6 ms·

Here in Brazil we use a system with copper pipes in an insulated "box" to heat water during the day using this energy from the sun. A couple of years ago, in a

Here in Brazil we use a system with copper pipes in an insulated "box" to heat water during the day using this energy from the sun. A couple of years ago, in a cold winter day with a minimum of 5 degrees (celsius), just after the sunrise the water froze, broke the pipes and the glass above it. I couldn't understand what happened because the ambient temperature was above freezing point, maybe it was something like this effect?

K0balt 3y ago
Fascinating! That does seem like the most likely explanation. This reminds me of the ancient ice ponds that made ice thousands of years ago in Persia. I read somewhere that they were able to make ice through a combination of radiative and evaporative cooling at night temperatures around the same as you experienced, about 5C.
- mamediz 3y ago
  Yes, I like this explanation, when that phenomenon happened in our house I thought one of our neighbours was dumb because he just put a blanket over the collector on the roof, as he said, "to keep it warm". But now I think he was right. Now, I don't know if this exists but it would be nice if there was a kind of glass that let radiation pass only to one side and not the other way, a kind of "valve", this could solve the problem of water frozing from radiation in our solar heating.
  - Enginerrrd 3y ago
    >Now, I don't know if this exists but it would be nice if there was a kind of glass that let radiation pass only to one side and not the other way, a kind of "valve", this could solve the problem of water frozing from radiation in our solar heating. This doesn't exist and can't even in principle because it would be a fundamental violation of thermodynamics. Basically, it would be a Maxwell's demon for radiation that would allow you to arbitrarily reduce entropy.
    - KMag 3y ago
      But, it might be possible to have a material that has different characteristics at different temperatures, as long as it's symmetric. If it's nearly opaque to IR in its cold state, hopefully sunlight at dawn would warm it rapidly enough that it would automatically "shut off" on cold nights, and still "turn on" shortly after dawn even on cold days.
      - sgc 3y ago
        Light meter controlled / tracking louvers would be the quick fix.
      - Enginerrrd 3y ago
        Yes I think that'd be ok. You'd basically just be taking advantage of the thermal gradient between the radiating body and the object being heated. It'd be analogous to adding more insulation as it heats up and removing insulation as it cools down. You'd be slowing the flow of heat into your reservoir just as much as you'd be slowing down the loss of that heat later though. You might still get some benefit in preventing freezing at the expense of needed a larger area to get the same amount of heat flow in to your water system though.
    - K0balt 3y ago
      I don’t think maxwells demon is impossible, it just is a device for converting información to energy. In theory, many such devices may be possible for the conversion of information to both energy and matter. This seems like it might be support the simulation hypothesis.
    - kbutler 3y ago
      We call this a one-way mirror. https://en.m.wikipedia.org/wiki/One-way_mirror https://en.m.wikipedia.org/wiki/One-way_mirror They are not perfect (intensity & wavelength limitations), but they exist. See also mirages and total internal reflection.
- pyrale 3y ago
  Relevant link: https://en.wikipedia.org/wiki/Yakhch%C4%81l https://en.wikipedia.org/wiki/Yakhch%C4%81l
smallnamespace 3y ago
The handwavey explanation in my head is that “ambient” for this emitter is not just the immediate physical environment, but also deep space, which is very very cold. This wouldn’t work if the temperature of space and the air were the same. An emitter is also an absorber so if space were as hot as the emitter then it would not shed heat.
tim333 3y ago
Yeah, on a clear night the pipes radiate heat to space but nothing much radiates the other way as space is cold and dark. It's also why the tops of cars get frosty on clear nights.

K0balt 3y ago

Fascinating! That does seem like the most likely explanation. This reminds me of the ancient ice ponds that made ice thousands of years ago in Persia. I read somewhere that they were able to make ice through a combination of radiative and evaporative cooling at night temperatures around the same as you experienced, about 5C.

mamediz 3y ago
Yes, I like this explanation, when that phenomenon happened in our house I thought one of our neighbours was dumb because he just put a blanket over the collector on the roof, as he said, "to keep it warm". But now I think he was right. Now, I don't know if this exists but it would be nice if there was a kind of glass that let radiation pass only to one side and not the other way, a kind of "valve", this could solve the problem of water frozing from radiation in our solar heating.
- Enginerrrd 3y ago
  >Now, I don't know if this exists but it would be nice if there was a kind of glass that let radiation pass only to one side and not the other way, a kind of "valve", this could solve the problem of water frozing from radiation in our solar heating. This doesn't exist and can't even in principle because it would be a fundamental violation of thermodynamics. Basically, it would be a Maxwell's demon for radiation that would allow you to arbitrarily reduce entropy.
  - KMag 3y ago
    But, it might be possible to have a material that has different characteristics at different temperatures, as long as it's symmetric. If it's nearly opaque to IR in its cold state, hopefully sunlight at dawn would warm it rapidly enough that it would automatically "shut off" on cold nights, and still "turn on" shortly after dawn even on cold days.
    - sgc 3y ago
      Light meter controlled / tracking louvers would be the quick fix.
    - Enginerrrd 3y ago
      Yes I think that'd be ok. You'd basically just be taking advantage of the thermal gradient between the radiating body and the object being heated. It'd be analogous to adding more insulation as it heats up and removing insulation as it cools down. You'd be slowing the flow of heat into your reservoir just as much as you'd be slowing down the loss of that heat later though. You might still get some benefit in preventing freezing at the expense of needed a larger area to get the same amount of heat flow in to your water system though.
  - K0balt 3y ago
    I don’t think maxwells demon is impossible, it just is a device for converting información to energy. In theory, many such devices may be possible for the conversion of information to both energy and matter. This seems like it might be support the simulation hypothesis.
  - kbutler 3y ago
    We call this a one-way mirror. https://en.m.wikipedia.org/wiki/One-way_mirror https://en.m.wikipedia.org/wiki/One-way_mirror They are not perfect (intensity & wavelength limitations), but they exist. See also mirages and total internal reflection.
pyrale 3y ago
Relevant link: https://en.wikipedia.org/wiki/Yakhch%C4%81l https://en.wikipedia.org/wiki/Yakhch%C4%81l

smallnamespace 3y ago

The handwavey explanation in my head is that “ambient” for this emitter is not just the immediate physical environment, but also deep space, which is very very cold. This wouldn’t work if the temperature of space and the air were the same. An emitter is also an absorber so if space were as hot as the emitter then it would not shed heat.

tim333 3y ago

Yeah, on a clear night the pipes radiate heat to space but nothing much radiates the other way as space is cold and dark. It's also why the tops of cars get frosty on clear nights.