Thursday, November 18, 2010

360 degree sunbox for Finland

17 Nov '10: I have had an interesting conversation on Navitron Forum with Sami, who lives in central Finland, and has a problem with very deeply chilled deep borehole - 210 metres deep serving his ground source heat pump. It is getting well below freezing every winter. His part of the world has no sunshine at all from November to February, but during the summer he has virtually 24 hour sunshine - with very low Solar Altitude angles coming from a 270 degree sweeping Azimuth this is a real challenge.
   With such a short summer and such shallow angles, how can solar heat get deep down when the ground a metre below the surface has been frozen for months? - and most of that solar heat is used in overcoming the thermal load of thawing that frost.
  There is this very short summer season, so there is a short time to pack a lot of heat down below, so a highly efficient device is needed that can work from 2am to 10pm!

  This design idea is scalable - for a small installation it could be say, 1 metre high, but it could equally be twice as big or more in every direction (i.e. eight times bigger). The central element would have to be black and cylindrical cluster of pipes carrying glycol, and the shape of the square box would be rotated at 45ยบ to north, so that the NE and NW faces get direct sunshine. Every face is surrounded by large bright mirror finish metal, so that there is maximum harvesting of the sunshine, even at very low angles.
  In this model, the central black cylinder could be larger. The whole thing is scalable, and it would be great to build a prototype. As I have found, it can do no harm to defrost one's borehole, even if the direct efficiency increase can take 2-3 years to measure numerically.

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