Frank, > The problem is getting this heat into a storage tank passively. The hot water tank would have to be mounted higher than the hose. I would like to employ the ordinary basement hot water tank. Hot water rises and will not go down to the basement tank.
Here is an idea for a system where a hot liquid can be engineered to fall, once it has been heated - and be replaced by a colder stream of the same liquid which will rise in a closed loop; within a magnetic field - so that you can keep the storage tank in the basement and put the hose on the roof. It would employ a magnetic slurry - not unlike "ferrofluid" but made with a ferromagnetic nanopowder which has a low Curie point. A few low-chrome stainless alloys would be fine for this - Curie temp around 100C. There would be a vertical magnetized iron pipe with the highest field gradient on the roof. Convection and magnetism work together on the upside. Once the ferrofluid is heated on the roof above its Curie point, it should have a tendency to be replaced by cooler fluid from below which is attracted by the magnetic gradient. Would it work? Not sure, and it would require a lot of nanopowder to try. After writing this, I did a quick search to see if anyone had thought of this before - and yes, others have come up with similar ideas. Here is an essay which is not exactly the same thing, but with some relevant citations http://www.freewebs.com/sunilphdstudents1234/Pavan%20Kumar%20Bharti/6a.pdf
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