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Mike's passive solar greenhouse design/build  RSS feed

 
Posts: 55
Location: Stroudsburg, PA (Zone 6a)
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Impressive, Mike. I see you are using a Swedish Skirt ala Ceres Greenhouse Solutions. Did you use 1 or 2 - 2" pieces? ....looks like 1 in the photo. How deep did you place it? ...looks to be a bout a foot deep
 
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Thanks Jim!  It's one layer of 2" foam that is 8-12" deep at the foundation, sloping down to probably 12-16" deep 3' away from the foundation.  I considered doing 4" of foam but found (or someone found for me) some data showing minimal benefit from the additional thickness.
 
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Please post data as you use the greenhouse.    If I recall you instrumented it.
 
Jim Guinn
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Mike Jay wrote:Thanks Jim!  It's one layer of 2" foam that is 8-12" deep at the foundation, sloping down to probably 12-16" deep 3' away from the foundation.  I considered doing 4" of foam but found (or someone found for me) some data showing minimal benefit from the additional thickness.



I did not learn about the Swedish Skirt system until after I built my greenhouse, and because there is a shale ledge just inches below ground, I wasn't able to insult with a traditional foundation. I did contact Ceres about using 1 vs 2 sheets. They recommended 2, but like you, I didn't think the 2nd one would yield that much more insulating protection.
 
Mike Jay
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Hey Ebo, I've started adding sensors but I'm a long way away from having them up and running.  So far I only have the temp sensors installed under the skirt insulation.  I ordered a light intensity sensor, moisture sensor and a humidity sensor that should arrive later this week.  I have an Arduino starter kit on my wish list for my birthday.  So hopefully by December I'll have some data coming in.  The moisture sensor will be buried in the compost pile so I can hopefully determine a good moistness for the pile.

For now, the doors still aren't on, the E and W walls aren't insulated and the South vents have 3" spaces between them I need to fill.  So it's not remotely air tight at the moment.  I'm going to build the compost chamber today while it's snowing out and fill it with wood chips before it gets really cold on Wednesday.  

I'll also try to get the holes filled with doors between now and then so if it builds any heat it has a chance to hold onto it overnight.  I have water drums in there that would be nice to not have freeze prematurely.

Jim, if it matters, I did go with 4" of styrofoam on the vertical part of the skirt by the foundation.

Since the last pictures were taken, I mainly worked on the second glazing layer.  My plan has been to put 1.5" tall spacers on each truss between the poly layers to both act as guides for the moveable insulation and to provide the double poly air space without needing an inflation fan.  The problem is getting them installed.  I got some cedar from a buddy and cut it into 3/4" by 3/4" strips since 3/4 by 1.5" ones wouldn't bend enough.  Then I screwed them on starting at the bottom.  I figured I could get halfway up with a ladder and then have to screw horizontal 2x4s across the face of the greenhouse to climb up on from there.  Luckily the geometry worked that I could do the whole thing from ladders!  As you can see in the first picture, the ladder is much flatter than it should be.  Luckily at the middle it is resting on a rib.  At the top I had a 2x4 that would span from the rib I was working on to the one on my right.  So it worked swimmingly.  

I then tested the moveable insulation and it worked just how I dreamed it would.  It fit in the space I had planned and it unrolls and rolls up nicely.  It doesn't want to unroll for the first 4' due to the slope being too flat but I anticipated that.  I'll add some weights on strings in the air gap to help pull them for the first 4' or so.

Then we put the second layer of poly on.  It was harder to pull tight and it doesn't look perfect.  I might fiddle with it or I might leave it as is.  I'm guessing it was harder because this is standard poly without the IR and anti-condensation properties.  Not sure why that would matter but it's the only difference I could see.
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Ebo David
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I would suggest getting the temp sensors up, or whatever other sensors you have, and running as soon as possible.  You may find that the information is useful, and also might run into a bug as it is collecting.  Better to find sooner than later.  Also if you are initially worried about the barrels freezing, only fill them 3/4 of the way.  If you have some temp sensors set up you can track the outside/inside air temp as a function of how much water you have in the barrels.  As a note, water stores a LOT of energy and can release it as it starts to transition to freezing.  So if you get enough solar gain to keep things just above freezing, the barrels will help with any dips in the night.
 
Mike Jay
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Thanks Ebo, I'd like to get them up and running but I'm struggling to just get the walls done before it gets below 10F outside

Since my last update we've been busy getting the last things done before there's snow on the ground.  Access to the greenhouse in the winter is by foot.  So this week I built the compost bin and over the course of three days, filled it with municipal wood chips.  I think I put about 10 cubic yards of chips in the bin.  They were mostly freshly chipped and there was lots of green bark in the mix.  The pieces were generally the size of one joint of my pinkie finger or smaller.  It mostly smelled like pine but since the leaves have been long gone here, there could be plenty of hardwood mixed in.  It just takes a few pine branches to make a load smell like Christmas.

The bin consists of eight 8' long pieces of metal roofing screwed to 8 2x4s.  The 2x4s are on the outside so they won't rot.  For access I used some 2' off cuts to span below and above the 4' door.  Filling the first couple feet was easy.  Once it was midway up the door opening it got a bit tougher.  I ended up finishing it off at 6' high (just at the top of the door opening).  I put about 50' of drain tile under the pile with an inlet to the room.  At the top of the bin I'll attach a 4" duct that runs to a radon fan to exhaust the pile (and aerate it).  This exhaust will run though the south planting bed to harvest the heat.  

This requires the top of the bin to be closed off.  So I framed up a platform on top of the bin.  Today I got a couple sheets of plywood on it but it isn't finished enough for a picture.  It will be a nice relaxation/yoga space.  It will measure about 12' by 9'.  From this platform I'll have a catwalk going down the center of the greenhouse to the East end where the rain barrel water tower will be.  Third pic is a view from the platform to the East.

I also got the East door installed.  This was a Habitat for Humanity Restore find that required building a frame (with weatherstripping) and flipping the door upside down.  I still need to add a door knob or live with one that is way too high off the ground.  For scale, it is an 8' tall door (second pic).

I started on the East siding and the missus insulated the E and W walls.  Once we get a vapor barrier on those sides it will help a lot.

It's been 25 to 30 for the high the last few days and last night was in the mid teens.  We got our first sun in over a week today (still had 50% clouds) and it warmed right up to 72F inside.  I hope the compost starts cooking soon.  Other than the gaps between the South vents, the building is getting tight.  There's tons to do but we got the critical things done before the snow and cold hit.  Yay!
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Mike, SUPER build. This is my kind of project! You are so neurotic about details that at worst it will be good and has a chance to be truly fantastic. If it is only "good" all the labor will still be worth it and you will have  seasonal extension, and if it is great this will just make the rest of us miserable with envy. Super well thought out, especially the interfaces which is what people tend to screw up.

Thank you sooooo much for going through the sources and materials you looked at. This is great documentation. Wow, just had a chance to read the thread entirely. I'm inspired.
 
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Yes! We're already green with envy.  Fantastic build, from those gorgeous trusses to the incredible skinning job. Thank you so much for relaying all your research and developments. Boy howdy you two are getting it closed up in the nick of time too. That must be a huge relief. Congratulations and thank you for sharing. P.S. I can't wait to see the rolling insulation in action.
Brian
 
Mike Jay
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Thanks guys! It is coming together just in the nick of time.  Since the last update I finished the platform on the compost bin, added a relatively well sealed door hatch and plumbed in the fan to aerate it.  The pile started cooking two days ago and steam (or possibly more accurately water vapor) was rising off the pile.  Yay!!  Now that it's capped I can run the fan.  It blows air from the fan, through the South planting bed and exhausts into the room robustly.  The intake under the pile is drawing air but not nearly as much as the fan is pushing.  So I'm sure there are lots of leaks but at least some air is moving though the pile.  

Now I just need to figure out how long to run the fan each day/week to keep the pile active.  Along with that I think a huge thing is that the hot/steamy compost air is cooling down in that planting bed and condensing a fair amount of water out.  I believe that counts as a phase change so the energy transfer to that soil is much greater than just the temperature of the air.  That's great but it does mean I'll have to add water to the pile to make up for it.  How much, I have no idea...

Yesterday I got to experience the temperatures and what I will have to play with.  I got out there after a cold night and worked inside the greenhouse from 7:30-8:30.  It was 28F inside I headed into the house for breakfast and found that the outside temp was a balmy 13F.  So overnight it held the temp 15 degrees above the outside.  That's with the E/W walls insulated but not vapor barriered AND 2" gaps between the 6 vent doors along the south wall.

I headed back out at 9 and was working above the compost bin finishing some insulation around the moveable insulation drive mechanism.  The sun had come out about at 9 and by 11 it was really hot in there.  I checked them temp and it was 100F (near the peak).  Nothing like going from frozen fingers to working topless in three hours...  It was in the 70s at ground level.  Once the sun went behind some clouds at 3:30 it started cooling off.  By 4:30 it was down to 45 at ground level.  After an 8 degree night last night, it was 22 this morning inside.

I also measured the temp of the air leaving the aeration exhaust pipe after the fan was running for an hour.  It was around 55F.  So the hot air from the compost is transferring some heat to the bed and still comes out with some warmth for the room.  

Construction wise, I got visqueen up on the West wall yesterday.  Still need to do the East wall.  I also talked to an electrical engineer buddy about operating the moveable insulation with a garage door opener and he said it would be perfect.  All I need is an older opener with a worm gear limit switch set up and some kind of timer to trigger it at dawn and dusk.  He'll help me figure it out so that's wonderful.

Tomorrow is supposed to be a near tropical 36 for the high so I'm going to close the gaps in the South vents and do some other exterior work while I can.  The missus sewed up some felt weights for the moveable insulation so I can get moving on that part of the project soon.  

Thanks for the support and envy!
 
Mike Jay
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With the deer hunting season and Thanksgiving I haven't done much work on the greenhouse.  The compost is still not getting very warm and I started another thread HERE to discuss.  

Today I rearranged the airflow through the bin so that the fan is pushing air into the pile from underneath instead of pulling it through from above.  That way the leaks in the top of the compost chamber won't be as much of an issue.  It seems to have delivered the desired effect.  The fan is pushing plenty of air into the pile.  A small portion of it is avoiding the leaks in the top and going through the planting bed and coming out the other side.  I'll work on sealing the leaks so I capture more of that heat in the planting bed.

I'm also getting ready to work on the moveable insulation.  Parts were bought today and plywood cut to fit.  Wednesday the sun is supposed to make an appearance so the missus can stain more boards for the interior siding.  Visqueen is up on the East side and the South vents are weatherstripped so the building is now tight-ish.

Outside it was about 15 last night and 22 during the day, overcast and flurries.  Inside the greenhouse it was 28 this morning and it heated up to 38 by the end of the day.  I'm surprised at that considering the solid overcast conditions.  It's also windy.  I don't think the compost heater provided any of that thermal gain.
 
Brian Rodgers
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I need to follow your thread about that badarse compost bin. Have you sealed up the greenhouse completely? Possibly you could add some heat for this first Winter to jump-start the greenhouse?  
Brian
 
Mike Jay
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The greenhouse is pretty much sealed up.  There are a few areas that are lacking.  One is the five 4x8' vents at the top are just sitting closed with little gaps around them.  I cut cedar strips today to install as door stops for them.  When I install those I'll weather strip them.  That way the weight of the doors/vents will press down on the weatherstripping and seal them pretty well.

Another detail is that the outer layer of poly is complete on the South side.  The inner layer is complete but it doesn't cover the full area.  At the top there is a 12" wide area where the moveable insulation goes.  Once the insulation is installed and that area covered, the inner "layer" of glazing will be complete.  So for now, air can easily get between the layers which gives me the effect of a greenhouse with less than two but more than one layer of poly.

I also need to put a threshold on the E door and a door knob.  Currently there's a 1/2" gap under it and a couple holes where the old knob was.  It's an 8' tall door and I had to install it upside down to use the hinges.  So the current holes are comically high.

I could add heat but since I don't have plants in it yet to fuss over, I'm not worried.  If I get a sunny day it easily gets up to the 70s inside.  So it can heat up fast on its own.  I just need to get the compost bin heating as well and get the moveable insulation installed and moveable.

The missus wants to put me on a basement remodeling job after Christmas so I need to get this puppy more done.
 
Brian Rodgers
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Thanks for explaining Mike,
I understand about  efforts needed on other projects. I too am currently being pulled in several directions. I can't wait to get back in my shop and play with power tools!
One of the projects I'm looking forward to is building barn doors for my shop after twenty plus years of attaching old wooden garage doors with screws to close up the shop.
Brian
 
Mike Jay
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Ok, I got a bit more work done.  It's been the cloudiest November and early December that I can remember.  I think we've had two mostly sunny days and two slightly sunny days out of the last 4 weeks.  Consequently the greenhouse interior has been hovering in the 30-40 range each day.  If it gets sunny, it warms right up and the missus can stain siding boards and I can get working on the moveable insulation.  So we're waiting for a couple more days of sun to get cracking on that.

But we had a heat wave so I could do the East exterior siding.  By heat wave I mean highs in the 25-35 range.  This was my first time doing cement board lap siding.  I wish it was a bit more environmentally friendly but I wanted something that would last.  

Other than that, I've been getting brownie points for installing doors and trim in the basement.  I'm still not sure how to redeem these brownie points...
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nice looking greenhouse!   have you ever thought of a lower portion that goes outside your footprint as a cold chamber so to speak???
 
Mike Jay
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I don't think I've thought about that Brad.  Could you elaborate on the idea?  
 
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Mike,  how were the temps today? We had a sunny day and my hoop house temps were 50 degrees. I would assume you had similar results.
 
Mike Jay
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Yup, yesterday and today we saw more sun than in the previous 4 weeks.  Or at least it seems that way.  The preceding nights were particularly cold though.

Friday:  20 for the high, -3 for the low outside the night before.  I have 6 water barrels in the greenhouse and they were starting to freeze up for the first time.  It was a bright overcast day.  Morning GH (greenhouse) temp was 28.  By afternoon it heated up to 35.  That's all from the thermal mass of the soil and the slight solar gain from the overcast sky.

Saturday: 25 for the high, 7 for Fri night.  Barrels frozen at dawn, morning GH temp was 26 (not bad considering).  Bright sunny day!!!  Heated up to 85 by noon  That temp is 2' off the ground, I didn't check what it was by the peak of the roof but I'm pretty sure it was over 100 up there.

Today:  25 for the high, teens last night.  Sunny with a bit of haze.  Weren't home till 1ish and it was 82 at that time.

So, what I'm seeing is that without compost heat, or moveable insulation, or any fancy thermal storage, or clear skies, the greenhouse seems to maintain about 15 degrees warmer than the outside.  It tends to heat up 10 degrees on cloudy days.  On a good sunny day, it will heat up 55 degrees in two hours and get into the 80s.  I think that if I can hold that heat through the night, the sun would be able to keep the greenhouse warm enough as long as it made an appearance each day.

Since it doesn't do that for me, I need to get the compost working to cover cloudy days.  Luckily in my climate, the cloudy days are usually warmer and in Nov/Dec.  The truly bitter cold weather is often associated with sunny days in Jan and Feb.
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Sorry,  repeat post.
 
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