Would it be possible for a root cellar to reach near-freezing temp using natural thermal inversion?

Hi all,

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?

Any thoughts on this? Or have any of you seen or heard of a similar system for chilling to near-freezing temperatures.

I would think it should work in some places, but not very many. without looking into the specific case you mention, my guess is that the average annual temperature would need to be below freezing for it to work.

rode my bike through Alto Adige a couple years ago. I really want to go back for a longer stay. didn't try nearly enough alpine bitters.

tel jetson wrote:I would think it should work in some places, but not very many. without looking into the specific case you mention, my guess is that the average annual temperature would need to be below freezing for it to work.

rode my bike through Alto Adige a couple years ago. I really want to go back for a longer stay. didn't try nearly enough alpine bitters.

The place where the natural phenomena occurs is actually in the Valsugana! If you ever go back you should definitely visit it! I don't think the Valsugana has an average temperature below freezing though. It is actually a very moderately temperature region (if you're not standing on the very tops of the mountains that is). Where I currently live, which is about the same height above sea level and region as the 'cold valley', it can become very hot in summer, while the winters so far haven't dropped much below -6 degrees celsius, and they did so only for a few days.
The homestead we recently purchased is in a nearly similar situation, which is why I was wondering if it could work.

we rode on the Via Claudio Augusta, which I believe goes through the Valsugana. I wish I had known about this.

if the average temperature is above freezing, there's got to be some mechanism that favors cooling the rocks in the winter over warming them in the summer. could be something as simple as the aspect of the slope keeping it in deep shade. the topography could make clear night skies common, which would cool the ground quickly.

I'm very curious.

if you're in a place that does reliably get below freezing for part of the year, it should be possible to keep a root cellar pretty cold. have to make it easy for cold air to get in and difficult for heat to.

sounds like you're familiar with these concepts already, but for the edification of anybody who stumbles on this thread I'll lay some ideas out here. I think of it in terms of three things:
-buoyancy (of air)
-insulation
-thermal mass

make sure that any time the air outside is colder than the air inside, the warmer air in the cellar will be displaced by the cold outside air. an air inlet low in the cellar and and outlet with a stack starting in the ceiling would achieve this.

the ceiling will definitely need insulated. if you want to stay colder than the ground temperature, the walls and floor will also have to be insulated.

the more thermal mass, the longer it will take to heat up in the warm season. it will also take longer to cool off in the cold season, but keeping buoyancy in mind will help with that.

Some deserts are known for having very high day-time temps but very low and sometimes freezing night-time lows. Lack of cloud cover is definitely part of that from what I've read. Having an automatic way of capturing the night-time lows, but insulating from the highs would help if you can't re-create exactly what nature has done.

Cloud cover vs no clouds appears to make a difference of 4-6 C in the overnight lows where I live, but we get a lot of "ocean effect" mixing in with that.

Jay Angler wrote:Cloud cover vs no clouds appears to make a difference of 4-6 C in the overnight lows where I live, but we get a lot of "ocean effect" mixing in with that.

to make that slightly more technical, water vapor is opaque to an important band of infrared radiation, so the higher the humidity, the more heat energy is absorbed and re-emitted back at the ground.

tel jetson wrote:we rode on the Via Claudio Augusta, which I believe goes through the Valsugana. I wish I had known about this.

if the average temperature is above freezing, there's got to be some mechanism that favors cooling the rocks in the winter over warming them in the summer. could be something as simple as the aspect of the slope keeping it in deep shade. the topography could make clear night skies common, which would cool the ground quickly.

I'm very curious.

Oh wow, I'm jealous, that's a gorgeous historic route! If you ever return, do let me know, I can always point you in the direction of some nice places to visit / good places to eat!

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 maybeyou 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 a black painted surface near the outlet?) to create the draft due to the temperature difference?

Sounds like you want an artificial ice cave. I don't know how large they have to be to work, but seem to work like tel jetson mentioned above.

Also see any posts or podcasts from Paul Wheaton re: a freezer WOFATI. It's a future project, hasn't been done yet, but he's after the same goal. (And has an engineering background.)

T Melville wrote:Sounds like you want an artificial ice cave. I don't know how large they have to be to work, but seem to work like tel jetson mentioned above.

Also see any posts or podcasts from Paul Wheaton re: a freezer WOFATI. It's a future project, hasn't been done yet, but he's after the same goal. (And has an engineering background.)

Oh cool! I will definitely check those out!

Addressing the OP, will the root cellar be used for storing bulbs and roots, or is the intended use for keeping edibles cool, or making ice?  

Studying natural cooling processes led to interesting history and practices here:

Ice:
http://www.historyofrefrigeration.com/refrigeration-history/yakhchal-ancient-refrigerator/

Cooling and storage of edibles with a zeer pot (5 minutes):


Similar (12 minutes):

Catherine Windrose wrote:Addressing the OP, will the root cellar be used for storing bulbs and roots, or is the intended use for keeping edibles cool, or making ice?  

Idealy I would want to store edibles in there as well, so I could use only a small fridge/freezer in the house, or maybe even go without one at all depending on the succes of the root cellar. The main problem would be storing raw meat, but in our current diet we don't implement a lot of uncured meats. Mostly dried or cured meats, which can be stored at a somewhat higher temperature.

Thanks for the links! I'll check it out!

When I searched the site earlier for freezer WOFATI, somehow I didn't find what I was looking for. I was looking back at your thread this morning, and found it in the related threads at the bottom. It starts as a description of the freezer WOFATI Paul has in mind, and a discussion about it. Later the conversation turns to other techniques for in ground freezers or cold storage that fall outside of the definition of WOFATI. Here's a link so you can check it out.