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designing a passive 4-season minnesota greenhouse with PAHS/AGS principles

 
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This is sort of a stub, I wanted to refer to something I just wrote which mentions it in passing, to allow follow comments on just the GREENHOUSE section to go here.

https://permies.com/t/103389/PAHS-AGS-style-heating-cooling

My first physical construction may not be the greenhouse, but I don't plan to wait for the workshop/shed to be fully verified working before starting construction on a small experimental greenhouse as well, which attempts to use some of the principles of passive annualized heat storage and annualized geo solar, along with a desire to implement moveable insulation paneling so that growing in the winter is a less burdensome affair.

The specific plan for the greenhouse would be to have a building which is part greenhouse, think something like a small steel arch building, and then adding some kind of clear arches the same radius on one side of it on the sun-dominant side, and have some kind of moveable insulation panel inside the outer clear arch which can move into place when solar gain is no longer happening.  I would like to combine this with PAHS/AGS style thermocoupled to an insulated dry ground area meant to serve as a thermal mass to considerably stabilize temperature although it need not be as rigorously controlled as areas for human habitation.  The reason for having it attached to the steel building is I can't think of a convenient way to have a moveable insulation arch move in and out of a pure clear greenhouse without blocking half of it.    So the other 'half' is just inside the steel arch building when not in use and the two structures are basically attached to one another, though there is also insulation between them to isolate the greenhouse temperature from the workshop/storage area.
 
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So are you thinking that the insulation arch part would move as a monolithic shape to cover the south side of the greenhouse?  Kind of like the buffet covers over the scrambled eggs at the continental breakfast in a hotel?
 
Brian Shaw
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Mike Jay wrote:So are you thinking that the insulation arch part would move as a monolithic shape to cover the south side of the greenhouse?  Kind of like the buffet covers over the scrambled eggs at the continental breakfast in a hotel?



Something like that.  :)  Having an arched steel frame containing the styrofoam panels, which doesn't have to be a very strong frame as styrofoam is light and it's indoors so not bearing any loads other than weight, and some kind of a track system at ground level so it can roll back and forth.

There would be an air gap between the flat pieces of styrofoam and the outer arched clear greenhouse shell - but this shouldn't matter by what I can tell because i've only separated the wind/rain/protective surface from the insulation and even airflow in the area between clear and styrofoam shouldn't matter PROVIDED that I have things relatively air sealed under this. (ie there isnt just a draft blowing around it)  This is my solution to a problem that seems to have plagued many greenhouse builders of letting the sun in when it shines without letting the heat out - i've seen systems involving soap bubbles (cool admittedly, and i'd try that too if it worked tho it clearly requires a double layer) and i've wanted to possibly play around with mirror concentrators (beaming in through a physically smaller slot so that you have higher solar gain for the exposed area of thermal loss/also saving on cost and fragility since you could have double panes or better more affordably if it's not covering the entire exterior) but my initial first experiments I wanted to do with the slide in insulation layer.  I think moveable insulation is a seriously underappreciated strategy esp for something to grow in the winter.  :)
 
Mike Jay
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Yes, moveable insulation that works and is automated would probably be the biggest thing for greenhouses since sliced bread.  I saw a cool greenhouse design in Michigan where they built a huge A frame greenhouse.  It was something like an equilateral triangle 40 feet to a side.  The whole south side was glazing.  Attached to the north side was an insulated "floor" that was hinged about 8' off the ground.  At night the "floor" would be lowered down until it was horizontal (8' off the ground) and reached from the south angled side to the north angled side.  So basically the whole triangular portion from 8' to 30ish feet off the ground was only in use during the day as a solar collector.  Then at night the pivoting insulated floor closed off most of that heat loss and they only had to deal with the losses through the 8' high south wall.  I don't remember but they certainly could have had 5 wall polycarbonate glazing down low for good insulation and cheaper stuff up high for more solar gain.

It was big enough they could run a tractor in it.  But it was also huge...  And I don't know how they didn't cook their plants on sunny winter days...
 
Brian Shaw
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Mike Jay wrote:Yes, moveable insulation that works and is automated would probably be the biggest thing for greenhouses since sliced bread.  I saw a cool greenhouse design in Michigan where they built a huge A frame greenhouse.  It was something like an equilateral triangle 40 feet to a side.  The whole south side was glazing.  Attached to the north side was an insulated "floor" that was hinged about 8' off the ground.  At night the "floor" would be lowered down until it was horizontal (8' off the ground) and reached from the south angled side to the north angled side.  So basically the whole triangular portion from 8' to 30ish feet off the ground was only in use during the day as a solar collector.  Then at night the pivoting insulated floor closed off most of that heat loss and they only had to deal with the losses through the 8' high south wall.  I don't remember but they certainly could have had 5 wall polycarbonate glazing down low for good insulation and cheaper stuff up high for more solar gain.

It was big enough they could run a tractor in it.  But it was also huge...  And I don't know how they didn't cook their plants on sunny winter days...



Could you make a sketch?  For some reason i'm having difficulty mentally extrapolating that right now.  :^)

Also it might even be possible to automate it using something similar to how freon trackers work with solar collectors - you could literally have the sun potentially pressurize a system to slide the insulation frame out on some well greased rails - once the solar radiance level raised above a designed level (ideally variable level based upon temperature) the freon turns to a gas and would push the pistons out.  Upon a notable drop of irradiance, even from say severe clouds, it would retract.  

It may not be super cost effective/an Arduino and electrical motors making it move is probably my first design. :) Just pointing out there is a totally automateable way without electronics as well.


I've wanted to do "sliding arches" for other reasons too including physical protection.  Hail storm on the way?  Gale force winds?  An OUTER shell of something protective (could even just be canvas but tough canvas meant to take the impact or forces) slides over the greenhouse so you arent replacing thousands of dollars of glazing.  This also lets you not have to overdesign the initial greenhouse to take abnormal forces since the idea is the physical protection would kick in under those circumstances - and in areas of snow like me i'd try to have the entire greenhouse and the outer tracks raised up eight feet or whatever is above the common drifting snow heights in the area.  This would mean falling snow would only fall on a rail which should be easy to clean with a scraper ahead of the protective arch instead of trying to dredge through built up snow if you aren't there to maintain it.  :)

I'm wanting to use styrofoam because it's one of the lighter insulations I can think of also available reclaimed secondhand very affordably, and if the 'frame' had to withstand outside forces it would have to be alot heavier - having it slide inside the greenhouse envelope lets it get as light as possible.  Even if I were to have something like the 'soap bubble insulation between layers' https://www.youtube.com/watch?v=3D516P0UYik http://smallfarms.cornell.edu/2011/10/03/soap-bubbles-to-insulate-greenhouses-a-new-approach-to-energy-conservation/ I would stlil want to consider engineering a protective outer arch layer like I mentioned above, so one way or another i'm still engineering a sliding rail system and frame of some sort.  :^)  

For me it's a MUST to have four seasons growing even though i'm in minnesota (this is part of a lifelong quest for sustainability and self sufficiency that can be copied by others and I hope it will work even further north/personally i'd like to know how to grow oranges above the arctic circle if I could), and the method of above ground insulation could be my arch, or the bubbles, or if anyone has any other cool ideas i'm game too - but in addition to the insulated upper layer, I want to use the annualized thermal mass strategy of PAHS/AGS to stabilize temperature.
 
Mike Jay
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Here's a very poor sketch of what they did.  The hinged floor was actually hinged again so that it could move into position without interfering with the south side.

The brown is the insulated north side (possibly only insulated for the bottom 8 feet).  The left side is glazing facing south.  I doubled it up in the lower part for nighttime insulation (twin or 5 wall polycarbonate?).  The black lines is the hinged moving floor in three positions (up, down and halfway).
MI-Greenhouse.png
[Thumbnail for MI-Greenhouse.png]
 
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