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Insulating Greenhouse - Walls and Ground?

 
Posts: 7
Location: Upstate NY
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I've posted before about my greenhouse and it's issues (mainly that I didn't build it and it used to be for a commercial flower operation). After burning through way too much oil trying to heat it last winter (I'm in Upstate NY) I am set on making a few changes this summer so that next winter I don't have to do the same thing.

One thing I know I need to do is insulate the walls, but the ground inside the greenhouse is another matter. I have a barn full of recycled 3 inch foam insulation board that I am planning on using. Ideally I would build a frost skirt around the whole structure to insulate the inside ground from the frost on the outside. But I have a few issues that I'm going to run into: one of the walls of the greenhouse is on the edge of a pretty steep down slope, and on the other end is a chicken house and some pretty well established grape vines that I don't want to mess with.

I guess my question is for the downslope - if I lay insulation on top of this slope and then sort of backfill over it (I could only do a few inches though as there is another greenhouse down that slope about five feet away) - do you think that will provide enough protection from both the frost and the outside air (I will also be insulating up that wall)?

For the chicken house and grape vines I'm very puzzled. There is a wall and a door that section off that part of the greenhouse and I am planning on insulating those, but the ground is another thing. If I leave the ground uninsulated will I negate all the efforts of insulating everywhere else?

My one other thought is to chuck the frost skirt idea and just insulate the floor inside the greenhouse. I was planning on putting in raised beds anyway since the ground is gravel and I can't really plant things directly into that anyway.
Any thoughts or suggestions?
 
pollinator
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I think whatever you could do to insulate below-grade, ideally to below the frost line, would be of great advantage to you, especially if you manage to install a ground-sourced heat pump, whereby the hot air from the top of your system, instead of it being vented to the outside, is piped underground to give up its heat to the ground under your greenhouse, which is then released when the greenhouse becomes colder than the ground.

This can most easily be achieved with a length of weeping tile dropped into a trench running the length of your greenhouse and then filled back, hopefully with patio stones or poured concrete/rammed earth. One end of the weeping tile connects to a length of ductwork that, via fan, pushes air over a certain temperature from the peak of your greenhouse underground, and the other is capped with something critter-proof, to provide ventilation to the system.

This is a great tool because it couples with whatever systems are already in place for heating the structure.

-CK
 
steward
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Location: Northern WI (zone 4)
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I think the first question is how hot are you trying to keep it in winter?  If you frost protect the perimeter, you should have 45 degree heat bleeding up from the core of the earth to help you.  Plus a metric shit ton of thermal mass to store solar energy on nice days.  Insulating the floor loses both of those benefits.

Does snow pile up in the 5' space between the greenhouses?  If so, it probably does the insulating for you.  If not, burying the insulation a bit underground would still dramatically help.  Depending on how well a few inches of dirt will protect it from damage, chickens, etc...

Can you insulate the north walls of the greenhouse?  Maybe even the north roof and the east and west walls?  Your foundation is bleeding heat towards frozen ground (20-30 degrees?) while those walls are bleeding it to even colder air.

What kind of glazing do you have on it?
 
Rinna Hoffman
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That is a good point about the thermal mass I would be losing if I insulated on top of the ground inside. I think the frost skirt is the way to go.
The greenhouse is kind of shaped like a house with vertical walls and a sloped roof so I'm planning on insulating the vertical walls all the way around (especially since the greenhouse is not really facing south).
The glazing is double polyurethane and I'm trying to keep the temp above 45 or so in the winter.
 
Mike Jay
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Sweet, so double poly like on a hoop house or double rigid poly like a twin-wall product?  I guess it doesn't matter but if it's the two layers of film, do you have a blower to keep them inflated?
Depending on how the building faces the winter sun, you may get a lot of solar energy through the south wall.  Insulating that wall may or may not be as helpful as the others.
 
Rinna Hoffman
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I do have a blower for inflating the two layers of film - but I may have a few holes in the film so that is a whole other issue....
Yeah the South side is weird because it has the door and a giant furnace (commercial operation previously) on it. Maybe I will just insulate the lower half of the wall and make sure the door seals really well?
 
Mike Jay
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Don't you love it when they put the furnace on the side where the sunlight needs to come in?     My main thinking is that copious sunlight adds a lot of thermal energy to a greenhouse, probably more than you lose through the glazing at night.  So anywhere the sun comes through for at least half the day in winter, keep it uninsulated.  Everywhere else, cover it up since you lose more than you gain for those surfaces.

Leaks are important too, especially if it's windy outside.
 
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