gregjohn a écrit :
> Hi. I had an argument with a friend about solar cooling.
> 
> I fully understand the physics of solar photovoltaics-- photon comes in,
> electron gets pushed somewhere.  I fully understand the physics of heat pipes--
> you can end up cooling something by having a phase-change object that gets to
> move around inside a pipe.
> 
> I had an argument with someone who was apparently an insider in the industry
> about passive solar cooling.  He couldn't describe it to me in a way that didn't
> seem to be a gross violation of physics.  It sounded like a heat pipe, where you
> heat up one end, but then because some heat is naturally flowing, extra heat
> decides to come along for the ride.  That just didn't seem to float.   I did
> some googling and the only thing I could find was the use of electric fans
> powered by solar cells.
> 
> Any ideas what is physically going on here?
> 
> 
Ever heard of Peltier cooling ?

You put a current through a peltier "system", which means the Joule
effect will heat the system (as it should), and one side of the peltier
is getting colder.

In fact, IIRC, the heat transfer is about 1/4 of the Joule heat, meaning
you can extract 20 W of heat with a 100 W dissipating hot side (and 80 W
of current). It's a heat-pumping apparatus based on the traversal of
connections made of different metals. From metal A to metal B, the
section is X, but from metal B to metal A (you need a lot of alternate
A/B/A/B/A/B/A... along the current path) the section is Y, so the
intensity per unit section in A to B is different from the one in B to A.

Thermodynamics (that branch of physics about heat and energies) forbid
to have a system with only two components where the cold one get colder
when the hot one get hotter (that would be against the laws, you would
need to reverse the time, something that is not possible at that scale).
But it does not stop you to have a third component which get colder
while the first cold get hotter due to the hot second one transfering
heat to the first: while the energy/heat is transfered from the hot to
the cold, it can also take away a bit from the third component.

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