greenhouse condensation

Discussion in 'HortForum' started by April S, Dec 3, 2009.

  1. April S

    April S Member

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    Location:
    Gabriola Island BC
    I wonder if anyone could suggest how I might reduce the condensation/humidity in my small greenhouse. It is 8'x10', cedar-framed with insulated kneewalls and the glazing is plexiglass verticals and dual-walled polycarbonate for the roof sections. I stapled 6 mil plastic over the glazed areas for the winter. The condensation was really bad before I did that a few weeks ago and now the condensation is building up on the inside of the plastic. I would like to try keeping the temperature at a minimum of 10 degrees C. and am using a small heater with a fan for that purpose. The humidity has been between 60-70% if my hygrometer is accurate. Yesterday I opened the door for an hour but that didn't have any noticeable effect. This afternoon I did that again, this time with a fan blowing outwards. When I checked after an hour, the humidity was up to 80%. Now that the door is closed again and the heater on, it is down to 72%. FYI, the temperature outside here has been above zero; last night there was a frost.

    So is there anything I can do to reduce the condensation? Any suggestions gratefully received!

    April
     
  2. April S

    April S Member

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    Well I didn't get a single response, but... for who knows what reason, the condensation problem is receding. I'll go for that! Now I just have to deal with the fact that I am coming to realize that there isn't a whole lot of point in keeping a greenhouse on Gabriola BC at 10 degrees C in December because there isn't a whole lot of anything that is going to go on. So I have modified my plan to try to keeping it a few degrees above freezing for the next month. (I'm trying to be ecologically responsible and also mind my hydro bills.) The heater that I have seems to do better at keeping it at 10 than at 3-5 C. I have it on a timer at the moment. Today I had it off for 15 minutes out of every hour. But with a low of -6 C forecast for tonight, I'll leave it on all night at 600 watts. It's all learning.

    April
     
  3. Dunc

    Dunc Active Member

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    Port Alberni B.C. Canada
    April, our relative humidity around here and there, is somewhere between 90-100% at this time of the year. The only way to lower it is to use a dehumidifier or an evaporater and exhaust it. We do live in a rain forest, although humid not warm. Just live with it.
     
  4. soccerdad

    soccerdad Active Member 10 Years

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    In my small greenhouse here on the west side of vancouver the relative humidity gets as high as 60% on rare occassions but right now is running at 35%. I would love to get it higher!
     
  5. April S

    April S Member

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    Well actually, with respect, Dunc, my hydrometer is reading about 38% outside right now. Don't know how accurate it is, but it isn't anywhere close to 90%. I think as it got colder the humidity both outside and inside my greenhouse has come down. I'll be interested to see what happens in the greenhouse when the temperatures outside warm up again (I mean to above zero). Soccerdad, I wish I could send you some! It has been down just under 70 for the past few days. At the moment it is reading 67% in the greenhouse but what really pleases me is that the plastic is no longer dripping condensation from above. Who knows what the future holds! Thank you for the responses.

    April
     
  6. Patrick Thirkell

    Patrick Thirkell Member

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    There is some hi tech anti condensation plastic film for polytunnels, maybe some google research would find some. A big problem is rot, algae, fungi, slime moulds and bacteria if left to sit.
     
  7. April S

    April S Member

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    Thank you, Patrick. This is not something I've come across. I'll check it out.

    April
     
  8. soccerdad

    soccerdad Active Member 10 Years

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    Isn't it just a case that (a) the warm air inside the greenhouse hits the cold - because one side of it is exposed to the cold outside air - plastic, and necessarily falls in temperature; (b) because colder air holds less water than warmer air the air can no longer hold as much water as it used to hold and (c) the amount that it holds might now exceed its holding ability and (d) so some of the water condenses on the inside of the plastic?

    Clearly this process depends on the outside temp, the inside temp (or maybe just the difference between them?) and the inside humidity, but I can't see how the material or its coating could affect anything.

    The plastic might of course have a "slippery coating" so that the water runs off the plastic as soon as it condenses out of the air ...

    Any engineers or physicists out there have a different view? I haven't stidied this stuff since 1974 ...
     
  9. bob 2

    bob 2 Active Member

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    Plastics can also have an anti-condensation (AC) coating, which reduces the amount of water vapor that accumulates on interior glazing surfaces. There are several benefits to decreased water droplet formation on plastics. For example, fewer water droplets fall on crops below (keeping the foliage dryer and preventing damage to young plants) and less light is blocked compared to a plastic film covered with water droplets. An AC coating enables water to condense as a thin layer, not as droplets. To work properly, the film must be installed so that the water can flow without interruption down to the edge of the film.

    http://www.onhort.com/Installing-Infrared-Polyethylene-Film-to-Save-Energy-article9450
     
  10. soccerdad

    soccerdad Active Member 10 Years

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    Interesting. I see from a search that anti condensation coatings work by absorbing water so that although it does condense out on the inner surface - which cannot be prevented - it is immediately absorbed by the coating, whereas anti condensation plastic is just treated so as to be slippery and thus the condensation does not form droplets and instead runs off right away. Physics dictates that condensation will occur, but technology tries to eliminate its effects.
     
  11. bob 2

    bob 2 Active Member

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    Probably no more than a durable surfactant but properly marketed it becomes more than itself.
    A similar chemical is used in dishwashers and refered to in that instance as a "sheeting action"

    Small world.
     

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