Unfortunately thermodynamics does not side with you on this one. In a closed system in thermal equlibrium, it’s impossible to move/extract heat from one part of the system to another without putting in work (at which point it’s no longer a closed system of course).
I assume the water here is doing the work. I didn’t say anything about a closed system, just passive. Maybe that doesn’t count as passive, I don’t know physics all that well.
I wouldn’t call it obnoxious, it’s just pointing out that they are using terms that don’t align with what they stated. If nobody ever mentioned the difference, how can they ever learn? Not saying everyone needs “taught” but it really didn’t seem malicious like you seem to believe
I do not think you’re trying to say the water “does work” in the physics sense, but to clarify, the water is just a large heat sink that has a much higher heat capacity than air. You can heat the water with air (which in turn cools the air), and that water can hold MANY times the heat (per unit mass) that the air can. Water also has a higher thermal conductivity than air. Allowing it to absorb and pass heat very well. This water is in the ground which also acts as a massive heatsink.
The air passes heat to the water which then passes the heat to the ground effectively cooling your air feed. A quick look online says current soil temp in Iran 21 inches deep is 35C or 95 F. That is your lower temperature limit. It’s physically impossible to become colder than the soil temperature (in this instance, as that is your lower temperature bound for heat transfer, in reality you wont even get there, because your driving force for heat flow is gone at that point) without putting in mechanical work (which is what a compressor does in your air conditioner) to compress your cooling fluid so that it may be evaporated repeatedly to exploit the tranfer of heat into an evaporating substance
The water does perform work in the sense that it’s moving and gets replenished with fresh cool water from the mountains. If it was just a stale pool, it would eventually reach thermal equilibrium with the ambient temperature. The wind performs work as well, it takes humid air away so the air doesn’t get saturated with it, negating
If you had to replace this with a equivalent mechanical system, you’d need fans to blow air through the water tunnels and the house, and a water loop with a pump that pumps the used water back up into the mountains, and a source of water to replenish the evaporated water. Pumps and fans require work to operate so there’s your work.
It’s physically impossible to become colder than the soil temperature
Actually, evaporative cooling can drop the temperature a bit below ambient temperature. It’s not classic heat transfer between two bodies, it’s the phase change of the water from liquid to gas that extracts heat from its surroundings.
That is the deepest depth I could find being actively tracked on the website I ended up on. I did not wanna do a deep dive into “great” average soil temp data lol. If you have a good source of data I will gladly change my comment to include the updated numbers. I wanted to say the average soil temperature at depth is ~50-55 degrees F, but I hopped online to make sure that was not a number that I know to be true due to where I live. Good to know that its roughly 6 feet where it stabilizes
If you go down deep enough the earth temperature is stable at 12 C. But I’m pretty sure that’s like thousands of feet down. Geothermal rigs drill 500+ meters (1600 feet) down. Having a hard time finding a source on the stable earth temp though.
I mentioned 6 feet because it’s well below the frost line where I am, but I guess in that part of Iran they probably don’t have to worry about that.
Mostly I was just wondering if you had found something on how deep those waterways were actually built.
Yeah thats exactly the issue I ran into. I started googling stable soil temp to confirm what I thought, and rapidly ran into a lack of answers lol. Any data I could find for free on websites didn’t seem to go very deep.
In terms of depth of the Qanats, yeah I was wondering the same. Without any modern tools I’m not sure how deep they would be willing to dig out (although I bet it’s easy digging in Iran, likely sand/dry dirt vs. clay and sopping wet boggy soil).
I am at work but I’ll see if I can dredge up info on Qanat depth
I assume the water here is doing the work. I didn’t say anything about a closed system, just passive. Maybe that doesn’t count as passive, I don’t know physics all that well.
Thought about this some more, and the water and the wind are both doing “work” here. The water gets continuously replenished, so that it doesn’t reach thermal equilibrium and the wind moves the humid air so it doesn’t get saturated with humidity from the evaporation.
As a thought experiment, if you’d have to replace it with a mechanical system, you’d need fans to move the air and a water loop with a pumping station to move spent water back up into the cooler mountains. So the work that the pumping station and fans would be doing is being performed by Mother Nature here, so we get it “for free”, but thermodynamically it is not “free” of course. The energy ultimately comes from somewhere, and like almost all sources of energy on earth except nuclear, if you break it down it ultimately comes from the light of our sun. Another thing is that this means that the principle is not generally applicable and depends on availability and reliability of those two sources of “work”.
Whether this counts as passive, is debatable and depends on your definition of passive. Is a windmill or watermill passive? You tell me.
Unfortunately thermodynamics does not side with you on this one. In a closed system in thermal equlibrium, it’s impossible to move/extract heat from one part of the system to another without putting in work (at which point it’s no longer a closed system of course).
I assume the water here is doing the work. I didn’t say anything about a closed system, just passive. Maybe that doesn’t count as passive, I don’t know physics all that well.
The person that replied to you is probably being scientific-literal and obnoxious. I understood what you meant just fine. :}
I wouldn’t call it obnoxious, it’s just pointing out that they are using terms that don’t align with what they stated. If nobody ever mentioned the difference, how can they ever learn? Not saying everyone needs “taught” but it really didn’t seem malicious like you seem to believe
The water does not perform work in this instance.
I do not think you’re trying to say the water “does work” in the physics sense, but to clarify, the water is just a large heat sink that has a much higher heat capacity than air. You can heat the water with air (which in turn cools the air), and that water can hold MANY times the heat (per unit mass) that the air can. Water also has a higher thermal conductivity than air. Allowing it to absorb and pass heat very well. This water is in the ground which also acts as a massive heatsink.
The air passes heat to the water which then passes the heat to the ground effectively cooling your air feed. A quick look online says current soil temp in Iran 21 inches deep is 35C or 95 F. That is your lower temperature limit. It’s physically impossible to become colder than the soil temperature (in this instance, as that is your lower temperature bound for heat transfer, in reality you wont even get there, because your driving force for heat flow is gone at that point) without putting in mechanical work (which is what a compressor does in your air conditioner) to compress your cooling fluid so that it may be evaporated repeatedly to exploit the tranfer of heat into an evaporating substance
The water does perform work in the sense that it’s moving and gets replenished with fresh cool water from the mountains. If it was just a stale pool, it would eventually reach thermal equilibrium with the ambient temperature. The wind performs work as well, it takes humid air away so the air doesn’t get saturated with it, negating
If you had to replace this with a equivalent mechanical system, you’d need fans to blow air through the water tunnels and the house, and a water loop with a pump that pumps the used water back up into the mountains, and a source of water to replenish the evaporated water. Pumps and fans require work to operate so there’s your work.
Actually, evaporative cooling can drop the temperature a bit below ambient temperature. It’s not classic heat transfer between two bodies, it’s the phase change of the water from liquid to gas that extracts heat from its surroundings.
Why only 21 inches? Soil temps aren’t stable until like 6 feet down, and then it’s closer to 12 C.
That is the deepest depth I could find being actively tracked on the website I ended up on. I did not wanna do a deep dive into “great” average soil temp data lol. If you have a good source of data I will gladly change my comment to include the updated numbers. I wanted to say the average soil temperature at depth is ~50-55 degrees F, but I hopped online to make sure that was not a number that I know to be true due to where I live. Good to know that its roughly 6 feet where it stabilizes
If you go down deep enough the earth temperature is stable at 12 C. But I’m pretty sure that’s like thousands of feet down. Geothermal rigs drill 500+ meters (1600 feet) down. Having a hard time finding a source on the stable earth temp though.
I mentioned 6 feet because it’s well below the frost line where I am, but I guess in that part of Iran they probably don’t have to worry about that.
Mostly I was just wondering if you had found something on how deep those waterways were actually built.
Yeah thats exactly the issue I ran into. I started googling stable soil temp to confirm what I thought, and rapidly ran into a lack of answers lol. Any data I could find for free on websites didn’t seem to go very deep.
In terms of depth of the Qanats, yeah I was wondering the same. Without any modern tools I’m not sure how deep they would be willing to dig out (although I bet it’s easy digging in Iran, likely sand/dry dirt vs. clay and sopping wet boggy soil).
I am at work but I’ll see if I can dredge up info on Qanat depth
Thought about this some more, and the water and the wind are both doing “work” here. The water gets continuously replenished, so that it doesn’t reach thermal equilibrium and the wind moves the humid air so it doesn’t get saturated with humidity from the evaporation.
As a thought experiment, if you’d have to replace it with a mechanical system, you’d need fans to move the air and a water loop with a pumping station to move spent water back up into the cooler mountains. So the work that the pumping station and fans would be doing is being performed by Mother Nature here, so we get it “for free”, but thermodynamically it is not “free” of course. The energy ultimately comes from somewhere, and like almost all sources of energy on earth except nuclear, if you break it down it ultimately comes from the light of our sun. Another thing is that this means that the principle is not generally applicable and depends on availability and reliability of those two sources of “work”.
Whether this counts as passive, is debatable and depends on your definition of passive. Is a windmill or watermill passive? You tell me.
The wind provides the work here. Wind and air flows.
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My dude, I have no idea what you’re trying to say here.
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These things are still there and if you aren’t an American you can go to them. They are very nice and cool inside.