Hi curlygirl, at least 6 hours is a must for sure and of course the more the better. On my property the winter sun is crazy different than in the summer. Our property tree line is an issue now that the sun is rising and falling differently.But I charted this as well, its a must! So can you explain your shcs is it the same as melsmiths basically?
Im working on lining my pit with xps board right now and then when my hubby arrives home from traveling with work we will start to lay the ads....still working on those numbers though! Sunnyjohns website was a bit of a help! Good luck,cindy

Ladyofthecariboo and web-friends,

Glad that we share similar interest in SCHS. Its good to find kindred spirit.

Mel's site Narrows Creek, has good pictures.

Glad you found sunnyjohn's SCHS site, the data in the FAQ are great! Check out this site too, by Dr. Roper http://www.roperld.com/science/YMCAsolargreenhouse.htm it has some hard data.

or you could check my site too--a test project of--of sorts. The data are very encourgaging. There will be challenges adapting it to my location, Seattle winter (for gardening) weather.

Best wishes,

MTW

Here is a link that might be useful: Michael's test of SCHS

I built a 10'x20' solar GH a year ago and installed a SCHS. I built it on a 3' high foundation and installed 2" Dowfoam around the perimeter. The north wall is about 60 % buried below grade (and insulated) and set into a hillside. South wall and roof are glass and poly (doubled), other walls and roof are well insulated. I'm in SW Colorado at 7400', just north of 37ú. Solar radiation here is amazing.

I was well into construction before I discovered the Sunnyjohn website so my SHCS consists of 100' of 4" ADS buried in 14" of 1" cleaned rock. I've added 14- 55 gallon plastic drums filled with water (half in direct sun) and have containers of soilless medium and hydroponics sitting on top of the barrels. The south wall is occupied by 30" wide raised beds and cool weather crops.

Lat night was the coldest (2ú) so I employed an 1500W electric heater. It was 62ú inside at daybreak. That's too warm because of the cost of heating. My goal is 50ú minimums. Before last night, lows had been around 10ú a couple of nights. Daybreak temperature was at 50-52ú inside the GH without heat.

I hope to build a second GH next to this one and will bury the SHCS at least 3', maybe more. (One GH for cool and one for warm crops.) I'm thinking of a solar system that would heat water and store it in barrels for nighttime circulation. I'd bet such a system would reduce my electric heating to a half dozen nights per year, tops.

I am still harvesting toms, peppers, cukes, zucchini and all of the cool weather crops. We eat 4-5 toms (3") per day and I've thrown some in the compost because we couldn't eat them all. There are some 20 ripe ones on the kitchen counter as we speak, with more in the GH. This past summer, without a shade cloth I grew lettuce all summer, something I can't do outside. Anyway, I'm quite thrilled with the setup so far.

Mark

Mark,

Thanks for posting. Really interested in your GH. Do you have pictures. Your numbers on temperature are very encouraging.

Could we stay in contact, just send me a message. Sorry, not for not posting email--because of junk mail bots.
http://michaeltwong.web.officelive.com/contactus.aspx

Thanks for sharing.

MTW

p.s. tried sending you message via this forum, seems not possilbe.

Check out

http://www.roperld.com/science/YMCAsolargreenhouse.htm

http://www.roperld.com/science/YMCASolarGreenhouseConstruction.htm

http://www.roperld.com/science/YSGHData/

http://www.roperld.com/science/solargreenhouses.htm

roperld-
Any information on how the plantings have gone?
Thanks.

Night time lows of 10F (-12C) with greenhouse soil temps reasonably steady at 50F (10C). My 150sqft greenhouse is very small compared to most that have a shcs installed.
The shcs consists of 180ft of 80mm perforated tube arranged in a 2 layer radial loop pattern (a giant 15 armed octopus buried in the greenhouse floor). The lowest tubes are 4ft deep with a central plenum driven by a 700cfm 10" duct fan.

Six hours of sun per day would be nice but its not very likely with only 6 hours of daylight available :)

hex,

Had I done an adequate job of research, I too would have increased the SHCS depth to 4'. Next solar GH will be built that way.

Mark

Hi Mark
There wasn`t much/any info around for shcs in small greenhouses, most are in large tunnels. I maximised the amount of mass by going deeper. Its surprising how quickly heat transfers even with very short tube lengths. I run upto 45 airchanges an hour in summer, the air temp can drop by 30-36F travelling through just 12ft of tube which takes around half a second.

hex,

As I stated earlier, I placed my 4" perf. ADS on clay and covered with 14" of cleaned rock. Raised beds and water barrels with containers on top sit on the surface of that. I assumed that the air needed an outlet which the rock provided. Otherwise, of course the blower would be unable to force the heated air in.

I'm thinking of a 24'x40' hoop house and plan to insulate the perimeter (the importance of which I've learned after years of building homes in Colorado). Would a SHCS be cost effective buried only in soil, no rock? Obviously, the far end would have to allow for circulation, maybe 1" rock, 1' wide x4' deep x 24' (the width of the hoop house). Either 1 large plenum in the center or two, one at each end.

Installation would involve digging virtually the entire footprint to 4'. Actually, since I'll probably bury 4x4's around the perimeter with foam against them, I'd leave 2 ' around the perimeter undisturbed for 4x4 stability. I'm not sure it would be cost effective in a simple hoop house.

I plan to use low row covers during the "shoulder" seasons so thermal storage in the soil might be utilized quite well. The idea, of course is to extend the season as much as possible.

Sorry, I'm just thinking out loud right now. Input from anyone who has built a SHCS in a similar sized hoop house would be most appreciated.

Thanks,

Mark

Hi Mark
My tubes are buried in heavy clay, no rocks etc. I guess the clay has settled into very solid mass now but i haven`t had any problems. I installed vertical perimeter insulation 2ft deep using 2" thick XPS.
I put a gentle slope on the 15 tenches and placed the tubes on a bed of pea gravel to direct any water towards the central plenum.
The plenum itself sits on a 2.5ft deep x 18" x 18" perforated sump surrounded by 3/4" shingle which allows the water filter into the sump. An automatic dirty water pump/float switch empties the sump when the water level reaches a set level. The bottom of the sump is 6.5ft below floor level. My greenhouse floor is circular and the layout and design is very different to normal.
It may give you some ideas though :)

hex,

I'm thinking that the perimeter insulation should meet or even exceed the depth of the deepest tube. Depth of tubes and thus volume of the system would depend on total BTU's available and HC requirements. It would be a waste of money to build a SHCS with larger thermal storage than BTU's available. I believe that most earth materials have similar thermal storage capacity.

So, the design depth of the system is regulated by solar radiation since total volume can only be adjusted by increasing or decreasing depth. The soils in the location where I'll place the hoop house drain very well to 9 or 10' (a rarity for SW Colorado) so I'm not sure I'd need a sump.

Is thinking in terms of thermal storage correct with a SHCS?

I had even thought of 2" of insulation beneath the soil, similar to an insulated slab, but it would have to be at a great depth (probably 5') so as to leave plenty of soil within the heating/cooling envelope for SHCS to function. Cost prohibitive, though.

Did I make any sense?

Mark

Hi Mark
Its not necessary to go full depth with the insulation, the temperature differential 2ft down will be much lower than at the surface and the benefit versus cost may not be worth it.
Horizontal "wing" insulation has almost no depth but is equally effective and will save a lot of digging if you have some space around the greenhouse.

Bottom insulation fixes the amount of mass, i didn`t bother as any downward heatflow is likely to be very small at 4ft deep in comparison to horizontal heatflow at 1ft deep.

You may find this of interest regarding wing insulation performance in alaska
http://www.crrel.usace.army.mil/library/specialreports/SR97_07.pdf

Even though I have no plans to build a thermal-storage greenhouse anytime soon, the idea has intrigued me for quite some time and I have followed many of the threads about it.

My question is do these kinds of greenhouses have to "thaw out" in the spring? Even with thermal storage I don't think that sunlight is intense enough to grow all but a few plants in the dead of winter (especially as far north as MN). So how does this all work come end of winter, but before spring is trully here? Do you have to keep them heated/circulating all winter so the ground doesn't freeze solid? I think you know what I'm trying to understand or ask... hopefully. =)

ladyofthecariboo, thanks for your reply -sorry it has taken so long to respond.

I have heard that about 6 hours of sunlight minimum but for my property, it is not that simple. And unfortunately, no, my property is not like Melsmiths' because I live in Massachusetts in an area where the average house lot is half an acre and there are lots of trees everywhere on other people's property blocking the low winter light. On top of that, despite our efforts to find a house with room on the south side for a greenhouse (literally years of looking), in the end, we had to settle for one that had room on the eastern side. So, we get some eastern and southern light but some of the western light is blocked by our one story house. The eastern and southern light have deciduous trees in its path and we are unsure if we need to cut them down (there are still other trees in the path of light on our neighbor's property so we only have so much control) or if enough light will shine through the branches (maybe do some pruning to thin them out). I have heard that we may want to keep the trees as natural screening in the summer. Currently, I am getting readings of 20,000 lux at 3pm on a sunny day. When there is dappled sunlight, the number drops to 7,000-10,000.

Hex, you said you only have 6 hours per day available total where you are, right? And you say you can keep your soil's temps at 50F -is that throughout the winter? Do you ever run out of heat? What are your air temps in the winter? What kind of envelope do you have? My goal is to maintain temperatures in a greenhouse that is used for growing tropicals so I need the lowest temperature (air temps) to be around 60F. We may heat the soil in the raised beds seperately as backup and we may need some sort of air heat as well. The greenhouse will be glass -preferably insulated. Any information would be appreciated.

Thank you!

Hi Curlygirl
The greenhouse is timber framed and triple glazed with 2 seperate still air gaps.
The soil temperature 4ft below the floor falls to a minimum of 50F. The lowest outside air temp this winter so far is -17C. I set the greenhouse thermostat to keep it frost free but i dont attempt to heat it above that as i don`t have enough hours of light to warrant it. I couldn`t keep tropicals alive here without running extra heat for sure.
The system manages to store some heat almost every day, the fan thermostat is currently set to run when the geeenhouse air temperature rises 12F above the soil temperature. It doesn`t take much sun to bring it upto 62F. The differential is adjustable from 3F to 36F.

Hello everyone, its so great to read your posts about the shcs! The weather up here has halted all progress so my greenhouse sits in our shop! I appreciate the links that are posted , some very very useful data! Im hoping that the 5 wall poly of my greenhouse will prove to be worth its cost and will help to keep my warth within.Happy gardening everyone! I have the winter to dream and plan and gather information for the layout of my shcs.

aztomn: I am in zone 5 (Massachusetts) and have had no thermal mass an no heating last year. I was able to grow peas and beets through the winter. I have no frost issues and there's no thawing needed. This year i tried a few additional things and the more tender plants died off as expected (Hey, ya got to play!) like beans, tomatoes and even a banana tree! What is doing well are peas, beets lettuce, strawberries, snapdragons, shallots.

Next year i';ll add more cold tolerant plants like kale, carrots and i don't know what else... yet.

Now that the night time temps can be in the teens, I expect growth to stop until mid-January if things follow last year's trend.

Additionally i moved some orange and lemon trees out there since they've gotten too big for the garage. They seem to be fine except that new growth has taken some freeze damage. Older growth looks fine.

I decided against the SHSC design simply because i thought it was too much of an expense (and work!), but i reserve the right to add it later. MY GH is 50 x 26 and double walled poly.

Lady of the cariboo... 5 wall poly?? Is that right? The one concern i would have is the amount of light that gets into the GH. I notice that with even 2 layers some plants definately suffer. Broccoli for example. Heads grown out of doors will be twice the size and much darker in color than those grown inside.

Good luck!
Poppa

Poppa- thanks for answering. So I would assume just leaving the a greenhouse be for the winter allows the heat of the day to keep it from freezing even though night temps would fall to the same as the outside.

Being in MN right now with 2ft of snow and 0f out today it's hard to believe sometimes that hell doesn't freeze over too!

aztomn: I have no proof, since i have not taken temps in the GH, but i would disagree that nighttime air temps inside are the same as outside. If they were, i wouldn't have anything alive. Temps have reached 8F overnight and very little damage inside. Yes, There may be some ice in the watering can in the morning, but i rarely see freeze damage to any but the more sensitiv plants. Of the plants i have left the only ones with any damage are strawberries and i suspect it due to the high daytime temps and not the cold night time temps.

I will not rule out that at some point i will have some freeze damage. I did see some last winter when we had a week of sub zero temps with the daytime highs in the teens. But I only saw dieback and regrowth when the temps moderated in january.

What i have not seen yet is a week of cold temps that also are overcast. That will likely be a sad day in my GH!

A couple of clarifications...
"I have no thermal mass..." - Well, the ground itself is obviously a heat sink, and i also have added a 1500 gal water tank, but neither of those are active heat sinks. There is no exchange mechanism as you have with SHCS. I think there would be some improvement with an active system, I wouldn't deny that. I'm just not sure it's worth the investment. I've seen picture's of hex's system and my back aches just looking at the incredible work he did.

"My GH is double walled Poly..." - well, yes it is but it's more than the common inflated design that most commecial GH's use. Mine is literally a GH inside a GH with a minimum of 2 feet of air space between the layers. If you will, where other's talk about using tunnels inside the GH, i just expanded those row covers to nearly the size of the GH itself. So while my outer GH is 26 x 50, the inner GH is 22 x 48.

Yes Poppa my gh is made of a 16mm 5 wall poly. It has a r value of 3.03. I purchased it from BC Greenhouses, its a Cross Country Greenhouse. My light transmision is 62% which isnt worrying me up here in central BC Canada. The benefits of the insulation factor was the bonus for me with it being 80% more efficient than the traditional twin wall poly, and 50% more efficient than double glass.The 5 wall poly gh's are the newest and most energy efficient on the market today they claim. My gh will be used to run my business supplying our local restaruants and catering companies with greens and garnishes, hopefully cool crop veggies as well year round. The 5 layers of poly will help to screen my crops during the hot summer days as well .I wont be growing things that need to bloom so the light transmission thing wasnt an issue for me. Im growing in a vertical hydroponic system and am really excited to see what my readings will be with the shcs insulated underneith at 4 1/2 ft with this gh. I have the option of removing my back wall, clipping on more sections and away I go.
Take care
cindy

I'd be interested in hearing how that works for you. I don't know what the light requirements are for various greens so I hope that works for you.

Do you have an established business and are looking to expand the season, or is this whole thing new for you. Just curious as it seems that it's a lot to take on all at once. I would like to do the same but i am much more caution (CHICKEN!) about it. I suppose there's nop way to determine the market other than going for it.

Good luck with the project!

Poppa

Any updates from anyone -melsmith, how's your greenhouse coming along? I have been checking your blog for updates.

We are still in the planning stages so nothing to report here but I was wondering if anyone has heard about tree roots affecting the tubing? We are planning on planting fruit trees in our greenhouse so we are concerned that the roots may eventually interfere with the system. I tried registering on Sunny John's site to ask that question but never got a response. It seems that site is not as active as it once was. Hope that's temporary!

Our plans have raised beds for the trees (some beds being quite high as we are stepping them to take advantage of the finite amount of light we have available) so that will help somewhat. But some of the trees we want to plant have a tap root that can go 20' deep! Any thoughts?

Leah

Wow Leah... what kind of trees are you planning to grow in the GH? With all the digging involved for a shcs i'd be REAL nervous about those roots. If your pipes have any holes for drainage i'd be concerned...

Sunny John's never was very responsive to questions and i'm sure i've tried for over 10+ years. All the links to projects were either dead ends ot those people who claimed to have built them never answered their emails either.

Good luck!

Greetings curlygirl and all. Winter set in and put a stop to my greenhouse progress until recently. I finished installing the rails to hold the plastic and then put on one layer of plastic on St. Patricks day. The greenhouse is now covered but the underground system got completely filled with water! (Like 6 to 8 feet deep!) Over the last couple of days I've siphoned out much of the water but will still have to get down and clear everyone of the 27 runs of drain tile with a wet/dry vac before I can start the fans circulating. Anyway, I'm back to working on greenhouse and the SHCS system. I'll be updating my blog with photos as I make progress. If I learn from my mistakes, I have a feeling I'll learn a whole lot before I get this project working like I think it should! Ha!

Here is a link that might be useful: My greenhouse project

Poppa -We are going to grow tropical and sub tropical fruit trees and among them are Mangos -those are the ones with the 20' tap root. I have also heard that Avocado tree roots are aggressive and sometimes destructive. From what I gather, the tubing for the SHCS would have holes in it so when the water vapor turns to liquid (the phase change) it goes into the soil, along with the heat. So, what's a SHCS enthusiast to do? It's possible that the conditions in my future greenhouse would not be favorable enough for the trees to grow aggressive roots and I could have the trees I am most concerned about in pots but I don't want to take any chances. Has anyone tried using another type of tubing that could resist roots? Also, Poppa, I see you are in Massachusetts. -What part? I am in the Metro West area near I-90.

MelSmith -My sympathies about your flooded tubing. Is your greenhouse in a high water table area? Looking forward to reading your updates!

Ladyofthecariboo -Are you making any progress?

Curlygirl - I'm in the western end, near springfield.
I don't know how aggressive those trees are. I know that certain types like willows will grow into pipes searching for water. It's a big problem for sewers. I'd also be concerned about the difficulty of removing the roots for whatever reason. They'll be wrapped around the pipes and my back aches thinking about it.

The issue with high water was something on my mind too. I learned that although i have mostly beach quality sand, i have a 8 inch layer of clay about 3 feet down which keeps the surface water high. I had a nice stream running through my GH this Spring! Had i added a SHCS I would have been out of commission for the early spring when i think the system would be most important. IF i ever do decide to add one, i will need to add perimeter drains as well as drains below grade. UGH!

So far I am happy with my double wall GH. Tomatoes are sprouting and so far have not been damaged by the 20F night time temps. I am unheated. We'll see what happens when the temps drop to 16F tonight. I am hoping i am safe with the nice sunny days that are going along with the cold temps.

Tropicals (Banana, orange/lemon) for the most part did not survive the winter. A surprise was Kiwi (not the hardy type). I am hoping with insulation next winter i can get some tropicals to make it through.

Hi Mel
You may need to dig a sump and install a pump if the flooding isnt too excessive. My sump is below the tubing at 6ft deep, the pump (2400 us gph) is automatic with a float switch. It doesnt run very often though as i`m on rock solid clay.

{{gwi:305796}}

Poppa -I'm think that because the tubing sheds the water through the holes and into the soil that the roots would not be that eager to go into the tubing. I am still concerned that the roots could interfere with it, however. In another GardenWeb forum about SHCS from 2008, Ingevald wrote about Ivan Stoilov growing figs in Missouri using SHCS. I read somewhere that his tubing is three feet down and it looks like from the photos that the fig trees are all planted in the ground (because of that, they grow really fast with the warm, moist soil). Does anyone know of a way I could contact him to ask how it is going? Or has anyone heard themselves? I am wondering if there was a way of laying the tubing that would keep it roughly out of harms way or if there was something I could do to protect it. Congrats on the kiwis!!!!

Hex -Have you been in touch with SunnyJohn? I saw someone with the username of Hex on his forums -is that you? -I am trying to get a username so I can post my root question on his forums and has has not replied. Thanks for the sump pump information. I will have to do that myself. We have two sump pumps for our basement (they run fairly often) and we plan on attaching the greenhouse to the house. I'm a little concerned about the water but we plan on harvesting the rainwater from our roof so perhaps that and some other precautions will keep most of the water out.

I'm collecting various blogs/websites on greenhouses, shcs, tropical fruit growing in Northern climates, and rain harvesting in greenhouses. If anyone has some favorites to send my way, I'd appreciate it. I don't suppose Ivan Stoilav has a blog/website?

Thank you! This is all very helpful!
Leah

Leah... roots will go where the water is. It's such a problem in sewers they actually have machines that will travel through a sewer to cut roots. It might not be a fast process so if you're only thinking ten years, then let the next guy deal with it.

I can tell you that i played with some citrus this year. The ones in pots above ground did not survive. The ones planted in the ground lost all thier leaves but may send out new shoots. Not a resounding success but it does support your research that planting them in the ground might make more sense.

For me, i plan to better insulate the GH during winter nights. I am hoping that might be enough. If not, I have a couple of other thoughts up my sleeve to try before resorting to all that digging.

Hex is da man for SHCS in my book. No one else has ever replied to my inquires either. Search through the forums for some of his threads.

Poppa

I took your advice hex2006 and bought a sump pump. I just lowered it into the flooded barrels on the lower end of the SHCS system and withing an hour it got rid of the water. I started the circulation fan and instead of having the inside of the greenhouse the same temperature as the outside, it's now running 6 to 8 degrees warmer. My underground system is cold from absorbing cold all winter long but even tonight the inlet air temp was 33.5 but the outlet was 42 degrees! I guess that's a sign that it's beginning to work. Encouraging! Daytime high today was 86 in the greenhouse and I pumped-circulated all that luscious warm air underground. The overnight lows are supposed to climb this weekend and with the improving operation of the greenhouse, I think I'll be able to begin starting seeds.

I'm posting every few days on my blog now with photos and monitoring temperatures, so anyone that is interested should subscribe there. I think it's beginning to work and I'm really encouraged.

Does anyone know of a pre-formatted spread sheet that one could keep? It would be nice if I could enter in values for outside temp, inside temp, air inlet, air outlet, on a template, and then have all that information displayed on a graph of what's going on over a period of time. There must be some correlations between sunny days and the night time outlet temperature of the SHCS among other things. Right now I'm writing notes but suspect a preformatted template would be really helpful and probably exists already somewhere. If I could remember what I learned in my Excell class, I think excell would do the trick but I'm not very good with spreadsheets. I'm much better if someone else has already designed the program so I just have to enter values and read results. Let me know if you have ideas for that.

Here is a link that might be useful: Stories from Narrows Creek

Hi Mel
Good to hear the pump did the trick. The system probably won`t perform optimally until the tubing and surrounding ground has dried out a little. The warm outlet is likely due to energy being pulled from the ground to facilitate evaporation of the excess water in the tube. The water has to gain heat from somewhere in order to evaporate and the soilmass will be somewhat warmer than the air.

Monitoring the inlet/out RH difference should give you some idea of how wet the tubes are and how the drying process is progressing.
I have digital hygrometers on the inlet and outlet to give me an idea of the RH change. I also installed a remote temperature probe 4.5ft deep in the ground between tubing, i located it as far away fom the inlet as possible so it gives a worst case reading. Its not what you might call state of the art environmental monitoring but does serve as a rough guide.

Dataloggers (for soil temp, air temp and RH) would the ideal way to collect data over time but it might get expensive as you`d need to monitor several different locations to get the overall picture as well as the soil/air outside the greenhouse for comparisons.

I agree that my system is going to take months to stabilize. It may not have to dry out though. I read about one system that used mud for heat storage and then the guy dried the system out and noticed no change in performance.

My system is already working. Tonight, the outdoor temperature is 30 degrees but the greenhouse is at 39 degrees and I just took measurements at the inlet (39.5) and the outlet (44.4)! It's drawing heat from somewhere! I just went out and took the measurements and found the ceiling fan cord had come loose and gotten wrapped up in the ceiling fan blades! The fan was stopped and Lord only knows how many hours it's been like that. I unwrapped the cord and the ceiling fan started up just fine!!! Wow!

If I can only learn from my mistakes, I'm going to be a genius someday! Ha! Ha! Anyway, I'm collecting data and I'm surprised that the results are improving so rapidly with the screw-ups that I've discovered.

Tomorrow I'm going to start planting seeds. April fools day is my day! I think the greenhouse will support starting seeds now. The high temperature today in the greenhouse was 94 and the low tonight will be above freezing for sure.

Here is a link that might be useful: My Greenhouse blog

Mel, congratulations! I got shivers of excitement when I read that you are already getting results! Can't wait for when it will be me! I'll be watching your blog!

I have been scrounging for information on the affects of roots on the tubing. Poppa, I see your concerns but I don't think that this is the same as a sewer where there is water constantly running through it. Mostly it is moist air and I don't think that is enough for the roots to go nuts. -I think my greenhouse would have to flood the tubing but even then, the water would be everywhere so I don't think the roots would be especially motivated to infiltrate the tubing. I searched some more on Sunny John's forums and found two discussions about this problem. One, Sunny John said not to worry about it because the roots would likely "air prune" which made a lot of sense to me. On another thread, he said that no one is sure what will happen but again mentioned air pruning and said that RotoRooter could clear out the tubing if roots did penetrate but that the system would have to be designed with that in mind. He also recommended filling the area around the tubing with sub soil then putting a weed barrier and then filling the planting area with rich soil so the trees would have no reason to penetrate into the subsoil where the tubing is. Anyway, I am encouraged. I'll keep you posted!

Great thread!
A couple mods on the standard SHCS GH design I am considering that i would love to get some feedback. Site is western colorado and size is looking to be 1000-1200 sq ft.
I am thinking about one short run of plastic chambers (http://www.infiltratorsystems.com/productline/quick4plus.asp) instead of all that ADS. It seems like it would maximize the amount of contact between the air and the (heavy clay for me) soil. i was thinking of piling up some chunks of clay or maybe some rocks in the chambers to slow down the air and add thermal mass. Maybe just a couple runs of ADS through the raised beds to keep the soil temps up.
Also i am looking at pounded tires (earthship fashion) for the below-grade insulation, actually going up a couple feet above grade to keep the north strawbale wall out of the ground moisture. Any thoughts on this?
Thanks!!

Nice to see this thread still active.

Soho hick... There is a greenhouse near me that was experimental and recieved some grants to build. Rather than use all that pipe (or chambers) they dug a decent hole and filled it with 3 inch gravel and rigged it so the warm air blew through the gravel. They were one of the few to reply to me and after a couple of years they were still happy with it. I'm not sure if that would be cheaper than what the SHCS is but it's worth a thought.

As a side note: I posted earlier that my experiment with citrus was a failure after we had several days that dipped to -14 F this winter. I never got around to tossing the pots and to my surprise in late July they acrually sprouted from the roots! I think it took so long to sprout as i had stopped watering them once they "Died" so they went dormant. When i noticed some flowers in the pots i started watering and lo and behold there were the citrus trees! They now stand about 3 feet tall. I am simply amazed what can survive in an unheated GH.

NO, i won't overwinter in the unheated GH again without the full solaroof insulation system, but it's interesting all the same.

Poppa

If you want a LOT more info on this, check out the archives of the solaroof group on yahoo.

I'm unconvinced of the need for perimeter insulation, with the possible aside of a couple feet of flat insulation extending the footprint.

My climate -- zone 3, won't permit year round use. I'm aiming to be able to start bedding plants in February.

However this doesn't mean that SHCS isn't working for you year round. Consider:

Bare ground outside in our climate will freeze to a depth of about 3-4 feet on a typical winter, and we bury water lines 8 feet deep for the tough winters. But even a simple leaky glass covered shed will keep a 55 barrel of water from freezing solid.

I want to plant in February. Turn the fans on in January, hooked up to a thermostat so the fans run only when the green house temp is above 15 C (59F) On warm days I'm pumping heat into the ground. I bet by Febrary I'll have ground temps warm enough for planting.

In addition: Suppose I put a plastic wall 1/4 of the way from the output end of the tubes. Now while the whole green house is collecting heat, I'm only trying to keep 1/4 of the greenhouse warm at night. Start stuff in 72 cell/flats for the first month. Transplant to larger cells afater the rest of the greenhouse warms up.

When laying out the tubing, in a cold climate go as deep as possible. 3 layers, with the bottom layer being 6 feet down, 2nd layer 4.5 feet down, 3rd layer being 3 feet down. Each layer is on a separate plenum.

Summer. You have the sides rolled up, the gable vents open, and it's still hot. Turn OFF the top layer fan. Your soil is probably warm enough. Keep heating the middle and bottom layers. Add extensions to the output plenum so it exits outside, if the exhaust air is too warm.

You may be able to get a 6 foot thick mass of soil to 35 C (93 F) That heat can trickle into the greenhouse allowing your crops to grow until November

Hi Sherwood Botsford! Interesting ideas!

Why do you think each layer should be on a separate plenum? Is it because the top layer will be warmer (heat rises)? Do you have a diagram of what you are talking about? What I am picturing would add cost and complication to the design.

Could you also explain your thoughts on perimeter insulation? To me, it sounds vitally important to the success of the design.

I have yet to install my system or build my greenhouse. At this point we are hoping to build in the spring of 2013. I'll keep you posted!

Leah

Hi all! Doesn't look like this thread has been active for a while, but maybe someone will get this...

I'm using SunnyJohn's well-known calculator to determine ROI for a SCHS... His default price for the 4" tubing is $0.30 and the default price for the Therm Cost is $1.55, whereas contractor discounted price of tubing in Jersey is $0.48 and Therm Cost is $0.50 for natural gas... these disparities skyrockets the Hardware Payback Years to 13 years (or 17 years if you put socks on the tubing), lol. Any thoughts?

ARittjr, A few thoughts...

SunnyJohn's site has not been updated in a while (no doubt due to John's passing away a while back), so it's not surprising that his numbers are out of date.

Not sure where you are getting your NG, but in Colorado it looks like a therm of NG is running about $1. Still in general NG prices are very cheap right now (below the cost of production for many providers), and I would not expect that to last for long.

On my project, I figured roughly a 4-5 yr payback at current prices (but I have propane not NG) which I was OK with, especially as I don't expect the price of energy to stay this low forever..

Is anyone still reading and reporting on this thread?

Nothing new in over 2 years so i`d guess not :)

Hex, maybe you can help me. I am looking for a copy of the SHCS calculator that I think originally came from Sunny John. Do you by chance have a copy of it?

Hi Haymaker
Numsum which hosted the calculator closed down a while ago (April
15, 2014). I have an offline version in html format which i`ve put in a zip file (145kb) and uploaded it to datafilehost. The zip contains a folder with the calculator files and a html file that you click to run the calculator. Be sure to uncheck the box that says "use our download manager" before you download the zip.
http://www.datafilehost.com/d/cbcd7ef8

Hope this helps

I set up a spreadsheet much like the sunnyjohn calculator, and ran some numbers for my climate, Edmonton, Alberta. I came to the conclusion that in this climate I needed to double the depth of the layers. E.g. 6-8 foot deep. This starts getting awkward, as they don't rent ditchwitches that do a narrow trench that deep.

Ballpark calcs: The worst case is a 'frozen fog' weather cycle. Cloudy days, so minimum heating, coupled with temps of -20C (-30F). Given an R2 greenhouse (typical for 2 layers of poly with an inflation fan, then every square foot of surface has a 90 degree temperature differential across it.

Because of the sides of a hoop house, I am going to make the approximation that there are 2 square feet of outer envelope for each square foot of ground. This is pessimistic. It's somewhere between 1.57 (pi/2) for a very long green house and 2.

So each square foot of greenhouse floor has to store heat for 2 square feet of R2.

With a 90 degree F temperature differential, it takes 45 BTU/hr x 2 square feet = 90 BTU per hour. Again, being pessimistic 5 day operation = 120 hours. So 90* 120 = 10,800 BTU

The heat capacity of dirt is about 1/3 that of water on a volume basis. Call it 20 BTU/cuft/F

If we are willing to let the greenhouse temp drop 20 degrees, then each cubic foot can store 400 BTU. That would mean 25 cubic feet of dirt per square feet of floor.

Ouch! If we are willing to go 2 days, it's easier. 2/5 as much heat = 10 feet.

Saving grace: If we are are going for long term heat storage, the tubes can be further apart.

Sunny John estimated on the basis of storing 1 days heat, so his pipes were a foot apart. If you want 5 days heat, you can put them further apart. It starts to make sense to drill vertical holes instead. E.g. Drill a 1 foot diameter hole 20 feet deep every 5 feet. Each one gets a loop of pipe going down and up. This does make for a less efficient heat exchanger, as the air going down will transfer some heat to the air coming. Worst case, the air out will be the average of the ground temperature and the air going in. E.g. With 50 degree ground, and 80 degree air, you will get 65 degree air coming out of the ground. This ignores the latent heat factor. You might be able to get better efficiency with concentric pipes, but this makes the plumbing complicated.

A cheaper way to do this may be to dig a pit 3 feet deep over the entire interior space. Put barrels in the space, filled with water, with a bit of space between them. Put in a lightly insulated floor. (R4 should do.) Barrels are about 22 inches. Put in a 2 inch space, and you have 1 barrel for 4 square feet. A barrel has 480 lbs of water. A 20 degree temperature variation is 10,000 BTU, plus whatever heat goes into the ground below the barrels. But that's for 4 square feet, so it's 2500 BTU/sqft Would do for a day and a bit of our worst case.

Lets look at a different solution: Natural gas. Winter gas prices are about $6/GJ and a GJ is about a million BTU. So our one day worst case is 2000 BTU/sqft. That .002 GJ will cost us about a cent a day. How much digging are you prepared to do to save 3 bucks a year?

That's worst case too. It's not always that cold.

Actual greenhouse operations are worse than this. When plants are actively doing their photosynthesis thing, they will use up the CO2 in a greenhouse in about 10 minutes. So you need an air change, or another source of CO2 every 10 minutes. Air has about the same specific heat as water on a weight basis. A cubic yard of air is about 2 lbs. Your square foot of ground with a 15 foot ceiling has about a pound of air to heat. Heating from -30 to +60 takes another 90 BTU. Every 10 minutes. So the air heating load is 6 times the building heating load. However, no sunlight, no photosynthesis. And when there is sun, it's providing even in winter about 600 W/m2 which is 200 BTU/sqft/hr

One greenhouse operator near here heats water in the day, pipes the CO2 into the green house to help the plants, does an air exchange every few minutes on top of that, and uses the stored hot water at night. They claim energy costs of $3.50/square foot.

Conclusion: It's a cool idea. If you are off grid, it's a great idea, especially if you have sunny winters. Is it practical as a 'best solution' at current energy prices for a cold climate? I don't think so.

Apologies to Hex2006 and Sherwood for taking so long to respond. We are full on into our irrigation season and I am still selling and delivering hay. I did download the files you provided a link to Hex2006. I assume I have to allow their program to unzip them. As for your comments Sherwood I can appreciate your situation. I live in southwest Colorado and while we do experience some cold temperatures at times, we almost always have sun. The coldest I have seen here in the two years we have lived here is -10 F. I had not thought about the need to supplement the CO2. Maybe I will have to attach a barn so the cows can produce the CO2. Hex2006, let me know if there is a trick to unzipping the files. Thanks.

If you have a barn, then coupling the barn and the greenhouse is an interesting idea. Consider making a greenhouse roof for the barn. Now you get cow CO2 and cow heat. (Each cow is a 2500 watt heater. Have to do some numbers to figure out how many cows you want per square foot.)

One possible issue is that of ammonia. Chicken manure is high in it. Don't know about cows. May depend on how much protein in their feed. Ammonia in the air is a killer. Make a minigreenhouse and put a few buckets of fresh meadow muffins in there.

In a milder climate, SCHS makes more sense. But if you are on natural gas the gas costs less too. Might make more sense if the price of gas goes back up to 12 bucks a gigajoule.

Might also make sense in a large operation. If you are building 5 acres of greenhouse, you get economies of scale with the installation. But you likely also get preferred rates on gas.

A third option: Look at some of the solar greenhouses that U of Missouri have done. You may be better off, for a small greenhouse to make one with an insulated north wall, with barrels of water on the north wall and some clever fan controls.

If the system can work for you with trenches made by a $100 buck a day trencher

OR

you don't have natural gas in your area it may be worth it.

Yet another option would be to hook up the duct work of the the subterrenaion pipes to the output of a rocket stove mass heater. This allows you to heat the ground to much higher temperatures. Bigger delta T = more heat stored. A mass heater that you could fire up only on excessively cold days, or on long strings of cloudy days could be a big win. All the scaling calcs now are reduced to coping with a single moderately cold day. Get some typical year data for your area, and simulate how often you would need to fire it up.

A rocket mass heater would require metal ducting for the first N feet of each zone. I would suggest that you used duct for the entire top layer, then re blow the output of that layer to the lower layers. The reblower would then continue to circulate from GH to top layer to lower layers to GH. This would move the heat downward into the lower layers.

Reason for top layer, is that I think the pipe will need to be replaced -- it will rust out.

You could also make a rocket mass heater as the central bench in the green house. I've seen this done. Works too well, however and plants on top of the bench get cooked. He had to take it apart and put a layer of styrofoam insulation as the bench's top surface

Hi Haymaker,
windows will open a zip (compressed) file, you dont need any special program.

Hi Hex - how long have you had SHCS system running. Looking back at your history... at least 6 years? What are the average winter outside temperatures and inside the greenhouse? Do you grow year-round w/o extra heating? My location is similar to yours (lat 58°), with very limited sunlight during late autumn early winter (thanks to global warming its getting warmer though). I dont have data noone has ever built an SHCS greenhouse back so north but Im going to give it a shot. Starting with backfill in a week.