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Passive Greenhouse

 
Posts: 16
Location: NW Arkansas
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I have been working on this greenhouse for over 3 years. I am getting close to finishing it, that is why I have been asking questions.  I hate to reinvent the wheel so have been looking people who have built one and can tell what they would have done different.

Right now I am putting vents and going to using passive openers. Has anyone built a vent?  looking at was not to loss a lot of heat.

south-side-greenhouse.jpg
south side greenhouse
south side greenhouse
North-side-greenhouse.jpg
North side greenhouse
North side greenhouse
 
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Location: Northern WI (zone 4)
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Hi Douglas, nice greenhouse!

I put huge vents on the insulated north wall of my greenhouse so that I didn't have to penetrate the glazing side.  I make mine 4'x8' and the frame is a 2x4 (or possibly cut down 2x6).  Inside that is 4" of polyiso insulation.  On the outside is metal roofing, the inside is exposed.  The metal roofing is 4+ inches long so that it overlaps well onto the roof below.  The outer edges of the polyiso are foil taped to the 2x4s so that any condensation on the polyiso runs out past the 2x4s.  I also made a small drip edge and taped that onto the 2x4 and pinched it down with the metal roofing.  

They're attached with standard door hinges.  Once I had them in place, I attached 1x1 cleats around the inside for it to rest on (instead of the metal roofing).  Between the cleats and the vent is weatherstripping which does a decent job of sealing.

I used Gigavent openers and they can handle the weight (luckily).

Issues:
Rain gets in when it's blowing from the side
Weatherstripping which says it's self adhesive on one side and waxy on the other side apparently changes its mind and sticks to both surfaces after a couple months.  Now I have to wax the weatherstripping if I want the vents to be able to open.

Here's a link to my greenhouse build about the time I was installing the vents:
https://permies.com/t/200/76165/Mike-passive-solar-greenhouse-design#751925
 
Douglas Cole
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Mike great post.  Great greenhouse how is it working?  I didn't read the whole post yet, but will.  What part of the country are you at?

Doug
 
Mike Haasl
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Thanks!  it's working ok.  I'm in northern WI so I have a bit more cold to deal with than you (I think).  It seems to hold about 25 degrees above the outside nightly low without any heat.  My compost heat plan isn't working so I'm researching another option.  Last winter on the coldest morning (-29F) it was +20F inside.
 
Douglas Cole
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Mike that is not a bad temp deferential -29 to +20.  Are you using only the 1 tote and 7 barrels as a thermal mass?
 
Mike Haasl
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Yup, that's about all the liquid thermal mass.  The compost bin has about 6-8 cubic yards of wood chips that have some mass to them and the ground and structure of the greenhouse are additional mass.
 
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If you want to have some things stay alive through the summer in there, you might want to have a way to open the ends completely or even remove some of the glazing from the front. That's my experience from years of living with and loving a greenhouse.
 
Douglas Cole
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Mike I got time to finish your post a year ago about building your greenhouse.  I like the look of it.  How did your movable insolation work?  

 
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I haven’t done it but Lodgson in his Food from Water book talks about a couple who put a small pond in their greenhouse as a heat sink. In VT if I remember correctly. Always appealed to me, a place for fish Helping veggies grow and stay warm.

I’ll see if I can find the exact  reference if you want.
 
Mike Haasl
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The moveable insulation works well IF there isn't snow sitting up at the ridge pressing the poly layers together.  I'm planning on drilling holes in the bottom so I can replace the weighted washer system with a spring loaded pulling system from below (retractable clothsline system).

If it was a steeper glazing angle or the gap between the layers was greater or the outer layer of poly didn't sag and touch the inner layer it would be better yet.
 
Douglas Cole
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Jennie thanks that would be great.

Mike do you have a photo of the movable insulation system you have?
 
Mike Haasl
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Here's a bit further along in that thread where there's a picture of the drive mechanism and you can see the bubble wrap at the top (white).  
 
Douglas Cole
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Mike OK I had a dumb minute there on your treated.  I did not realize you had 9 pages, so I have not read the whole thing yet.  GREAT greenhouse by the way, only hope mine turns out half as nice.  

I see the how the insulation rolls up, but is it track of some kind between the plastic?  
 
Mike Haasl
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No problem, it takes a little while to learn the nuances of the forum.   No track, other than the spacers along each rib that keep the layers apart.  The bubble wrap is probably 3/4" narrower than the width of the space it's traveling in.

For Arkansas I doubt you'd need such a system.  Just a well insulated solar oriented greenhouse should keep you warm enough.  I think...
 
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Mike Haasl wrote:For Arkansas I doubt you'd need such a system.  Just a well insulated solar oriented greenhouse should keep you warm enough.  I think...


My passive solar greenhouse in Utah runs between 9 and 15 degrees above the outside temperature during the winter (the higher difference is when it's the coldest). Waterwall, 2 55 gallon barrels, 9x11 interior, built into a hill on the north. No additional insulation inside. The structure is very different, but with Arkansas weather you should be able to do at least that.

Measured inside temperature this morning was 35, 21 degrees outside.
 
Jennie Little
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Douglas Cole wrote:Jennie thanks that would be great.

I’m on my tablet, so this is going to be short and probably full of typos!

It’s pages 280-2 in my copy of the book.

“What Bob and Ellie Huke are doing in their Vermont backyard is an almost perfect example of homestead fish production. In a greenhouse they built, which is heated only by the sun, the Hukes are raising catfish in summer, trout in winter, and fresh vegetables 9 months a year. The sun provides the heat that grows the vegetables. The tank of water in the center of the greenhouse acts as a heat sink, releasing the stored warmth at night and on cloudy days, while keeping water temperatures high enough in winter so the trout remain active. The fish, in turn, enrich the water with their wastes, and the water can be used to irrigate and fertilize the vegebles.

The greenhouse is a two-frequency geodesic dome, shaped roughy like a hemisphere, with a diameter of 17 1/2 feet on the ground. The enclosure provides about 225 square feet of soil surface under cover. The dome is set on 12 cedar posts that anchor it in place. Around the outer perimeter, 3” thick sheets of foam insulation extend 4’ into the ground. This insulation prevents winter loss of soil heat to the frozen ground outside.

(I skipped a description of the dome.)

The tank measures 6 x 12’ on the sides and is 34” deep, — actually the bottom half of a prefab, concrete, 2000-gallon septic tank.”

There’s another paragraph or two, but I think this is the important stuff.
 
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