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passive solar greenhouse ventilation

 
Posts: 22
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I am new here so sorry in advace if I posted this wrong.  I am building a passive solar greenhosue with a earth battery.  I am looking a ventalion system that wont lost heat when not in use.  What are you guys using?  
 
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Hi Douglas, welcome to Permies!  I'm using a series of vents along the ridge and along base of the south wall on my greenhouse.  Some of them open with automatic openers, others I just prop open.  When they're closed, their weight keeps them shut and weatherstripping keeps them somewhat sealed.
 
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My greenhouse is attached to my earthen house, so it's also like an earth battery I guess.

I live in the high desert, with very cold winters but sunny most of the year, so in the summer it would overheat terribly if left to its own devices. I have a window at one end and a door at the other, as well as windows and doors on the north side into the house. So when I want the heat in the house, I open the doors into the house. In the shoulder seasons, ie fall and spring, I open the door and window at both ends for ventilation during the day whenever it seems likely to get too hot. In early fall and late spring, I leave those open day and night. For summer we take the plastic glazing right off, fold it up and store it away.  Last year we put the plastic up on 15th October and removed it in mid-April. Mid-Oct worked perfectly (tomatoes and other things didn't freeze in the greenhouse space before that even though they were open to the sky till then), but mid-April was too early, and my warm weather seeds didn't germinate until June. Every year the weather is slightly different.

Eliot Coleman says that a ratio of about 1:7 end:length ratio is good for ventilation, if you can remove the ends of a greenhouse for the summer. In my climate I think that might still get too hot in summer and cook the plants.

This window is not large enough to ventilate well, and at first I couldn't close it because the cat needed it as a door. Later I made a different cat door down at ground level and nailed plywood over the window.
attached-greenhouse-november-with-window-as-cat-door.jpg
Attached greenhouse with too-small window (used as a cat-door)
This window is not large enough to ventilate well, and I couldn't close it because the cat needed it as a door.
2018Oct-stone-raised-bed-before-greenhouse-was-covered-for-winter.jpg
Stone raised bed in an an attached greenhouse with glazing removed
October before the plastic was installed
 
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Automatic vent openers they do not have to be electric. This type opens due to expansion when heated. The word I was looking up for you was "bimetal greenhouse vent openers" there are a lot of them around. Bimetal Vent opener at Lowes.

These are what people mean here when they say "automatic openers" not some electrical device on a timer system.

:D
 
Douglas Cole
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Thanks for the info.  I got an openner that opens at 70 to 90 degrees.  If I put vent on south wall at the bottom what temp should it be to open.
 
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Can you put the opener on the upper vent?  Mine opens around 90 degrees (up at the ceiling) so the greenhouse down at floor level stays in the 80s.  The lower vents stay open so air only moves through the greenhouse when the upper vents open up.
 
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I've been looking for an automatic (no power required: work on bi-metal principles, or else solar powered) vent opener for my little greenhouse. I've found articles saying which ones are best rated, but then when I look at them on (sorry) Amazon, I find they are, in fact, not that well rated. Do any of you have recommendations for ones that do what they say and are long lived?
 
Mike Haasl
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Mine works great but it's the biggest one they make so it probably won't work for your application...  It's called a gigavent.

And I think most of them work on a wax filled cylinder principle.  Heating up expands the wax and pushes out the cylinder.
 
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Does it need to be passive? If you have one of those drier vents with flaps and a solar powered fan you're good to go. Sun is shining? Ventilation. No sun? No ventilation.
 
Barbara Kochan
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Johan Thorbecke wrote:Does it need to be passive? If you have one of those drier vents with flaps and a solar powered fan you're good to go. Sun is shining? Ventilation. No sun? No ventilation.


That's an interesting possiblity, but i still want it to kick in at a certain temperature, say 75 F ... do you know of a solar powered fan that does that? Or just start if the sun is shining? Thank you
 
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