I've done a lot of research and I think I've made up my mind on the climate battery for my upcoming greenhouse design but I want to get some input to check my assumptions.

Some of this is based on the "The Year Round Solar Greenhouse" book.

From what I've read and presumed, these systems do a good job in the summer of taking hot greenhouse air and circulating it underground to cool it and keep greenhouse from overheating.  As they do that they store that heat underground for use in the winter.  In the winter on sunny days, the same process is used to take excess daytime heat and pump it underground for use that night.

I can see how this works very well in cold sunny places (Colorado, Nebraska, great plains, etc).  My issue is for the upper/East part of the Midwest and northeast USA.  Our winters are more often cloudy and very cold.  Luckily when it is sunny, it also seems to be the colder snaps.  From what I've read for cold/cloudy climates, the ground battery uses up its summer charge sometime in the early winter (Dec?) and then has to rely on the day time sunshine to pump new heat into the ground.  If there isn't sun, the battery returns to the normal ground temperatures for your area.  There's the other rub.  I always hear that the deep soil temperature is 55F everywhere.  But it isn't.  In my area the temperature 4' deep averages 39F in the winter.  I'll concede that with a warmer greenhouse sitting on top of it that ground may be a bit warmer (45?) but I seriously doubt it will be 55.

So with one of these systems, it seems like your winter heat source would be pumping out chilly 39 degree air once you're past Jan 1.  I guess I can't see how that would keep a Wisconsin greenhouse above freezing in Jan and Feb with overnight temps at or below zero and daytime highs under 20F.

Am I off-base here?  Am I missing something?

Thanks!

I have a greenhouse that I keep unheated during the winter. It extends my frost-free growing season by about 5 months, even without doing any sort of active klimate or daily temperature bufferring. That's just from the heat that's stored in the flat greenhouse floor. I could do better if I included a daily heat storage sink in the form of barrels of water, and even better if I stored summer heat underground... So what if the ground is only 40 F during the winter, that's still 60 degrees warmer than -20 F.

Edit to add: I just went out and checked temperatures in the greenhouse, about 3 hours after sunset.  Air temp 26 F. Ground temp about 4" deep was 32 F, but probe easily inserted so ground isn't frozen solid. Outside temp was 14 F. That's up from 0 F last night.

Here's some fotos from last winter.

Even with no klimate battery, I get month's worth of extra growing season.


Even on a little stand-alone greenhouse which is drafty as can be.

Thanks Joseph, I agree that 40 degrees is better than -20 and any greenhouse should extend your growing season in a cold climate.  I'm looking for year-round growing though.

My main curiosity is if a climate battery can keep a greenhouse above freezing in a cold, cloudy place without back up heat.  My concern with 39 degree dirt underneath the greenhouse would be that if you're counting on circulated air at that temperature to keep your greenhouse warm on a -5 night, I think it will lose that battle.

I forgot to add in my top post:   If anyone does have a system like this working in a cold/cloudy area, please report back on how well it works, what your minimum temps are inside over winter, what your growing zone or region is and if you need back up heat.

Thanks!

Mike Jay wrote:I'm looking for year-round growing though.

Which crops/animals? What's the lowest temperatures they can tolerate? Are you intent on maintaining 70F for an orchid? Or is 26 good enough for some kale?

For a similar yet different approach to your situation, I highly recommend:

https://www.amazon.com/Forest-Garden-Greenhouse-Design-Permaculture/dp/1603584269/ref=pd_sim_14_2?_encoding=UTF8&psc=1&refRID=CG52H57K65SJQGXHAXCN



I find it has more (very accessible) math and general rules of thumb to accomplish your goals.

I live in sw michigan and am working on a design for next spring.

The highlights to get it to work in a cloudy and plenty cold climate is you have to insulate the earth under the greenhouse.  If you don't, the earth will just suck all the extra heat out (in the summer) into the surrounding soil (pretty much) and you won't get much heat out when you need it (in the winter).

His system uses lots of buried perforated plastic pipe.  It also uses the condensation and evaporation of water into your climate battery to store and release heat even more efficiently.


Insulating the greenhouse becomes more important in cold/cloudy climates.

He also has the genius solution to those few super cold days/weeks when the earth battery is insufficient, to use the built in wood sauna.  When it gets really cold, he has to go fire up and use the wood heated sauna--what a sacrifice...

For the purposes of this post I'm interested in a hypothetical greenhouse that would be for cool season veggies.  Minimum of 28-34 degrees with 34-40 being more ideal.  My reason for starting this thread was the Chicken Greenhouse Thread where Todd mentioned using a system like this in WI.  I wanted to verify my assumptions about the system and get more information out there.

In my particular case I'm looking for tropical temperatures.  I know I'd need serious additional heat to make that work (or saunas and hot tubs).

Thanks Troy, I haven't read that book yet but it's on my list.  Especially now that you mention that it has good math in it.  I've watched hours of Jerome's videos on Youtube.  I take it you mean that for cloudy areas you need to insulate under the climate battery?  It makes sense that if you enclose that 8' deep chunk of ground it would store the heat much better.  Jerome/CRIMPI is high up in the mountains but I believe he has lots of sun in the winter.  I'll be interested to read any details on making their system work in cloudy areas.

Thanks!

I am intrigued by this,to the point that my chicken coop/run/greenhouse has a the rudiments of such a system in place.
I agree, insulating the climate battery from the surrounding soil is key. I did not have the resource to do that,so when I finally get the system operational, I expect it to be flawed.
Because of this I am planning on using a rocket mass heater and/or biochar producing oven to boost the air temperature, and the air to earth heat exchanging system to store that heat for later.
I have even considered boiling water and pumping the steam directly  into the system,but I am concerned that the results might be a humid atmosphere,bad for the chickens.


When I do this again at my grow yard I will build the system into raised beds.
This will let me avoid digging into the urbanite riddled soil, and let me insulate easily.
I see one long central raised bed with an air to ground heat exchanger,inside a high hoop house.
Add a wood burner and a second smaller hoop house over the bed itself.

Here are some links to discussion of these kind if systems:

http://forums.gardenweb.com/discussions/1625183/is-anyone-using-a-shcs-in-a-cold-climate

http://forums.gardenweb.com/discussions/3098381/any-updates-on-data-from-those-with-shcs-greenhouses

http://forums.gardenweb.com/discussions/1607983/subterranean-heating-cooling-system


https://www.permaculture.co.uk/articles/how-build-solar-greenhouse


http://www.jc-solarhomes.com/pb/plant_bed_heating.htm

Mike Jay wrote:For the purposes of this post I'm interested in a hypothetical greenhouse that would be for cool season veggies.  Minimum of 28-34 degrees with 34-40 being more ideal.  My reason for starting this thread was the Chicken Greenhouse Thread where Todd mentioned using a system like this in WI.  I wanted to verify my assumptions about the system and get more information out there.

In my particular case I'm looking for tropical temperatures.  I know I'd need serious additional heat to make that work (or saunas and hot tubs).

Thanks Troy, I haven't read that book yet but it's on my list.  Especially now that you mention that it has good math in it.  I've watched hours of Jerome's videos on Youtube. I take it you mean that for cloudy areas you need to insulate under the climate battery? It makes sense that if you enclose that 8' deep chunk of ground it would store the heat much better.  Jerome/CRIMPI is high up in the mountains but I believe he has lots of sun in the winter.  I'll be interested to read any details on making their system work in cloudy areas.

Thanks!

No, I meant the above ground portion of the greenhouse.  The entire north wall can and should be insulated, and depending on how you build your greenhouse, part or all of the roof can be insulated as well.  Don't use fiberglass or any other insulation that can be damaged by moisture/humidity intrusion.  Usually that means some kind of foam.  You could easily cut your heat loss by 50-60% by insulating the north wall, and part or all of the roof, and possibly the east and west walls, again...depending...

Are you growing day-length sensitive species?  Then you will need glazing on the east and west walls, and/or artificial lighting to stretch the day length.

Absolutely, the "walls" of the earth battery need to be insulated.  The "floor" of the earth battery, it depends.  It depends on the temperature down there in the winter, and if that temperature constitutes a help or a hinderance.

Thanks for all the links William!  I read or skimmed through all of them.  I saw some posts from people that sounded like they were from New England but I didn't notice any cases where people had good luck with them on a free standing greenhouse.  Maybe I skimmed too fast?  I'm pretty sure I didn't see any from a zone 5 or colder area (that is also cloudy).

Thanks for the clarification Troy!  My current plan is for an A frame shape greenhouse oriented E/W.  I'll have glazing on the South roof face and quite likely the south half of the side walls.  I'm hoping to figure out a way to use straw bales as the insulation on the E, W and North sides down to the footing (footing on grade).  Then I'll do 2-4" of pink styrofoam vertically along the outside of the footing and then horizontally outward for a total of 4'.  That way I'll protect the footing from freezing and keep the frost away from the greenhouse soils.

Good news!  The missus approved a priority change for next summer and now the greenhouse is 2nd on the list.  Previously it was slated as a 2018 project.  Now the design really has to come together.

Troy, my plan (unrelated to the "hypothetical" nature of this post) is for a tropical greenhouse.  I'm not sure how day-length sensitive bananas, pineapples, avocados, etc are but I'll have to find out.

And to put it out there once more, if anyone knows of a SHCS or Climate Battery or GHAT that is keeping a greenhouse above (or ideally well above) freezing without significant use of back up heat in a zone 5 or colder climate with frequent cloudiness in the winter, please chime in with your examples.  ( I don't ask for much )  Thanks!!! 

The mere act of placing a piece of glazing over a piece of earth creates a climate battery. As a wild-ass guess, I'd say that a piece of glazing over a piece of earth is approximately equal to a garden that is 300 miles further south, or 300 feet lower in elevation. Then, for a growing space that approximates even warmer areas, mass can be applied to the equation: jugs of water, stone walls, underground heat storage, etc... Supposing that the battery gets exhausted by temperatures under -20F? So what. How often do temperatures like that envelop the greenhouse? Maybe a few  hours per year. Perhaps start a heater on  those rare occasions. It's no different than starting an electrical generator after it's been cloudy for the 17th day in a row and the solar-electrical charged batteries are depleted. I add supplemental heat to my greenhouse about 10 nights per year, only on exceptionally cold nights, and only when I'm growing exceptionally frost tender plants.

Batteries can be made as big as people want to make them. But at some point, the cost of the battery ends up being greater than the cost of a heater...

Another tool in the toolbox is movable insulation for the glazing.  I have seen various schemes online, but have no firsthand experience in a greenhouse.

In the house house, we use big bubble wrap and a little soapy water to add more insulation to the windows in the winter.  That's not enough r-value (by itself) to maintain the heat delta you're looking for.

Here is an intriguing book:

http://knowledgepublications.com/heat/movable_insulation_full_desc.htm

On the front cover they show reflective panels that lay in front of the glazing on the outside.  AND, the panels incorporate insulation, so on a cold night, or perhaps every night, you fold the panels up and your glazing becomes an insulated wall.  So these do double duty by increasing your solar input in the winter, AND restricting heat loss at night.

Yes, you would have to get out there and flop panels up and down, and snow would be a pain in the neck, and the reflecting surface would be problematic to maintain.

Your situation is almost the worst case design scenario in case you hadn't figured that out yet.

Not insurmountable...but a tall order.

Thanks for the book link Troy.  Moveable insulation is on the list of things to consider.  Once I figure out how best to present my plans for feedback, I'll do some more in-depth posts in the Greenhouse forum.  My heat gain/retention plan for now is:

R2 glazing on south side of A frame
R40 straw bale insulation on sides and North side
Entry vestibule
Shallow frost protected footing for ground insulation
Compost inside greenhouse for additional heat generation
Water barrels for thermal mass
Phase change materials to act as heat battery

Back up ideas (or Oh Shit, what can I do now):
Moveable curtains
RMH
Adapt to temps with cooler trees (citrus, etc)

I like those closable flaps on the book you linked.  But snow would be a real pain in the butt.  Maybe I could come up with a huge insulating panel that sits on the North side of my A frame during the day and then it flips up and over the ridge line and flops gently down on the glazing to seal in the heat all night.  That would be awesome, but the mechanism to move it would be a nightmare and if it's windy, forget about it.  I'll keep thinking on it.....

Mike, I've been researching this pretty extensively for a year or so now.  One of the things you mention is the 55 degree number that gets thrown around a lot.  Truth is, for our area the number is close to 46, but you have to go much deeper than you are talking about.  The Greencube people that put out the "Citrus on the Snow", the Finch-style vs a hoop house, etc.  say that in our area, you have to be at least 10' deep.  They mention that you can go 8', but would need insulation above your ground tubing.

In my mind the ground battery part of this is irrelevant to me.  That sounds like blasphemy to some, I know, but I can tell you what I am basing it on.  There are two main ways you can implement the ground tubes.  One is in the area directly under the greenhouse.  I would assume this is the only way the ground battery could be utilized, and as you say, I would think it would "run out" pretty quickly here, with the very cold temps and days in a row with little sun.  The other way to use the ground pipes is in a trench in a long line, where the pipes are just laid out in a straight line from the structure and back to it.  In my mind, this would eliminate any appreciable ground battery.  This is actually the way they recommend the pipe be run, for a number of reasons (cost of laying the pipe, ease of maintenance if there are problems, etc).  The systems have been tested extensively and work well.  My thoughts are that with an insulated north side, east and west ends insulated partially, and part of the roof insulated, pumping 55 degree air into the greenhouse will let me grow all winter, for just the cost of the fan to circulate air thru the greenhouse.  I'm actually more concerned about over-heating than I am about it not being warm enough.  With my single sheet of plastic over metal hoops and gaps throughout, I am getting 50 degree gains on sunny days.  I believe I can keep a temp of 40 or higher, year round, without supplemental heat and with nothing except the fan circulating the air thru the tubes.  I'm going to try without even using water barrels initially.  I'll be happy to post figures once I have the greenhouse up and running.

Todd Parr wrote:The other way to use the ground pipes is in a trench in a long line, where the pipes are just laid out in a straight line from the structure and back to it.  In my mind, this would eliminate any appreciable ground battery.  This is actually the way they recommend the pipe be run, for a number of reasons (cost of laying the pipe, ease of maintenance if there are problems, etc).  The systems have been tested extensively and work well.

Hiya Todd, could you explain what you mean by, "this would eliminate any appreciable ground battery"?  I thought the ground battery in question is the soil in contact with the earth tubes and the fact that this is held reasonably steady by it's mass and the surrounding ground's temp.

Also, is this the way the Citrus in the Snow folks recommend? I've been mighty tempted to get their book.

Thanks for your perspective Todd.  One question though.  If you run the tubes out from the greenhouse a fair distance and then return, those pipes would have to be 10' deep in our area in order to produce 46 degree air, right?  If they were run 4' deep I'd imagine you'd get 32-40 degree air out of it.  Do I have that right?  And if so, how do you plan to get 55 degree air out of your system?

I can see how that either layout would definitely provide really good cooling in the summer.

Sorry Mike, it was a typo   I think I will get 46 degrees as a minimum.  I'm not certain that you would get 32-40 degree air at 4 ft, but my assumption is that that is accurate.

Bryan, when I hear most people use the term "ground battery", I take that to mean that the heated air from the greenhouse in the warmer months heats the ground to a higher temp than it's norm, and then recovers that heat later.  In other words, the ground is used as a battery to store additional heat above and beyond the normal earth temperature.  I can understand how that would work if you ran the tubes back and forth close together and contained under the greenhouse.  There would be a much smaller area of earth containing the tubes, and that amount of earth could be heated by the tubes.  On the other hand, if you run a 4" tube straight out from your greenhouse, say 100 ft out and 100 ft back for example,  I can't believe that any significant area of earth around the tube would be heated to above it's normal temperature, and so no real ground battery effect would be observed.   If, on the other hand, you are calling the constant temperature of the earth 10 ft underground the ground battery, then yes, it will always be there and is very significant.

The man that wrote the Citrus in the Snow book contained his tubes immediately under the greenhouse, but the people that publish his work and have done much testing on these systems have put out others publications documenting their work in the area and they recommend the tubes be placed in a trench in the manner I mentioned.  I purchased CitS and the Geo-air A-Z publication and I found them to be excellent.  The Greencube people are adding other free publications showing some of the their testing to people that have purchased those items.  In the most recent one I read, they test an above ground hoop house against a Finch-style (CitS) greenhouse.  I found it very interesting.

Gotcha, now I'm on the same page.  Might you have a link to the Greencube publications?  My google-fu is letting me down when I try to search for it. 

How are you going to trench your lines 8-10 feet deep?  I'm just curious how hard it will be to accomplish.  In my design, I'll be doing a skirt insulation so I could probably hide some air tubes under that insulation for summer cooling.  Running 400' of 4" drainage tile 18" deep around the greenhouse should provide some decent cooling.  And maybe some heat gain for the winter.....

I ordered the CitS here Citrus in the Snow.  You can get the Geo Air A-Z pub here Geo Air A-Z

I have a friend that works for a company doing earth-moving work.  I am going to have him dig the trenches for me.  It's much cheaper and easier to have trenches dug than have someone come in with a bulldozer  and remove all the earth under your greenhouse down 10 ft and then fill it back in.    After trenching, you put the tubes in sand and tamp it around them well to get rid of air pockets or your tubing will collapse.  Once you have sand around them and a few inches deep over them you can have the trench filled back in with machinery.

Thanks for the links and the excavator sound like a good way to go.  Good luck and keep us posted!

Todd Parr wrote:

The man that wrote the Citrus in the Snow book contained his tubes immediately under the greenhouse, but the people that publish his work and have done much testing on these systems have put out others publications documenting their work in the area and they recommend the tubes be placed in a trench in the manner I mentioned.  I purchased CitS and the Geo-air A-Z publication and I found them to be excellent.  The Greencube people are adding other free publications showing some of the their testing to people that have purchased those items.  In the most recent one I read, they test an above ground hoop house against a Finch-style (CitS) greenhouse.  I found it very interesting.

Todd, do these people explain why the tubes should not be run directly under the greenhouse structure the what that CRMPI has found? I think we should be supporting CRMPI here because they are making the best practice data available for climate batteries for free, although I'm struggling to find it on their website. In the book "Forest Garden Greenhouse" they say they are making the information available for free...

It might be worth your doing some research into John Hait and Passive Annualized Heat Storage.  Hait wrote about this as a system for maintaining comfortable temperatures in houses year round, in places like Montana. He explains it pretty well and as near as I can tell, all of the greenhouse variations have been developed off of his initial work for residential climate control.

For information about growing year round I might recommend looking to Elliott Coleman, who grows pretty much year round in Maine, with no heating systems at all in most of his - moveable - green/hoophouses.

Coleman reports every layer as shifting his climate a hardiness zone further south.  So the house moves him one zone, a light row cover over the plant moves them another zone, do a mini-hoop over that and you're three zones further south, with no form of heating whatsoever.

Coleman does not grow straight through the winter, he has a Jan-Feb gap where he doesn't have anything growing - but that's more his choice for having some time off than a case of not being able to grow at that time.  Of course, choice of crops is critical, don't try and do this with frost tender plants.

Also worth understanding that much of a plant's ability to survive freezing is related to how fast the temperature drops and not just how cold it gets. Hardiness relates more to speed of adapting to the dropping temperature than to an absolute difference in resistance.

Joseph Lofthouse wrote:The mere act of placing a piece of glazing over a piece of earth creates a climate battery. As a wild-ass guess, I'd say that a piece of glazing over a piece of earth is approximately equal to a garden that is 300 miles further south, or 300 feet lower in elevation. Then, for a growing space that approximates even warmer areas, mass can be applied to the equation: jugs of water, stone walls, underground heat storage, etc... Supposing that the battery gets exhausted by temperatures under -20F? So what. How often do temperatures like that envelop the greenhouse? Maybe a few  hours per year. Perhaps start a heater on  those rare occasions. It's no different than starting an electrical generator after it's been cloudy for the 17th day in a row and the solar-electrical charged batteries are depleted. I add supplemental heat to my greenhouse about 10 nights per year, only on exceptionally cold nights, and only when I'm growing exceptionally frost tender plants.

Batteries can be made as big as people want to make them. But at some point, the cost of the battery ends up being greater than the cost of a heater...

I think it was Eliot Coleman who said that each layer of glazing is like going one climate zone south. A cold frame or low tunnel in a greenhouse is like going two climate zones farther south. Adding a couple of blankets on coldframes is what we do in our greenhouse, with one of the coldframes against the north wall which is banked into the earth (leave blankets in place on really cold, cloudy days). The north roof has reflectix insulation. Works in Minnesota for cold weather crops and overwintering biennials for seed production. No fans or complicated underground storage, just using the soil in the beds themselves as the thermal battery. One thing I dislike about underground rock or tube heat storage is that molds can get established in them and there is no way to clean them out (really a problem for living spaces but can affect air quality even in a greenhouse).  K.I.S.S. is my motto when doing design of any system (keep it simple, stupid) and I remind myself of it whenever things start getting too complex or with only one key component that can make the system fail entirely.

Larisa Walk wrote:
No fans or complicated underground storage, just using the soil in the beds themselves as the thermal battery. One thing I dislike about underground rock or tube heat storage is that molds can get established in them and there is no way to clean them out (really a problem for living spaces but can affect air quality even in a greenhouse).  K.I.S.S. is my motto when doing design of any system (keep it simple, stupid) and I remind myself of it whenever things start getting too complex or with only one key component that can make the system fail entirely.

Larisa, a large part of the reason I am going with the underground tubes is because it isn't complicated.  The system uses one fan.  I can't really envision a system that is less complicated other than building a greenhouse that you do nothing at all with, like the one I have right now.  There is really nothing complex about the system.  You bury tubes in the ground and use a fan to pull the air through them into the greenhouse.  That's it.  The issue on mold, fungus, etc. in the tubes is absolutely not true according to all the research I have seen, and it has been tested very extensively, both in greenhouses and houses, as well as other structures. 

Kevin Swanson wrote:
Todd, do these people explain why the tubes should not be run directly under the greenhouse structure the what that CRMPI has found? I think we should be supporting CRMPI here because they are making the best practice data available for climate batteries for free, although I'm struggling to find it on their website. In the book "Forest Garden Greenhouse" they say they are making the information available for free...

Kevin, there is nothing wrong with putting the tubes under the greenhouse.  It is just simpler to do it in a trench.  It's much cheaper to have a trench dug than to have 10ft of earth removed for an area the size of your greenhouse.  If you have a problem with a tube getting crushed (which only happens if you don't tamp carefully), it is much easy to dig up and repair if you don't have to tear your greenhouse down to repair it.  It is easier to space two tubes the proper distance apart than it is to lay out all the tubes in rows of proper spacing inside the same area.

As I talked about earlier, I believe the climate battery stuff is irrelevant to what I am doing, and I don't believe it comes into play here.

Todd, thank you for the links for CitS and Greencube. For somebody looking to save money, am I inferring correctly that the Greencube folks co-authored the CitS stuff and are the folks doing the most current/updated work in that vein?

Kevin, I don't have the "Forest Garden Greenhouse" book, but I took a look at the CRMPI website and likewise couldn't find any best practices info on their climate battery work. Do you happen to have more info on how to search for that info on their website or a related site?

Bryan, I'm not sure if they co-authored it or if they just published it.  If I were looking to save money, I would buy the Geo-Air A-Z manual.  It has much more detail as far as figuring the length of tubing, exactly how to lay it out in the trench, how to build the manifold for the tubing, all that type of thing.  One interesting thing they suggest is to use a piece of chicken wire or the like, lay your tubing out on it and connect it to the chicken wire.  That way when you lay it in the trench, the spacing between the tubing stays consistent.  I also found it interesting that there doesn't seem to be an advantage to using more than the recommended tubing length.  There is a guy on youtube that built a similar greenhouse, do a search for "youtube LDSprepper greenhouse".  I think a person could build the greenhouse just from watching his videos, but he does put the tubing under the greenhouse, rather than in a trench.

Todd, thanks! Actually, I think I've already watched all of LDS Prepper's videos, including the construction and 1 year after vids. Feel better having a written reference though.

I feel the same way.  It's good to have a reference to know how long to make the tubing and all that sort of thing.  The manual also goes into more detail.

Look at http://www.ceresgs.com/, loads of free articles and things, as well as purchasable plans. I've emailed and corresponded with them (they're on the forum sometimes), but never purchased the plans as I'm not in the US and have a very different climate of which they don't have any great experience.

I just bought Lindsey's book, but haven't had a chance to read it yet.  I hadn't seen the website yet though.  Thank you for posting the link.

Bryan de Valdivia wrote:Todd, thank you for the links for CitS and Greencube. For somebody looking to save money, am I inferring correctly that the Greencube folks co-authored the CitS stuff and are the folks doing the most current/updated work in that vein?

Kevin, I don't have the "Forest Garden Greenhouse" book, but I took a look at the CRMPI website and likewise couldn't find any best practices info on their climate battery work. Do you happen to have more info on how to search for that info on their website or a related site?

I think I was going to the wrong website, it's on  this website of theirs.

We should probably have two separate threads going regarding this.  The process of using the ground under the greenhouse as a storage battery for heat is entirely different than a system that uses the constant temperature of the earth for the heating and cooling of the greenhouse.  Both are interesting systems, but they are not the same.

Even with regards to the tube systems themselves I see differences in information between the website that Kevin linked and the Greencube folks.  For instance, the Greencube folks say the air must always be pulled through the tubes, never pushed, and show the problems with pushing the air in one of their examples by a person that didn't think it mattered and tried pushing the air through the tubes.  In addition, the eco-systems website talks about using the maximum number of perforations in the tubing, while the Greencube site recommends non-perforated tubing.  The eco-system is also more complex with regards to fan speed, only running the fan at certain times, just much more monitoring in general than I am willing to do.  It also isn't necessary if you simply want to introduce 48 degree air into the greenhouse all year and use proper venting on hot days.

We can split off another thread if you'd like.

As far as my original question goes, I think this is what I've gotten from the discussion:

A climate battery system (pipes under the greenhouse) would probably not store enough heat to last into January in my climate.  Daily solar gain in the winter is spotty and would likely not recharge the battery.  So after the first month or two of battery depletion, I'd just be getting the subsoil temperatures out of the system.  Since a warm greenhouse would be above that soil the temp may be a few degrees higher than outside the greenhouse footprint.  I'd guesstimate that the air from those pipes in January (6' deep) would be around 45 degrees which would be a challenge to keep a greenhouse above freezing in 0F conditions.

An external piping system (like Todd's) wouldn't store any appreciable heat but if dug deep enough it could provide 46 degree air which is as good as the above system.  Once again I believe it would be hard to keep from freezing on cold winter nights. 

In either case, thermal curtains, lots of thermal mass, backup heat and other arrangements could make it work.  But I'm not sure. 

Thanks for the thoughts and if anyone else has one of these systems in a similar climate, please chime in!

I am interested in both the "earth tubes" (long lines run underground not under structure) and the "climate battery" systems (tubes under structure in insulated envelope) I've spoken to a number of professionals who recommend one or the other.  I would love to see direct data comparisons between the two systems in different climates.  The earth tubes is a better system for a retrofit, climate battery essentially has to be done in the construction phase. 

Personally, from the research i have done, to keep a greenhouse warm enough at night the key is keeping your daytime gain inside the structure.  If you have sufficient sun for good daytime solar heat gain then developing an insulation system to keep that heat contained through the night will do more than either of the earth coupled systems.  if you dont get sufficient solar heat gain during the day then theres not much you can do except supplemental heat.  but I would think in that case you might not have enough light to grow anything during the winter anyhow...

1.  Don't use a single fan.  Use several smaller fans.  A single fan is a point failure, and fans in greenhouses have short lives.

2.  Earth runs about 1/3 the heat capacity as the same volume of water.  (About 1/5 by weight, but it's denser).  Suppose that you have a 10 m x 30m green house, and you have trenches under the entire floor so that you are using 3 m deep worth of earth.

So you are using 10 * 30 * 3 cubic meters of earth = 900 cubic meters.  That's equivalent in heat capacity to 300 cubic meters of water.

300 cubic meters of water = 300,000 kg of water.

If we allow a 20C swing in temperature, our heat battery will store 20 * 300,000 = 6 million kCal = 24 million BTU

Now the floor area of the greenhouse is 300 m2 = about 3000 ft2.  If it's double poly, it's effectively R2.  Let's suppose that you have a north wall, and so you have 1.5 sqft of wall/roof for each sqft of floor.  So you have 3000 * 1.5 =4500 sqft at R2.

This will take 2250 btu/hr/F to heat.

Outside at -0F.  Desired interior temp of 40 F.  Heat requirement for this day would be 40 * 2250 * 24 hours. =~ 2 million BTU

So your heat battery will store about 12 days of winter heat.

Wait:  Even on a cloudy day you will get some heat.   And it may not be 0 for the entire 24 hours.

This in essence will multiply your heat storage by a factor of 2 or 3.

Maybe your climate isn't routinely that cold, which may give you another factor of 2, but it doesn't look to me that you can store a year's worth of heat. 

(In passing:  If it was a house instead of a greenhouse, with 15 times the  insulation this is a year's heat.)

***

Here's another way to calc:  If this system works in a sunny climate, then find one that is similar in temperature regime to yours.

Suppose that the sunny climate one can maintain a an average differential temp of 40 F. with 20% cloudy days.
You have 80% cloudy days.

Let's approximate that on a cloudy day you get half the heat you do on a sunny day. 

Sunny climate:  10 days = 8 sunny days + 2 cloudy days equivalent to 9 days sun.
Your climate  10 days = 2 sunny days + 8 cloudy days = 6 days sun.

Everything else being equal, your unit would support a 6/9 of 40 degree average temperature differential.



***

So you will need some supplementary heat, if you are going to grow year round, or at least you have to be prepared for that.

***

Option 1. 

Don't heat the entire greenhouse during the cold season.  Start new plants during that season.  Have a greenhouse in a greenhouse, which gives you 1 more layer of plastic (R1)  and you are using the entire green house to collect heat, but only trying to keep a much smaller one warm.

Option 2

Use R3 or R4 poly carbonate cover.

Option 3. 

Cover more of the roof.  It's still a 3 season greenhouse, but it's the summer you don't grow in.  In effect you have a low shed that is illuminated from vertical south facing glazing.  Tuned for winter months.

Option 4.

Build a rocket thermal mass stove.  This recharges your heat battery.  1 ton of dry wood has about 12 MBTU

Option 5.

Heat as needed with natural gas.  Burn the gas during the day, and run the exhaust through the heat battery.  This gives you CO2 for the plants.

Option 6.

Decide that you aren't going to run it during the coldest month of the year.

     I am in process of building my greenhouse using a "hybrid" climate battery. A combination of many ideas Paradise

     Am in zone 7a in Maryland with 55 deg average temp, 59% sun and a 47" average rainfall.

    Greenhouse is ~160 square feet with insulated walls on the north, east and west with a half wall on the south. The glazing is Solex.

     They say the amount of underground tubing (4" perf drain tile) should be 10% 0f the total cu ft if directly under the greenhouse, or 25% if outside of the greenhouse. This is according to https://www.youtube.com/user/LDSPrepper/featured

     It would seem to me (perhaps in my ignorance) that these climate batteries would, like all batteries, need to be recharged from time to time. This could be done on a daily basis by using the heat at the peak of the greenhouse being pumped into the ground tubes, the use of a compost heating system, solar heating tubes, RMH, water storage for mass. use of aquaponic water for mass etc.

     The climate battery will be a portion of my overall system to be modified as need be, but only a part of the whole.

     The experiment continues...

henry Trott wrote:    ....or 25% if outside of the greenhouse. This is according to https://www.youtube.com/user/LDSPrepper/featured

     It would seem to me (perhaps in my ignorance) that these climate batteries would, like all batteries, need to be recharged from time to time. This could be done on a daily basis by using the heat at the peak of the greenhouse being pumped into the ground tubes, the use of a compost heating system, solar heating tubes, RMH, water storage for mass. use of aquaponic water for mass etc.

     The climate battery will be a portion of my overall system to be modified as need be, but only a part of the whole.

     The experiment continues...

I'm an experimenter, not an expert, but I don't think you will get any appreciable soil battery effect from the system that runs the tubes outside of the greenhouse.  The climate battery does indeed need to be recharged, and it is done exactly as you said, by pumping the extra heat from sunny days into the ground via the tubes.  To take advantage of that, I think it would be much more effective to use the tubes under the greenhouse.

I'm not sure about using perforated 4" tubing.  I've read conflicting research on it.  Right now I'm leaning towards non-perf tubing, but I haven't entirely made up my mind yet.

Best of luck on your experiment.

Todd Parr wrote:I'm not sure about using perforated 4" tubing.  I've read conflicting research on it.  Right now I'm leaning towards non-perf tubing, but I haven't entirely made up my mind yet.

(only conjecture as mine isn't up and running) it is said the perf helps with removing some of the humidity as well as decreasing the chance of molds.

According to the Geo-Air Technology A-Z publication, geo-air systems are vulnerable to Radon gas contamination if you use perforated pipe, but solid pipe acts as a barrier against it.  Also "I've seen NO water accumulations from condensation in any of our tests, and therefore the perforated drain pipe, and drain pipe with slits are a liability in many ways."  In areas with high water tables, solid pipe will block the infiltration of ground water into the tubes, although that is not a concern where I am.  They give other reasons for solid pipe as well, and are pretty adamant that only solid pipe be used.

Thanks Todd, I'll have to get that book.

     Soooo much new information coming out in the last months it seems. If you have time I'd appreciate you taking a look at what I have done. I don't have a lot of funds for this venture, but look forward to increased food production, even from this little greenhouse if I get it somewhere near right. Paradise

Henry, I'm happy to take a look, but I am by no means an expert, just a guy experimenting like you are.