CO2 in solar collectors??

[Xringer]

Found this paper about using CO2 as a solar heat-transfer medium..

http://www.ewp.rpi.edu/hartford/~cha...c_tube_CO2.pdf

But, the conclusion of the solar-CO2 study, says it's too complicated (to paraphrase).

I started thinking about that heavy duty CO2 plumbing..
And where to find a good CO2 pump..?. That's going to be the hard part..


Solar space heating with hot air is so simple.. Can CO2 be done 'simple'?

I started wondering about a basic wall mounted space heater.


Cool air from inside the house flows into the bottom, is heated and flows out the top..
Seems like it would work, even when you don't have a fan running..?.

How could CO2 be made to work in a free-flow mode..?.
If your collector had high pressure copper pipes? CO2 replaces the water?

Or maybe use a CO2 Header line with evacuated tubes plugged into it? (but gas isolated).


Indoors, your HX would be arranged so the heated CO2 would flow into
the top and out the bottom, as it was cooled..

Spring loaded Check-valves on the input and output of the indoor HX would allow the gas coming
into the HX to condense (as it lost heat) dropping it's pressure.
This pressure drop would cause the input check valve to cycle open
and allow more heated CO2 to enter the indoor HX.
The cycle would be repeated continuously (a pumping action).
The indoor HX could be a water tank or a liquid-to-air coil (with fan).


When compared to using water, what (if anything) would be gained by using such a system?

Maybe due to the weight of H2O, it couldn't self-pump?
Would the heat transfer rate be a lot higher, using CO2?

I'm wondering if this scheme would even work at all.
If it is possible, wouldn't it have been done by now?

At least there would be no worries of frozen pipes on cold nights..