass to get to the food.  I'm guessing the tubes will be the coldest spot in the system so why not put that inside the freezer?

4.  I'm guessing there will be a strong stratification of air in the freezer.  Air near the floor could be 20+ degrees colder than at the ceiling.  Would a second air tube system to vent the warmer ceiling air straight up through the ceiling be worth considering?  Then anytime the air outside is colder than the air at the ceiling of the freezer it would exchange itself.  Anytime it's warmer it would self plug.  Just like Joseph's ice caves

5.  Anywhere a tube enters the system, I'd imagine that having a 10' circle of shade around that spot would help provide even colder air.  On a 0F day, it sure feels colder in the shade of a spruce tree.  Plus it would keep the sun off of the intake tube.

6.  If the entire wofati was put in the shade it would probably help as well.  Perhaps a series of angled junk pole fences that would shade the snow, trap the snow and reflect sunlight back up.  Or just site it to the North of some tall conifers and grow some snow fence plants to trap/encourage snow to settle on top of the freezer.  

7.  If you want to have a root cellar as a back up option, having the tubes go into the freezer compartment would allow for the ventilation root cellars need.

8.  I like the idea of a phase change material.  Especially if salt water could be that material.  Would salt water stay in solution so that the whole vessel freezes at the same temp?  How would a phase change material be best implemented?  Stick some drums of the material in the freezer?  Route the "U" tube through a tank of the material inside the mass?
 
paul wheaton
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MJ1:  Moving more is, I think, not the thing we are looking for.  Moving more cold air is.  If one is lower, then when the outdoor temperature is warmer, then the cold air will drain out through the lower tube, thus pulling in air that is warmer than we want.  

MJ2:  I agree.   I think the tubes need to be ten inches in diameter for this to work.   8 inches can work, but I think that ten inches will work about six times better.

MJ3:  I think that when you open the doors, there will be some air exchange - and not in a wholesome way.   I think the system is more likely to succeed without including the chamber in the tubes.

MJ4:  I agree that there will be a strong stratification.   I also worry about oxygen vs. CO2 levels in there.  I think I want to file these design thoughts under "for version 2.0"

MJ5:  Not a bad idea!   I like the idea of more shade - and even exploring opitimizations to the site in general that would encourage more cold air to concentrate in the space while simultaneously encouraging water to go away from the space.

MJ6:  Interesting.   What about putting layers of woody debris on top of it that are lined up in such a way to keep 90% of the water off and provide more shade?

MJ7:  see MJ3

MJ8:  possibly for version 2.

 
Mike Haasl
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Thanks for the responses Paul!  

MJ1:  I'm imagining both tubes are sloped up and out of the mass.  Imagine one tube is at 45 degrees from horizontal and the other is 60 degrees from horizontal.  Then when it's colder outside, cold heavy air wants to drop down into both tubes.  Slightly warmer air wants to get pushed out of the tubes.  With them at different slopes, I think the warm air would rise easier out the steep tube and help suck in the cold.  My hunch is that 10x more air would flow in this arrangement.  When it's warmer outside, both upward angled tubes would still work as cold plugs.  

MJ9:  Yes, I thought of another one.  How impossible is it to have the tubes go vertically up through the umbrella?  Probably very risky...  But if it were possible, the "U" tubes could be replaced with 40 vertical tubes with caps on the bottoms (Like Joseph's ice caves).  The tubes would surround the freezer, maybe one every 3 feet.  They'd take in cold air whenever it's colder out and hold it whenever it's warmer.  The warm air replacing cold air flow pattern would be stronger with the pipes vertical.  But the penetrations of the umbrella would likely doom this.  I think?
 
Chris Kott
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As to air stratification, I thought that was the point. That's why the "exhaust" (where the warmer air goes) is at the top of the freezer. I would even raise that corner of the ceiling to enhance that effect.

Also, if the intake (where the fresh, cold air comes in) isn't at floor level, but at a level just below the exhaust, the cold air would fall, pushing the warmer up and out the exhaust, much like the diagrams of the 45 degree tube from earlier.

This also allows for some selectivity in terms of storage temperature. It would be possible to store that which must remain rock-solid on the ground. Shelves could store things at progressively higher levels, corresponding to perhaps a 20 degree stratification, which might be desireable, depending on what's being stored.

-CK
 
Mike Haasl
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Hey Chris, just to make sure we're on the same page...  The air exchange piping is a huge "U" that wraps around the freezer but doesn't enter the compartment.  So the frozen food doesn't have a path to outside air (per the original freezer wofati concept).  The cold air sinks into the "U" to freeze the mass around the wofati freezer and that frozen ground keeps the contents (air and food) frozen.

I agree that stratification can be useful or at least worked with.  Keep the stuff that needs to stay frozen down on the floor and things that could handle thawing up higher.
 
paul wheaton
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MJ1:  drawing?

MJ9:  wofati design violation.
 
Mike Haasl
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MJ1:  I hereby present the crappiest Paint drawing of the year, perhaps of all time.  I can do better on paper later if needed.  Both tubes are pointing the same direction (south?), one is just inclined more than the other.  The connecting tube between them that is behind the wofati is level and running E/W.  Where they exit the ground, one is maybe a foot higher on the hill than the other.  So the cold air would go in the lower one and the warm air would exit the higher one.  But only if the outside temp is colder then the mass's temp.  I believe.

MJ9:  Ok
freezer-wofati.png
[Thumbnail for freezer-wofati.png]
 
Chris Kott
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Mike Jay wrote:Hey Chris, just to make sure we're on the same page...  The air exchange piping is a huge "U" that wraps around the freezer but doesn't enter the compartment.  So the frozen food doesn't have a path to outside air (per the original freezer wofati concept).  The cold air sinks into the "U" to freeze the mass around the wofati freezer and that frozen ground keeps the contents (air and food) frozen.

I agree that stratification can be useful or at least worked with.  Keep the stuff that needs to stay frozen down on the floor and things that could handle thawing up higher.



I must have conflated two diagrams.

Could the idea of a stratification tube be implemented? I mean, it shouldn't be difficult to have a break in the "U", probably near the exhaust port, with a wider diameter piece of pipe set vertically (though probably not much of a tall one, so as to avoid a chimney effect, creating draught), with the continuation of the "U" set at its top, where warmer air could settle out and vent, and the cold air you want to keep would settle on the bottom until it's finished it's exchange with the pipe and thermal mass and is ready to exit the system.

I was also looking at the design shown side-on, that appears to indicate an airlock arrangement with the door. I like that arrangement. Also, I think the fact that you have to descend into the airlock corridor adds that stratification as another measure keeping heat out of the system. Though I wonder, are there any conceivable advantages to having a slanted door arrangement, like in some cellar doors? My thought is that if you can avoid having a door a person high, that means that you don't have a person's height of cold air in that insulated space that falls to the other side of the door and is replaced by warm air. If the door was set into the hill, or into the ground itself, the less-dense warm air would have to displace the denser cold air that isn't moving. It's the self-sealing plug mechanism again.

And as to shelf stratification, as an example, you keep your ice cream on the top shelf. It won't be melty, but it also won't break spoons.

-CK
 
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Imagine filling it with water.  The mission is to allow water in and hold the water.   So the lower side will determine the overall water level - the higher side will have less water and will let some non-water (warm air) in.  

 
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Paul, what am I missing?
In the single tube at 45*, you have warmer air escaping at the top of the section, and colder air entering at the bottom of the section. This seems like it will act as a counter-flow heat exchanger, no? Diluting the "coolth" coming in with the "warmth" going out.
Your sketch shows the tube low inside the "wofreezer", making a bell where the warmer air could accumulate without escaping...

What's needed is the John Hait model, which is a "well", not a "bell".

Chris Kott wrote:As to air stratification, I thought that was the point. That's why the "exhaust" (where the warmer air goes) is at the top of the freezer. I would even raise that corner of the ceiling to enhance that effect.

Also, if the intake (where the fresh, cold air comes in) isn't at floor level, but at a level just below the exhaust, the cold air would fall, pushing the warmer up and out the exhaust, much like the diagrams of the 45 degree tube from earlier.

This also allows for some selectivity in terms of storage temperature. It would be possible to store that which must remain rock-solid on the ground. Shelves could store things at progressively higher levels, corresponding to perhaps a 20 degree stratification, which might be desireable, depending on what's being stored.



CK, I thought the point (definition) of stratification was to not mix the air (fluid) and therefore inserting the new "colder" air at the lowest point, not dumping it in from up high, and stirring things up?
 
Mike Haasl
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paul wheaton wrote:



Imagine filling it with water.  The mission is to allow water in and hold the water.   So the lower side will determine the overall water level - the higher side will have less water and will let some non-water (warm air) in.  


I think the thought experiment doesn't work if you imagine it as water in a surrounding environment of air.  IE if the whole arrangement is underwater, then the cold trap will work again (I think).

Let's assume the temperature of the outside air is 10F.  And the mass is at 30F.  As you travel down the tubes they experience an earth temp that is a gradient from 10 to 30 degrees.  Each tube has that same gradient.  The 10 degree air will try to fall into both tubes.  The 30 degree air will be pushed out both tubes.  I think the 30 degree air will prefer to travel out the steeper tube.  That would set up a cold siphon and draw in more 10 degree air through the shallower angled pipe.

If it's 40F outside and 30F in the mass, both tubes have the same gradient but now it's from 30 to 40.  The outside air won't want to drop into either tube, they are both denser and colder.

I guess regardless of if this will or should or could or won't work, I'd propose that when the first trial wofreezer is built, maybe build it with two tubes on one side.  So the tube on one side is at 45, it curves around the back of the freezer and then where it would turn and come back out, have a Tee so that two tubes can exit the mass.  One at the same angle as the first and a second at a steeper angle.  Then by plugging one or the other, this effect can be tested and understood.

Top view sketch below.

Chris, I like your idea of a slanted access door to keep the stratification from hurting you.  It's kind of like why a chest freezer is better than an upright when you open the door.  If the access could be via a horizontal hatch near the ceiling, it would allow you to enter in the summer and not lose much coolth at all.
freezer-wofati2.png
[Thumbnail for freezer-wofati2.png]
 
paul wheaton
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Kenneth Elwell wrote:In the single tube at 45*, you have warmer air escaping at the top of the section, and colder air entering at the bottom of the section. This seems like it will act as a counter-flow heat exchanger, no? Diluting the "coolth" coming in with the "warmth" going out.



When the air outside is colder than the mass, the warmer air will hug the top edge of the pipe and the colder air will hug the bottom part of the pipe.  
 
Kenneth Elwell
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Anyone have a FLIR camera? Seems like a practical experiment with two cardboard boxes, a cardboard shipping tube and a bag of icecubes would go a long way towards figuring this out.

I know a guy, but he’s away on vacation at this moment...I’m sure he’s game to try when he gets back.
 
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Boy, this is a very tall order because it really is trying to overcome the laws of physics in several areas.

It really boils down to density, because that is how an ice house works, the cold ice has a a lot of cold density that overcomes the space constantly being heated by ambient air temperature and the ground. But ice in a building unto itself would fail, and fail in short order, if it was not for the ice covered in sawdust that helps keep in check evaporation and has its own insane insulating effects.  But ice and sawdust work in conjunction to maintain cold density which has a density 600 times higher than that of air. Air is easier to work with than water granted, but is less effecient, just as a forced hot air furnance is less effecient then a boiler in heating a house, only in this application, the exact opposite is trying to be accomplished. Still the same laws of thermal dynamics are in place.

Lets say there is a Freezer WOFATI that is 10x10x10 feet. That would mean, at least 500 square feet of surface is constantly being "heated" by a ground temperature of 45 degrees all the time, 24/7. BUT that ground is has a much higher thermal density then the cold air that is inside it. Insulation will help, but insulation only limits thermal dynamics, not eliminates it, which in in this case, time is very much against someone trying to build a natural freezer.

I might see some of the design ideas working, but only if fans were in place to move the air at the right time, and into the right place. In short, the fans would "pack" the space with more cold density. That would also maintain the vacuum that would be required to make this thing work, since a vacuum is the best insulator of all. But maintaining a vacuum in nature is extremely difficult., if not impossible.

One thing to keep in mind is, hot air does not rise, never has, and never will. Hot air changes the density of the air, and so the cooler air comes in, and being more dense, displaces the warmer air. That is how a chimney works, and seems like a moot point, but really is not because without factoring in cold air coming in, a thermal siphon will never take place.
 
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Paul, your original post with the sketch, mentions that some details were left out, such as the wings and the umbrella.

My understanding of the umbrella, in John Hait's house design, is to keep the soils around the house dry thus preventing the groundwater/rainwater from wicking away the stored heat, and creating a "bubble" of the constant year-round soil temperature closer to the surface under the umbrella.

I imagine that after a few weeks of <32F air entering the wofati, that the interior walls would be freezing to a thickness similar to the "frost line" depth in the surrounding soil. How does the umbrella affect this? If the soil around the wofati is dry, will it be in a "warm bubble", and will it be as efficient in turning to "frost" if there's not water in it? (I understand that water is the enemy of the wood in the wofati structure...but if it was permafrost? maybe not so evil?) Would the membrane be better as a "raincoat" close to the wood, rather than an "umbrella" over the whole site? (maybe allowing more frost to occur?)

I don't think you addressed Ashley and Joseph's suggestion of heat pipes yet? Which is in a way related to Len's use of phase change...
I imagine an array of them in concentric rings around the wofati, spaced laterally at a distance equal to the frost depth for the area, and as deep as feasible (maybe even short ones over the wofati roof) in order to create more frost in the soil than would naturally occur.
Maybe the above ground part could have dismountable fins, to reduce the thawing effect in the warm months (even though the heat pipe acts like a diode, it is still a metal rod in the ground, and I seem to remember another idea of using metal rods in the ground for the purpose of warming the soil, so...)
 
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With a wofati house, in order for the ATI to work, there needs to be a human being in the house that will open and close windows to:

    1:  optimize comfort, and

    2:  warm the mass in the summer

But a freezer wofati does not have that human element.  

I imagine that after a few weeks of <32F air entering the wofati, that the interior walls would be freezing to a thickness similar to the "frost line" depth in the surrounding soil. How does the umbrella affect this? If the soil around the wofati is dry, will it be in a "warm bubble", and will it be as efficient in turning to "frost" if there's not water in it? (I understand that water is the enemy of the wood in the wofati structure...but if it was permafrost? maybe not so evil?) Would the membrane be better as a "raincoat" close to the wood, rather than an "umbrella" over the whole site? (maybe allowing more frost to occur?)  



The concept is the same, but rather than setting the mass temp under the umbrella to 72, we are shooting for something closer to 10.  


I don't think you addressed ...



I wish to start with a simple design and see if it works on the first try or needs some optimization.

There used to be a rocket mass heater in allerton abbey that was riddled with fancy stuff and it was the builder's first build.   It didn't work.  

In software engineering we have an anti-pattern called "early optimization".   The idea is that too many people start optimizing before any code has been written - and they end up with massive code that doesn't work.  

I wish to encourage oodles of discussion in this space, but I feel like I have a pretty clear and simple design that I would like to try first.   I am glad to share my thoughts on what is in my head - maybe somebody else will go and build it.

And if you and seven others want to talk about fins and chemical conductors and more, I think that is excellent!  I gave birth to a thing that has developed a life of its own!   But these things feel a lot like early optimization to me - so I am going to simply step out of the way.


 
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Point taken about keeping it simple.
 
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I do not have a lot of time right now, but I do have the means in which to try a WOFATI Freezer and think I will actually try this.

I am on the fence on whether or not this would work. But I figure it is a 50/50 shot, so I might try and see.
 
Mike Haasl
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One more thought came to mind.  When I did skirt insulation on my greenhouse (aka Swedish skirt) I saw schematics that suggested that heat is coming out of the core of the earth.  By trapping it under a building and not letting the cold air freeze the soil around the greenhouse, the resulting heat bubble helps the greenhouse, pole barn, house stay warm.

Now that we built a freezer wofati and have an insulated umbrella, I wonder if that thermal energy coming up from the earth will be a problem.  One way of saying it is "The earth is 40F down there and I'm only trying to drop it by 30 degrees, piece of cake".  Alternately, someone could say "I'm trying to freeze a huge chunk of dirt during two months of the winter and then a 30 degree warmer furnace is sitting under it for 10 months".

Long story short, should we put some insulation under the wofati mass as well?
 
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Mike Jay wrote:Long story short, should we put some insulation under the wofati mass as well?



Let's try it without first.
 
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Mike, I think you and I are both overlooking a couple of things:
Me thinking that the umbrella is making a warm bubble, as an impediment to quickly freezing the wofati. Which isn't really the point of ATI.
You thinking that the umbrella is making a warm bubble, as an impediment to keeping the wofati frozen by warming it from below. When the larger heat loss is from above during the Summer.

My idea of a "raincoat"(smaller) instead of the "umbrella"(larger) leaves more of the earth around the wofati exposed to seasonal changes.
Your idea of insulating the floor maybe cuts off a resource?
Let's say floor, roof, and walls all have equal surface area... each 1/3 of total, and the floor is insulated. Now the roof is warming up because of the Summer heat, now it is effectively 50% of the area determining the temperature of the room.

There's a man I know in New Hampshire, who just the day before I saw him this one year, had been cutting ice and stocking the local museum's ice house. He was proud of all they had cut and put up, since they had more to do to replace the ice on the floor (ground?), which had been lost over the past year, owing to the previous Winter being too mild to cut much ice, if at all. Ordinarily the ice on the floor stayed year after year, he said.

I wonder if the steep slope above the wofati could be advantageous for harvesting snow from upslope and piling on top of and/or around the wofati site?
You could be super-lazy about it too, just leave your "slip-n-slide" setup after your summertime-freezer-wofati-ice cream-fun-fest, and the snow will slide down all winter...
 
Mike Haasl
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Kenneth Elwell wrote:Your idea of insulating the floor maybe cuts off a resource?
Let's say floor, roof, and walls all have equal surface area... each 1/3 of total, and the floor is insulated. Now the roof is warming up because of the Summer heat, now it is effectively 50% of the area determining the temperature of the room.

There's a man I know in New Hampshire, who just the day before I saw him this one year, had been cutting ice and stocking the local museum's ice house. He was proud of all they had cut and put up, since they had more to do to replace the ice on the floor (ground?), which had been lost over the past year, owing to the previous Winter being too mild to cut much ice, if at all. Ordinarily the ice on the floor stayed year after year, he said.


I guess I'm seeing the floor (and all the dirt below the wofati) as a drain, not a resource.  As long as it's warmer than your freezer, it's working tirelessly to melt your freezer.  It's not able to work as hard as the summer heat above, but it's still there, sapping away at your frozen ground.  At least that's how I am seeing it.

Let's take that same example you give but change from percentages to real made up numbers...  Let's say summer heat from above generates 100 units of melting heat, summer heat from the sides generate 40 and the deep earth does 10.  At first blush you'd say the floor is only contributing 1/15th of the heat to the freezer.  But you insulate the ceiling and walls (umbrella outside the mass) which cuts those numbers by 2/3rds.  Now the ceiling of the freezer experiences 33 units from above, 13 from the side and 10 from the floor.  Now the ceiling and walls are only heating it during maybe 8 months of the year, in Montana.  But the floor is heating it year round.  So the annual heat load is 368 (ceiling/walls) plus 120 floor.  If the floor was also insulated, it would cut that year round total of 120 down to 40.  So the annual total drops from 488 to 408 (20% better).  Of course these are made up numbers, and I'm typing this when I can't sleep so I probably did the math wrong, but I think it shows that even a colder floor with constant heat load from below would still contribute a possibly deceptively large amount to heating the freezer.

I wish there was a museum with an ice house around here (need to look in case there actually is).  That technology seems pretty cool to me.  
 
Travis Johnson
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The reason the ice on the bottom of the ice house did not normally thaw has to do with the ice above it. The cold from that ice dropped down to floor level and chilled the air MORE than the heat radiating out of the ground. This is where density comes into play once again. The frozen ice above has 600 times more cooling density then the warm air coming up from the ground, so the ice never melts. And keep in mind, in an ice house there is always sawdust to help insulate the ice and keep down evaporative effects.

In a freezer WOFATI the opposite is at play. The freezer interior is air, so it is 600 times less dense then the warm earth that surrounds around it.

The real question is not whether the ground will eventually warm te freezer above 32 degrees, the real question is, can insulation surrounding the WOFATI delay the inevitable long enough over the summer to be recharged with cold air in the winter again.
 
Kenneth Elwell
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Mike, as Travis points out, the air inside has little mass, without mass there's no Inertia to Annualize the Thermal...
And the earth tube is working on all the nights and cold days, all winter long, to turn all the soil under the umbrella and surrounding the chamber to frost.

If instead, there's insulation all around, then the mass is only the foodstuffs and the air inside. (which now I understand, maybe, your suggestion to pass the pipe through the chamber, since in your mind, the coolth isn't coming through the walls...in your mind that's the constant earth temperature stealing the coolth.) Let's call this a picnic cooler WITHOUT ice packs. If you open it to check on things, you let warm air in and melt it all...so maybe it's storing Schrodinger's popsicle?

Except we are adding ice packs, in the form of freezing the surrounding soil under the umbrella...but in your example, it is still insulated all around the chamber. Let's call this a picnic cooler WITH ice packs ON THE OUTSIDE. It's keeping the outside warming effects at bay, but there's no inside cooling effects (other than we maybe froze all the food first, and it's more than one popsicle.) This is similar to the "how long will my food last in the freezer during a power outage" scenario. More food, fewer entries, cool room, all add to this.

So if you skip the insulation... Let's call this the picnic cooler IS THE ICE PACKS. Now the walls of the chamber are contributing. Dick Proenneke had something like this in Alaska, a hole in the earth (maybe frost?) with a lid made of moss, for holding some food for a short period of time.
 
Mike Haasl
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I may have gotten my terms mixed up.  I'm envisioning a freezer compartment full of air and frozen food.  That is within a set of wofati walls.  Outside those walls and ceiling is 2' of dirt, then forest duff/insulation.  Outside that is the umbrella (poly layer to keep the mass and insulation dry).  Outside of that is a bit of dirt and some plants before you hit the air.

I'm suggesting a layer of insulation/duff a foot or two below the whole thing so that the duff/insulation is continuous around the wofati.  Inside of that insulation layer is several feet of dirt or mass before you get to the freezer compartment.

So the goal of the whole freezer wofati is to freeze the dirt around the freezer compartment.  That dirt is protected by the layer of insulation that's under the umbrella.  I'm just thinking that we should consider extending that insulation layer under the dirt that's under the floor.

To play with the cooler analogy, the original design as I understand it has a picnic cooler with its bottom missing and it's sitting on the ground.  The interior of the cooler has a layer of frozen dirt (or shall we say ice blocks) and in the middle is the bag of frozen peas.  I'm proposing to put a bottom on the cooler so that the lower ice blocks don't thaw as quickly.
 
Travis Johnson
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Mike Jay wrote:So the goal of the whole freezer wofati is to freeze the dirt around the freezer compartment.  That dirt is protected by the layer of insulation that's under the umbrella.  I'm just thinking that we should consider extending that insulation layer under the dirt that's under the floor.



But I do not see that happening.

IF the soil is only 2 feet deep, then in the winter it will freeze through from the outside, but at the same time, that little depth also means that it will thaw just as quick in the spring, and not be frozen in the summer or fall.

And the WOFATI will not freeze the dirt by an induction of cold winter air from the inside because as I have been saying, you are trying to use something that is 600 times less dense (air), to freeze something with much more mass (dirt)...and then there is insulation in the way to impede that process to boot.

And that dirt is constantly being heated as well. Frozen ground always thaws from the ground upwards because the earth is "warm." Yes it is 45 degrees, but it is warmer then 32 degrees, so it is constantly trying to heat the soil.

Now if you make the soil deeper, nothing really has changed because frost does not penetrate that deep in the winter, and everything else stays the same too. The earth is still warming the soil, the winter air will not freeze the soil because the soil is denser than the cold air in the WOFATI Freezer, and that pesky insulation is keeping the cold winter air from being effective.
 
Mike Haasl
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Maybe I'm imagining this thing all wrong.  Here's an end view as you look at the freezer from inside the hill.  The brown stuff is dirt.  The grey layer is the insulation.  The brick red line is the umbrella (waterproofing).  The green stuff is lavender hyssop and aronia.  The weird shapes are food.  The black circles are the air pipes.  They exit upwards as they go away from you in this view and they cross and connect in the foreground.

So the winter frost doesn't really help significantly due to the insulation.  The goal is to have the frigid air circulate through the pipes and freeze all the dirt between the freezer compartment and the insulation.  Then you have to hope the insulation keeps it from thawing before November.  

I agree Travis that the thermodynamics of thin cold air freezing all that soil could be a challenge.  But the insulation won't be in the way.  The more frigid air flowing through the pipes, the better (I think).

Since the whole thing is sitting on 40-45 degree deep earth temps, that's why I'm thinking a layer of insulation a foot below the freezer may be worthwhile.
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Travis Johnson
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Mike Jay wrote:The goal is to have the frigid air circulate through the pipes and freeze all the dirt between the freezer compartment and the insulation.  Then you have to hope the insulation keeps it from thawing before November.



But there will not be any fridgid air.

As soon as the cold winter air enters the pipes, it is surrounded by warm (45 degree) dirt that by VOLUME is huge in ratio to the teeny-tiny pipes that wrap around through it. And to make matters worse, the air in those pipes are 600 times less dense.

I can say this with authority because I have built what you propose for my sheep waters, but in my case I built them purposely TO KEEP MY WINTER STOCK TANKS FROM FRREZING. That is because the warm earth heats up the air in the tubes, in my case they were 15 inch culverts that broght enough heat out of the ground to keep my insulated stock tanks from freezing.

This will not work...not without some sort of brine, propane, freon or ammonia to have the needed density, or in the case of propane or freone, a shear amount of cold, to overcome the huge volume of warm air in the ground. Packing cold winter air under presure from fans MIGHT also work.

But this is no different then making an apple pie. The "baking" is really just the ingredients getting to the same temperature as what the oven is set at. The oven is just an enclosed environment which is heated, and at first the cold contents of the apple pie try to bring the temperature in the oven down, but the heat inside is so overpowering that after twenty minutes, the apple pie ingredients reach the same temperature throughout the pie. It takes awhile because the crust and filling act as a sort of insulation to the heat surrounding it.

Cold winter air going through your pipes will do the same thing. Within a foot or two of entering the pipes, that cold air is warmed by the ground surrounding it. The air will try to chill the ground, but the 45 degree heat of the ground is so overpowering, it will just heat the chilled air, just as it does with an apple pie baking in an oven. It does not matter what the temperature is. It could be one degree warmer, and this convection...the law of thermal dynamics...will take place. 350 oven vs 70 degree apple pie, or 45 degree ground vs 0 degree winter air.

You see this in the frozen ground in the Spring. Frost does not come out of the ground from the top, but from underground. Spring takes away the cold from the top, but the heat of the ground beneath the frost thaws the frozen ground.
 
paul wheaton
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:)

Let's try it and see.

 
Mike Haasl
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Thanks Travis, I understand your concerns and it seems like we're both on the same page regarding where the insulation is relative to the mass.  That's all I was trying to confirm with my most recent posts.  

So, if the mass (earth) will sap the air temps rapidly, that tells me that the more cold air we push through there, the better.  And if it the piping is ribbed, that would increase the heat transfer (for good or bad).  Hmm, maybe we'd want smooth pipe in some places and culvert/corrugated pipe in others?

I'm wondering how the geometry will work in order to have the air pipes stay under the insulation/umbrella AND be at 45 degrees AND reach all the way around behind the freezer.  If it's 15' from the frost pocket outside the door to the back of the "U", that means the bottom of the "U" needs to be 15' lower than the frost pocket...  I'm probably not seeing that in my mind correctly.

Hey, this whole thing could be tested for a science project using an aquarium of warm sand in a cold room.  Build the scale model wofati and see how it works.  Or at least use a model to test how the air moves in the pipes.
 
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Hi Paul,

I recently made a post about a natural occurring phenomenon where underground air drafts create freezing temperatures in summer, and if it would be possible to replicate that natural system to produce a root cellar with (near) freezing temperatures. Someone in the thread mentioned that you were also looking into creating an underground freezer (although you are much further along than I am), which is how I found this thread.

While most of the physics behind this go way over my head, I thought that natural phenomenon could be an interesting addition to your research. For the convenience of this thread I’ll copy what I posted in my thread. You can find the full thread here: Creating a near freezing root cellar using thermal inversion

Here is my original post:

Near where we live here in the (lower) Alpine mountains, there is a certain valley (basically called 'the cold valley'), that has a very interesting natural phenomena.
The valley itself is always at least 10 degrees colder then elsewhere (I'm not kidding, the cold hits you like walking into a freezer), and all throughout the summer icicles and ice formation can be seen near cracks between the rocks, despite the valley being facing south-west, sheltered from the north winds and at a height of 740-760 m.
The phenomenon is explained by scholars with the presence of airways or channels of air between the rocks that from the high and steep area descend, within the mass of the earth, down to the base level near a lake (which is a cold mass in summer), where it leaves the subsoil. In these channels, when the external air is warmer than the internal one, an air current is established, similar to a descending breeze, which transports cold air to the lower outlet and exiting, gives rise to the refrigeration. And apparently the thermal inversion is so strong it creates freezing temperatures.
Because of this phenomenon the local people have been using the cracks and caves in the ground to store their food for centuries.

Now I know that some root cellars already use the principal of a high air inlet and a low air outlet, but in that case it is often used to regulate humidity and to avoid condensation, while dragging in cold air and letting warm air leave. But I haven't heard of instances where it has been effectively used to create near-freezing temperatures.
I'm just wondering, if you're on a terrain with a large enough height difference, could it be possible to mimic this natural phenomena to chill a small root cellar, or even a buried, insulated box?

The beauty of this system is that it chills the air best in summer (which is when you have the biggest temp-difference, I think) which is when having a freezing root cellar is most useful.

As for the mechanism I'm guessing it's the specific mix of the presence of the rocks with the position of the lake. But i'm by no means a physicist, so I could be completely wrong here
In winter the rocks cool down and they form the cold mass. Then in summer there is the lake where the air channels meet that is another cold mass. The place where the channels exit is a south facing slope, so one that heats up decently, creating a tremendous draft throughout the rocky hill. You could actually feel this draft if you held your hand in front of the openings. And apparently this draft is enough to chill the temperature to freezing degrees.

So I'm thinking maybe you could replicate this by having your inlet of air near a cold body like a lake or river during summer, letting it pass through the hill upwards, and having the exit of the airflow near something that heats up during summer (perhaps even adding a black painted surface near the outlet to heat the surrounding air even more?) to create the draft due to the temperature difference?

Not sure if this is worth anything, but I saw no harm in sharing it either.
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How it probably works
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Icicles in summer!
 
paul wheaton
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How much elevation difference would be required?
 
S. Bard
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paul wheaton wrote:How much elevation difference would be required?



Honestly I have no idea. I just remembered my visit to the valley where you had that phenomenon while I was thinking on how I could build my root cellar and started wondering if you could somehow replicate the system.
But I have no technical or mathematical background so I haven’t a clue how I could calculate that yet. Was hoping you guys could help me with that part.
I suppose the main thing here would be creating a sufficient draft, so I would assume temperature difference would be more important than height, as it is the difference that creates the airflow?

I’m sorry if this isn’t of much help!
 
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