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pollinator
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Regarding the double layer poly this video will answer most of the questions about the blower and how to make the 2 layers air tight and fastened so it won't blow away. Also overbuilding for ridged but the economics would never work out.  Also a flat north wall is much more practical than a curved one. The whole upper part of the north wall could be covered with black pipes with a solar panel to pump water into them and allow it to drain into storage tanks at night.
 
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I seen this via the Permies threads you didn't see email.

I am a materials person.  While I have built some things, I don't claim professional expertice in building stuff.

I have been considering something similar, but with "lab space" on the north wall.  I want to be able to culture and scale-up bacteria and fungi, and thought the north side of a greenhouse made sense for that.

I've seen a few licenses (CopyLeft ?) for OpenHardware.  I don't know if any are applicable to buildings.

If you are getting your "climate statistics" from the weather office, it is possible that data is not what you will be observing in 10 or more years time.

I think how much insulation you bury around the perimeter of your foundation is a function of where you are.  Both in terms of area and thickness.  Such a foundation where I live (56N - Dawson Creek, BC) would need more insulation than you "might".  The isotherms take a dive through Manitoba, Minnesota, Wisconsin, ....

Concrete is actually a pretty good conductor of heat (much more so than wood or most "other" polymers).  As such, the exposed exterior foundation and pony walls will transfer heat into (summer) and out of (winter) the structure.  This will result in a much larger temperature gradient between the wall/floor and the interior at the perimenter.  I have thought of putting layers of aluminum sheet down on top of the concrete (next to the walls), where the aluminum metal transports heat much better than the concrete to "level" the temperature gradients.  Does the much smaller gradient over a much larger area save on net heat movemnt?  If you use multiple sheets, the oxide thickness will increase over time, and you should see a decrease in effective contact area between sheets, which means better insulation with age.  Perhaps you have heat transfer tubing in part of the foundation "floor"?

Venting.  What I've thought about, is to have vent air come underneath the foundation in buried tubing from the north side, instead of draw it from the south exterior.  This buried venting should actually help in winter heating, as well as the expected summer cooling.  Perhaps build a solar chimney on the north wall to increase draft?

If a person calls glazing as glass or plastic, might you want many (5? 10?) thin (single sheet of thin plastic) glazings on the inside and maybe just a couple of substantial ones on the outside?  Coatings on the glazing?

You might want to tilt off E-W depending on local geometry.  For example, I live on a north facing slope, and the hill is taller to the west.  On the winter solstice I get more morning sun than afternoon sun (with direct illumination disappearing before 3pm?).

You want your buried insulation to have a slope to it, so that water percolating down through the soil "rolls" downhill and falls towards the centre of the Earth further away from your foundation.

It sounds like conventional pony wall construction (block and mortar).  I haven't yet built one, but I really like surface bonding of dry stacked block.  Especially for a wall which doesn't get that tall.  The cheap way to surface bond is also a mortar, with plastic fibres in it which go on both outside surface (inside and outside).  That is a commercial product, and USDA has data on using it for farm buildings.  An alternative is glass fabric/epoxy, which is going to be more expensive (at least double).  But, you end up with two membranes (the epoxy) that are near water proof and vapour proof.  To dry stack concrete block, you may need to insert shims, as the blocks are designed for the tolerances of mortar, not dry stacking.  Normal construction would be to "bed" the first layer of block on the foundation using mortar.  I've thought (not done work) of using "T" shaped (probably prepreg) glass/epoxy on the foundation/pony wall "join", but my thoughts assume that the pony wall abuts the outside edge of the foundation (good shear transfer from wall to foundation).  Could easily be holes in that idea.  Like wood, concrete is porous and will absorb epoxy.  So you need to look out for dry joints.  Exterior epoxy needs to be shielded from UV.  With epoxy on both surfaces, you can't fill the cores with "water".  Dry sand or dry gravel might be okay, but pouring in concrete could easily trap a whole bunch of water inside the blocks.  If you have enough epoxy around to bond the surfaces, you can have extra to prepare your truss interfaces.  I've no idea if there is established rules on this.

For avoiding thermal bridging (wood to concrete walls mostly I think), it is possible to find 0.25 inch thick aerogel strips that are sized for 2x construction.  That gives you R2.5 extra resistance just where the wood is.  I don't know what the price is, it probably isn't cheap.

Your compost bin - if you are doing glass/epoxy surface bonding of dry stacked concrete, the glass/epoxy also gives you a thick (if you use 6 ounce per square yard glass fabric, the epoxy will also be on the order of 6 ounce per square yard, actually more because the surface you are probably applying to is porous) membrane which is chemically stable and nearly moisture and vapour proof.

I've read about a bunch of phase change materials, but I have no idea on pricing.  There was a drywall product with phase change material in it?

If instead of propane auxilliary heating, you had natural gas auxilliary heating; could it also use compost off-gas (possibly contains a lot of methane).  Or does that have too much sulfur?

If you had acryllic/polycarbonate rods, you could mount LEDs at the end to pump light in.  And you sand the surface (scratch it) to get light out.  That might give you a way to distribute auxilliary lighting.

The two best white pigments are both titanium dioxides.  I think next best is a zinc oxide.  I believe all three are white quite a ways into the UV.  I don't remember how "white" they are into the infrared.  Some woods are almost transparent to infrared, and some (I believe) absorb quite strongly.

There was news recently, about D&T Farm of Japan and a Mongee (I think I spelled that correctly) bananas and something called a freeze-thaw awakening.  The best news article I found was at nekkei.com (spelling?).  The researcher's surname is Tanaka.  These bananas are very thin skinned, and are treated at -60C in some manner.  The plants also grow in 4 months to a height typicaly of a 2 year banana palm.

For summer cooling, having a radiator inside a solar chimney might work?

Seeing your comment about solex, you probably won't like glass/epoxy.

I think if you are going to pump air between two layers of plastic, that you need to condition the air.  It probably needs to be dry all year long.  What temperature it is with respect to inside the greenhouse and outdoors would probably need to be considered.

Not spell-checked (but then, I don't use autocorrect either).
 
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Thanks Hans, the video was good and it was fun to read through the comments that people put on there.  It seems like it would make more sense to use outside air to reduce the chances of condensation between the layers.  I also don't know why he has an outlet.  That would get at Mike P's concerns about pushing lots of air through the air gap and eliminating the static air against the film (which is where you get most of your R value).

I guess I don't see the insulation value of the blower as compared to using spacers to keep the two layers apart (and no blower).  I do see the advantage to the blower for film longevity and wind resistance.

I did see a plan to put a blower on a check valve so that once the layers are inflated, the fan turns off.  When the air leaks enough to drop the pressure, the fan kicks back on.  I wonder if there are other simple ways to create 1psi of pressure without a fan?  Simple windmill that pumps air?  

I will use wiggle wire, that stuff looks like it is better than sliced bread.

Now that I'm leaning away from the "triangle" at the top for solar gain, I do like the idea of a solar thermal collector high on the North wall.  

I'm not sure if a flat North wall is more practical than a curved one.  A flat one of that size would require some pretty big rafters.  Unless they're built with the truss technology that I'll use on the curved ones.  In that case it's just as easy to go curved.  I also like the curved since it gives more headroom on the North side and it allows the compost bunker to tuck out of the way farther.  I am planning on a relaxation deck on top of the compost which would also benefit from a curved wall.

Thanks Hans!
 
pollinator
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Mike Jay wrote:Thanks Hans, the video was good and it was fun to read through the comments that people put on there.  It seems like it would make more sense to use outside air to reduce the chances of condensation between the layers.  I also don't know why he has an outlet.  That would get at Mike P's concerns about pushing lots of air through the air gap and eliminating the static air against the film (which is where you get most of your R value).

I guess I don't see the insulation value of the blower as compared to using spacers to keep the two layers apart (and no blower).  I do see the advantage to the blower for film longevity and wind resistance.

I did see a plan to put a blower on a check valve so that once the layers are inflated, the fan turns off.  When the air leaks enough to drop the pressure, the fan kicks back on.  I wonder if there are other simple ways to create 1psi of pressure without a fan?  Simple windmill that pumps air?  



I spent a couple days reading everything I could find regarding the blower/insulation thing.  Without fail, people say it increases the R-value, and without fail, they don't give any real evidence of that.  I'm going to keep looking because now I'm curious as to whether it's just an old wives tale or if there is a reason, but it makes sense that having the layers not touching and with an air gap insulates better than if the plastic sagged and the layers touch.  As far as whether having the pump keeping the layers inflated is better than just making sure they don't touch, I haven't found anything conclusive yet.
 
Mike Jay
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Hi Gordon, thanks for joining in the discussion!

My climate statistics are based on observation for the past three years.  I'm going to design for what I'm experiencing now and hope it can handle whatever comes in the future.

Since I'm so far South of you, I can get by with less perimeter insulation.  I'm planning on R20 styrofoam that goes down a foot and then out 3 feet.  So it should handle our 4' frost depth.  And I was going to slope it as it gets farther from the foundation for drainage.  Good idea.

I may have forgotten to mention it but I will do 4" of styrofoam on the outside of the pony walls as well.  Now that I think about it, I may just do a 3 course wall so that it takes a 1/2 sheet of insulation to cover it.  I was planning on the surface bonding on dry stacked block but I was worried about them not sitting flat as you mention.  I hadn't thought about shims.  But now it's moot because a member of our homesteading club is a retired mason and is willing to host a workshop to do the block.  Yay!

Good thought about allowing ventilation air to enter from below grade.  I could lay 4" (or bigger) drain tile under the styrofoam skirt insulation and then route it into the greenhouse.  That should do the trick in the winter.  I'm not sure there'd be enough flow to handle all of the summer cooling but it would help.  Does anyone know how far a 4" or 6" black corrugated pipe needs to travel underground in order to transfer its heat/cold to the earth?  I'm sure it's a function of air speed so let's assume a pretty low flow (unless you have the math and we can do some calculations)

More glazing would definitely help with the R value but it would decrease the transparency of the glazing.  Each layer of poly is approximately a 10% loss.  So five layers would take you down to about 59% and 10 would drop it to 35%.  You mention conditioning the air if I blow it between the layers.  I was thinking about the winter when the air is so dry I shouldn't need to worry.  But in the summer that's a valid concern.  I'll have to noodle on that a bit.

Regarding the pony wall to footing alignment...  I was assuming the pony wall needed to be centered on the 1' wide footing.  Does anyone know if that is the case or could I shift the pony wall so its outer surface matches the outside of the footing? If I could do that and it wouldn't affect the strength of the pony wall, it would make insulating the outside of the wall and footing much easier.  Keep in mind there is some outward push from the rafters on that pony wall.  I'll have rebar embedded in the footing and running up the core of the blocks at each truss location.

For the wood to cement connections I was planning on using sill sealer foam insulation.  Primarily to keep the wood from rotting but it would also seal for leaks.  I was planning on having the trusses supported by post bases so they don't touch the cement.  But on the E and W sides I'd likely have a sill plate and more "standard" wall framing.  

While the compost will off gas something, I'm not sure what will be in there for sure.  Other than CO2.  So I'm not planning on using the gasses for anything but plant growth.  If there is too much methane or other harmful gasses I'd vent it outside.  If methane was being produced reliably enough, I'd consider using it for something.  But that's way down the road....

Interesting pigment info.  I was assuming any whitewash or white paint would work to reflect sunlight around.  Do you have a particular paint/pigment product that you'd recommend?

How would a radiator in a solar chimney help with summer cooling?  What would be in the radiator and/or where would that heat be sent?

Thanks Gordon!
 
Mike Jay
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Todd Parr wrote:I spent a couple days reading everything I could find regarding the blower/insulation thing.  Without fail, people say it increases the R-value, and without fail, they don't give any real evidence of that.  I'm going to keep looking



Thanks Todd!  
 
Mike Jay
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Mike Phillipps wrote:I'm reading this book at the moment:
http://ia800306.us.archive.org/30/items/fe_The_Solar_Greenhouse_Book/The_Solar_Greenhouse_Book.pdf


I just finished it.  That was a really good book!  I'm amazed at the data and charts they had in there.  I haven't seen anywhere near that sort of data in a newer book.  There are some good sections at the end too (after the attached greenhouse, pit greenhouse and cold frame parts).
 
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Hi Mike. I have the same design in mind , arched cabin design with compost heat at north side. The one difference is my foundation to sit on 2 gabian berms made with gabian baskets. Both for cost and thermal mass. Like to avoid cement and put charred posts right thru the gabian baskets to below frost line. Cross beams joined to posts. Gabians above ground maybe 2 feet sitting on 3 in of gravel.
 
Mike Jay
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Hi Andre, it sounds like great minds think alike  If I had any rocks on my property that would be a tempting option.  So the gabions will be below grade to your frost depth?  Will you insulate outside them?  Why do the charred posts need to go through the gabions?  Could you somehow just build off the top of the gabions to avoid any ground contact of wood?

If I could put a rock gabion in my greenhouse, I'd consider something in the aforementioned Solar Greenhouse Book about blowing hot air from the peak through the rock mass to store that thermal energy during sunny days.
 
Gordon Haverland
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Where I live, is called Zone 2b, but I suspect we are transitioning to Zone 3.  Which is why I figured you should use modern data.

I had run into mention of that tolerance issue on blocks a couple of years ago.    I ran into that idea about running ventilation pipe underground in some passive solar house construction stuff.  I think you want to run smooth wall pipe, to cut down on flow rate losses.  I don't remember seeing anyone do calculations on how far to transfer heat.

I can see where 90% transmission would not work on glazing.

I am pretty sure that civil engineers would want the wall in the middle of the footing.  Sort of like trying to balance on the edge of a surfboard, instead of in the middle.

If you are going to put a primer on before the white paint, epoxy primers are hard to beat.  But they don't stand up to UV.  Polyurethane is compatible with many UV agents, and so that is a good base for a "oil base" white paint.  I've used a PU white paint meant for boats on outdoor wood work, and that stayed quite cool on a hot summer day.

As I understand solar chimneys, they are black on the outside with the idea of further heating the air in the top of the chimney, increasing how fast it rises.  Which sucks air from down lower more.  If your radiator is near the bottom of the solar chimney, it will be seeing the coolest air entering the solar chimney, and heating it up a bit.  As the air continues to rise, the normal processes continue.  Has anyone done this before?  Not that I have read about.
 
Mike Jay
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Good point on smooth vs corrugated.  I was thinking corrugated to get maximum heat transfer.  But since there would be very little pressure moving the air, smooth may be better.  Good food for thought...

I've seen solar chimneys used to pull air out of an area.  I haven't seen them used to draw enough air to cool a radiator.  Unless someone comes up with a really slick way to have a chimney help my greenhouse, I think I'll let someone else run that experiment...  
 
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Hi Mike. Its the charred posts that will be below ground level. Not the gabian wall. Only to reduce any shifting of the gabians in frost heave. All wood exposed is charred as in Japanese method called shou sugi ban. To preserve the wood. Also post should go upside down in the ground where possible. As the tree naturally wicks water the other way. The gabians also serve to retain heat at night and wick or absorb heat in the day. They also collect moisture in condensation. All my Apple trees have good sized boulders beside them and grow 2 times faster then those without. Night heat seems to have this increased rate from the rock.
 
Gordon Haverland
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I ran across a PDF from UKentucky (AEN-10.pdf) dated 1973, which substantially agrees with some of the numbers you have put up Mike.

If we look at how an uncharged particle (such as a photon of light) interacts with matter, the problem is a differential equation where the solution is a decaying exponential.  A common way to use this, is to calculate a "half value thickness", and then for any particular material you divide the actual thickness by the half value thickness to find out how many "half values" it is thick.  You then raise 0.5 to that power, and that tells you the transmittance.  That is total transmittance, which will be partitioned into that bent by the refractive angle in question and the remainder which is diffusely scattered.  The half value thickness can be a function of energy (or wavelength or frequency).

However, I am not finding tabulations of this half value layer for this problem.  The original glazing was glass.  Polycarbonate (PC) is a common alternate material; Lexan is a trademarked name for a particular (family of) polycarbonates.  Polyethylene (PE) is a common sheet film material that is sometimes used.  There are a few other materials which could show up: polyester (possibly called Mylar (probably a Trademark)), PVC (polyvinyl chloride, possibly just called vinyl), urethane (or polyurethane - I've seen no data on specifics) and some fluorinated polymers: Tedlar, Tefzel and Teflon.

A typical sheet of PE transmits 80%-ish.  Back in 1973 (the UKy paper), the ultimate transmission for state of the art PE was 93%.  It might be higher now.  The expected values for the fluorinated polymers is about 95% and the expected values for PC, polyester and PVC are about 86%.  The fluorinated polymers are expensive, and what typically makes the most sense for them is to be a coating on something else.  These fluorinated polymers tend to have good UV properties, including UV degredation properties.

I've no idea whether DLC or ND can be found a coatings for PC or fibreglass.  DLC is daimond-like carbon and ND is nano-diamond.  Both would have good wear resistance.

The outer glazing of a greenhouse can be subject to: hail, tree branches, baseballs, wind and snow.  PC is considered a good material for an outermost glazing.  Its possible that it can be found coated.  It is apparently possible to find fluorinated coated fibreglass.  Fibreglass of this kind (optical purposes) probably doesn't have epoxy as the matrix, I would guess a polyester or vinyl ester is used.  Fibreglass would also be considered a good outermost material.  PVC is considered to have better wear resistance than most of the others (cleaning can be a wear exercise).  So having the innermost layer be PVC might make sense.

With a rigid outer glazing, and a wear resistant inner glazing, any other glazings between the two should have very few environmental forces acting on them, which means they can probably be quite thin.  Part of the object is to partition the space between the outermost and innermost into many sub-volumes, that do not have mass flow from one to the next.  Having looked at some acoustic problems before, it is possible that these inner glazings could even be perforated, and still work well.  The holes would need to be the right size.

The infrared transmission of these materials ranges from 10 or so percent up to 80% for typical film thicknesses.  So, even if they are optically transparent, they may not be IR transparent.

A nice thing about polyesters, which is why they are commonly found in the winter window sealing kits, is that after you "mount" them, you can bring a hair dryer towards them and gently heat them.  And they will shrink, to tighten up the film across the window.
 
Mike Jay
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Wow Gordon, that's a lot of science right there.  I haven't looked into actual films other than to see what the normal transmission amounts and prices are.  

Here's one I just found that has 91% transmission and lots of other good features: Thermal Anti-Condensate Film.  

Here's a cheaper version with the same transmission but fewer other features.  Standard Film  Maybe this could go on the outer layer and the fancy stuff on the inside?

Here's an article I just found that explains some of the options.  Choose the right plastic film.  I haven't looked really hard but I have not run across some of the fancier options the article mentions (scrim reinforced for instance).
 
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A while ago, I was looking at "clear" finishes for outdoor wood, and had run across HALS (Hindered Amine Light Stabilizers).  They apparently are not compatible with epoxy, so that was one reason why epoxies had lousy UV durability.  As products containing HALS are exposed to UV, the HALS does get used up.  At some point, there is no longer enough HALS to counteract the UV exciting the base polymer, and the product will then rapidly degrade.

In terms of anti-drip coatings, my guess is some kind of silicone (silicon containing polymer).  Whatever it is, they aren't mentioning any particular chemical name, so it will be some proprietary compound.

I hadn't thought of UV transmission being important for bees before, but it makes sense.  Bees and hummingbirds do see in the UV, in large part because the "sugars" with the highest energy tend to be bright in UV.  Both bees and hummingbirds use a lot of energy, so they like the high energy content foods.  Which is a bee will pick one flower over another that look exactly the same to us, the one they pick is brighter in UV.  (Or more purple or however you want to refer to it.)

I don't know if 6 mil of any of these films is thick enough for most hail.  They probably are effective for sleet and small hail.  But if you get baseball sized hail, probably not.  But, strong enough glazing to withstand large hail is expensive.  Is it better to just let the hail punch holes in your glazing?  That is largely an economic issue.

I guess for greenhouse use, it is more common to have bumblebees inside than honeybees.  They are also social bees, but the colonies are much smaller.  I don't know if solitary bees would want to work in a greenhouse.

Some polymers scatter more light, which  spreads out well collimated light so that things on the other side are more uniformly lit, reducing shadows.  PE is apparently known for having more diffuse light.

The first two links I would have to see if there are Canadian sources of the same/similar materials, if/when I get around to this kind of project.  The last link I also thought was a good article.

There are many different kinds of nylon (which is a polyamine).  One particular nylon is ballistic nylon.  It is often added to other made up products, because it can stretch a lot, and hence "contain" fragments.  Kevlar and Nomex (both trademarked) are both polyamines as well.
 
Mike Jay
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I'm torn on the UV transmission part.  I do want the bees to be able to see.  But I also like to not worry as much about skin damage while lounging in the greenhouse.  Hopefully they're different parts of the UV spectrum or it blocks 75% leaving enough for the bees...

Luckily I'm not worried about hail.  If these coatings work in general in the US/Canada, they'll be fine for me.  The biggest hail I've ever seen is marble sized and the 100 year hail for my area is probably quarter or golf ball sized.  If it does punch holes through, it would be in the summer when I'd have plenty of time to repair/replace it before winter hits.
 
Gordon Haverland
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One glue that does stand up to UV, is CA (cyano acrylate - superglue).  It may be that you could apply patches to holes made by hail.  Some CA glues have an activator (or primer?).  I don't know if that would allow you to stick plastic film to plastic film.  If the film is treated to reduce condensation, I would guess that you might need to "wipe" the region to be glued with some solvent to remove that coating.

I think your tanning/burning UV is probably close to what the bees see in.  Just a little more energetic than the blue end of the visible spectrum.

I don't know how bumble bees compare to honey bees in terms of UV vision.  The bumble bee being bigger, may not need to look for as high of energy food as a honeybees does.

How that fits with navigating is dubious.
 
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I just came across your post and site while researching passive  greenhouse cooling.  I have not quite figured out where your greenhouse is, I'm guessing BC maybe, but I thought I would post a link to some general guidelines I came across for passive cooling greenhouses:

https://ag.umass.edu/greenhouse-floriculture/fact-sheets/ventilation-for-greenhouses

This was considerably more venting area than I was expecting, and has caused me to rethink my own greenhouse ideas.  This might be a nice reference if you ever put together an online library.  As a note, I would be interested in any literature you have seen on the engineering/design of passive solar greenhouses.

 Thanks and best regards,

 EBo --
 
Gordon Haverland
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I believe the greenhouse builder is from Wisconsin.  I have a greenhouse on my TODO list, but that list is long and it isn't near the top yet.

My greenhouse would need space for aquaculture, and probably lab space (behind the north wall) for culturing and scale up of bacteria and fungii.

Thanks for adding to my reading list.  
 
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Hi Ebo, I am in Northern Wisconsin, zone 4a.  While I am mainly concerned with holding in heat, I have been thinking through ventilation a bit.  I'm hoping to get away with automatic ridge vents and ground level South side vents.  I'll probably leave the lower vents open all summer and let the upper one actuate as needed.  In the winter I may do some sort of underground air intake with one of the ridge vents operational.

Thanks for the link!  One of the best resources I've seen yet is the one Mike Phillips had a link to above.  
 
Ebo David
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@Mike_Jay, thanks for posting the link to The Solar Greenhouse Book.  Very good design info there!  I've skimmed maybe 3/4 of the book so far.  I am having some trouble reconciling the reported ventilation against other recommendations.  Interesting enough, the Maxatanny PA greenhouse has about 0.30 side vent ration, and very little up top.  This discussion has got me rethinking everything.  I have been dreaming of eventually having something along the lines of the one at the school in Invermere (B.C., Canada)  http://www.huffingtonpost.ca/david-dodge/greenhouse-gases_b_5227446.html  With what you have sent me, and other things I have stumbled upon, I see how I could actually build a smaller/simpler version that would meet my needs.  Thanks!

I also came across a research project in New Mexico (which also has a plant hardiness zone of 6a, so generally useful to you if I am not mistaken:  

   https://web.wpi.edu/Pubs/E-project/Available/E-project-050313-175341/unrestricted/SF13-GREEN_REPORT.pdf

The nice thing here is that they experimented with a number of retrofits to see how they work.  
 
Ebo David
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@Mike_Jay,  sorry for the mental trip.  I see that you are in zone 4a and not 6a...  BTW, my wife grew up on a dairy farm in Lodi (maybe 20 miles from Madison).
 
Mike Jay
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Hi Ebo, Mike Phillips deserves credit for the book, he originally posted it.  Regarding the ventilation requirements, I wonder if it depends on an endwall fan vent vs a ridge vent?  I honestly haven't looked into it much but that may be an important difference.  My ridge vent will be about 15% of my foot print.  Hopefully that's good enough for my hot summers (80F).

The Invermere greenhouse and the Colorado one mentioned in your Santa Fe research project both sound great.  I suspect that they both rely on a relatively constant supply of sunlight in the winter (based solely on my wild assumptions about their climates and location).  I learn a lot from them but I'm hesitant to invest in some of the more costly systems that they use to store heat.  With my winter clouds I don't think I'll have as much heat to store
 
Gordon Haverland
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I ran across another book.  I am at page 36 or so, and there is a looooong way to go.

National Design Handbook Prototype on Passive Solar Heating and Natural Cooling of Buildings
http://mirror.unhabitat.org/pmss/getElectronicVersion.aspx?nr=1230&alt=1

There are lots of links to this document at various different URLs, which was written (or published) in 1990.  I am not seeing an updates to it, or localizations (dropping the word prototype).
It was sponsored by the UN.  This work was produced in Australia, and so far all the writeup is about Australia.  Other than extensive use of SI units, it should be quite applicable to Wisconsin.

 
Ebo David
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My thanks then also goes out to Mike Phillips for finding that reference.  Mike Jay, I definitely hear you with the ventilation.  I have seen greenhouses in northern climes that got so hot in February, that they had to run the vent fans nearly contently.  I seem to remember that it was over 80F in there, and then i have been in some that it was cost prohibitive to grow anything over winter.  It is a fine line.  When I read through this I was thinking of how to design the roof, so that it can be easily modified later to install more vents.  I've got an idea, but it is not completely fleshed out yet.

Mike Jay, have you thought of earth batteries/geothermal?  That seems like an expensive way to go, but might be a the ticket.  I wonder if there are any examples in Canada that you could use to answer some of your questions.  I was lucky in that I found 4 or 5 that are in similar environmental conditions.

@Gordon, thanks for the new doc.  The UN has a number of programs.  Maybe something in their Millennial Development Goals (which include sustainability) would help.  Actually, if I have time I will dig around and see if I can find some contacts dealing with related stuff at the UN.  They might know of a up to date lit review or better yet a systematic review.
 
Gordon Haverland
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In a Chinese style greenhouse, the ceiling/roof abutting the back wall (north in northern hemisphere) doesn't have to be glazed.

Probably about the time I start on a greenhouse of my own, I might get to another project.  Making hay with a robot.  There are reasons to crimp the hay, and I thought something that started with a profile like a Roots blower (with a pinch point) would work).

Looking at Wikipedia, the high efficiency point of a Root's style blower is at low pressure ratios and low speeds.  Which sounds like ordinary ventilation conditions to me.If a person made the rotating lobe structures out of styrofoam, you could easily have at least as much insulation thickness as a normal ceiling, except you have a small gap.  Again, because this is low pressure ratio and low speed, perhaps that gap can be closed a lot.  You need to seal the styrofoam surface, and epoxy can be used for that.  People have incorporated PTFE, graphite, graphene and other solid lubricants into epoxy.  On the top of the roof, you have a box which shields the "blower" from sunlight, and which has a "door" which can be opened allowing air to exit the cavity/greenhouse.

That could be an almost positive displacement air pump.  I would think the minimum clearance you could work with would be a function of the temperature difference from inside the greenhouse to the inside of the box on the roof (and thermal expansion of the styrofoam and epoxy).  Glass fillled epoxy is about 36E-6 for thermal expansion, and polystyrene is about double that.  Aluminum is about 24E-6.

Probably too complicated to make, and besides it might not work.  It would look neat through.  
 
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I've been wanting to build a greenhouse for a number of years and in my mind come to a similar design as yours. First off let me say I'll be watching this thread very closely, I'm excited especially for the arches, I need to make a jig and arches like you... hopefully I can contribute some things too! A few things I thought of when reading your design.

North wall roofing: Use  recycled bill board material. A guy in my area got his for free and roofed his north wall with it.

Glazing: Solawrap is great stuff, it's been used in the EU for a while and recently available in the states. It gets rave reviews and is super durable with an excellent warranty, light diffusion and insulation properties are excellent as well. As soon as I read about it I was sold over poly carbonate and everything else.

North wall windows: I think you original design of overlapping the arches and having the vents be vertical instead of built into the roof is better. Sealing out water and ice is going to be challenging with a vent built into the roof. Additionally if your vents are ever open during a rainstorm you will get water in through your roof which could lead to erosion inside your greenhouse. I've seen this happen to someone with a hoop house greenhouse and north roof vents built into roof of the northwall.





 
Mike Jay
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Hi Kevin, welcome to the conversation!  That's a neat site for billboard covers.  How do you hold them on the building?

I looked at Solawrap but the $2000 price tag was a bit much.  My plan is double poly for a couple hundred bucks.  My experimental upgrade from that would be a solar pool cover (which looks very much like Solawrap but not designed for the purpose).  A pool cover would also be in the $200 range.

Hmm, good point on the vertical vent.  I think that's why I came up with it in the first place.  With the roof vent I was planning on a 4' vent covering a 3.5' opening.  So there'd have to be a bit of wind to blow rain in.  Then again, our rain comes from the NW so it could be blown in easily.  I guess it depends how much venting I'll need to do in Dec, Jan and Feb.  I wonder if an end wall vent near the peak could handle winter ventilation and a roof vent for the spring/summer/fall?  I was kind of grooving on the simplicity of the symmetrical arch design...

Edit:  Can the billboard tarps go on either way and have UV protection?  I'm guessing it wouldn't fly with the missus if there was a big advertisement on the greenhouse...
 
Ebo David
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@Kevin Swanson, thank you for the billboard material link.  I have read in places that some people use the rain coming in the vents as a source instead of a problem.  That would take some planning.  This discussion is exactly why I was looking at building a clear-story with the vents installed there.  Maybe we could put a dual clear story (or whatever they are called this is the closest image I can see for such a design --
https://i.pinimg.com/736x/4d/c8/5d/4dc85d5a304ed0e29f7638280612ab71--shop-buildings-pole-buildings.jpg).

@Mike Jay and @Kevin Swanson, also look at "silage tarps".  You can get them with a white/black side in 6mil thickness.  I use this for soil occultation (and I can get more heat by placing the black up, or less heat and place the white side up...).  I have also used old bilboard material for the same purpose.  No printing on those...  Also, if the printing goes on the inside, no one would be the wiser.  I can see having the print on the outside could be disturbing -- depending on what was on the print.  Also, if you look at the site you should find they have white or black backing.  So you can choose which to purchase.

Hope that helps.
 
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Hi Mike, I just skimmed through your thread... I like the concept. I have been thinking about similar systems for heating, and have read Gaelan Brown's book, as well as having done several experiments over the past few years.
I wonder if your plan for the compost bin inside the GH is sound. None of the systems in GB's book are IN the GH, except for the NAI/Fulford system, which was manure compost loaded/unloaded frequently, and there were issues with air quality for people.
One of my experiments, our first winter with a 17'x34' GH, was composting brewer's grain with leaves/woodchip/cardboard, plus kitchen scraps. It was unpleasant, with lots of ammonia, mainly my own fault for not enough brown material, but also due to the enclosed space.

If you are using some plumbing (air or water) to harvest the compost heat, you could do that without having it inside the high-priced real estate of the GH, and maintain the air quality inside.
You could make the chamber adjacent to the GH, just on the other side of the end wall from where you proposed. That opens the possibility of making the pile larger without sacrificing more of the GH space, as well as easier loading/unloading (possibly by machine or truck).

As far as the "low-grade" heat, running a loop under the soil in your beds would be a way to use it (works with either air or liquid system, or both?) warming the root zone, and charging the soil as a thermal battery. Lots of examples online.

Inflated poly has a few benefits, the extra layer of air insulates and tensions the skin protecting it from wind damage, but it does "wiggle" which seems to help shed snow in my experience (especially in windy storms). The inflation air used is outside air to take advantage of the relatively dry winter air causing less condensation between the layers. The air is essentially still in there (the fan is providing pressure, not circulation) unless you have a big leak, and there is a system (on Builditsolar.com?) with a manometer controlled fan and a check-valve, allowing the fan to pressurize the double poly, then switch off until the pressure drops and the manometer switches it on again. Saves running the fan constantly, plus holds the air a while in a power failure...
 
Mike Jay
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Hi Kenneth, welcome to the conversation!  

I am a bit worried about the compost IN the greenhouse for the ammonia reason.  Some of my thinking/hoping:
  • With a primarily "brown" wood chip compost it may not produce as much ammonia as a "properly" C:N balanced hot/fast compost pile.  I believe the NAI/Fulford system and the Bioshelter Market Farm have compost inside but both are manure intensive.
  • By putting it inside the GH I get to harvest all the heat it generates, not just the bit I can circulate away with water.
  • If the gasses are overpowering I could seal the compost chamber to keep the ammonia in.  Aeration air would still route heat through the South grow bed but then exhaust outside.  Downside is no CO2 benefit from the compost.
  • I don't have any room on any side of this greenhouse for an external pile.  So if I want it outside, that reduces the size of the greenhouse.  If I had a big field to put it in I would have more options.

  • But my hopes/thoughts are based just on reading and dreaming.  Do you think your compost would have offgassed as much if the C:N ratio was tilted more towards "browns"?

    My main compost heat harvesting methods will be:
  • Radiation/convection off the surface of the hopper
  • 4" pvc pipes that enter the chamber near the bottom, rise up through the pile and then exit the top to create chimneys of ambient air heating
  • Aeration air being sucked through the pile and then blown through the South planting bed
  • Option to add coil of pipe on the underside of the roof of the chamber to circulate water through.

  • I'm hoping to not coil pipes through the middle of the compost so that loading and unloading won't be a massive pain in the ass.

    I do like the simplicity of running low grade heat through pipes that are shallow in the ground.  Perhaps on the surface and covered with mulch so that when I'm digging I don't have to worry about puncturing pipes.

    I did see the Builditsolar plan for the check valve at one time but the link isn't working any more.  Do you have a copy of it by any chance?
     
    gardener
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    Hey Mike, nice design! I have one bit of input, the corrugated piping holds water in the indentations. I don't know if that matters in your climate, in mine it means mold heaven. I'm using smooth walled pipe, and putting clean outs, in case I need them.
     
    Mike Jay
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    Thanks Pearl!  My plan has been to use perforated drain tile to keep water from collecting.  Hopefully I don't forget between the planning phase and the implementation....
     
    Mike Jay
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    Ok team, I did a new sketch.  I think I may have found a balance between the benefits of the "triangle" in the original sketch and a traingle-less version.  So I took the South roof from the original sketch and left it alone.  Then I pivoted up the North wall to meet it at a new ridge point that is a couple feet off center (to the North).  Please refer to the new drawing below.  The scale on the upper view is 1 foot per square.  For the lower layout view the scale is 2' per square.  So the greenhouse is still 20' by 40' and now the ceiling is about 16.5' high.

    With this geometry, I don't need the removable winter insulation under the upper vents.  They can just be insulated panels that stay mostly closed in the winter and open on actuators in the summer.  On the summer solstice the sun will reach nearly all the way to the back of the greenhouse.

    The upper vent is pretty steeply mounted so I don't think snow will hinder its operation in the winter.

    When the upper vent is open in the summer it has a decent overhang on its opening so I think rain entry won't be very common.

    A ridge beam is now possible and it wouldn't block much sunlight.  For reference, the solstice and equinox sun angles are highlighted with red lines on the right side of the top layout.

    This also increases the solar window for the glazing in winter to 18' by 40'.  The "triangle" design had a 16' by 40' window, plus the triangle if I could harvest heat out of it.

    Circulating water in black pipes can now be done on the North wall.  With the triangle design I needed a drain back system.  Now it can stay filled all the time = simpler.

    Snow may build up on the upper part of the South roof but if it's not sunny out I can leave it there as added insulation.  If I want to remove it I can probably poke it from inside with a stick or pulse the blower that is inflating the two poly layers.

    The steeper North wall now allows for more headroom when walking on top of the compost bunker.  This will be a relaxation space kind of like Gerome Ostentoski's CRIMPI greenhouse.

    One downside is that I need two layout templates to build the non-symmetrical trusses.

    Another downside is that I'm increasing the low R value glazing and decreasing the high R value North roof.  I'll be even more dependent on the moveable insulation part of the design.

    Feedback request:
    Does anyone see any issues with this revision?
    Should I have the trusses pass one another and be bolted together or have a ridge beam or something else?

    Greenhouse-sketch-40.jpg
    [Thumbnail for Greenhouse-sketch-40.jpg]
     
    Ebo David
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    A couple of thoughts, -- and mind you this is from my readings and no experience what soever...  Reading from McCullagh's book on The Solar Greenhouse Book (pg 45+), they show the thermal profile when installing the foundation insulation straight down, but you have it at an angle away from the greenhouse.  I have seen drawings of a couple of people do this, but I have no intuition of bring it out compared to bring it down.  There might be some optimal angle for this.  

    I cannot speak to the trusses other than if they are designed to be free standing, then you will not have to have a ridge beam.  Not sure the best way to go.  For my own space, I am leaning toward sell standing tresses and heavy purlins.

    re: two layout templates...

    You might be able to build it out on a single one which has one under the other (that is if I am following the objection correctly.
     
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