Welcome to OrchidsForum.com. We are a friendly online community for Orchid Growers all over the world. If you haven't joined yet we invite you to register and join our community. Hope to see you on our forums!

Vacuum based greenhouse insulation

Discussion in 'Everything Else Orchid' started by Chris, Jul 8, 2009.

  1. Chris

    Chris New Member

    Messages:
    1,479
    Likes Received:
    17
    Location:
    Austin, TX
    So, I work with thousands of gallons of liquid nitrogen and argon. The boiling points of these two liquids is -320 F and -300 F, respectively. So in order to keep them liquid, we have to keep them isolated from all forms of heat transfer from the outside environment to the liquid. In order to do this, we use cryotanks. Cryotanks utilize the best form of passive insulation known, vacuum. They isolate the liquid in an interior vessel, separated from the exterior vessel by an evacuated space.

    I was wondering, has anyone tried to make a double layer-skin for a greenhouse with an internal void? The internal void could be plumbed via bulkhead to a rotary vane pump to maintain vacuum. Such a configuration, in theory, would be the best means of insulating a greenhouse against sensible heat transfer from inside the house to the outside environment during the winter.
     
  2. Mary Jane

    Mary Jane New Member

    Messages:
    4,342
    Likes Received:
    15
    Location:
    Duluth, Georgia USA
    Session beer, eh?
     
  3. Forrest

    Forrest Really Neat

    Messages:
    2,300
    Likes Received:
    26
    Location:
    Northern California
    very practical
     
  4. Jon

    Jon Mmmm... bulbophyllum...

    Messages:
    4,437
    Likes Received:
    102
    Location:
    Denver CO, USA
    Seems like a solution to a problem, but it kinda seems like overkill. I mean, I understand the premise, but it would likely be cost-prohibitive. Just the design alone would probably cost more than a few years' heating. The mechanics of it would be pretty expensive as well.
     
  5. abaxter

    abaxter New Member

    Messages:
    499
    Likes Received:
    3
    Location:
    6B Southeast KY
    I have three dead air spaces in my gh walls and roof...one dead air space is 6" and
    the other is 2". It works quite well. Of course, there ain't no vacuum. The cost of
    construction was very reasonable, but the doing was a bit of hassle.
     
  6. abaxter

    abaxter New Member

    Messages:
    499
    Likes Received:
    3
    Location:
    6B Southeast KY
    Excuse please. Two dead air spaces...sheesh!
     
  7. mrbreeze

    mrbreeze Anglican Supporting Member

    Messages:
    1,362
    Likes Received:
    35
    Location:
    Oklahoma
    Nature abhors a vacuum.
    Don't mess with Mother Nature!

    (angs are awesome) (#13)
     
  8. Chris

    Chris New Member

    Messages:
    1,479
    Likes Received:
    17
    Location:
    Austin, TX
    Agreed. The mechanics of it are simple, actually, old working rotary vane pumps are a dime a dozen in university physics and chemistry departments, and that's really all you need. The nightmare I think would be building the skin with a void in between that is propped apart to keep the inner and outer wall from touching when under vacuum.
     
  9. abaxter

    abaxter New Member

    Messages:
    499
    Likes Received:
    3
    Location:
    6B Southeast KY
    Why would the inner and outer walls touch when under vacuum? I don't quite understand that.
     
  10. Chris

    Chris New Member

    Messages:
    1,479
    Likes Received:
    17
    Location:
    Austin, TX
    What happens when you suck all the air out of a ziploc bag?
     
  11. Clark

    Clark Gator Member

    Messages:
    1,297
    Likes Received:
    37
    Location:
    The Gator Nation
    Why not use twin or triple wall polycarbonate sheets, its rigid and should not collapse. It is readily available. But then again, using two sheets of uv treated polyethylene, with a fan blown air pocket works great for me.
     
  12. Ray

    Ray Orchid Iconoclast Supporting Member

    Messages:
    1,657
    Likes Received:
    475
    Location:
    Oak Island NC
    With insulation of any kind, the trick is to interrupt the energy conductivity path. When going from a single-layer- to a double-layer, inflated polyethylene cover, you've gone from
    1. pass it through the plastic
    to
    1. pass it through the plastic
    2. pass it through the air pocket
    3. pass it through the plastic
    With bubble-wrap pasted to the inside, or the use of multiwall polycarbonate, it's the same thing.

    Chris is absolutely correct that a vacuum is the best insulation against heat conduction - if there ain't nuthin' to conduct the heat to, no heat will go! Unfortunately, the mechanical engineering behind designing a transparent, yet rigid window seems prohibitive.

    With Dewar flasks (thermos bottles) the "envelope" is glass that is evacuated then sealed. Using plastic won't work well, because polymers are actually porous, so you'd have to continuously or repeatedly pump it down, which would have an impact on the energy savings...

    About the only thing I could think of would be a bunch of sealed, evacuated glass tubes lined up side-by-side, enclosed on both sides by glass sheets for protection and cleaning. Trying to vacuum-seal the whole thing is essentially impossible, as the sealants used are polymers. Even the best thermopane windows are filled with argon (a very low-conductivity gas), rather than evacuated, for that reason.

    However, imagine what such a greenhouse panel would weigh, and what kind of structure you'd have to build to support it!
     
  13. mrbreeze

    mrbreeze Anglican Supporting Member

    Messages:
    1,362
    Likes Received:
    35
    Location:
    Oklahoma
    Putting aside the problem of having anything touching the walls of the vac chamber and thus becoming conducters, what if the space was filled with a highly porous yet structurally rigid media such as expanded foam, limestone, swiss cheese, or even leca pellets?

    Obviously those wouldn't let light through which would defeat the purpose (unless one was only using artificial light), but what would it do to the vacuum? Does a true vacuum have to be empty space? Like if there was a stray rock or piece of fluff within the void space of a thermos, would that screw it up? (I got D's in physics...)

    Maybe it could be done on a micro scale whereby the void space is very small/thin, and the walls could be seperated by some kind of plastic matrix. Kinda like bubble wrap but having one continuous void space. Does the thickness of the vacuum barrier have any impact on its ability to resist the passage of heat?

    Is this about orchids??? :D
     
  14. Dave

    Dave Active Member Supporting Member

    Messages:
    663
    Likes Received:
    169
    Location:
    Northern CA
  15. Ray

    Ray Orchid Iconoclast Supporting Member

    Messages:
    1,657
    Likes Received:
    475
    Location:
    Oak Island NC
    Ed Merkle tried that in regular paint and claimed he saw savings. I don't remember where that discussion is posted....

    In another vein, when I was active in the ceramics field, we played with silica xerogels, which were mostly transparent, but still had amazing insulating properties. wedged in between two layers of thin glass, it could be a "go" (exccept of course for the cost).
     
  16. EdM

    EdM Member in Good Standing

    Messages:
    201
    Likes Received:
    46
    Location:
    Nashville, Tennessee
    Right, Ray. I used a product to insulate a steel shipping container against summer heat and its worked perfectly. We are painting the interior of our home this summer using the same product. See: Hytechsales.com Its their ceramic additive that you add to virtually any paint, stain, or liquid coating. It may work as an additive to clear resin, at least it would give some insulative value. Two coats of paint with the additive is supposed to provide an R20 insulative value. Three or four coats adds additional insulation. I've not done any testing with a clear-coat resin, but according to their website, adding the ceramic additive to clear-coat gives it a faint "milky" look to it.