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Pentahedral Balloon Dome

Better insulation, and (maybe) self-supporting
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The main reason why people build greenhouses is to regulate the temperature of the air inside. Naturally, the best way to reduce the amount of energy needed to do this, is to make the greenhouse's "windows" out of some insulating material.

If the greenhouse is a dome (geodesic or otherwise), one not uncommon way of constructing the windows is to use pairs of sheets of ETFE, weld them together along the edge, and inflate the resulting balloon with some insulating gas.

Doing so, alas, produces a window which is well insulated in the middle (where the sheets bend outwards), and poorly insulated near the edges (where the sheets are welded together).

This idea addresses that problem, by making windows that are pentahedrons -- specifically, an inner triangle, an outer triangle, and three connecting trapezoids. Each window/balloon would closely resemble a triangular prism, except for the inner triangle being slightly smaller than the outer triangle, and the quadrilateral sides not being parallelograms.

As a possible added bonus, it might be possible to construct a dome out of such balloons without additional structural support... especially if we stiffen each balloon, by adding a tether between the middles of the inner and outer triangles.

To minimize the amount of welding that needs to be done at the construction site, the balloons would be factory assembled, and have their edges labeled to prevent mis-assembly.

For the truly impatient, the entire dome would be factory assembled, the balloons filled with liquid ethylidene fluoride, and the entire dome shoved into a pressure vessel before the liquid boils. The user would pull a cord on the outside of the canister, activating cordite which cuts apart the canister, after which the dome inflates as it sucks heat from the air.

goldbb, Mar 04 2010

Cordtex http://en.wikipedia.org/wiki/Cordtex
Entertainment on a roll .... just add detonators. [8th of 7, Mar 04 2010]

The kind of pentahedron I'm envisioning, sorta http://en.wikipedia...riangular_prism.png
Imagine this, but with the top and bottom two different sizes [goldbb, Mar 09 2010]

[link]






       Pic?
MaxwellBuchanan, Mar 04 2010
  

       Also, why not two domes, one slightly larger?
MaxwellBuchanan, Mar 04 2010
  

       You had us at cordite. [+]   

       Actually, we think you mean "Cordtex".   

       <link>
8th of 7, Mar 04 2010
  

       //Doing so, alas, produces a window which is well insulated in the middle (where the sheets bend outwards), and poorly insulated near the edges//   

       Is this really a problem? how much would you estimate your system would improve the insulation?
xaviergisz, Mar 04 2010
  

       30% of a bun for an interesting solution, 50% of a bun for an interesting problem, and 20% of a bun for explaining it successfully *without* an illustration (pace [MaxwellBuchanan])
mouseposture, Mar 04 2010
  

       (Pedant)Balloon. Otherwise [+]
DrWorm, Mar 04 2010
  

       /Also, why not two domes, one slightly larger?/   

       In a way, there already are two domes -- specifically, the inner (smaller) triangles make up one dome, and the outer (larger) triangles make up the other.   

       But if we *only* had two domes, *without* the quadrilateral pieces connecting the inner to the outer, the structure would have much less strength. In particular, strong winds would easily move the outer dome almost independent of the inner one, causing the two to press against one another at times, allowing heat to be conducted in or out.   

       8/7, you're quite right -- I should have said detonating cord (I don't have a brand preference, though).
goldbb, Mar 09 2010
  

       // *without* the quadrilateral pieces connecting the inner to the outer, the structure would have much less strength//   

       OK, so two concentric domes with tethers between them?
MaxwellBuchanan, Mar 09 2010
  

       Possibly because doing so would leave the resulting structure vulnerable to accidental punctuation. With this design, even if one section got ripped, the rest would remain intact and highly-insualting, and the single damaged section could easily be replaced.
gisho, Mar 09 2010
  

       Good point. OK, [+]
MaxwellBuchanan, Mar 09 2010
  

       Would it be possible to build this like an igloo without fixing the pieces in place, perhaps just having a tether from the top 'key stone'?   

       Edit: Actually, you'd need to hold at least some of the bottom pieces in place to stop them from moving outwards.
marklar, Mar 10 2010
  

       If you apply some velcro to the edges the whole thing could be assembled or repaired without tools.
Forthur, Mar 10 2010
  

       marklar, Sure, but only if there's no wind to blow the pieces away! :)   

       Forthur, For a structure meant to be frequently assembled and disassembled, Velcro (or, alternatively, toothed zippers) would be ok if air (and rain!) leakage from outside the outer dome to inside the inner dome is acceptable.   

       Toothless plastic zippers (like the ones on ziploc bags) would probably be a better choice, since they can be made almost airtight. Some air / rain will probably leak at the points where three zippered seams meet, but not nearly as much as if we used Velcro.   

       Of course, if one of the balloons gets punctured, you'll need a proper patch kit, not just Velcro, to fix it :)
goldbb, Mar 10 2010
  

       The Idea's last paragraph sounds very entertaining... as viewed from a distance... and upwind.
FlyingToaster, May 18 2016
  
      
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