Mike's passive solar greenhouse design/build

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

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.

Please post data as you use the greenhouse.    If I recall you instrumented it.

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.

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.

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.

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!

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.

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

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!

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.

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

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.

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

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...

nice looking greenhouse!   have you ever thought of a lower portion that goes outside your footprint as a cold chamber so to speak???

I don't think I've thought about that Brad.  Could you elaborate on the idea?  

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.

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.

We've had a few days of sun (finally).  The missus has been staining more pine boards white.  These will go on the E and W interior walls.  She also stained some bits and pieces for me to close in the moveable insulation chamber with up at the peak of the roof.  

I've installed the moveable bubble wrap insulation in 5 of the 10 truss cavities.  It operates surprisingly well.  And it cuts to size with quality scissors surprisingly well.  I did have to add washers on a string to help pull the insulation down the gap between the poly layers.  I bought out the Ace hardware of their 1" washers and that turns out to be 1/3 of the number I'll need.  

I installed the pulley and bike chain and it raises and lowers very easily.  Phew.  At least it raises/lowers one of the 10 very easily and I think it will do all 10 without much sweat.  For now I have a pedal to turn the shaft, eventually this will become a garage door opener on a fancy switch.

I've done a pretty good job of vapor barrier installation on this building but one area of concern is the bike chain chamber.  I insulated it with 3.5" of extruded polystyrene on the outside of the chain (against the exterior siding).  But I had to leave access from the outside so the pieces aren't continuous.  I had installed visqueen across the chamber on the inner surface of the wall but had to cut through that to install the chain (see photo).  The chain will be accessible from the exterior access hatch for the long haul.  Any ideas if condensation on the styrofoam will be a problem or is 3.5" of styrofoam enough to prevent that?  I could try to make a visqueen funnel at the bottom to catch any dripping condensation and guide it back to the inside of the wall (instead of soaking into the studs below).

I've also installed weatherstripping seals on 3 of the 5 upper vents.  Another day or two and the scaffolding can come down (yay!).

Today was full sun all day.  The greenhouse was hot and muggy at 11 and I was down to shorts and a tool belt at noon (sorry, no pics).  On these sunny days with warm outside temps around 30, the greenhouse easily gets up to 90-100 at ground level.  Yesterday I took a thermometer up high where I was sweating working and it was 108.  So the solar collection capabilities of the design are working great.  Just need the insulation to hold it overnight, a mini climate battery to store it and the compost to add more heat for cloudy days.

The compost is not working yet  I've dug in and added coffee grounds and hot water and that spot heated up.  But it's cooling down now despite still being damp.  I'm running the fan 3 hrs, twice a day.  So IF the problem is lack of water, lack of Nitrogen or lack of air, I think I've tested all of those.  At one time I was aerating it for 12 hours a day.  Now I'm wondering if I have too much air.  So I turned off the fan entirely to see.  95% of the pile is just cold wood chips, I'm screwing around with the bit by the access door that I can reach without climbing in.

First photo is foggy due to a cold camera in a hot greenhouse.  It's of the gear drive for the shaft that turns the moveable insulation.  Second photo is of the thermometer taken at 2pm today.  It's in the shade, 3' off the ground, 3' from the N wall.

Excellent work!

Looking great!  Wow - almost too hot!

Thanks guys!  Sorry I haven't put up an update in a little while.

We were gone for 10 days over the holidays.  And it's been cloudy nearly every day of the last month.  I can work in there just fine on cloudy days but my basement remodeling work is more appealing.

All the moveable insulation is installed.  But I need weights to help it extend down through the gap between the poly.  I got some 1" washers and painted them and the missus made felt pockets shaped like hearts/flowers/suns to hold them.  I have two sets of weights installed and they are working so far.  I need to install the other 8 and make sure they work reliably.  Then I'll seal up the chamber they are in.  At that point the two layers of poly will be effectively fully installed.  Currently the outer layer covers the building and the inner layer stops a foot short at the insulation chamber.  Sealing off the bottom of the chamber will keep humid greenhouse air from condensing on the outer layer and filling the gap with condensate.

I've started putting pine up on the East wall.  As part of that I needed to put up part of the future water tower that will go over the E door.

I also had a buddy come over with his blower door test equipment to see how tight the building was.  It wasn't as tight as I hoped.  I guess when you add up the vents, it has 13 doors, all but two with homemade weatherstripping.  It tested around 450cfm.  Most of the leaks came from:

holes in the vent doors from where the handle hardware had been

air coming in through the cinder block mortar and then up into the building through the block holes

penetrations by the chain drive for the moveable insulation

I can fix all of those.  The cinder block leaks were the most surprising.

We haven't had many sunny days (maybe 2 since Christmas) which is very very unusual.  Along with that it hasn't been as cold as normal.  The compost is barely warm, there is a 90 degree spot near the door.  So this is an interesting test of the building.  It regularly increases in temp 10 degrees on overcast days.  On sunny days it gets up to around 100 at ground level and 110-115 near the ceiling. The coldest temp recorded yet has been 26 degrees.  Most mornings it's around 35.  In a "normal" winter I'd expect it to have gotten much colder inside.  But typically with cold temps we have sunny days.  Storing that heat will be critical.

One pic is of the first couple boards, the other is some 2x4s I put up to eventually hold the IBC tote water tower.

I've been working in the basement much of the last two weeks but today it was sunny so I ventured out to the greenhouse.  Due to a polar vortex cold snap I tracked them temperatures closer than normal.  After a low at dawn of -23, the greenhouse was 16F inside.  I still don't have the compost heat working.  Nor the moveable insulation.  By 12:30 it was up to 88F.  I put siding boards on the East wall nearly up to the ceiling.  Cutting them to match the curve of the trusses is fairly persnickety.  

If I was to build another greenhouse I'd think long and hard about making it a triangle instead of curved gothic shape.  Much less headroom but a hell of a lot easier to build.

By 1pm I was working in my underwear.  At 1:20 it was 95 at 3' off the ground in the shade.  I was up on the wall in the sun so it was warmer yet.  At that time it was -6 outside so we had a 101F temperature difference inside vs outside!

I finished working at 3:30 when it had dropped to 60 degrees.  Two big white pines that I'll cut down later this winter start shading the greenhouse at 2:15 and the distant canopy starts shading a little after 3.  I got the moveable insulation about half deployed and we'll see how that helps overnight.  Should be around -30F tonight.

Once I get the siding finished I'll move on to the water tower and a catwalk that will give me easier access to the peak of the roof.  Currently I can get to the peak from the compost bin or from a set of scaffolding that I can move with some effort.

Very impressive!  Sounds like in addition to deploying that insulation you need more heat storage to get the full benefit of that solar gain, and moderate temperatures for your plants.

Thanks Phil, yes I need the insulation, I need the compost to generate heat and I need to store solar gain better.  One solar gain storage approach that I'm going to attempt is a simplified geo thermal air loop.  Suck air off the ceiling and blow it through 4" drain tiles buried 12-18" deep in the greenhouse.  I'm not counting on tons of storage since we don't have that many hours of hot temps in the greenhouse (3 a day on a sunny winter day).  So if I can just heat the soil a bit with that and moderate air temps it will be worth it.  Plus I could probably store a lot of BTUs in the ground over the course of the autumn.  Nothing like a GHAT system but I'm ok with that.

I might also do the phase change material things I talked about in the initial post but I'm not sure if it's worth the bother.  I do have 180 gallons of water in barrels but they froze a few weeks ago.

Mike Jay wrote:I got the moveable insulation about half deployed and we'll see how that helps overnight.  Should be around -30F tonight.

Ok, it was -29F last night.  I went out in the morning and the greenhouse had only dropped to 20.5 degrees!!!  So thanks to some solar gain during the day and the insulation, it managed a 50 degree temp difference to the outside.  It's sunny again today so I'll go out there and sweat and work for a few hours...

I'm hoping to make a similar greenhouse this year and was glad to find this thread. I'm in Upstate NY, 43 degrees lat., considered zone 5A. I'm thinking of a simple 15ish (whatever a 20 foot pipe bends to in making a curved arch) x 36 foot greenhouse with 2 foot sidewalls, also going down 2-2.5 feet to stop thermal bridging. I'm happy to follow this post since I think it's already answered some curiosities of mine, but my question is this- is there a somewhat hard and fast mathematical rule for the cubic meters of a thermal battery in relation to the square meters of collecting surface of said battery? Also, at what point does the size of a thermal battery make it a liability on a cloudy day (i.e. more depressingly cold mass that you're stuck paying to heat!). I guess a follow up question of mine is at what point does a phase change material make sense? The efficiency of phase change would only matter if there was enough solarization to heat it up in the first place- which begs the square meter to cubic meter question again, I think. I like natural materials that are easy to acquire and I have a mid scale beekeeper friend who has 5 gallon buckets of beeswax I could probably get at a reasonable (ish) price. I'm just curious if a phase change really is necesarry versus, say, making a 4inch thick wall in the interior of the greenhouse, northern long side, out of reclaimed brick or native stone and gravel.

I'm planning on using Solawrap since it dodges all the issues of inflating airspace between simple poly. Solawrap has 1.9 r Value.

Also, a general question, can someone explain at what point (latitude wise, zone wise, r value wise) it's better to insulate east and west ends instead of having them in glass or plastic? Genuine question cuz it seems that there are two sides to the story usually. What's the determining factor for a climate? I'm guessing based on Mike's design that it's about how many below zero degree nights he's slammed with versus my cushy 5a area? We're getting the polar vortexes and all but less often and less severe I think.

EDIT:/ I was also originally thinking of a compost system for heat but it seems there may be a lot going on to get one working? I'd worry about the inconsistency of the "burn," too, as if I did get it working would I have a very fast exothermic process that would crash too early? Honestly for my system, the goal is a very warm greenhouse from March 1st to December 1stish, and if it proves more capable than I thought, then it becomes year round, and I don't know what heating system I'd do yet. Anything like wood or propane starts to have oxygen issues in a well sealed system, right?

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

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.  

For example I am at 47.25 latitude, this time of year the sun is on the horizon so I get very little benefit from the overhead glazing. The morning sun is blocked by trees and fog so my east wall is solid and insulated but the west wall is glazed because the setting sun is often all we get in the winter. So the lesson is plan your glazing and insulation specific to your site.
You may have heard that it snowed in Seattle. So right now my roof which has a one foot slope over 16 feet is insulated with snow. Interesting how much radiant heat is reflected back by that layer.
My next phase is to replace the roofing which is in 8 foot lengths and make the north half solid and insulated. My north wall is insulated with layers of carpet and padding which can be removed in sections so the whole north wall can be open in the summer.  My high/low registering thermometer hit 20 this morning and 15 outside.  I bought a thermostat plug for 2 red heat lamps which comes on at 35 and turns off at 45 shining on my sensitive plants and they came through fine.

First I would like to congratulate you Mike on a great GH build and thread.  I have been reading it now for months and it is impressive how it all came together.

Why did you decide [against] compost pile outside the greenhouse?  You are going to get approx 1k BTU per ton of compost for 12+ month.  It needs to be big to be of any use for building temperature regulation.  https://smallfarms.cornell.edu/2012/10/01/compost-power/

I read you cold cloudy climate post and another, yet I am not seeing any tangible information to sort that question out with an answer.   I was reading soil temps for Marshfield and they are stating the ground at 40 F at 60 inches even on and after the Polar Vortex days.  Does a earth battery sys really need to charge the underground air chamber layers or just exploit the temp differentials?  

[edited]

Hi James, welcome to Permies!

Don't worry, the pile is inside the greenhouse.  Most articles about compost power have it outside but I thought I'd rather put it inside to capture more of the heat.  I'd have to deal with fumes and logistics more but I thought it would be worth it.  Time will tell.  I attached another picture looking west.  The compost bin is the galvanized roofing tin contraption in the NW corner with the platform and ladder on top.  It's 8' in diameter and 8' high, though the wood chips are only 6' high within it.  

I checked out that link you included and it's actually 1k BTU per ton per hour of heat.  My main reference for heat generation is the book by Gaelen Brown on the Compost Powered Water Heater.

From what I understand of it, an earth battery system can work either way.  It could be like the Citrus in the Snow greenhouse where it just draws greenhouse air through a huge earth loop to gather deep soil temps.  Or it could be like the CRIMPI greenhouse where it actively stores heat all summer and on sunny winter days to draw back out temps that are greater than deep earth.  I may be mischaracterizing either greenhouse a bit but I think those are the two approaches.

In my case, I wanted to get temps greater than deep earth for my area (40ish if I remember correctly) and since I don't have enough sun I didn't feel I could go with either option.  While someone may say "40F is pretty good for northern WI", I'd counter by saying if your furnace put out 40 degree air on a -20 night, you wouldn't have a 40 degree house in the morning.

Hopefully I answered your questions, if not, please take another shot.

I thought I posted this a few days ago, but it did not show up in the thread, so here it is again...

re: minor air leaks in the system...

I remember reading that even very small air leaks can completely destroy your ability to keep the heat/cold where you want them.  In my readings I remember someone writing about how much cold air came into his house through the electrical plug boxes in an old house where the walls were either inadequately insulated behind the receptacle boxes.  Try sealing all holes you can with plastic, or however, and see if that helps. Maybe you already got that done, but...

re: thermal mass...

I forget how far down you went with your insulation along the walls.  But as you mention the mean annual temperature is ~40F in your area, and is why you did not want to go with a low grade geothermal like the Citrus In The Snow and similar greenhouses, and why you made a comment about a heater putting out 40F air, and the outside air being -20F then the house would not be 40F in the morning.  Ok, but also consider this -- if you did not insulate the soil under your greenhouse then you have a constant heat sink sucking the temperature in the greenhouse soil (basically in an insulated box) down to that temperature.  I remember reading about someone that built a greenhouse back in the 70's -- insulating just the underground perimeter walls and not the bottom.  They were hopping to keep the soil temperature high.  They found that all the heat was being sucked out of the bottom.  That said, this is part of what makes the climate battery and low grade geothermal work, or at least as I understand them.  So all of this said, I would be surprised if you could keep the greenhouse soil much above the mean temperature year around.

I also found the following: "The 24-hour cycle of air temperatures disappears at a depth of one-half foot; five feet down, ground temperatures lag three months behind seasonal air temperatures. The lag is six months at 15 feet. Soil temperatures are constant below 30 feet, and, incidentally, about equal to the average annual air temperature."  At first I thought the 12" to 18" depth was to little, but then read in the context of pumping the soil temp up makes sense.  That said, if you are growing plants in the same soil, they will get down to where your are heating the rootzone, and that might cause some issues depending on the temperature fluctuation.  But with a 115+F between inside and outside (as reported a -6F and +110F previous)I am guessing you really need a lot more thermal mass to stabilize.  I could be wrong.

re: changing the design from an arch to triangular/rectangular...

Take a look at Citrus In The Snow greenhouse <http://www.citrusinthesnow.com/>.  That profile might be a good compromise.

I need to jump back on my projects here.  I hope that all continues to go well on your end!  Thank you so much for sharing the details and allow us all to think along.

Hi Ebo, it's good to hear from you again!  I do plan on fixing all the leaks I can.  It should make a good difference, especially given the height of the building (greater stack effect).

I insulated down one foot and out three feet on the exterior of the footings.  I think it's called a Swedish Skirt insulation method.  And I've read the same thing regarding soil temperature cycles.  One detail that will help me is that by insulating this 800 square foot area from the cold of the surface air, I'll create a heat bubble underground.  I suspect that the temps 5' down will be 5 to 10 degrees warmer under the greenhouse vs under my nearby garden.  That would get me closer to 50 degrees and also to my desired interior minimum temp.

I struggled to figure out the heat loss to the soil given the unknown R value of soil and the challenge in determining where that R value is occurring.  Is it at the top 4" of soil or below that daily temperature swing?  In any case, I assumed an R 4 (say for 8" of soil) and a delta T of 10 degrees.  That heat loss was insignificant compared to the losses through the glazing.  So hopefully between the heat bubble and the minor delta T of the situation, I did good.  I wasn't about to dig up the whole floor of the greenhouse to put insulation under it since I want to plant trees in the soil.

That is a beautiful building, and a monumental undertaking.   It's nice to know that the sun is just as effective at your lattitude.

For what it's worth, and I know I won't be too popular in the midst of all of the praise here, but those of us who have passive-solar greenhouses and passive-solar houses get these same results.  What may come as a surprise, since you've had winter kill in your soil where you are, is soil-borne diseases and leaf diseases that thrive at those high temps.  

Air flow is important all year long to keep these diseases to a dull roar.   The condensation and humidity inside can bring in molds the likes you had no idea were there, unless you've run into them in a basement or house.   This may affect you as a worker inside there, as well as the plants.   If the soil doesn't freeze, the soil-borne diseases live 12 months out of the year, and are lurking all the time.

There is still a huge swing of temps, from 29 to 100 that is really tough on food plants.  They might stay alive, but producing food is another matter.  I have to get special tomato plants that can take a swing of 40 up to 100 in the summer, and not many can do that.  Tropical fruit trees (citrus/avocado) still can't do 29 without some help.  But if it's 100+ up at the ceiling when there are short days, they are getting signals they've never gotten before.   100 degree temps go with long days in their world, and when you get high temps in January, with short days, they are going to bloom sooner when the pollinators aren't out yet....it's just a whole 'nother world.

I have fruit trees under what I thought were ideal conditions that still won't produce fruit.  I'm not even dealing with your winter temps.

So just be on the lookout, and get the toughest of fruit trees that can really take some "abuse."  :-)

Mike!  Good to be back.  Lots on my end, but that is for another discussion.

I agree with Cristo.  I remember reading about a rare high elevation plant that daily survives freezing temperatures at night, and very hot during the day.   Very few plants can withstand that, much less food crops.  Realistically we need to help you keep the temp range down.

Hi Cristo (and Ebo), I do realize that this will be an interesting environment for plants.  I hope that with the compost heat working the low will be closer to 40-50 at night and 50-60 during cloudy days.  With some venting or ideally a shallow air to soil heat exchanger from the ceiling, I hope the sunny winter days will be kept closer to 90.

I'm hoping mold and other things aren't an issue, I don't have a good fix for that at this point....

I'll probably aim for plants that don't need insect pollination at first so that they can flower whenever they feel like it.  I haven't gone through my dream plant list yet to see which pollinate which way.  If needed I could dress up as a butterfly and do it myself.  Or...  Get some butterflies and have them live in there in the winter.  

Mike Jay wrote: I hope that with the compost heat working the low will be closer to 40-50 at night and 50-60 during cloudy days.  

Mike,
I am curious as to why your compost could be a viable heat source if you cannot fit approx. hundred tonnes of compost in the Greenhouse.  
I say that under the impression that the BTUs/h on a -20 F night is going to be in the hundreds of thousands to warm the airspace to +45 F.  
Am I mistaken on that?

Hi James, the main number I've been working from has been 1 million BTUs per month from a cubic yard of compost.  I think that was based on Gaelan's book but I don't have it in front of me.  There are many variables, of course.  But based on that, my current pile is 12 cubic yards which "should" give 400 kBTU per day.  Based on my average solar collection (per charts and NOAA) I should accumulate an average of 483 kBTU of heat in a December day.  My building's heat loss while maintaining a 60 degree delta T to the outside should be approximately 590 kBTU per day.

These numbers are all based on my design and I haven't adjusted them to actual building shape changes and the blower door test results.  

So as the young engineer always tells you, "It works great on paper"