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!! Mike's passive solar greenhouse design/build  RSS feed

 
Posts: 14
Location: Wisconsin: 4b
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Thanks mike,
You are giving me hope for a multi-use compost pile of practical size.
 
master steward
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Location: Northern WI (zone 4)
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I've had a few sunny days to work out there in the last two weeks.  The siding is up on the East wall.  White stained pine is a lot prettier than insulation

The water tower is built and the IBC tote is in place atop it.  I got a bunch of IBC totes and one was the extra tall style.  That's the one that is the water tower tank.  I miscalculated and struggled to install it.  I wanted the tank as high as possible but I forgot that it would put the tank between the trusses.  Thus I couldn't build the tower and then put the tank on it.  Instead I had to block and tackle the tank up there and build the tower under it.  My local OSHA rep wouldn't have approved.  The structure it's sitting on is about 12' off the ground so I should have decent water pressure.  The missus just finished staining it today (involving much swearing and moving of ladders).

I got the catwalk partially in place.  It's there for several reasons.  The primary reason is for easy access to the vents, moveable insulation chamber and water tower.  Secondary reason is to have a cool canopy tour walkway.  Tertiary reason is to have more places to hang pots.  Quaternary reason is a place to route drip irrigation header pipes down the length of the greenhouse.

The catwalk is two 2x8's on-the-flat with a 2x4 vertically between them and at each edge.  It's pleasantly sturdy despite the 8' span.  The middle 2x4 is for stiffness, the edge ones will give extra stiffness and act as toe kick safety rails.  It's about 6" higher than I wanted but it will work.

Next is to connect the catwalk to the yoga platform atop the compost bin.  Then I'll either work on the West wall siding, start into electrical or begin a shallow climate battery.

In other news, we've received over 30" of snow in the past three weeks and the greenhouse is still standing.  We dug out the snow from the south side to give more room for sheeting snow twice now.  Since the two poly layers aren't inflated, the snow sitting on the top of the greenhouse has kind of pressed the layers together.  The R value is still fine due to the foot of snow.  The snow is melting/sheeting off anywhere the glazing is exposed, the only accumulation is on the topmost foot.  In the exterior picture of the base of the greenhouse, you can see where we removed snow prior to the latest 12" snowfall.  The pile against the greenhouse comes just over the patio door vents (as evidenced by the shadows in the first picture).  So the snow is about 5' high up the greenhouse.  We'll probably dig it out tomorrow if we get a chance.
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Enjoyed reading your adventure in building your greenhouse. I'm also designing a greenhouse for zone 4 and have been studying the various ways to keep low temps above 50f with sub zero winter temps.
It seems from studying the available info on the web  a lot of effort  and thinking goes into finding ways to store or add heat during night time lows and not much thought goes into addressing the elephant in the room ,the huge heat loss thru the glazing at night. I was glad to see you at least have attempted to minimize this.
I'm assuming since the snow is pushing the poly layers together it's not easy to get the rolled insulation to fall down. I had a similar idea but instead of poly id use two layers of polycarbonate with a high r  value rollup blanket in between them. Have you tested to see if your insulation has an effect on inside temps when it's deployed? I'm assuming it has an r value around 4. Is that about close?
 
Mike Jay
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Location: Northern WI (zone 4)
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Thanks Glee, it has been an adventure!  Welcome to Permies by the way :)  I agree, the heat loss through the glazing is the biggest challenge.  You need to do plenty of insulating elsewhere (foundation, North side, etc) to make a greenhouse work well here, but the glazing kinda blows all those heat losses out of the water.

Yes, the snow pressure is keeping the insulation from moving currently.  I've kind of given up on it for this winter since I need to trim the edges on some pieces to allow them to slide down nicely anyway.  I'd think a more rigid glazing would work better.  I'm not sure if polycarbonate can span 4' or not at my uppermost roof slope.  I might have to upgrade to that but it will be a real pain to install without tearing the inner layer of poly in the process.

Yes, the insulation does help.  I did get it halfway deployed on our coldest night and it helped.  -22F on our second coldest night with no insulation and the inside temp in the morning was 16F.  The next night I had the insulation 50-60% deployed and it got down to -29 and the temp in the morning was 20F.  So 11 degree larger temperature difference with the insulation and it wasn't fully down.  I don't know how to calculate the R value with and without but I suspect it's 3-4 when deployed.  
 
Glee Skals
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Thanks for the reply mike. I've been working on all kinds of methods to cover the glazing at night and I'm finding out why there isn't any real info about how to do it, because it's not an easy thing to have something moveable with a high r value.  When you think about insulating the north, east, west walls to an average r value of say 24  then have half the structure (the glazing) at r2 the high r walls are not saving all that much. Increasing there r value is not cost effective above a minimum without also addressing the glazing heat loss. Now if we could get that glazing to r24  at night then  storing solar heat in the floor, or water ,or even heating the greenhouse become a real asset for cold winter growing in our zone.

I haven't come up with any way to do that yet, at least not if I want a conventional looking greenhouse but I'll continue  thinking it thru.

I Wasn't suggesting you put polycarbonate on your greenhouse just that I had thought of a similar idea but had thought about the polycarbonate because I live where its windy all the time and plastic just wont hold up. I do think though it might help to allow your insulation to endure the rigors of repeated opening and closings. Maybe one day when you have to change it for some other reason

Ill keep following this thread and see how it turns out for you and if I come up with a way to get that r24 glazing covered at night ill share it.
 
Mike Jay
master steward
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Location: Northern WI (zone 4)
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One way to cover a smaller greenhouse could be an automated grain cart cover.  Here's one example: Carolina tarps.  It could be done externally with some higher R value material.  Normally exterior moveable glazing insulation is a challenge due to wind and snow but these systems are ok for highway use so they're probably pretty tough.
 
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Mike, I'm so excited. You're doing fine
 
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Hi Mike,
A few days ago you reacted to my post on coldsinks. I didn't realise you've got such an amazing extensive post on your design, with inputs from so many knowlegable people... Great! I'm going to read all of it!
Thanks a lot for your thumbs up, by the way.
Greetings,
Michiel
 
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Mike Jay wrote:Hi Daren, welcome to the party!  So I take it you will do two curved 20' pieces of pipe, joining at the peak?  I built my curved trusses a bit beefier to handle snow load.  I haven't had much snow to test it against but so far I'm very confident it can handle any snow it will encounter.  I was also going with beefy trusses to handle the weight of all the insulation, siding and roofing on the north side without bulging out the south side.  If I were to build another one of these greenhouses, I'd be very tempted to attempt an A frame with straight trusses.  The curves probably added 1/3 to the timeline of the project and 60% to the brain power needed.

With your question about cubic feet of battery to glazing, what kind of battery do you have in mind?  Are you thinking of a GHAT or climate battery with air pipes underground?  I decided against that type of system due to our cloudy winter climate (My first Permies post asking about climate batteries in cloudy cold places).  The systems seem to work well in sunny cold places (Colorado, Nebraska, great plains, etc).  This year, I think we had about 15-20 sunny days between Nov 30 and today.  A battery system couldn't gain enough on those days to give back heat on the other 50 (in my climate).

There is a Sunny John calculator for climate batteries that has been posted and lost and reposted.  I think you can get info on sizing through this link: ecosystems-design.com

Regarding if a greenhouse heats up enough to charge the battery, my greenhouse on a frigid sunny day will heat up to 100+ in the middle of the day.  That lasts from about noon till 3pm.  So that's three hours of hot air to put into the battery.  And 21 hours where that heat is needed to be drawn back out.

I think I'll do a poor man's climate battery by digging shallow trenches in the greenhouse (18" deep) to circulate hot air on sunny days.  The main goals of that would be to store that heat when it happens (avoid opening the vents) and maybe heat up the roots of the plants by a degree or two.  I wouldn't use it to return warm air to the greenhouse.  We'll see if I actually do that...

Regarding the phase change, I haven't decided if I'm really going to do that or not.  I think the 6 water barrels I had in there did help moderate the temps until they froze.  I think until I know the temperature swing of the greenhouse when it's "done" I won't be able to pick a good phase change material.  For instance, if the greenhouse swings from 30 to 70 degrees, a phase change material that melts around 50-60 would probably be ideal.  It should melt most days and freeze most nights and hold the temp nicely.  Using water as the phase change would only really kick into action at 32 degrees (too late to protect your tomatoes).   Water, or any phase change material, or a stack of bricks, all act as thermal mass regardless of the temperature.  That just slows down the temperature swing and takes away the peaks.  So they're good too.  I think between the footings and the cement blocks I have about 20,000 lbs of thermal mass.  Add in the top 4" of topsoil and it's a bunch more.  So if I add 30 barrels of water it will help and it will distribute the effect, but I don't know if it's worth the space it takes up.  So that's a long way of saying, I don't know what you should do.  

I managed to avoid the blower on my two layers.  A 1.5" spacer keeps them apart except for one spot in the middle.  But Solawrap or twinwall polycarbonate would be slicker than my installation.

I'm not sure the perfect answer for your endwall question.  I think it depends on your goals for the greenhouse.  If you're going to try to keep it warm through the winter at our latitudes, I think they have to be insulated.  I'd only get a bit of light (and solar heat) through them for an hour a day.  Then I'd bleed heat out through them for 23 hours a day.  If you are just going for a much longer growing season, glazing part of them might start to make more sense.  Maybe glaze the south half of each and insulate the north half.  Another way to think of it is that at 10am the sun is hitting the outside of the E wall and not entering the greenhouse.  But the sun that goes into the greenhouse and hits the solid W wall is reflected back towards the plants.  If those endwalls were clear, that 10am sun would enter the E wall but the sun going through the greenhouse and hitting the W wall would escape and light up the snow outside.  So am I gaining any sun if they were clear?  And keep in mind the tremendous heat loss through those walls 24/7.  

Regarding the compost heat, I haven't got it figured out yet.  I hope to so that we can all heat our stuff in a wonderful way.  But I fully understand your concern.  My current mix is too slow of a "burn".  I'm going to pull some out and change the mix and see if that fixes it for the second half of winter.  

If you have enough ventilation for the summer (meaning a lot), then it's hard to have a really well sealed greenhouse.  Mine has the equivalent of 13 doors on it.  All but one are homemade and sealed with weatherstripping.  I'll fix more leaks but it will always breath more than I want.  So I wouldn't be too worried about wood heat for cold nights sucking up all the oxygen.  Maybe if you're burning a face cord every three days...  Plus the plants should be giving off oxygen.

As you get your plans together feel free to start a build thread like this one.  You'll get lots of good info and we'll all get to watch your progress



Actually, I meant one single 20’ pipe bent to an arch- the side walls would be achieved by 2.5-3 foot straight pipes. But due to the advice I’m seeing here, I could very well scratch that idea in favor of insulating the snot out of my entire north wall instead of glazing it, and possibly doing the same for the east and west gable ends. It’s almost like a chimerical design- one exact half being well insulated, possibly stick built, but with moisture resilient materials, and the other half being a plastic greenhouse.

Due to snow considerations, and wanting to be able to leave on vacation with no worries of snow clearing chores, I’m def thinking a 12/12 pitch.

A side note for others to think about, and something I’m leaning towards, is making the construction such that it could be converted to a more regular outbuilding if the need ever arose. I’m thinking of using PT stickbuild for everything and if I ever had to, I could remove plastic and put up board and bang-presto, have a barn. Just a thought.

I actually had never looked into the air pipes idea, though that seems interesting. I guess I have to look at real climate data for my area versus my own memory...I feel like we have an often-sunny winter (definitely January and February) but I don’t have numbers on it. All I had come up with for thermal batteries was to make a long thin wall of bricks on the north side of the greenhouse, not touching the outside wall (to avoid thermal bridging) but just there to capture sunlight before it streaks out the north side. If not bricks, I’d also thought of wide thing jugs of water, like those military type 5 gallon gas cans that are mostly rectangular. I'm not as good at physics/engineering as the folks I see here, but I do know most brick/concrete/rock has one quarter the thermal capacity of water but has a higher capacitance before it starts to shed that heat? So depending on climate a mix of rock's higher temp capabilities versus water's volume to heat advantage is what we're looking for?

If the $$ made sense, I could also get beeswax from someone, because its phase change temp is closer to the number I’d be theoretically aiming for. I’ve worked for a veggie farm for years that did winter greens in high tunnels via rowcover, etc, so I know the whole “keep it close to 32 and keep the plants alive but not growing much” game- I’m more interested in winter production at 50-70 degrees or more. If that goal is unrealistic, then I change more to a simple goal of a thermally efficient greenhouse that is good for allium and tomato starts by Feb 23rd or so.

I have no idea how to solve the ventilation question. I have very low goals for using it in the summer, actually. Some people in the Northeast don’t realize that 70% of the benefit of a greenhouse for tomatoes is just getting the darn rain off the foliage, which causes disease. You also get an earlier harvest by several weeks and a later harvest, but I can accomplish some of that with field tricks like row cover and careful timing of plantings (brave, and early, with hardened-off starts). Anyways, that’s all to say...I don’t even know my ventilation plan, haha. I’ve been thinking of making modular walls (like for the gable ends) and having dedicated wall builds for winter versus the other seasons. If I could design removable walls that weigh less than 100lbs each, I could just swap em twice a year. I don’t know exactly how I’d do it but I feel like it’s doable. Alternates are to use plastic and wiggle wire to mitigate any drafty parts of the venting system that are extraneous during winter.
 
Mike Jay
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Location: Northern WI (zone 4)
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So you'd take a 20' piece of conduit and bend it into an arch or an L?  You said arch at one point but also a 12/12 pitch at another.  Not that it matters for the discussion but the peaked roof at a 12 pitch would shed much better.

Sorry about the climate battery confusion.  The phrase "climate battery" is often used to mean underground heat storage so I thought that's what you were talking about.

It's good to have back up plans in case it doesn't work.  My goal is bananas and tropicals.  If that fails I'll go for citrus.  If that fails I'll go for Mediterranean stuff.  If that fails, I'll have a highly extended growing season for annuals.  If that fails I'll turn it into a wedding chapel or barn.

With beeswax or other phase change materials, it's good to look into their suitability for the process.  Many materials have been tested for their phase change reliability.  Some peter out and stop phase changing after a while.  Glycerin is only "ok" as a phase change material.  A bunch of waxes are really good but they're not natural waxes like beeswax.
 
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Hi Mike
I have read many of the screens detailing the evolution of your greenhouse design. Many of your "steps" or ideas aren't much different than mine or a hundred others. I am wondering if the thinking stopped, a strong line was drawn and construction completed. Somewhere, you have to stop thinking and build so, if for no other reason, you can see what should have been build differently. So, just as I did after building my first small greenhouse I wonder if you have discovered what you would do differently with the second greenhouse.

My location is southwest Nova Scotia, Canada at approximately 44.6 degrees north. You, in Wisconsin, would be around 43.8 - closer to the equator than I but we both know our daily average temperatures annually are not similar though this Climate Change thing s causing our temperatures to slide closer to yours. I lived in Calgary, Alberta for almost 50 years before returning home and returning to the land.

Part of my research the past year and a half has been to go back in history and see how greenhouses used to be built. Ever since fossil fuels became easier to ignite, we have forced energy to heat our greenhouses and, as a consequence, we can now grow less variety of fruit and veggies than the mid to late 1800's. Now we complain bitterly of the cost seemingly unaware of the loss of so much food. China was ahead of Europe for centuries. England grew pineapples for the dining room table twelve months of the year without electricity or burning fuel.  

The lessons learned from the first construct and more studying are being applied to the second greenhouse.

Of the texts, abstracts, documentaries and listened to those who have built - your written effort would have to be the most complete, practical, detailed, simple and workable effort to date. And, the only one I have posted a request to learn what would be different, what was "one step" short and other thoughts you would like to share.

Thank you for your efforts so many have benefited from!

Dave
 
Mike Jay
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Posts: 3384
Location: Northern WI (zone 4)
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Hi David, welcome to the journey.  Yes, many of the things I've incorporated have been thought of by others but I hope I've brought some originality to the overall greenhouse.

I don't have a clear delineation between when the design ended and the construction began.  I got as much design done as I could last winter and drew the line at the point where I could start to dig the foundation.  Nothing like the weather dictating when you get to start.  Several elements were figured out on the fly and the design evolved a bit.  But I don't think I back tracked on anything major, other than not pursuing some ideas.  Or at least not pursuing them yet.

I haven't put together my full thoughts yet on what a second greenhouse would look like.  Some of my greenhouse's compromises were due to the space and terrain in my back yard.  My initial thoughts on how to do a second one would be:
  • Build into a South facing hill a bit
  • Make the south cement block stem/pony wall about 8' high
  • Have an A frame (not curved) N and S roof faces
  • Dig a dry pond on the south side to allow snow to slide off into

  • Luckily, I think you're in a much warmer and more southerly location than me.  I'm half a degree north of you and my winter temps are about 10F lower (both highs and lows).  Or at least that's compared to Halifax, I'm not sure where in SW Nova Scotia you actually are.  I think my design is suited to frigid and often cloudy areas.  If it's cloudy all the time I'm not sure it would work as well.  If it was sunny 95% of the time in winter it would be a slam dunk.  When I get the compost heat working it will be awesome.  If I totally gave up on avoiding fossil fuel heat I think it would be quite affordable to keep at 50 at night.

    Last night (March 3rd) we had our second coldest night of the year.  -24F!!!   I trudged out there and the temp inside before the sun hit the building was +26F.  50 degree F delta T without the moveable insulation engaged.  It's been full sun all day and I was working in there with shorts on.  It was 95 in the shade.  Our latest snow has covered the south wall about a foot over the patio door vents so I'm missing out on about 3'x40' of solar gain.  But maybe that helped insulate it overnight a bit...

    Thanks for the kind comments on the thoroughness of this journal, that's kind of what I was going for.  Some people might want to build something quietly and only show off if it works.  Here I wanted to get outside input and share the process and the success (or failure).  Plus I like reading other people's build journals so I figured I'd do the same.

    Edited to add the temp charts for Halifax (first) and my area (second)
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    Halifax
    Northern-WI-temps.png
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    @Mike, do you have any of the temp probes up and plotible?  I forget your background, but if you need help setting up some code to generate plots (and maybe also display details from local weather forecast, etc.) let me know and I will try to break away some time.  Actually I have plans for doing the same for myself...
     
    Mike Jay
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    Location: Northern WI (zone 4)
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    Hi Ebo, I have a couple temp probes in the ground and in the compost bin and I have an Arduino but they aren't connected.  

    I can work on putting siding on the West walls, start on electrical service wiring and the panel, digging and burying a "poor man's GHAT" or setting up the Arduino.  I'm least confident about the Arduino so it keeps getting put off
     
    Ebo David
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    Well... looks like you have your priorities about right ;-) meaning do what you need and you know first...  I have the embedded electronics and similar stuff sitting in my room to poke at when I wake up and have a moment to play.  BTW, it looks like the house part of my renovation will *finally* get done in a week or three...
     
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