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Subterranean Heating/Cooling System

Posted by maryhm z5b-Colorado (My Page) on
Sat, Mar 22, 08 at 9:48

In my internet wanderings, I came across this site:
http://www.sunnyjohn.com/indexpages/shcs_greenhouses.htm

Sounds like an interesting and fairly inexpensive method. And they actually listed a greenhouse that is implementing this process in my little old town of Durango!
http://www.sunnyjohn.com/photos/greenhouses/grnhs_woodland_gardens/index.htm

I'm just curious if any of you have installed this or have any ideas about it.


Follow-Up Postings:

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RE: Subterranean Heating/Cooling System

This sunnyjohn.com site and its idea come up about every 6 or 8 months, so we talk about it regularly. Yet in the roughly 5 years I have been following this and other GH forums, I have never seen or heard of anyone else actually building a structure like this.

I'm not saying that it doesn't work, I'm just saying that I have never seen any independent confirmation of the idea.

I also have a lingering suspicion that altitude plays an important role with this system...more solar gain at altitude. That may work in your favor.

SB


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RE: Subterranean Heating/Cooling System

Hi MaryHM. I'm also near Durango, currently building a small 12 x 12 hoop house. :-)

I don't suppose you know of anyplace local to buy wiggle wire and the channels? I could swear I've seen it somewhere, but can't remember where.

Cheers,
Michelle


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RE: Subterranean Heating/Cooling System

Hi everyone

You can buy wiggle wire and the channels through Farmtek. I think its www.farmtek.com


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RE: Subterranean Heating/Cooling System

hey SB
Altitude is the main factor with all greenhouses.
If we could get 24 hours sunshine every day we wouldn`t need to worry about shcs,insulation or thermal mass..cooling would be the only issue :)

Regarding independent confirmation of the shcs idea, did you miss this report? www.nurl.us/7tm


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RE: Subterranean Heating/Cooling System

Forgive my newbie ignorance, but what effect does altitude have on a greenhouse? I'm at 7000'.


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RE: altitude

Hi Maryhm
At higher altitudes the air is usually clearer so the quality of light is better. Lucky you :)


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RE: Subterranean Heating/Cooling System

Yeah, lucky me with my -10 temperatures and 3 feet of snow!! :)


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RE: Subterranean Heating/Cooling System

hex2006, thanks for the link. That's a good report. The supplemental storage seemed to make a big difference.

Regarding altitude, it has been my observation that those with greenhouses at altitude report much more dramatic effects from design features to maximize solar gain than do those closer to sea level. Put another way, compared to those at altitude, those at sea level more frequently report that storing water is not worth the space given up in the GH. Those at altitude report more impressive results from their thermal mass features than we do at 600'...just my opinion.


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RE: Subterranean Heating/Cooling System

Hi SB
The report does seem to recommend using it in conjunction with insulation for best results. I do like the way it utilises the excess heat and humidity to benefit the plants rather than just blowing it outside with an exhaust fan.. how wasteful is that :)
I think you`re absolutely right about the diminishing returns of sea level vs higher altitudes, solar radiation is the driving force.

Maryhm,
I bet your plants grow faster they would with higher temps and overcast skies ;)


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RE: Subterranean Heating/Cooling System

Mary... i have been watching that design for a while along with the soloaroof (bubble insulation) group for about 9 years now. Until the recent report from the Appalachia university crew, there was pretty much zero positive feedback on either system. No one that i could find continues to use, or was successful at running a GH using those technologies long term. That said, i suspect the greatest drawback to those systems is the business knowledge of the owners and no fault of the design.

I am in the process of building such a GH that incorporates both concepts into a hybred design. I have to start with some real numbers soon rather than flying by the seat of my pants as i have been. So at the moment i have no hard data to give you.

I would love to hear from anyone who is still using either of those designs.

I have contacted the team from the appalachia university but the contact person was just an advisor and not actually involved with the team. She forwarded along my queries, but i have not heard from them other than that. I will be trying to contact them again as they were supposed to get some data online right about now...

If anyone finds the webpage, i'd love to get the link.

Poppa


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RE: Subterranean Heating/Cooling System

Hi Poppa
Shcs has been around in one form or another for maybe 20 years, the conclusions from admittedly limited data is mostly favourable.
The only way to know for sure is to get cracking on the gh and install it :)

One of the the things that is usually missed about the shcs is that it elevates the soil temperature and moisture levels. Having insulation is great for holding in the heat (mostly in the form of warmer air temps) but thats not much help to the plants if the soil temp is only 5C vs maybe 11C for the shcs :)

The ideal plan is to use both shcs and insulation but if someone could only choose one or the other, a shcs would provide more of a return with the increased soil temps/moisture (aka plant growth) than by using insulation alone.


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RE: Subterranean Heating/Cooling System

Another alternative, skiping the insulation, is to use row covers or mini tunnels over the crops. Combinine that with the SHCS should be a winner.

Yes, i have to get cracking. Frost is out of the ground, time is wasting. :-)

Poppa


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RE: Subterranean Heating/Cooling System

Just an update to this old thread.
A year on and i have almost finished installing the Subterranean Heating Cooling System (SHCS)in the clay floor of my never ending greenhouse project :)
Apart from the digging,it seems a good low tech solution to heating,cooling and dehumidifying a greenhouse using mostly natural resources..sun,water and soil. It does use electrical energy but hopefully a lot less than normal. There are at least a couple of installs that are using solar panels and 12v fans with good results.

There are shcs installations up and running in greenhouses ranging from a tiny 36 sqft to well over 1000 sqft. Mine is at the small end of the scale with 154sqft floor area.
As Stressbaby pointed out the lack of real life performance data is an issue for some that have looked into it. The data is beginning to appear as more pioneering spirits "take one for the team" and go for it anyway.

If anyone else has a shcs up and rumnning it would be great to hear from you to increase the knowledge base :)


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RE: Subterranean Heating/Cooling System

Hex, pics needed.


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RE: Subterranean Heating/Cooling System

I guess a pic may be helpful to illustrate what i`m upto.

Here`s the 15-arm subsoil monster before i buried it in the greenhouse floor to frighten the worms :)
Image Hosted by ImageShack.us
By A_mad_scientist

The monster can influence around 30 tons of clay soil which has perimeter insulation. A fan controlled by a differential thermostat drives the entire greenhouse air volume underground.
I wanted plenty of scope for experimenting with the flowrate so i went for a fairly big fan coupled to a speed controller.
I designed the plenum so it also allows for experimenting, it incorporates a variable recirculation feature.This allows me to recirculate some of the air underground many times in a closed loop while adding new air to the mix from the greenhouse. The mix is completely variable from 0% (just once through) to 100% (the air trapped underground in a constant loop with no new air being added)

As yet theres no roof..but it is on the mad scientists to-do list ;)


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shcs

Hi SB,
I was busy posting so i missed your reply but it seems the telepathy is working fine :)


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RE: Subterranean Heating/Cooling System

Tres cool.


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Thanks SB,
It wasnt much fun digging the trenches by hand, taking out the bare minimum needed was a lot of digging.
At one point i had a pond, a sub pump with an auto float switch fixed that problem but it meant digging 2ft deeper for a sump. Its been interesting every step of the way so far :)
Image Hosted by ImageShack.us
By A_mad_scientist

Image Hosted by ImageShack.us
By A_mad_scientist


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shcs

Here`s the 15 trenches i dug just to fill them back in again :)
Image Hosted by ImageShack.us
By A_mad_scientist


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RE: Subterranean Heating/Cooling System

wow.

I am not sure wether i am impressed, stunned, jealous or relieved. Maybe a bit of all of those.

I am impressed that anyone could build such a thing. I now understand how things like stonehenge could be built with nothing more than stone tools.

I am stunned that anyone has the patience to dig through that soil. What tool did you use to dig those narrow trenches? If you said your bare fingers, at this point i'd believe it. I would have been freaking out after that rain. I would be so worried that the walls would collapse (i have mostly sand with some clay layers)

Jealous because i have been "building my greenhouse" for some 3+ years now and i think it's now a race whether the galvanized pipe will rust away before i get it covered. Please tell me you have no children who suck up all your free time. (I love them anyway!)

Relived because my back aches just looking at those trenches, and i am darn glad i didn't go that route.

What i have decided to do instead is to dig a 4 foot x (?) trench along the center of the GH line it and fill it with discarded soda bottles filled with water and use those as my heat sink. I should be done with that in 2385 or thereabouts. (sigh)

Good luck and i hope it ends up working for you. I am still trying to find the results of the U of V expanded test of the SHCS and SolarRoof designs. Was due out last year but I am told scientist types can be awfully slow in publishing their results. :-(


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RE: Subterranean Heating/Cooling System

Just a few links in case i hadn't posted them before.

Summary of the phase II trials..

"Project Summary and Status

It has been concluded that subsoil heat storage adoption can be most effectively promoted by providing growers with clear and accurate information about the systems. Because greenhouse growers are geographically dispersed and the systems are relatively straightforward to install, a "subsoil heat storage system installer" is likely not a viable profession. Instead, growers, who usually have all the skills and tools needed to install a system themselves, can benefit from realistic performance and cost savings estimates to help them make informed decisions and form practical guidelines that describe design, materials, and installation best-practices.

Valuable experience was gained in retrofitting an existing greenhouse with a subsoil heat storage system. However, the energy saving capability of the system was not quantified. In order to meet the goals of this prong, the system will be quantified in terms of energy exchange in a matrix of varied airflow and soil-to-air temperature differences, and in terms of moisture return at night.

Liquid foam insulation is quite effective at reducing greenhouse heat loss at night. However, it is not a candidate for a do-it-yourself project. It is a specialized technology, which is relatively complex to design, install, and operate. Adoption can be best promoted by providing growers a predesigned kit they could purchase and self assemble. "

Link to the phase II propoasal ($75,000 grant) update report:
Phase II update Still waiting for the final report... :-(

Link to the original viability test (phase I ~$10,000 grant) abstract:
Phase I Abstract


Link to the Phase I final report:

Phase I Final Report


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RE: Subterranean Heating/Cooling System

Hi Poppa,
Thanks for the kind words.
I can`t take the credit as i`m simply following the path cut by other pioneers. I have added a few origonal twists of my own to the install which will hopefully result in more practical data being available for those that are brave enough to do something similar :)

The trenches were dug by hand using a modified digging spade as i`m too tight to buy a proper trenching spade.I cut the sides off it to give it a narrow taper, you can see it top center in the last pic. Every ounce of clay had to be bagged up and removed to allow room to move, i reckoned around 5 tons in all. I`m glad this phase of the project is over with as it was hard going and tedious.

The next step is going to be more fun and i`m looking forward to it as its the most unique feature of the entire greenhouse. I have to cut 75 panel sections and assemble them so they are completely airtight as they form the triple glazed inflated pillow covering. I may have that part done in the next year or two hehe.

Life is too short to be waiting for reports..get your spade out and go for it :)


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shcs

If you were worried about the rain you wouldn`t have liked the crevasse stage i had to deal with over the winter :)
Image Hosted by ImageShack.us
By A_mad_scientist


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RE: Subterranean Heating/Cooling System

I had the opportunity to meet w/ John of Sunnyjohn fame @ a permaculture workshop in Durango several years ago @ Oakhaven. At the time The greenhouse was newly completed and we all had the chance to experience the effect of the SHCS which John installed. Without opening vents to the outside I remember there was a dramatic reduction in temperature. I was skeptical about something like this working but it definitely does. The larger the house the more effective this system will be. I'm sure you could contact Tom @ Oakhaven and he could tell you how well this system has performed over the last 7 or 8 years.

Here is a link that might be useful: Oakhaven


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RE: Subterranean Heating/Cooling System

Hi Anasazi
I don`t agree with the statement that the larger the house the more effective this system will be.Current data suggests that as long as the system layout is optimal for the size of greenhouse and local climate it will perform equally as well.
With a small house, the ratio of mass to air volume versus solar gain and related system running costs will be pretty much the same as a large house. It is also much easier to experiment with alternative tube arrangements and increased airflow with a smaller structure.
My system can provide upto 45 complete air-changes per hour, it may prove prohibitively expensive to attempt a similar test with a much larger 10,000ft3 structure :)


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RE: Subterranean Heating/Cooling System

I'm guessing that anasazi refers to the "fact" that a larger GH is supposedly more stable than a small GH. That's what i am told over and over.

I still haven't found the final report to the last grant given to the group from Appalachian University testing SHCS vs. Solaroof. *sigh*


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RE: Subterranean Heating/Cooling System

I am building a lean-to greenhouse and I am installing this earth charging system. It will be 10' by 20'. It will face due west & I am thinking about painting the brick black. I have no idea if it will work or not but I am going to try it and see. I had a back hole dig a 5 foot deep hole next to my Carriage house. I plan to pour concrete footings at the bottom, lay concrete blocks up to ground level. Gonna insulate the outside and bottom with 4" of Styrofoam panels. I am planning to use the 55 gallon plastic drums for the plenum and attach those corrugated plastic drain pipe with the slits in them. I am planning to use 3 layers for a total of 2 feet deep. I plan to pour crusher run limestone gravel in on top of the pipe. Then I plan to build that system John used with the re bar, chicken wire and mortar mix to make the 40" beds on either side with about a 3' walkway in the middle. Then I plan to add another 2 layers of pipe in the bottom of the beds and cover them with gravel. Then begin putting in good garden soil mixed with about 50% mushroom compost. I have 2 solar collectors from an old solar hot water heater that still work very well. I am thinking that I will put the collectors on the roof of the Carriage House and then run 5/8" pex down into the earth beds, maybe 4 layers of them every 3 or 4 inches. Not sure about that yet. But I don't want them to be too near the top of the soil, perhaps 12" below the surface? The other collector I plan to heat the water in an old 150 gallon hot water heater and attach a temperature activated pump to it and when the earth and gravel gives up all their heat and the temp drops to a certain point, it will activate the pump and heat up the soil near the top of the earth beds. Hopefully this will mitigate the need for auxiliary heat. Then I will build the greenhouse on top of that (I have 24 old double pained sliding glass doors that someone gave me) I will take them out of their frames and build a frame of Pressure treated wood and install them. North wall will be insulated wood with an insulated working window. Going to turn a pair of narrow sliding glass doors sideways and use as vents and put those things that open and close automatically when it gets too hot. Then collect the hot humid air from the top of the greenhouse (about 12') and run an insulated AC duct from there into the plenum. I hope this works. I have just now dug the hole and getting ready to pour the footings so if anybody has any ideas that I may need to modify I welcome their input. Will keep you posted on how it goes. I hope to have it ready before the end of the year but who knows?


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RE: Subterranean Heating/Cooling System

Hi
Sounds like you will have a lot of systems in place which is good for redundancy.
You can work out how much pipe you`ll need by using the floor area and the fan capacity from the air volume of the greenhouse.
I`d try to keep all the tube lengths about equal if possible otherwise some will steal more air and leave others with very little flow which reduces the amount of working mass. You can use varying lengths if you tune them to balance the flow.
The intake duct to the plenum wont need insulating if the air is being taken from inside the greenhouse, any heatloss will be to air that ultimately ends up in the same intake duct :)


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RE: Subterranean Heating/Cooling System

Thank you for you help. Do you calculate the pipe by the volume, IE. 6" or .5x20'=10 cubic feet per 20' of pipe. They suggested on the that site to use an inline fan from a Heat and Air company. What do you think about that? That is a good idea to keep the pipes all the same length. I read somewhere that plain dirt worked almost as well as gravel as a heat sink. I have lots of dirt that came out of the hole we dug and if it would work as well, it sure would be cheaper and I have got to do something with it. I was afraid that it whould stop up the holes in the pipe and there would go the whole effect of the entire project.
Thanks for your input, I feel like a blind man in the wilderness but am determined to try this. :-)
Buddy


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RE: Subterranean Heating/Cooling System

Hi Buddy
My greenhouse is quite small compared to yours and to add a twist my tubing layout is non standard too. This calculator will give you an fairly good idea of the total amount of tube needed and you can play around with the fan cfm.

http://numsum.com/spreadsheet/show_plain/4681

Its best to gear the fan to provide at least 10 complete air changes per hour based on your greenhouse air volume.
I wanted to experiment with much higher airchange rates so i used a 10" (700cfm) duct fan for my 900 cubic foot volume to provide upto 45 airchanges per hour.It uses a variable speed controller along with a differential thermostat which senses the difference between the air and soilmass temperatures.
I used heavy clay to surround the tubes which compacts into a pretty solid mass. Gravel would be ok but you`d need more of it. For each cubic foot of gravel you`ll have 60% solid mass and 40% air spaces :)

I wish i could have used a back hoe for the digging ;)


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RE: Subterranean Heating/Cooling System

Thanks, Hex2006! Wow! That calculator is too completed for me! I am a lowly jeweler! I think my cubic feet of air volume is going to be approximately 1,800. What is the air volume of your GH? I wonder if the same 10" fan would work for my application. Did you get that differential thermostat at a heat and air place? Is your greenhouse up and running yet? What zone do you live in? Did you say your greenhouse was 154 sq. ft. of floor space? Mine is not much bigger at 200 sq ft. (10x20) Apparently the clay does not compact too much around the plastic pipe if yours is working... Did you use a sock? I have the clay/loam soil to put back if that is better than the gravel. I would MUCH rather do that! This idea of "phase change" is so interesting. Thanks so much for you encouragement!
Buddy


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RE: Subterranean Heating/Cooling System

Hi Buddy
I had to make my own diff stat as they have silly prices here. i`m located in the uk so maybe equivalent to Zone 7? We see temps down to about -6C so its not too cold.
The greenhouse has 900cu.ft air volume due to the dome shape, it isn`t fully operational as yet..you can`t rush one of kind projects :)

According to the calculator, if your greenhouse is a 20`x10`x 9` high box (1800cuft) you`ll need 270ft of ads tube and a 300cfm fan for 10 airchanges/hr.
Judging from the tube airspeed (4.34ft/sec)it would be useful to use a 600cfm fan and a speed controller to have the option of 20 airchanges/hr and a tube airspeed of 8.7ft/sec. I can get about 17ft/sec with my fan flat out.

As an idea for a simple tubing layout, you could bury a rectangular box plenum across the 10ft width at each end of the greenhouse (something similar to an underground retaining wall made of treated timber perhaps) and run 5x 18ft ads tubes on 3 levels between the two plenum walls. The inner and outermost tubes being 1ft from the walls and the three in the middle on 2ft centers.
Ideally you want each layer 1ft deep on centers. Reduced spacing is ok although it may bias the system towards heating somewhat as theres not quite as much mass inbetween tubes.


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RE: Subterranean Heating/Cooling System

Wonderful! Thank you Hex!! That is what I shall do. I love the PT wood plenum idea!!! Thank you so much. I think that will work very well!! Excellent! I needed you help thank you so much!!
Buddy


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RE: Subterranean Heating/Cooling System

You`re welcome.
I had to use treated timber for my plenum too but it should last a good few years. If you plan to go ahead you might find joining the sunnyjohn shcs forum quite useful for stateside related info.
(http://plaintosea.com/phpBB2/index.php)
There`s a project in progress in Oregon with over 5000ft of ADS tubing going in the ground, thats some serious digging :)


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RE: Subterranean Heating/Cooling System

oops, its in Idaho with 5,500ft of 4" tube and 260ft of 12" tubing :)


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RE: Subterranean Heating/Cooling System

Hi Buddy and Hex 2006,
I am getting ready to to a SCHS greenhouse. I am unsure if I can use my heavy clay soil as backfill or if it will clog the tubes. Can you give me guidance please?
Thanks! Waterstar


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RE: Subterranean Heating/Cooling System

I think you will be fine with heavy clay soil. The holes in the slotted ADS tubing are pretty narrow. Whatever little bit that comes in won't be a problem and I think the rest will solidify nicely for you once you mechanically compress the soil.

Have you contact David Roper in Blacksburg, Virginia? He could give you some further advice.

http://www.roperld.com/science/ymcasolargreenhouse.htm#why


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RE: Subterranean Heating/Cooling System

I think you will be fine with heavy clay soil. The holes in the slotted ADS tubing are pretty narrow. Whatever little bit that comes in won't be a problem and I think the rest will solidify nicely for you once you mechanically compress the soil.

Have you contact David Roper in Blacksburg, Virginia? He could give you some further advice.

http://www.roperld.com/science/ymcasolargreenhouse.htm#why


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RE: Subterranean Heating/Cooling System

THANK YOU SO VERY MUCH Curly Girl for your response.
I did email David Roper several weeks ago, but had no response.
I found a very clear article re: a small greenhouse built by Andrew Collins in the UK, so I think I pretty well understand what to do now. The link is below if you want to see it. The only thing I think I need to change is that he did not use any vapor barrier to keep the water out...which I will do, as well as add drains, in high water table areas.

It also seems that SunnyJohn also leans toward larger tubes, as ADS culverts, instead of just the barrels (so easier to get all the holes for the tubes in place?). But, mine should be smaller, so I think I can stick with the barrels.

Anyway, Curly Girl, I very much appreciate your response. It is a bit confusing for me to figure out how to do this in a small prefab greenhouse. ( :

I will be hand digging mine, so I hope to start soon. The soil is more moist this time of year and much easier to dig!

http://www.permaculture.co.uk/pdfs/Solar_Greenhouse_Article_Web_Ed.pdf


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RE: Subterranean Heating/Cooling System

Happy to help! :) I am in the middle of building our SHCS greenhouse and have been stressing about the details. We have a high water table so we opted to use gravel as our storage medium so that if our water table does get too high, it won't bring soil into the tubes. David Roper suggested we go that route because of that. Try Roper again -it is worth a shot. He was so helpful and so generous with his time. We also put in a footing drain and we are harvesting rain water from the roof which will keep some of the water away from the foundation. We also have a berm on the north side which should shed some of the surface water.

We went with culverts because it made the most sense for our design. How big is your greenhouse? When you say "hand digging" you don't mean with just a shovel, do you? I can't even imagine how much work that would be! But, if you had a party, maybe you make fast work of it and have a fun time while you are at it! We did that with our tubes. Since we used gravel for our heat storage medium, we did what Roper did and widened the holes to a quarter inch. I think we drilled something like 54,000 holes! We had over 40 people come over, provided drill bits and a few drills (most brought their own), and we provided lots of good food and music. It was quite an undertaking but very rewarding. I like having a bit of everyone we know in our greenhouse!

Unfortunately, I can't say how well the heat sink works because we don't have electric yet. We are getting there but have had some delays. I don't expect to get enough heat to harness until March or April, though, so it is not a big deal to wait. In the meantime, the passive solar design has kept our greenhouse in the 40s without any heat despite the 0 degree temperatures we have had lately. It will be interesting to see how much heat we can capture this summer and how long that will carry us next winter.

Where are you located? How big is your greenhouse? What is your greenhouse made of?

Thanks for the permie article! I had not seen that one before and will share it with others.

Keep us posted on your progress!


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RE: Subterranean Heating/Cooling System

Hi Curly Girl,
How exciting that you are building one right now. Would love to see some pics.
Yes, by hand! Can you believe it? But, for now that is the plan. Slow and sure. Has to be, I'm closing in on 70 y.o.
I have a inexpensive Harbor Freight Greenhouse, 10x12x10. In other words, I am on a tight budget for this! I have read it is harder to do this method with the smaller greenhouses, but oh well. It would be wonderful if folks all over could do cheaper ones like this. ( :
The party idea sounds good. Was it the holes in the 4" pipe that you were enlarging or were you drilling holes in your culvert pipe?
I am in SC and have a high water table. Looks like I'll be shoveling gravel too.
My north side is also the uphill side of where this will sit. So, I am going to put the "dug" soil on that side to make a berm and I am going to put in drains. I too will catch the rain water, both to reduce soil water, but also just because it is so good for the plants. This will also sit close to where my hubby has had all the roof water drainage end. So, will capture some of that too. I will have more water than I know what to do with. Will you be storing your rain water just outside the greenhouse or inside it? What pumping system will you use to get it from the barrel to the plants?
I see on your page that you want to grow tropical trees. I want a lemon and an avocado (will espalier on the North side and keep other plants shorter than them) in here. I am thinking I could make a large area for them to root in the ground and have the rocks and tubes perhaps run outside of the greenhouse to make up for the room I'd take up. At least if I use gravel I shouldn't have to worry about the roots coming into the tubes.How are you going to do yours?
Where did you read about Roper enlarging the holes? I missed that article. Also, maybe I'll give him another try. Maybe I wasn't far enough along with the first contact, or maybe I had the wrong email? I thought perhaps he didn't have the heart to tell me that my inexpensive Harbor Freight wouldn't work. ( :
It is sooooo exciting to hear about your project and be able to chat with someone who is actually doing this! ( : Have a blessed day, Waterstar


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RE: Subterranean Heating/Cooling System

Hello again,

I meant to share this with you.This fellow had his pipes swamped and had to put a sump pump in. Yikes. So that is what caused me to think of a water barrier on the uphill side and a drain as well.
http://narrowscreek.blogspot.com/2011/03/weathering-first-storm.html


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RE: Subterranean Heating/Cooling System

After reading the SHCS data exchanges I have a question: for an existing gh would it work to dig a 3' deep trench 50' long and lay layers of 4" pipe, with slits, in the trench. Starting at the end in the greenhouse, running thru the trench to the end and coming back to the gh. Then, use fans to pull air out of the gh, thru the pipes & back into the gh.

Would this method either cool the air that was hotter than the ambient soil temp or warm air that was colder.


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RE: Subterranean Heating/Cooling System

Hi gwoods34,
I don't think it works. I thought I read Sunnyjohns saying that numerous small tubes are needed. Otherwise the length of the tube interferes with the airflow and exchange. I will be waiting to see what someone more experienced says. But, I don't think the tubes have to be under the greenhouse, they just have to leave and enter in the greenhouse if that helps you.


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RE: Subterranean Heating/Cooling System

You might want to read this:

http://www.appalachiannativeplants.com/id12.html


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RE: Subterranean Heating/Cooling System

Hi gwoods34,

Depends on what you mean by work, for running the SHCS outside the GH soil.

That method is used for climates when little/no heating is needed, and you are primarily trying to cool the GH. I think you'd likely still want a plenum of some type so that you could run several pipe in parallel in the outside trench, and lower the overall length of each run, but it is quite doable. However if you do this, then you will not be storing the heat from the summer for use later in the year (at least not much), and your plants will not have the advantage of heated soil in the cool season.

I think it depends on what you are trying to do. Do you need heat in the winter or are you just trying to cool your GH space.


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RE: Subterranean Heating/Cooling System

Great information Steve333, thanks! I'll keep my tubes under the greenhouse. I am interested in heat gain in winter. ( :


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RE: Subterranean Heating/Cooling System

Thanks for the help; to explain more of what I'm after: I have peach, nectarine, & apricot trees in my house, so I'm just looking at cost effective ways to balance the temps. (cooler in the summer and a little warmer in the winter) The main focus of my gh is the fruit trees but I also want to plant mellows etc and be able to extend the growing season a little in the spring and fall.

I'm not planning on the ground acting as my heat sink but more as a source of constant mild temp air.

So, from what has been said, could several 2 inch pipes, starting and ending at a plenum inside the gh be used to pull hot air in the summer or cold air in the winter out of the gh and replace it with 45 to 50 degree ground temp air.

Also, does anyone think this would be worth the considerable effort it would take? I would hate to do all this work and see just a 1 or 2 degree temperature change in my gh.

Idea?


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RE: Subterranean Heating/Cooling System

Gwood34, here's my take, based upon my readings, a course with John C, and very preliminary results on my still under construction SHCS.

!. It is possible to achieve significant cooling of GH air with SHCS. When I initially turned on my SHCS fan last fall, it would take 100+F air from near the roof of the GH and the exit temps would be 40+F lower in temp. I should caveat that this was with a very cold soil heat storage bank, as I had not been running the system and storing heat all summer prior to this. No doubt as you pump more heat into the soil storage, it will warm that soil, and the amount of cooling you will get will go down. Since I have not had my SHCS running over a full year cycle, I can't give you any numbers as to how much that cooling would diminish.

2. Whether some 2" pipe would suffice or not will all depend upon the size (volume) of your GH, and how much cooling you want. The spreadsheet calculator at John C's SHCS site does a pretty good job of giving you air volume needed and lengths of 4" tubing. That might be a good starting point and then you can do the calcs to translate it to 2" piping if that's what you want to use. It may be more practical to use plenum sized tubes to exit the GH to wherever the soil storage is located, and then reduce to the appropriate size and number of tubes running in the soil. That spreadsheet can give you an idea of the amount of tubing surface area and air volume you'd need to effectively transfer heat. Not that those numbers are cast in stone, but they are probably a good starting point.

3. The problem with any SHCS is that your underground storage is fixed, whether it be under your GH or off to the side somewhere. That means that it won't be at a fixed ground temp, because you are going to be pushing extra heat in during the summer, and pulling heat out during the winter. That soil temp will fluctuate. Still it can be a very useful balance if things are sized right for your climate and GH, and you can use that summer heat during the winter. Or your climate is sunny enough during the heating system that it will replenish the heat you pull out on cloudy days.

Even if your soil bank is outside the GH, and uninsulated, it will still be warmer than the surrounding soil from the heat you pumped in there during the summer (at least at first). And if you don't insulate it, it may not offer much in the way of available heat for long during the winter.



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RE: Subterranean Heating/Cooling System

Hi Steve333,

What a blessing to chat with someone who has taken a course with John C and already has his system in place. Good for you!

I am in the planning stage of my SCHS system and greenhouse. I would really appreciate your advice on this question.

I want to grow dwarf fruit trees and even a heavily pruned avocado tree. Thus, I think I need to put the tubes off to the side of the greenhouse so those tree roots won't ruin the system. But, my other option is to just have the roots in burlap containers, or something like that so the roots would be air pruned and not get quite so root bound. I could also build a raised bed inside (from sheet earth bags) and designate the beds only to the trees. I am leaning toward the earth bag raised beds and the tubes under the greenhouse.

I know what I want to do with the avocado tree may not work...but nothing ventured..... I think the dwarf lemons should be ok tho.

If you were me, what would you do? THANKS SO MUCH for your time and expertise.


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RE: Subterranean Heating/Cooling System

I agree, Waterstar! We are lucky to have you Steve333! Please keep John C's work going forward!

And Waterstar, sorry for being out of the loop. -I have been busy with construction details of our greenhouse. I can't believe you are going to dig your hole for your greenhouse! DEFINITELY have a digging party! Many hands make light work! And, it is always more fun when it is a party.

Yes, our drilling party was for drilling holes into the 4" tube and not the culverts. I wanted to do the culverts too but I ran out of time and there were a couple of them in there anyway that were already a quarter of an inch. I don't think you need to enlarge them if you are using soil as a storage medium because the heat transfer probably does not need to be as fast. Plus, soil could navigate into the tubes more easily if the holes are enlarged and you get high water table infiltration. If you are using stone as your storage medium, then I would have a gravel shoveling party too!

I agree that it would be great to make these affordable to all people and I think having a community "barn raising" activity like a digging party makes it possible. It also inspires others to do it and then you have a few people with experience who can help make it happen for others as well.

Best of luck!


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RE: Subterranean Heating/Cooling System

Hi Waterstar-

I hesitate to portray myself as an expert (I am not), but I am happy to pass on the info I have and my thoughts...

I don't think that you need to worry about plant roots growing into the SHCS pipes. Tree roots do invade sewer/water lines around houses, but that is due to the sewer line being a source of water and perhaps nutrients. The SHCS pipes are filled with air (usually moving) all of the time. There is no reason for the roots to invade, and if they did they would be air pruned I would think. Jerome at CRMPI (also a good source for SHCS info) had to rebuild a GH which burnt. When he was digging up the old SHCS he noted that there was no dirt infiltration or roots in the tubes.

I think you'd be better off doing the SHCS grid over the whole GH, I don't think it will be a problem. Tree roots will travel quite a ways anyhow, so moving the tubes a little further away within the confines of the GH probably would not fix this issue anyhow, if it was present...

I think that a SHCS GH should work for lemon/citrus (I am planning to put a couple of Meyers lemons in mine). Avocados may have higher heat requirements, I am not familiar with them. Were you planning other fruit in addition to citrus? Reason I ask is apples/pears/peaches/etc have chill requirements. That is they need a certain amount of time when it is below freezing (more or less) each winter to grow and fruit properly. Those winter heat requirements are the opposite of citrus and other tropical fruits. So the two may not work well in the same GH (unless you partition it and keep different temps in each part).


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thermostat for a swamp cooler

I just installed an Essick Air swamp cooler in my gh; my intent was to plug it into a plug in thermostat but the cooler won't turn back on unless the fan & pump buttons are manually pushed.

I want the cooler to turn on when the thermostat switches the power to it's outlet. I know you're not electricians but has anyone encountered this problem before and can the evap cooler be wired to be on whenever 110v power is available?


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RE: Subterranean Heating/Cooling System

Hi Curly Girl, Steve333, and Gwoods34

Curly Girl~ So happy to hear from you again. And, good news, I have come up with the money to either rent or hire a back hoe. Whew! My knees will appreciate it. ( :

Steve333, Well duh, duh and duh again. What was I thinking? Thanks for kindly explaining that the roots won't go after air!!!! I'll put the tubes all under the greenhouse.

The only trees I will plant in there will be the tender ones. My peaches, apples etc. will be outside the treehouse.

So, now I need to figure out what to use for backfill. I'd really like to use my soil, but it is heavy clay and on a downhill slope, so I am concerned about my high water table. I think I should perhaps put some kind of drainage system so water running downhill will have a place to keep going. Do you think if I mix it my soil with some rock that would be better?

Steve, did you backfill with soil or rock? Curly Girl, you opted for rocks, right?

Gwoods, sorry to hear about the swamp cooler problem, but maybe it is for the best. Your SCHS should only need a small fan. Maybe I misunderstand. Steve333 is right, some trees need a chill times. I think your peach needs that.

Curly Girl, I like your "barn raising" idea. I hope to encourage my neighbors to begin this type gardening by sharing some of my crop with them. We could have so much more variety if we were to share with others, or just convert a lot of our area to food instead of lawn!

Also, Steve333 and Curly Girl, how about some pics? Would LOVE to see some.

Blessings,
Waterstar


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RE: Subterranean Heating/Cooling System

Waterstar, glad to hear you will use a backhoe to help you out! You'll save money on doctor's appointments!

And yes, we did opt for stone because of our high water table. We were worried that the rising ground water would eventually bring dirt in through the holes of the pipe so we went with stone. I wanted to save money and just backfill our subsoil but David Roper thought it prudent to use stone. We used the same size he had for his YMCA greenhouse.

Here is a pic of the south side of our greenhouse. The shed in front will eventually be relocated so it won't block our sun.

Can't wait to get the raised beds built!


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RE: Subterranean Heating/Cooling System

I backfilled the SHCS layer with local sub-soil which was dug out for the foundation, which for my location was decomposed granite. Basically a coarse sand like fill made from very old granite rocks. A few larger chunks of rock, but they crumble fairly easily. Perhaps an ideal backfill, other than it being a source of radon gas.

I don't have many pics of the GH/barn yet, but here is one looking at the S side

 photo barn12-2013.jpg


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RE: Subterranean Heating/Cooling System

Thanks Steve333 for your counsel and advice. I am probably not understanding the dynamics of a SHSC system. I really can't see how using the earth as a heat sink would possibly hold enough heat through summer use to be of any use during the long months of winter cold.

I was thinking of the soil as an absorber & disperser of heat thus always providing a fairly constant mild/balancing influence on whatever temp air is pumped thru it. 100 degree air coming back cooler & 30 degree air coming back warmer, and, in sufficient quantities to move gh temps closer to an ideal.

I understand the temp of soil to be a fairly constant 45 to 50 degrees year round. So, in my inexperience, I hoped I could expect large amounts of 50 degree air being pumped into the gh year round.

In your opinion, could I achieve what I trying to do by building a full fledged SHSC with 4" pipe an insulated trench and proper heat absorbing material fill, outside my house.


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RE: Subterranean Heating/Cooling System

Waterstar, I think it would be a good idea to put in a drainage system to keep water from moving through the volume of your SHCS storage. Even with insulation around the perimeter of that soil area, you can loose stored heat if there is significant water moving through that soil (to say nothing of water filling the air tubes and making moving air difficult).

Something to intercept the ground water on the uphill side and route it away/around the GH would be key. Along with grading and gutters to move rain water away from the GH as quickly as possible.

Not something we generally need to worry about out West (recent flood excepted), but in wetter climates it is something you want to plan for.


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RE: Subterranean Heating/Cooling System

Wow, what beautiful and large greenhouses you have! Absolutely great. Mine will be a micro-greenhouse. But, I think it will be all I need. If I find I need more then I've got space for it. thanks for the super pics. Absolutely divine!

Thanks Steve for the drainage info. It's not the amount of annual rainfall, it is just that it has a tendency to all come down at once! I get areas that resemble small streams and ponds at times. So, I will do as you say and have a diverting/drainage on the uphill side and the downspouts also. My hubby will be very good at figuring that out.

Do folks no longer use clay soils with a little rock mixed in as the backfill? I would like at least enuf for a dwarf lemon and heavily pruned or espaliered avocado.

Thanks again for all of your help!


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RE: Subterranean Heating/Cooling System

Gwoods34. I don't know the details of your climate (or even your planting zone), so it's a bit hard to say what can or can't be done there.

But I can tell you that in my zone, an SHCS can significantly reduce heating costs, and put some of that extra summer heat to use in the winter. It can definitely extend the growing seasons on both ends. And may be sufficient for cold temp crops like greens during the winter months. It certainly is not going to let you grow orchids without some additional heating over the winters here.

I don't view SHCS as the sole heat source for my GH. I will have backup heat. What I am looking to do is reduce the amount of fuel I would otherwise need by using a SHCS.

For example, we recently had 5-6 days of cloudy cold weather. Nightime temps as low as -20F for a couple of nights and in the 0-20F range the other nights. Daytime high temps ranged from 10-34F. I did an experiment on my almost completed GH, I left the SHCS fan running all the time. (Normally now I only run it during the day to store heat. But by running it at night it pulled some heat from the ground storage to the GH air.)

On the coldest nights, The GH stayed above 28F when it was -20F outside. In general, I saw a 40-48F rise in GH temps over the outside air temps. That difference went down towards the end of that period, as the subsoil heat was getting used up and we had no sunny days to help replenish it. And the temp difference was also less on the warmer days.

There was no other source of heat in the GH besides the SHCS. For me, I would much rather have to pay to bring the GH up from 28F to 40F, than to bring it to 40F from -20F. A significant portion of the heat I would need was being supplied by the SHCS. All this with my previous stated caveats, the GH is uncaulked with probably the equivalent of 1 sq ft of opening to the outside. And the SHCS was not run all summer, so the storage was not as well charged as it should have been. Still not bad results; I am satisfied.
Without knowing your climate details, it's hard to say whether you could expect similar results. If your climate was similar to mine then I think you could.

Given that you just asked about automating a swamp cooler in Feb, I'd guess you are in a much warmer climate than I am. In which case you may be looking for more cooling than heating help. If so, a SHCS can probably help with that, if you run the subsoil tubes outside the GH. I just don't think that such a system will be all that useful in warming the air in the winter (that soil that you heated will loose much of its heat before you want to use it).

SHCS does not use the level of soil which is at a constant temp. That is much further down in most places (6' to 12' depending upon the climate). No reason you couldn't dig your tubes down that far, but that would be a lot more work. A general indication might be the frost depth in the soil for your area. That's the level that freezes some winters, so the constant temp level in the soil is going to be well below that. Another indication of how deep you'd need to go for this is to ask heat pump installers how deep they run their in ground lines and if that is the constant soil temp level.

In regards to your swamp cooler question, you might ask the manufacture if it is possible to put that unit on a thermostat. Often manufactures will use such a system to avoid having to put delay circuitry into their product, and rely on the owner to push buttons instead. You might be able to work around this by adding some delay circuits to the unit yourself, but if you just bought it, probably better to return it and get one that can come on with the power.


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RE: Subterranean Heating/Cooling System

Hi gwoods,

This is just a note to encourage you to keep studying and reading.

My journey started when my hubby have me a 10x12 Harbor Freight Greenhouse for Christmas. Yes, a teeny tiny starter greenhouse that I am thrilled to have.

When I read about heating it during the winter I realized it was going to be VERY expensive. Thus I found the info on SCHS, or earth batteries. It took me several readings and re-readings of Sunnyjohns information to finally begin to understand the systems. Lots of new abbreviations and terms as well as concepts took a bit of thinking on my part.

I did find some simple videos and other sites that helped me understand the concept and materials involved. If you want me to post links, be happy to do so.

I'll tell you one thing tho, we are BLESSED to have experienced folks help us on this site. I am happy I am not laughed out of the forum when folks find out my greenhouse is almost an oversized play house. ( :

Keep up the good work,
Waterstar


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RE: Subterranean Heating/Cooling System

Thanks Steve333 and Waterstar,
for your sharing your knowledge and experience. I'm convinced that I need to rethink my plans. I 'now' intend to think of the ground as heat storage. I'll use the same trench with 4" pipe, insulated and filled with heat absorbing material.

Now that I understand the concept a little better is there a source of detailed readable plans that a newbie can look at? I am an Ironworker and own a steel construction company so building just about anything is doable for me but plans would sure help.

Any suggestions?

again, thanks for the help and kind words.


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RE: Subterranean Heating/Cooling System

Hi gwoods,

From one newbie to another, take my advise with the grain and rely on other's with more experience. A good example is that in my earlier post I referred to SCHS and it should be SHCS (Subterranean Heating and Cooling System). So consider yourself WARNED. ( :

I would recommend you do your reading differently than I did! I started on Sunnyjohns site. He is excellent as Steve will tell you . But the information was way over my head. After reading and re-reading for about 3 days and dealing with term like , SHCS, AUCT, plenum vs culvert plenum etc. I was still quite lost. I told my hubby I needed a "SHCS for Dummies".

Thankfully I found a much simpler article. I would recommend you start on the page (the first link, Andrew Collins). His greenhouse is very simple and it makes it easier to understand. Also, the picture is very helpful.

After you read Andrew's then go to sunnyjohns site. Start at the link I put here, because it defines some terms and basic concepts. As you study the material on his site you will get loads of info. You will also get a link to a super website that has a calculator you can use to figure out how much tubing you need for your size greenhouse etc. That calculator is in the format of a spread sheet, and works nicely.

What zone you are in and what is the size of the greenhouse you are planning?

Have fun and don't think your going to get this done overnight!!!! ( :

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

http://www.sunnyjohn.com/indexpages/shcs_faq.htm


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RE: Subterranean Heating/Cooling System

PS
gwoods, I see our post says you will fill the tubes with heat absorbing material. With this system you leave them empty. The solar heat is pushed thru the tubes, leaks into the soil and warms it. At night it is pushed out of the soil and heats the greenhouse. In the summer the air is still pushed, but the soil will be cooler and thus your greenhouse will be cooler (and make sure you keep the vents opened as appropriate). So you are using air and sun for heating. Look at Andrew Collins for the simpler example.

Steve can probably explain this better. I do not fully understand the summer cooling bit. But, I can't understand all about my car either and it still gets me where I need to go. ( :


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RE: Subterranean Heating/Cooling System

This topic fascinates me. The breaker switch to our hot tub flipped during a power surge and since it doesn't reset itself, we didn't notice until the water froze. We had a slight thaw and the tub self drained - obviously a broken pipe. If the tub is pooched and unfixable, I was goofing around with the idea of using it's footprint below the deck (7x8x 2deep) to create a heat sink before we resurface that area. It is about 8 feet away from the GH and I could insulate the intake pipes and feed under the deck so they have some protection from the elements.
I guess my major pain would be trying to insulate it by creating a box for the contents to fill?

I have already resolved that my little gh 6x8 will be completely shut down from Christmas until approximately march break.

Just looking at ways to reduce my heating costs during those few months.

Of course this could just be wishful planning on my part as the hot tub might be fixable but was wondering if this would be sufficient to help store heat in the early spring/late fall months.
Feasible or stupid thinking?


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RE: Subterranean Heating/Cooling System

Hi Canadian Lori,

Not sure if it will work. The first thing I would do is to go to the spread sheet and figure out how many feet of tubing you will need for the size of greenhouse you have.

You would have to run insulated pipe to and from your deck, but that is a long ways go if you don't need much tubing. You would also (I think) have to insulate the ground around the tubes....so it might be easier to dig a new sink for your GH.

Post again and let me know how much tubing you need. ( :
I am fascinated with the idea of folks being able to use teeny GH for starting veggies etc.

Here's the spreadsheet link from Sunnyjohns site:

http://numsum.com/spreadsheet/show_plain/4681


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RE: Subterranean Heating/Cooling System

Canadian Lori,

In addition to what waterstar said, there may also be a couple of other issues:

1. Typically in SHCS (in cold climates at least) the underground heat storage is insulated at the perimeter, to keep it from losing all its heat to the surrounding soil. That may be hard to do if your soil is under a deck, but then again if you are digging it up to put in the air pipes, perhaps not an issue.

2. Similarly, the soil heat storage is typically located directly under the planting soil of the GH. That has the effect of acting as a top insulation for the heat storage, and allows the heat that escapes up to warm the GH. If your GH is on a deck above the SHCS soil, you would lose that effect as well.This could be partially fixed by insulating to top of the soil.

Or perhaps both of these would be a non-issue, if you made your GH rest directly on the soil under the deck, with a built up foundation of some sort. Then you would have a "traditional" SHCS system, and your GH would just happen to sit in a hole in your deck. Of course this would only be possible if your deck did not sit to far off the ground. It would also solve any potential problems with the deck supporting the weight of the soil in the GH.


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RE: Subterranean Heating/Cooling System

Hi Waterstar,

A 12' x 10' greenhouse is nothing to laugh at! -Be proud! This forum is for all types and sizes of greenhouses and the variety keeps the discussion interesting.


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RE: Subterranean Heating/Cooling System

Hi All,

Steve, intersting idea of the greenhouse placement. I wouldn't have thought of that in a million years.

Curly Girl, You are right. I am so blessed to have one.

Does anyone know of a source for aircrete in the USA? I have emailed the plant, but not heard back. Seems like it would be a super product for walkway in my GH and maybe even the foundation layer.

My hubby said he would anchor the GH with spikes that go deep in the earth so it won't blow over. (Some folks have problems with the Harbor Freight GH blowing over).


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RE: Subterranean Heating/Cooling System

Hi again everyone.

Another question for anyone willing: everything I have read so far makes me think the sun and outside air temperatures substantially influence the temperature of the top half dozen feet of dirt, so wouldn't corrugated pipe 3 to 4' deep covered with a layer of high R value insulation installed a foot or two above the pipes be as good as the same piping buried 6' deep.

I intend to build my own SHCS system this summer so I'll spend this whole spring reading and asking questions of everyone I can find that'll answer; I wanna build it right and workable and hesitate to cut corners at the expense of an efficient system but from what I've read so far it sure seems that digging a shallower trench would help off set the added cost of the rigid insulation.

Any ideas, is my thinking anywhere close?

gwoods


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RE: Subterranean Heating/Cooling System

I am so excited to build a SCHS greenhouse!

I have been planning the building of my SCHS greenhouse for about a year now. We will start construction sometime this spring/summer. I have followed all of the calculations on Sunny John's page and it appears that compared to the greenhouse kit that I will be purchasing adding the SCHS part shouldn't be too cost prohibitive. I wanted to share (attach) my initial plans here to get some feedback. Can you guys look at my proposed plan and provide some thoughts of something that are good or bad about the plan? How can I improve it?

I am in Zone 6a in a mountain valley in Utah. We get a good amount of strong sun in the winter (and snow). The greenhouse will be in a residential neighborhood that has nothing blocking the plot from the south. The only limit for shading will be clouds even in the December.

The greenhouse will have about 2050 cu ft of air inside (without anything in it). In my plan I will dig 4 feet down and place 3 layers of tubing. I plan to have 6 tubes at 70' each. Given the fan I already have this should allow the air to be underground for about 8 seconds.

On the surface I will be building some 18" grow boxes while leaving other areas open for potted plans and a semi-mobile potting station. My winter plans for this greenhouse include overwintering frost sensitive plants, growing lettuce and cole crops for my family, and if I can get away with it citrus.

Any thoughts would be very appreciated!!!

Here is the legend for the attached picture:

Left: Greenhouse structure, Center: Underground tubing, Right: above ground grow beds and greenhouse space.

Here is a link that might be useful: Greenhouse I plan to purchase

This post was edited by grandwheatgrass on Mon, Feb 24, 14 at 11:04


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RE: Subterranean Heating/Cooling System

Sounds like a good project grandwheatgrass. A few thoughts:

Your location/climate is similar to mine, but about 1 zone warmer. I expect you will need significant cooling in place to keep your GH at reasonable temps. Certainly in the summer but likely also some in all the other seasons as well. In my GH, with the SHCS fan running, on warm sunny days it still can get to 100+F in the GH (I don't have my cooling fan and vents operational yet). Just something to plan for.

I am curious, why are you going down 4' seems like that is more than would be needed, especially if you are planning raised beds on top. I know John C did some SHCS's where he brought the air tubes up into the bottom of the raised beds. I don't think you want to bury those pipes too deep.

Also, I assume the raised bed diagram was more symbolic than an accurate drawing, but you probably will want to put the ground level planting area closest to the S windows, and put the higher raised beds to the N of them, so that they all will get light.


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RE: Subterranean Heating/Cooling System

Hi All,

Gwoods, go to Ropers site and look at his plan for a small back yard greenhouse. As a beginner, I found it a little less confusing to start with that Sunny John's. Also, did you go to the link I sent you for Andrew Collins? I found that to be a great simple explanation. Sunny John's is a huge site for much info later. ( :

Hi grandwheatgrass, CONGRATS. Steve333 has great feedback. I too was wondering why your higher planting bed was on the S side, but perhaps it is the plenums you need to relocate.

I will be lurking and learning along with you.


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RE: Subterranean Heating/Cooling System

Hi Curly Girl and Steve333,

I just finished reading your posts about the plastic under the walkways to reduce the heat loss. Is a tarp ok? Also, I am confused about the distance the holes need to be. Seems like Roper said to make them closer together than Sunny John said?

As a reminder, we have very heavy clay soil. Last year I dug a large hole about 3-4 ft. deep and filled it about 1/3 with water. It took 4 days to drain. Sigh. The greenhouse will sit on a fairly level spot within a gradual downhill slope.

I know you both used rock, but I hope I can use my clay soil~mixed with something? but what...I hear I should not use my favorite compost because of the organic material being near the tubes???? I want to grow a lemon, olive and an avocado tree on the north side. That's a lot for a teeny house, but I will espalier them and see if they can still fruit. If not, the lemon will go in a large air pruning "pot" and move in and out of the greenhouse. I already have the lemon ans it is the "Variegated Pink "Lemon tree because it is a good patio/houseplant variety with tasty fruit.The avocado will be the "Holiday" because it is a strong tree with a dwarf (12 ft), weeping habit and the fruit is large and tasty. I have not researched the olive yet.

I thought we would put about 2-3 inches of gravel about 1 foot (?) under the deepest tube layer to provide drainage.My hubby says he thinks he should put in on a grade and then put a sump pump in a 5 gallon bucket buried lower than the gravel and just outside the greenhouse. It would pump it into a drain headed well away from the greenhouse. That way we hope to keep our tubes dry when we have our sudden thunder storms. We seem to get almost all of our rain in heavy falls over a short time period. Will this water movement under the tubes suck out my heat? How deep do I need to go below the last tube layer?

Also, I am going to lay my tubes in a serpentine pattern as I hear that produces more air turbulence and heat exchange. Have you heard of that? Here is a photo of that type pattern. Not sure about their tubes though, but mine will be the usual 4" slotted ADS pipe . This photo is from a heat sink to help pre-heat air before it enters a heat pump for a house.

Curly girl, I got confused if I need to widen my tube holes to the to a quarter inch like Roper said. I think you said to do that? Duh.

Thanks you two for being so very generous with your time and knowledge. I am trying to draw a plan for you to look at, but I am slow to figure out all the details.


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RE: Subterranean Heating/Cooling System

Hi Waterstar!

A tarp should be fine under the walkways.

I would think you could still use your clay soil. I would not waste your compost on it though. Perhaps mix the clay with sand? Save your nutrients for the soil above the heat sink. This will keep the roots from going too far into the heat sink and possibly disrupting the tubes and will save you some money. (I agree that if they do, they will probably be air-pruned so it is not a big worry but Sunny John did suggest this as a strategy)

Exciting about the espalier plan! From what I have read, espalier developed in fortifications where space was scarce but the need of food sources during times of siege prompted them to experiment. They were pleased to see that pruning trees against a wall extended the growing season because the stone absorbed the heat of the sun during the day and kept the tree warm into the chilly evenings late in the season. Pruning itself also helped production, of course. I have often thought espalier in greenhouses made a lot of sense for these reasons.

I have also read about planting several fruit trees in one hole to keep the trees small and to use the space efficiently. I have not heard of that being done in a greenhouse, however.

When you put the layer of gravel down, be sure to put some sort of landscapers cloth over the top to prevent soil from getting in around the gravel. Without that measure, the gravel does nothing to improve drainage.

Interesting about the air turbulence -I had not hear that. The last I heard, Sunny John seemed to think the straight across design between culverts was preferable but perhaps Steve333 could weigh in on that. Either way, I don't think it makes a huge difference. Although, I can see how the twists and turns would create more turbulence. Some greenhouses it makes sense to do one method versus another and I think that becomes more the determining factor.

About widening the holes -I would not do that unless you are using stone in your heat sink. I could be wrong about this, but I think 1/4" slots would be just a little too big and would allow soil to come through into the tubes. The perforations of the tube are long and thin (some don't go all the way through) which does not allow soil to infiltrate. When I saw it, I wondered how well the heat transfer would be without widening them even if I was using soil as a storage medium. I think that for longer runs (longer than 30') it works fine but I suspect the shorter the runs, the less efficient it is. Because I was using stone as my storage medium, I took Roper's advice (his storage medium is stone as well) to widen the slots to a 1/4". This is no small job! I had a big party and 40 people came over with their drills and together we drilled 50,000 holes. We did not get it all done that day but others came by every so often to help for a bit. If you can avoid doing it then great! -Put that energy into another part of the project!

Best of luck!


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Hi Waterstar

I too had not heard about turbulence in curved pipe layouts, but it makes sense. Having put in curved pipes in mine, I will say that it can be a bit of a pain, getting equal lengths with different curves on each of the pipes and keeping the right spacing. Nice to think that effort might pay off.

I'd be cautious about adding sand to clay. Everything I have heard is that sand will not loosen clay and may make it worse. Adding calcium and organic matter will help, but that is for soil at the top, not sure if you really would need that down low. And the extra organic matter there would probably lower the density and heat storage capacity some. I think I'd stick with your straight subsoil, perhaps with a bit of limestone if that is appropriate per your soil tests.

It's hard to say on your drainage plans without know a lot more about your site, soil structure and water table, and what foundation your GH will have. Typically for a GH is is not water inside that you need to worry about getting rid of, but keeping ground water outside from coming in under ground. That can generally be done by control measures (gutters, grading, diversion channels) outside of the GH proper. However if you are in a wet spot, with high levels of ground water, you may need a more complicated system. One should be careful about putting drainage layers inside the GH, as it may also attract/store ground water. Might be worth talking with an expert in your area, someone familiar with your soils, climate and water table. In general though, the key is putting enough of a system in place to keep the water table from rising up into the SHCS layer. Putting drainage beneath the SHCS layer alone won't do that, you need path(s) for that ground water to go somewhere else. I suspect you really will need some drainage around the outside of the GH plus some grading, nothing really inside. Perhaps a couple of circles of the same ABS drainage pipe wound the perimeter with an exit downhill from the site (if you have enough slope).

I can't see any reason to widen the drainage holes in the pipes. Those holes are there for condensate to go out into the soil. Air really isn't meant to flow in/out of them. There are enough of them for this pipe to be used for collecting water around a foundation, should be plenty for SHCS purposes.


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Hi You Two!

Wow, Curlygirl, I have never heard of "planting several fruit trees in one hole”. Now that would be super exciting! Can you tell me more about it? If not, I will research it. I always thought the roots would compete too much. Mine will almost be planted in one hole not matter what! ( :

Also Curygirl thanks for the tip putting some sort of landscaper’s cloth over the top of the gravel because "Without that measure, the gravel does nothing to improve drainage". Yipes, I did not know that! Will do.
Steve333,

Yes, I agree about the sand. I have read the latest info is that adding sand to clay soil may result in cement like soil. I’ve decided to just leave the clay, except I will have nice topsoil and compost in the first top 2 ft. inside the greenhouse. That will be penty for my citrus trees and I can keep the seedlings on wire shelves far a few weeks in the spring. Other than that I will only plant wintergreens on the S. side if the citrus tree roots are not there.

Re: “One should be careful about putting drainage layers inside the GH, as it may also attract/store ground water.” Yes, I think so too, especially since this is on a small slope. I have enough of a slope to take your advice and will put a “ABS drainage pipe wound the perimeter with an exit downhill from the site (if you have enough slope).

Both of you:
Whew! Glad I don't have to widen the holes in the tubes!!!!Okay, so how does this sound for drainage then?

Drainage:

Trench with ADS pipes routing uphill water drainage around and downhill from the greenhouse.

One foot under the bottom layer of tubing will have a layer of landscape cloth covering 2-4 inches of gravel, which is sloped to a sump pump buried beneath the grade. The sump pump will have a PVC drainpipe that drains downhill from the greenhouse. The sump pump will have an "access" hole to it as well as a insulated wire attached to the pump so it can be easily lifted out of the bucket for maintenance/service etc.)

Gutters will be installed on the greenhouse and rainwater caught in rain barrel for watering plants inside. The water barrel will be placed on cinder blocks on the NW side of the building so that gravity will feed a hose to water plants in the greenhouse. Outdoors on the west side will be deciduous vines (Jackman Clematis) to provide shade to the greenhouse water barrel in the summer but sun in the winter. (Note: that particular plant will be cut to within a few inches of the soil during fall and mulched. It will also be planted a ways from the greenhouse..but it can get to 18' high)

After the hole is dug and gravel, sump pump etc. in place we will flood it some and see how long it takes to dry out. Then we will add a foot of backfill and repeat. If all goes ok, we will let it dry and lay down the first layer of ADS tubing.

I would like to skip any tarp under the “Trex” type walkway because most citrus fruit roots grow about 6-12” under the soil and I’d like to keep the entire “floor” space for a 2’ layer of good topsoil/compost for those roots. If I have to put something under the walkway, I would do a not-punctured tarp under a “Trex” type walkway. The tarp would slanted to the N wall to drain water into the fruit trees instead of directly into the heat sink underneath. Would that be ok?

See any problems in the drainage part you two? I have tried to draw diagrams for you, but I don’t have very good software for it. This is what I have so far.

The “foundation” if just going to be a “Trex” type board, anchored deep to the soil to keep it from blowing over. The heat sink will be set one foot inside the foundation to allow for anchors to be drilled without hitting the tubing as well as stable soil for the greenhouse.


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Sounds good, a couple of things...

First, in addition to gutters, it would be important to divert the uphill drainage around the GH, so that that water does not flow downhill into the GH (just grading should do it).

Still not sure you'll need the gravel layer underneath. I suppose if you do, it will be good that it is there. But if the gutters and perimeter drain and grading work, you should not really need it. [Although I may have lived too long in a dry climate to remember what can happen in wet climates]

You may still want some perforated tarp/plastic under the walkways to reduce evaporation and heat loss in there. John C had suggested that as a way to put the heat coming off the ground to best use; heating planted areas instead of walkways.


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Hi Steve333,

Yes, I like the idea of grading and no gravel and/or sump pump. I am going to talk to my hubby about it. Seems like with gutters and grading there should be no need for a sump pump. I am concerned that the gravel and sump will just attract a lot of other water to the area. ( :

Thanks to your comment, I now understand about the loss of heat and moisture under the walkway...but I am concerned about the soil under the plastic in the walkway. Since the soil can't breathe or handle water, will the citrus roots grow there? I thought of using brick for the pathway, so it could adsorb sun in the winter, but I am concerned it might be too hot for the summer. I just don't know what to do.

Do you have any experience with how any roots react to the plastic cover?

THANKS


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I do not yet have any first hand experience with a membrane under the walkways (still trying to get my topsoil delivered and into my GH). However there are several youtube videos which show this, and some discussion of this on the sunnyjohn site.

It won't totally seal the walk area from air, because you are going to drill 1/4" holes thru the tarp before putting it down (a wood drill bit drilling thru the folded tarp is the wasy way to do this; holes roughly 6" oc both ways). The holes should allow some air in, and water to drain thru too.

The idea is to limit/slow moisture evap on the walkways, as that is a major heat transport mechanism. Unless your walkways are very large, it should not limit soil life under them, I would think.


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Hi Steve333,

What do you think of this idea? I could put solid red clay brick directly on the soil (no sand) and use a rubber hammer to make them as close as possible. The brick would be exposed to the sun because only the trees (N side of building) will be there in the winder. To avoid the heat gain in the summer I could do something simple like put a white sheet over it. Is that nuts?

You are right about the plastic breathing...I may be overly cautious about the plastic. The reason is that years ago I had to remove plastic in a garden bed that the previous owners had put down. The soil under it stunk to high heaven. Of course it did not have any holes put in it. ( :


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Now I have a really ignorant question. Actually 2. ( :

Don't I want to have the 4" ADS running between the area where the two barrel plenums sit? I know I will have to really wind them around so that they would remain the same length as the other tubes. But, I can't seem to find a diagram that shows them there. That is where my trees will be planted.

Also, in such a small greenhouse, those barrel plenums will be really close together. To avoid the intake just sucking in the outflow air, do I just aim them different directions? They will only be about 10ft apart on center.

THANK YOU for all the patience you have with me!!!


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Steve333,
I forgot to ask. How much topsoil are you putting in when you can finally get it?


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Waterstar-

I think the clay tiles laid without mortar should be a reasonable replacement for the perforated plastic. You will likely be able to tell if heat/moisture is coming off the tiles at night, and if it is you can always add a plastic layer under them in the future.

I'm not sure why you don't want to run the 4" air tubes where your trees will be. Don't you think they will appreciate the heat? The tubes are run 24" oc, so only 4" out of every 24" is taken up by the tubes (measured horizontally). I think that will be plenty of subsoil for the trees to work in; they still have the topsoil layer to work with too. But this is only my opinion, as I have not tried it yet.

I am planning on putting in 16-18" of topsoil over the SHCS layer. This was limited by my geography, there is a layer of bedrock under the site, which determined the level of the foundation and the bottom of the SHCS layer. I think (hope) this will be enough. I may do some shallow raised beds which would add 6" or so to that number, but probably not the first year.


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My husband and I have two 6'x8' HFGH kits. We will be putting them with their doors opening into a shed that is between the two greenhouses. The foundation will be built of 8"x8"x16" cement blocks filed with concrete. The foundation will start at least 24" underground and continue at least 32" above ground with the floor inside the greenhouse being at ground level. We will have a 6'x24' area for the underground tubing (actually two 6'x8' sections with an 8'x12' section in the middle). I am currently planning on each greenhouse having its own SHCS so that I can have different growing environments. If I want to have one greenhouse warmer in the winter, should I have the two systems share the underground space so that one greenhouse can take advantage of the heat stored by the other? Would the longer lengths of individual tubes be a problem? My initial estimate is a bit over 40' (24' + 16' + turnaround distance) for each tube. I am thinking two options. The first where tubes from one system would loop lengthwise in the 1st, 3rd, and 5th foot while the other would loop in the 2nd, 4th, and 6th foot of the width of the greenhouses. Each tube would be at one level at the beginning of the loop and a different level at the end.  If two levels for a single tube would be a problem then the tubes could return at the same level but then I would probably use 3" tubing and a closer spacing so that each level would have room for two loops. In either case, I plan on having each tube exit directly into the greenhouse, similar to How to Build a Solar Greenhouse. Have there been examples where half of a tube is above the other half? Would it matter which half is on top?

In this part of southeastern Arizona, our summer high temperatures are between 100°F to 112°F and our winter lows are between 28°F and 7°F. I want a couple citrus trees in the warmer greenhouse and want fresh winter greens in the other.

My greenhouse plans include adjoining 3' raised beds surrounding the greenhouses but not the central shed. There will be an external structure over the external raised beds and greenhouses to support shade cloth, as needed, in the summer and frost protection in the winter. If it gets hotter in the greenhouses in the summer than can be handled by SHCS, additional ventilation, and shade, it would be possible to temporarily replace one or more polycarbonate panels with window screening.

Any suggestions or potential problems? Thanks in advance.
Anna


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Hi Anna,

Could you post a drawing of your ideas with some notes?


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Hi Steve333, Curlygirl and Annalog,

Yes, I do want the tubes under the trees. It is just that in all the drawings I saw I did not see tubes put there. I may have seen it earlier and forgotten. So, THANKS for confirming that I can have them there. Also, thanks for the feedback on the brick pathway. I'll start that way and then add plastic later if needed. ( :

Wow! I'm so fortunate not to have hit granite that close to the surface. What a challenge.

Annalog, sounds very interesting. I will look forward to seeing some drawings and Curlygirls and Steve333 comments. Re: the pipes coming right out of the ground like Andrew Collins does, I am not sure what to think. I had not noticed that when I read his column.

Steve333 and Curygirl, here is what Andrew Collins says:

" Each pipe connects to a part buried central 'plenum', made, in this case from a plastic bullet bin, and they exit at soil level around the side walls of the greenhouse. The exits are screened with wire mesh to keep out unwanted rodent visitors. Solar powered fans are mounted on the top part of the plenum and these draw down warm, moist daytime air from near the top of the greenhouse through an improvised duct."

We are going to start digging in a couple of days!


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Hi  Curlygirl, Steve333, and Waterstar,
I am working on drawings and will post. Creating the drawing identifed a problem with the doorways. ;-)
Anna


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Anna-

I think I have a picture of what you're planning, but a fuzzy one. Had a few thoughts:

1. If I understand your SHCS layout, it sounds like there will be a tube every 1' horizontally. If so, that is twice as close as is typically done, but maybe I don't have the right picture. I'm also not clear how the looping back will work, in that typically the next pipe would be either 2' horizontally or 1' up and 1' over horizontally. Again, not sure I am picturing this right.

However I can see why you'd want the pipe to loop back so that the air in entering and exiting in the same GH.

Have you been to John C's free calculator?
It's fairly easy to get bsaic lengths and fan sizing there.

numsum.com/spreadsheet/show_plain/4681

2. Others may have had different experiences, but snaking the ADS around, trying to keep equal distance and same total lengths was enough of a hassle at one layer at a time, that I would not want to consider it with two levels at a time. But maybe with a good plan it would be fine. Any reason not to loop them back horizontally?

3. I'm not familiar with the HF GHs, but you might want to consider adding an outside door for summer ventilation. You will likely need some in AZ. (but that might get in the way of the outside raised beds so perhaps a window instead?)

4. Just curious, why are you filling the concrete block cores, seems like overkill except maybe at the corners and key strength areas. Have you thought about how you are going to insulate the SHCS area? Foam exposed to panting beds tends to get chewed up over time.


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Hi Steve333,
Responses to your thoughts:
1. I misunderstood the standard spacing, maybe because the UK solar greenhouse was using pipe that was closer to 3" than 4" and he used a closer spacing. The width of the space between the cement block foundation walls will be about 5 feet. That would be one loop at a 2' spacing or two loops (one per greenhouse) at a closer spacing. Your comments caused me to think of a third option where only the space under the central shed is shared. I saw, but have not yet used, John C's free calculator. I will next time I use my laptop instead of my tablet. Edit: I used the calculator with my tablet. It looks as if a two level plan including the area under the central shed will exceed the suggested total tubing length. Also a single small fan per greenhouse will be sufficient for the system.
2. You convinced me to stay with a horizontal plan.
3. Instead of a door or a window, I will probably replace one or more panels with window screen in the summer. I could add plastic inside to cover the screen panels if needed. Maybe plastic curtains to close at night. ;-)
4. The main reason for filling the concrete block cores is that there will not be any mortar between the courses of blocks. We will stack the blocks, add vertical rebar in the corners and at appropriate spacing and then fill with concrete. There will be one horizontal bond row, probably at ground level. The concrete fill will only be for the foundation walls of the greenhouses, not for the raised beds. Our ground is clay quite far down (ancient lake bed) and there are problems in this area with subsidence of the soil.

We will probably insulate the SHCS area under the central shed where there will not be any planting beds. I was not planning on insulating the greenhouse area. I had read that not insulating helped with cooling in the summer and in the winter the outside raised beds and the greenhouses will be covered with an additional layer of plastic so I am hoping that will work as a partial insulation for the SHCS area under the greenhouses. (Essentially a cold frame over the greenhouse. ) If it is not sufficient, then I can add insulation outside the greenhouse/inside the raised beds.

This post was edited by Annalog on Mon, Mar 3, 14 at 2:28


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Hi Annalog,

I too have a 10x12 x 10' peak HFGH. I found the calculator to be inconsistent ( couldn't figure out it it was the browsers of perhaps the formulas did not work for such a small GH or just me) Anyway, figured mine out the old fashioned way with math. I will be very interested to know if the calculator works for you. ( :

It would be good to double check our figures. Mine comes to 180ft. of tubing. I am running them 10 ft long, so will need 18 tubes. They will be in three layers, 1' apart (on center ) vertically and two ft horizontally. So, I need 6 tubes each layer (and the area is 8' wide, so I might add another tube if I can squeeze it in and if Curlygirl and Steve333 don't tell me that's a bad idea.) I have to still do some drawing to figure out how much room I will have after the plenums are in place etc. What I like about the 10' length is that we can buy them already cut to the length and save a bit of labor and time there.


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Annalog,

My apologies, I see you have an 8x6 not a 10x12. Oops.


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Hi Waterstar,
The calculator is geared towards larger greenhouses but it calculated volume OK. At least it seemed OK late last night. ;-) Did you remember to clear the hoop cell using the clear cell function?

I will need to use the calculator again as I didn't record the results (and I will double check manually). However I should only need two levels and 4 tubes as I am using longer tubes and the extra area under the central shed. (I put that in the calculator as a second greenhouse section zero feet high.) My tubes will probably be 33' long (100' cut in thirds).

I now have a hand drawn plan I like but it looks too easy so I am suspicious. Intake plenums in the north corners of the greenhouses near the central shed. Four tubes per plenum with two on each level. One tube per level snakes back and forth in the greenhouse and exits at the edge above planting bed level, far from the intake. The other tube snakes under half the shed area (north or south) and returns to the greenhouse to exit along the south wall. The other level is similar but uses the opposite half of the shed area and follows a different path when snaking back and forth. 6'x8' is too small for an exit plenum. I could get by with a 100 cfm fan per greenhouse but 200 cfm would be perfect. I plan to run them from the solar panel we bought a couple years ago but never used. The roof of the shed will be perfect for it.


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Hi Waterstar,
No worries about the different GH size. My two 6'x8' greenhouses on block knee walls are probably similar to one 8'x 12'. My total tubing length is either 200' or 266' (25' or 33' lengths) but I increased it quite a bit to focus on summer cooling. The coldest winter lows here often follow sunny days while summer can seem endless.


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Hi Annalog,

Will be happy to double check your math for you if it helps.
Yes, I cleared out the already filled in values, but then I noticed that when I changed the roof height the figures did not change. So, I just switched to regular math. It could have been my browser.

I thought I had this pretty well figured out, but now that we are ready to rent a back hoe I am getting confused again. sigh. What got me confused is you (thank you!) pointing out that Andrew Collins did not put his tubes back into a plenum. I don't want to go that route because it would be a huge hassle to put critter screen on each tube and keep it in place etc. But, it has made me question the purpose of the outlet plenum and I can't find the answer. Do you know?

Re: going only 2' deep. I keep reading that we need lots of short tubes, not long ones. I would love it if I could make a couple of long tubes, but I am suspicious that the air flow toward the end of the tube won't be as good as the beginning of the tube and therefore that part of the soil would suffer. Also, in older posts, I keep reading the colder the winter (and I would assume the warmer the summer) the deeper you want your tubing. I'd be afraid to go only 2' deep, but I will read with interest Curlygirl and Steve333 responses. ( :

Since we have such a tiny floor space, I am thinking we do not need such a large plenum as the 55 gallon barrels and/or 12-18" ADS plenums and am thinking of building a thin box to run along each short end of the greenhouse and then my ADS tubes would be much easier to keep the same length and perhaps I could save some underground room.


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Hi Annalog,

Can you scan and post your plan? I am confused about your tubing...is each GH having it's own system or are they sharing? I am pretty visual....


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Hi all,
I took a photo of my plan so far.

The square C shapes on each end are the exterior raised planting beds but this is showing a level 2 feet underground. (The blocks for the raised beds go down that far to anchor the 1/2" hardware cloth to keep out the evil gophers!)

The two 6'x8' greenhouses are on the inside of the square Cs with the central shed between them. The door to the shed is on the south but is not pictured in this drawing.

The unfilled circles in the north corners of the greenhouse represent the intake plenum. There is a separate system for each greenhouse. All that is shared is the heat storage area under the central shed.

The filled circles represent the exits of each tube. I showed different possible tube paths in each greenhouse. I am planning on having the tube exits at the same height as the top of the block knee wall so they will be above soil level.

I am thinking about having a second layer of 1/2" hardware cloth above the top level of tubes to prevent rodents from getting to the tubes. This layer would be aimed at the field mice, not the evil gophers. ;-)

The interior foundation walls in the central shed area will be insulated with foam insulation. This will be protected from above by a floor of concrete pavers (and the shed, of course).

The North symbol is pointing to geological north, not magnetic north. We made sure our house was set up that way and can use it as an easy reference. :-)


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Hi Waterstar,
I think the purposes of the exit plenum are:
- It makes it easy to keep the tubes the same length if they can just run the length or width of the greenhouse to the opposite plenum.
- Only one or two exits to screen and protect from critters.
- Less floor space affected.

There may be other reasons which I am sure the others will mention.


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Hi,
I used the calculator (numsum.com/spreadsheet/show_plain/4681), this time with better numbers for the size of the greenhouse and using half the volume of the central shed, with the assumptions that the greenhouses will often be open to the shed and that I should use that when calculating the volume of air for the fan size calculations. The numbers below are for each system (one greenhouse and half of shed).

Heat storage area just under 90 square feet with 51.5 square feet inside greenhouse. This resulted in initial ballpark of 120' of 4" tubing.

A fan of 200 CFM would provide for an exchange rate of 16.42 times/hour.

Three layers of two 25' tubes would result in 150' of tubing per greenhouse while three layers of three 20' tubes would result in 180' of tubing per greenhouse. Tubing lengths much shorter 20' would not allow sharing the heat storage under the central shed.

I am willing to dig deeper for three layers now that I have convinced my husband that we do not need to dig down more than 8 inches under the exterior raised beds. The raised beds can have a separate level of hardware cloth to keep out the evil gophers. :-)

Anna


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Hi Anna,
I hope Curlygirl or Steve333 will comment on your tubing estimate. Seems ok to me, but I have no experience. ( :

RE: fan. here is some info I read on an older post here:

The origonal shcs data suggested 5x an hour but the recommendation now is to use a lot more :)
The 5x was geared to keeping the air speed in the tubes down to 2-4ft/sec but new data has proven its not the airspeed but the amount of time the "entire" greenhouse air volume spends underground.
More airchanges/hr results in a longer duration underground. With fan speed control I can use upto 45x.
Here are a few test results from my shcs, the soil temperature was 55.4F
14 ac/hr Inlet: 82.4F Outlet: 55.4F (2.28sec 27F drop)
27 ac/hr Inlet: 86F Outlet: 59F (1.14sec 27F drop)
45 ac/hr Inlet: 86F Outlet: 62.6F (0.67sec 23.4F drop)
Notice at 14x the air still drops to the soil mass temperature, 5x would transfer a lot less heat overall :)
The energy transfer increases with the cfm, 14x: 1.72kw/hr, 27x: 3.45kw/hr, 45x: 5kw/hr.
Phase change is responsible for a very large percentage even at high flow rates. Notice how it takes just 0.67 seconds to drop the air by 23.4F at 45x? 
There simply isn`t enough time in the tube for air to lose the heat by conduction given the tube area and temperature difference. Its mostly due to the phase change component.

I have a 170w (677cfm) mains powered fan controlled by a differential thermostat and a speed controller. I`ll be replacing it with a more efficient 155w (870cfm) fan in the near future.

There will be a certain amount of pressure loss dependant on the tubing layout. As the loss increases the fan will produce much less flow than the rated output of 500cfm.


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RE: Subterranean Heating/Cooling System

I also found a less expensive way to buy the 4" perforated ADS pipe. I am getting it for 44 cents a foot instead of the 62 cents charged by home depot and Lowes. The rep sells it cheaper than the company can quote you. Maybe there is one near you?

http://www.ads-pipe.com/en/


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Hi Waterstar,
Thanks for the additional information. I will think of 200 cfm as a bare minimum but look for higher cfm fans. Also, since I was including the volume in the central shed, I can almost double the greenhouse air exchange rate by closing the doors between the greenhouses and the shed. ;-)

Was that ADS pipe price with or without a sock?

Thanks, Anna


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Hi Anna,

The ADS was without the sock. My understanding is that you only need a sock if you have sandy soil. I have heavy clay.

Shutting the door to the shed will help, but remember, you are trying to heat the soil around the roots too. So I am going to put in ADS every 1' horizontally and 2' vertically. No closer horizontally or the airflow may just go from one pipe to another and not warm the soil. So, I will have a bit more tubing than required, but I also have the prefab HFGH that I thinks needs more. ( :
I think both sunnyjohn and ropers sites have links to sources for fans. I read that john died, so that is why his info is not updated.
Bless you, keep working on this! We are not the only ones out there with affordable HFGH. ( :


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Hi Waterstar,
My soil is very dry sandy clay. It is OK when undisturbed but turns to powder if disturbed when dry. If disturbed when wet, the resulting mud dries with a concrete-like consistency. So I am only concerned about dirt infiltration during installation. I suspect that I will use ADS without the sock but cover it with strips of landscape fabric that I have onhand before I fill with the dry subsoil. My plans are for ADS every 1' vertically and 1.5' - 2' horizontally with the exception of near the plenum and possibly through the doorway. I am considering putting at least some the underground cement blocks sideways on each side of the doorway so that the tubes have more space to go between the greenhouse area and the central shed area. I agree that the smaller greenhouses (especially HFGH ;-) ) may need proportionally more tubing.

That is interesting about the horizontal airflow. That has me thinking about adding small vertical barriers where the tubes need to be closer together. I have some scraps of vinyl siding material that could work perfectly. (This is left over from when we had to replace the siding with a block wall. We have been using it for various projects, mostly for chicken furniture such as nest boxes, but we have lots of short pieces left.)

I found a link to a blog entry remembering John Cruickshank from the SOPI Permaculture Blog.


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RE: Subterranean Heating/Cooling System

Hi Anna,

I think you may want to go ahead and get the sock covered ADS. Did you check Roper's site to see what he says? And, oh my! your soil sounds much worse than mine! ( :

I don't think I'd add any vinyl in-between the ADS pipes. It might interfere with the roots sneaking around and getting places. ( : Besides, I don't think you will need it, but that is just my opinion.

How soon will you start digging? I hope to have mine dug this coming week if the rain holds off. I'd really like to get my seedlings in there this spring....we shall see.


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RE: Subterranean Heating/Cooling System

Waterstar, I will start digging as soon as it is not so windy here; we are getting 30 mph wind forecasts. Digging with a shovel is not as much fun in the wind. :-) My soil is great once I add lots of compost. I am very glad we do not have the underground caliche we had in Tucson.

Did the rain hold off; did you start digging?

I posted some images of my greenhouse structure plans in the other thread. I will post one here after I model the pipe layout for the SHCS. Since it is too windy to dig, I have been planning instead.

Anna


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Hi Anna,

I was going to dig by hand, but Curlygirl talked me out of it...thank heavens! Maybe you could barter, trade or rent or something. We found a local who will dig the hole for about $250. Less than for which we could rent equipment.

I am soooo fortunate to be in 7b. We had three days of 75 degree weather. Worked my head off outdoors. Before that it was in the 30's or less for a bit. Rain and cool today, so no digging yet. But the truth is that we are still gathering our other supplies. ( :

Start seeds next week. Have a sneaking suspicion the GH won't be ready and my windows and rooms will be packed!

Blessings,
Waterstar


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RE: Subterranean Heating/Cooling System

Curlygirl and Steve333,

This is what I thought I'd use on the walls for insulation in the heat sink and on the N side of the greenhouse wall.


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RE: Subterranean Heating/Cooling System

Waterstar-

Extruded styrofoam is the way to go, but typically one uses a 2" thickness around foundations. On my smaller GH (~12 yrs old now), I used styrofoam forms for the foundation concrete, stripped the inside layer off after it cured, and put it all on the outside, for 4" of thickness total.

It will up the price some if you go to thicker insulation, but it's one of those things that you only can do (easily) at this point in the construction.

Lowes, Home Depot and all the building supply places should have the 2" thick version of that same stuff too.


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RE: Subterranean Heating/Cooling System

Steve333,

THANKS for the help. I will get the 2".

The only styrofoam forms I found are for horizontal foundations. Do they make one for a vertical hole (at the bottom we will put a sump pump if it turns out we need one.)?


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RE: Subterranean Heating/Cooling System

When insulating underground concrete walls around the SHCS heat sink, is it better to put the insulation on the inside or the outside of the walls? Can the walls act as part of the heat sink?
Thanks, Anna


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Hi Anna,

You don't need a concrete foundation with the HFGH. My hubby is using very tall chain link fence posts set in concrete on the four coners. He will anchor the inside of the GH to the posts. We will also use these posts to hold wire so I can espalier dwarf fruit trees.

Trex type boards will be placed on top of the post concrete and used as a base for the GH to sit on. (Note: we may also bury it a little in the ground so I can wheel things in and out...flush with brick walkway on outside that continues on the inside....but we may not need to bury it.).

If he thinks he wants more security, he will drill a hole in the Trex type board and use a large screw (foundation anchors? don't know the name...about a foot long) to anchor into the soil (put at an angle so it does not hit the heat sink).

The insulation will go right next to the dirt. The nice thing is, we won't have concrete in the heat sink to syphon off heat/cool air. ( :


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RE: Subterranean Heating/Cooling System

Hi Carolyn, the 6'x8' HFGH is much shorter than the 10'x12' HFGH. The door is only 5'4" tall and my husband would need to duck to avoid hitting his head. (I could walk in OK as long as I am not wearing heels. ;-) ) To avoid problems with headroom and for other reasons, we are putting the greenhouses on kneewalls about 32" high (four rows of 8"x8"x16" cement blocks.

Also, we have severe rodent problems here (gophers, field mice, and rats). Cement block walls and hardware cloth are the only solutions we have found to work to keep out unwanted rodents. I am planning on layers of hardware cloth anchored in the concrete walls above and below the heat sink. I am concerned that if we do not wall off the SHCH heat sink, then rodents will eat their way through the ADS tubing and use it as their climate controlled home.

The attached image shows the current plan for the two 6'x8' greenhouses with their doors opening into a central 8'x9' shed. The front wall of the central shed is 8' tall with a standard door shown. The rectangle in the roof that looks like a window is meant to represent a solar electric panel. The ground is represented with a transparent brown so that it is possible to see the bottom two rows of the four underground rows of blocks. If the ground was level then I would be digging down 34" but it will be less on one end and more on the other. The outside raised beds will take care of the difference in ground level as well as providing some extra insulation for the knee walls.

There are some reasons other than cost why we will be digging the heat sink hole manually. These are:

-- There is a small yucca growing where the central shed will be. I want to try to save it so that I can relocate it to my mother's house. These have deep tap roots and I should be able to get it out while digging the heat sink area.

-- I do not want to disturb the yuccas that are to the south and north of the central shed. Also there is an existing shed to the north as well as trees to the east and west that impede easy access with digging machinery.

-- I can certainly afford to burn calories and build muscles digging. My back and knees are in good shape. I may be crazy but I find digging in this soil a good meditative activity. ;-)

Anna


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Hi Anna,

Your design looks absolutely BEAUTIFUL!!! And what a great job drawing it!!!!

The only thing I can think of (and it is probably already planned) is to change the entrance into the shed from steps to a ramp so you can wheel plants/soil in and out easily.

I would copy your design in a flash, but we have fire ants here, so that will be my problem. They LOVE raised beds. I am planning on instant grits for the GH. They are not active in the winter, so I can then, but in the summer only the fruit trees will be in there and I'll be watching it like a hawk for any signs of them.

Blessings,
Carolyn


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Hi Carolyn, there are no steps. The entry into the shed is level. Those brown blocks are actually directly under the shed door two to three feet underground. It is an optical illusion due to me selecting a transparent color for the ground in the modeling program that I used. I cannot draw but I can get a computer program to draw for me. ;-)

We have some fire ants here but mostly other kinds. Fortunately we also have horned lizards that love to eat ants. ;-D

Anna


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Carolyn, while thinking of ants, have you tried sprinkling ground cinnamon on the ant trails and where you don't want the ants to be? Both my daughter and I have had success driving them away with cinnamon.
Anna


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Hi Anna,

Did you try it on fire ants or sugar ants. I know sugar ants need to smell their trail, so that will work. ( : Fire ants , I don't know how they work..... Sounds like I need to import Lizards. ( :

Such a super plan you have. Be sure and post pictures as you go!


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It was fire ants at my daughter's house. I had first heard about using cinnamon to get bees to leave. I used it when a swarm was investigating our shed. I had an old can and tossed the contents up in the air of the shed so that it fell all over. The swarm left.

My daughter had problems with fire ants in the raised bed along the back of her yard. She did not want to use poison because of her two small dogs. I suggested trying cinnamon. She did and the ants did not like it. She had to keep reapplying it after watering her lawn. The newer ant outposts disappeared fairly quickly while the main nest took several applications. Now she rarely needs to sprinkle cinnamon outside. Large economical boxes can be found if it works on your ants; it would be too expensive using those tiny cans that are in the spice section. Asian and Mexican groceries, CostCo, and Sam's Club are where I find them.

This post was edited by Annalog on Thu, Mar 13, 14 at 11:40


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@Steve333 and @waterstar,

It may be the way that the image looks based upon the perspective, but both beds in the GH are going to be the same height (18 in.). I plan on using the reserved space that is not beds for overwintering potted plants/trees, germination stations, and a mobile workbench.

I am still learning and exploring my options. @Steve333 said that 4' may be too deep. My initial calculations were at 3', but I wanted to make sure this system was effective so I thought I might just go a little deeper. Maybe I am just overplanning. I am concerned with the need to cool in the summer and thought that deeper would help in storing and converting heat underground. I saw on Ropers' site that temperatures still got 140+ ºF even with SCHS working.

@Steve333, what is the temperature range that you have seen in your SCHS greenhouse during December - January? My main goal is to overwinter plants that can't handle freezing and secondary possibly grow citrus or similar plants more tender plants.

I love your advice!

Hopefully this new picture can help give you an idea for what I have in mind. We recently got some bids from landscapers for the other parts of our yard, I bought our fruit trees and have potted them until we are ready for them and I will be gathering the materials to do the digging and underground work myself. It's starting to come together! I can't wait to get gardening!


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@Annalog

I can certainly understand your efforts to exclude rodents. We have gophers as well as the other varieties (rats, mice, voles, rabbits). From what I can tell, I did not have any move into my underground tubes, so far at least. And those tubes were un-enclosed for 4-5 months. But it's hard to say how long this will last.

@waterstar

There are several foam based concrete forms systems out there. Typically for pouring the walls of a house foundation. These days they even make ones that are designed to make it easy to take the inside foam off. So yes you can get them to make a sump pump well.

In general, you want to keep the concrete/block thermal mass inside the insulation. It just adds extra thermal mass, you paid for it may as well use it is my take. Also exposed foam on the inside does not stand up very well to gardening activities.

@grandwheatgrass

My memory is a bit fuzzy on this, but I think I recall a thread on digging the SHCS deeper on one of John C's forums. The gist of that was that it was a waste of effort, and that it worked better at the shallower 3' depth. I suspect that it actually will depend on the details of your project: temp range you're working with, type of soil etc. It would be nice to have some good simulation program to run this by, but I don't know of any, so we just have to take our best guess. As I said though, I can't be sure on this.

I've seen a fairly wide range in the GH this winter. It got down to 20F or so on nights I did not run the SHCS fan. With the fan it stayed ~45F warmer than outside on the really cold nights. During the day, it got up to 120F on very sunny days with no cooling or venting. SHCS helped lower the temps some, but it was very clear that I will need shade cloth or additional ventilation to keep temps in check for the summer (as expected).

I expect to be able to use the GH all winter for greens and the like, and I am hoping to keep a couple of hardy citrus in there too. I will use aux heat when needed, but my initial tests lead me to believe that my heating bills should be fairly low. Heating on only maybe 5-10% of the nights.


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@Steve333

Wow, 120F on sunny days is amazing. This summer I will plant some sacrificial heat tolerant plants in there to see how the temp problem goes.

If I cannot keep it cool enough this summer, I will plant clematis and/or pole beans outside on some of the south side of the GH as well as the west. I will have hubby sink extra pipes outside the GH, about 1-2 feet away?...and these can be used as the trellis supports.

Thanks for the advise on the forms. I really appreciate your help. I have another question now. I am going to use 12" ADS as my plenums (Roper said that size would be ok). Is that what you (and Curlygirl?) used? If so, I hope your experience will help me. The adaptors between the 4" tubes and the plenum tube are really expensive. My hubby says if he can't find the right size bit for the drilling then he is going to use hot glue for a temporary hold while silicone dries and is the permanent hold. I just want to double check the reason for the adaptors. If he can get a good fit and a good seal it should be good, right?

@Annalog,

I will try experiments with the fire ants and cinnamon this summer. Goodie.

@grandwheatgrass

Are your intake and outlet pipes on the North Side and your planters on the South side? ( :


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@steve333, thanks for confirming that the insulation should go outside the underground concrete block wall around the heat sink. Now I am considering adding a fifth row of underground blocks so that the foundation is 40" instead of 32". Then, if I use 4'x 8' insulation panels, only 8" will be inside the raised beds. On the other hand, even if 16" is at the lower back of a raised bed 24" high, my normal gardening activity should not disturb it. I would prefer to stay with four underground rows of blocks. Now, I am beginning to think that I am going to need a water barrier between the outside raised beds and the greenhouse foundation walls. If so, then it is the water barrier that will need the most protection from gardening activity. Off the top of my head, I can think of Tyvek or something that is painted on. Painting the outside of an underground wall means digging a bigger hole. More to research! I did not think I would need to worry about waterproofing foundations in the desert. :-) Surface water is not a problem for the greenhouse site; it is already channeled elsewhere.

Does the wall above the heat sink need to be insulated or should the outside raised beds be sufficient, especially if the beds are covered in the winter?

Rodents are persistent. Field mice ate holes in the plastic plumbing lines under our house requiring plumbing and insulation replacement, as well as adding a block wall under our manufactured house. We put rat poison inside that space as no other wildlife should go there. That area is also treated to prevent termites. We will not deliberately use poison elsewhere on our property. Gophers seem to become more of a problem as more neighbors cut down and pull out native desert plants and do not replace them with anything else. (Maybe because the gophers ate what they planted before moving to our acre.) I am certain that our gopher population density is at least triple the normal for this area. Fortunately, we have not had severe problems with the rabbits and rats that live here. I suspect that is due to us leaving their natural food supply alone and that the actions taken for mice and gophers works for them also. In addition, the snake population seems well fed.


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@annalog

I would think that one of the paint on foundation waterproofing materials would be the way to go. If you get a water based one, it should be safe for the foam, and can even be used to coat any foam that is above the dirt to prevent the sun from degrading it. There are co's that spray these coatings on, so you only need a 1' of clearance (as long as the dirt isn't falling in).

Typically I have insulated the wall all the way up. But I am in a much colder climate and don't have the outside beds.

@waterstar

I looked into larger ADS for plenums, but backed off once I got some pricing. I would have ended up spending more on the plenum ADS and fittings than I did on the ADS for all the tubes. I ended up using those blue plastic 55g drums; like you see in some of the youtube vids. I found it was pretty easy to fit them to the drums, I drilled a hole with a 4-1/8" hole saw and just inserted the ADS. Key thing is to do this in warm weather or heat the ADS with a heat gun/hair dryer. If the ADS is warm it becomes very flexible. When it was at 35F (the outside temps when I was doing this) it was impossible to get it into the holes. Experiment on the exact size of the hole. You want it so that it is sized for the indents in the ADS. That way once the ADS is in there the taller ridges will hold it in place. No glue needed.


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RE: Subterranean Heating/Cooling System

@steve333

THANKS for the tips about the heat. I'll give your tips to my hubby ( :


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RE: Subterranean Heating/Cooling System

@steve333, thanks for the tips for connecting the ADS with the plenum. I found a locally available water-based waterproofing coating that looks good and that we can paint on. We will decide when it gets closer to time to use it. I will probably have the insulation go all the way up. If the total foundation wall is under 6 feet (half above and half below ground), then that will be manageable. We might paint the below grade section before building the above grade section.Then we would be able to fill in the outside sooner.


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Annalog, I know this is off topic, but using rat poison under your foundation does not prevent other wildlife from exposure to it. Rat poisons do not act immediately, they take hours to days to kill an animal. So the targeted animal ingests it, then runs off, often times filling their cheeks with vast quantities that they move to other areas to cache it away for later consumption, and then go back for more. the product works by inhibiting blood clotting, so they bleed to death. any predator (including domestic pets) who then consume the dead aniimal or their caches of rat poison that were moved around, will suffer the same bleeding problems. Hawks, owls, cats and dogs and any other exposed animals will suffer the same effects. Please don't use it! There are sticky traps, snap traps, and other effective means of eliminating these unwanted visitors that don't kill other animals. I am not a "bunny-hugger", I am a veterinarian and wildlife rehabilitator who sees the end effects of these poisons often. I wish the companies who make these poisons were required to tell consumers what is actually going on! I hope this helps you make a more informed decision. You probably had no idea!


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Myfrozenlittlepond, it was almost four years ago that we put the one package of rat poison bars under our house inside the block wall enclosure. We have not added any since and I am not sure if any was eaten. If it is still there, should I bury it in place or dispose it another way?
Thanks, Anna


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Life is full of surprises! YIPES! We got our heat sink dug today. I was so excited. And then we hit a pipe.....a sewer pipe, YUCK!

Turns out there is an unexpected drain field from the septic tank here. Good grief. All of the drain field was supposed to be 40 ft. away from this area.

We replaced the pipe...it hooks onto a perforated ADS on each end....guess it a "y" just outside the hole.

It only had a little bit of moisture in it, so I know it is not the main line. I am going to run some washing and observe what happens. Also, it is going to rain tomorrow. We are going to leave the hole open to the rain. I want to see how the drainage is.

Fortunately, the pipe is right at the 4 foot level. This means we can put 1 foot of gravel on top of it, plus one foot of clay soil on top of that and our deepest tube will go on the level. By observing the water levels I can tell if this will be a problem.

If need be we can always put a sump pump in place and pump it underground a long ways away. Oh my.


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Annalog, that is a great question. Disposal in a landfill risks critters accessing it if it is not buried well. Burying it yourself risks the same - I am not a chemist and am not sure how stable these chemicals are in soil. They are very stable in the body. I guess I would go the landfill route, with hopes that they properly bury waste and that it will degrade with the garbage over time. try to put it in a container that would at least temporarily keep it safe.


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Hi Guys
Good to see some shcs digging action going on, its the best part..not ;)
It seems that everyone is destined to run into "something" while digging their trenches. I hit an old clay land drain about 3ft down, it looked just like a clay sewer pipe until i dug under it and found it was only half a pipe.

I have an odd shaped plenum, nicknamed "the birdhouse", made from 4x1 pressure treated timber and punched galvanised metal strip. Its been in the ground for about 5 years and hasnt fallen apart so far. Its a good option if you`re struggling to find something suitable.


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@steve333,

Regarding the 3' vs 4' hole for the SCHS would 3' provide more warming for the winter, but 4' more cooling for the summer? I am just trying to understand if in zone 6a if I will have more problems with heat or cold.


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@hex2006,

What kind of performance to you get from your SCHS in the summer for keeping temperatures down and the in the winter for keeping temperatures above freezing? Did you follow the calculations provided by Sunny John? I will be digging in about 2 months and I want to see if following the recommendations provided by Sunny John exactly will give the best results.

Thanks!


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Hi
The system has performed well for moderating summer greenhouse temps and keeping it frostfree over winter without any additional heating.
In the 4 seasons its been running i cant say we`ve had two summers or winters that were the same but i havent needed to resort to anything extreme like forced summer venting or running the system at night to ditch excess heat from the mass to increase the following days cooling capacity. A cold summer followed by a harsh winter would be the ultimate test but it hasnt happened yet.
I used John`s calculations for the overall tube length vs greenhouse size but the layout is non standard. I use a much higher cfm than the recommended 5 airchanges per hour, i find the most efficient heat transfer in summer peaks at 20-25 air changes per hour with diminishing returns at 45 air changes. A lot depends on your local conditions, both inside and outside the greenhouse but it really doesnt have to be 100% perfect in order to work well.


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@grandwheatgrass

I can't really say precisely what the effects would be (it was 4-5 years back when I was reading John C's blogs on this). I recall (vaguely) that the consensus was that it wasn't worth the extra expense to go down further. But if for other reasons you had to go down deeper than 3' (deep frostline, or whatever), then I don't know that it would be bad.

My guess would be that a deeper (and bigger) SHCS storage volume would store more heat, and perhaps have a slower transfer of that heat up to the topsoil level. Depending upon the situation, that could be good or bad.


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RE: Subterranean Heating/Cooling System

If you get plenty of sun it could be worth going to 4ft if its not too much extra effort (back hoe vs manual spade). The added depth gives you more mass and buffers against direct heat gains from the surface which can reduce the cooling capacity later in the season.


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RE: Subterranean Heating/Cooling System

It seems to me that the payback calculations focus on winter heating. My primary concern is summer cooling. I'm going to dig with a shovel but I hope to get to 4 feet before I need to stop.

I am now thinking that maybe it will be better to have two systems for each 6x8 GH, one for tubes under the greenhouse and one for tubes under the central shed. The plenums would be in the same place as in the image in an earlier post but side by side. I could then use the systems together or separately. Does that make sense or is it overkill. The total tube length will be about the same but I could have two different lengths for individual tubes.


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I`d be concerned about the coupling between systems,particularly when the shed doors are open to the greenhouses. The intakes will favor taking air from the shed as its the path of least resistance, much closer than the far end of the greenhouse.
Its worth investing in a handheld windspeed meter/anometer for balancing the tubing, calculating the actual cfm in the system and checking for blocked tubes..The skywatch xplorer 1 is cheap but effective. Small smoke bombs normally used to check chimney flues are ideal for highlighting the airflow path, short circuits and dead spots,


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RE: Subterranean Heating/Cooling System

@hex2006, good point about the system coupling. My intention is to have both greenhouse doors closed most of the time but it would be good if the system worked nearly as well with the doors open. I could move the intakes to the far ends of the greenhouses for the lines that go under the greenhouses and just leave the intakes for the shared shed space in the ends near the shed. I could also add airblock curtains (overlapping strips of vinyl) to the inside of the greenhouse door openings to limit airflow when the doors are open. I will keep thinking for a while and then post some other ideas.

I will definitely invest in some testing equipment. Thanks for the suggestion.

It will be a while before we are close to the installation phase as we will be excavating the entire space in order to install the gopher exclusion system (hardware cloth/metal mesh with 1/2 inch openings under the space and a block foundation wall around the space). We will add moisture barrier and insulation outside that. If we are speedy, it will might be this fall but more likely next spring. ;-)


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RE: Subterranean Heating/Cooling System

The bonus of having a system in each greenhouse is you can make direct performance comparisons between the two by using different settings.
The shape of the plot makes for an interesting tube layout, if summer cooling is the primary goal i`d be tempted to incorporate the subsoil under the raised beds (increased mass) to make 2 square (ish) areas for the tubing layout rather than the 3 rectangles. Foundation block walls being in the way of the tubing is the tricky part ;)


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@hex2006, tubes through the walls could be done by inserting 8x8x8 blocks turned on their sides. It is digging the 12'x24'x3' hole and buying nearly twice as many blocks that makes me cringe. :O ;-) :-)


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It probably wouldnt be worth the extra expense and digging :) We dont have destructive critters llike gophers to consider which makes the job much easier. With limited space for bends you may find 3" tubing easier to install than 4". The 80mm can handle a 12" minimum radius bend if that helps any.


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@hex2006, I like the idea of running some of the tubing in the outside raised beds. Each greenhouse could have two systems, one to store heat under the greenhouse and shared shed and one using the outside beds for cooling. I might not dig as deep for the outside raised beds (maybe just a foot or so. That would save on blocks and digging. The inside heat sink would still be insulated but the outside wouldn't.


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Questions on Questions and Calculations:

You can use different tube lengths with different quantities of tube sections and have the same overall tube length. How do you decide how long to make the tubes and how many tubes? Sunny John says anything between 30 and 70 ft individual lengths for the tubing. Why within those constraints? Would it not depend on the size of greenhouse you have? I am planning 16 ft lengths. If I follow the underground design of Roper's matrix then 16 ft. lengths should be great for a 16.5 ft long greenhouse.

I have seen different estimates for Tubing Air Speed FT/SEC and Time in each Tube. Sunny John says that the tubing air speed should be between 8 and 16 ft/sec. Has anyone found results that would favor this estimate or would you suggest other values?

My greenhouse will have a base of 192.5 sq/ft. According to Sunny John's calculator I should have 1/3 more length of tubes as compared with the square footage of the greenhouse (257 ft).

Would this be an appropriate combination of individual tubing quantity and length?

  • Average Length of tubing = 16 ft.
  • # of tubes in each plenum = 15
  • Total Feet of Tubing = 240

Referring to "style 1" below, I plan to use (2) 12" ADS for the plenums. I will have 3 vertical layers (1' on center) of 4" tubes with 5-6 tubes horizontally (2' on center).

Finally, I have seen many different ways of doing the underground part of the SCHS. Which methods have you used and why? What are the pros/cons?

Style 1

Style 2

Style 3


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The air volume of the greenhouse is more important than the floor area. The shcs has to move the air volume to keep pace with the constant solar gain that would otherwise cause the greenhouse to overheat, For effective cooling, you should aim for a relatively small temperature differential between the inlet and outlet of the tubing and maximise the flowrate.
Taking the air down to the soil temp may seem like the best idea but accepting less of a drop and moving more air is a better approach.

If the air drops to the soil temp halfway along the tube, the other half isnt doing anything for cooling, or to put it another way, you`re only cooling half the amount of air you could be. If you accept 50% or 25% of the temperature difference between the soil and air as your shcs outlet temperature you can move 4x-8x the volume of air through the same tube.
Be aware that doubling the cfm in the tube increases the velocity which can result in a 3 fold increase in losses. To minimise losses its better to use two tubes half the length (they have the same surface area as a tube twice the length) to move the same amount of air without any of added loss. If the shorter tube length can maintain the desired in/out temperature differential for cooling purposes, it doesnt need to be any longer.
Getting even coverage of the mass, balancing the flow and positioning the shcs inlet and outlets can be more of a challenge with multiple short tubes.


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RE: Subterranean Heating/Cooling System

Hi All,

Hex2006, I simply do not understand the cfm as well as you. I was thinking of getting something like a 677cfm inline fan (based on the person I quoted in my post of Thu, Mar 6, 14 at 15:31). Your point of cooling only half of the soil is very helpful. Now, I am confused again by what size fan to get. (As a reminder I have a 10x12 HFGH with 120 sq. ft. of floor space and 1,044 cu ft. I am putting in the standard 4" tubes with the usual spacing...three layers. This will accomodate 21 tubes about 9.25 feet long (layed in a serpentine fashion) for a total of 194 feet that feed into two 12" ADS pipes as the plenum. Do you think my fan of 677cfm is good?

Also, good news on the pipe we found on the dig. It turned out to be a connecting pipe, not a drainage pipe...so no drain field under the GH. WHEW! It rained several days, and I also ran the washer lots and no problems except considerable standing rain water (pic 1). After I put a fill of about 2 inches over the pipe it rained a lot more. Very little water standing (pic 2..on next post because I can't figure out how to put 2 pics in one post). We will still put a pipe in that can hold a sump pump in case we find we need it later...but don't think we will have to do so. What a RELIEF!!!


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RE: Subterranean Heating/Cooling System

Here is the pic of rainwater after only little fill.


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RE: Subterranean Heating/Cooling System

The 677cfm info came from testing different airflows with my shcs :) My gh specs are 154sqft floor, 900cubic feet volume which translates into 75cfm for 5 airchanges per hour , I have 200ft of 80mm perf pipe arranged as a fifteen armed octopus in a radial pattern (like a flower). Each arm consists of a13ft tube which loops out and back from/to a central plenum. My floor is circular so it seemed like the most logical layout.
When i tested the heat transfer with different fan cfm it became very clear that at 5 airchanges per hour only a small part of the 13ft tubes were in use, even though i saw a 27degF drop between inlet and outlet.
At 200cfm (13.34 airchanges/hr) the difference was still 27F, 400cfm (27ac/hr) it was... 27F.
When i ramped the fan upto 677cfm (45ac/hr) the in/out temperature difference dropped to 23.4F which indicated the full 13ft was being used. At that point i ran out of fan power so i couldnt tell how much cfm it would take to get the inlet/outlet temps to match (ie; airflow needed to outrun the shcs) but it would probably have been 1000`s of cfm ;)
You`ll get more efficient cooling by moving a lot of air with a 10F drop in temperature than moving a small amount of air with a 30F drop.
Your greenhouse isnt a million miles away in terms of floor area and volume but rectangles dont lend themselves to radial tube layouts and not many would want the plenum in the middle of the floor ;)
Looking at the numbers i`d say you could use a fan upto 1000cfm, a speed controller is a good idea as it allows you to alter the cfm through the season. A big fan running on a low speed is far quieter than a smaller fan running flat out, both will move the same amount of air.

Note: anyone with a running shcs system can test this theory by comparing in/out air temperatures at different air flowrates. A system with a fixed cfm fan can be tested by blocking half the tubes in the intake plenum to increase the cfm and velocity in the other half. Be aware that the top tubes may be in warmer soil than the bottom tubes in a standard barrel plenum, which can affect the results.

This post was edited by hex2006 on Tue, Apr 1, 14 at 4:25


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RE: Subterranean Heating/Cooling System

Thanks! I'll get the larger fan!!!

I was thinking of this type of layout, except I will put mine in a serpentine pattern to increase the air turbulence. I am confused as to how I would put this in the middle and still keep the tubes the same length. Duh.


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RE: Subterranean Heating/Cooling System

The corrugations in the drainage pipe will create plenty of turbulance, The bends in a serpentine layout tend to increase pressure losses and make balancing the tubes more interesting, Wavy trenches take a bit more digging than straight ones :)
I would use a layout that fits in with how you plan to use the greenhouse, no sense putting a plenum right in the middle if its going to be in the way :)
In my case, the central plenum was the best choice. The highest point of the greenhouse is right in the middle of the roof. The central location takes advantage of the curved walls which act like a chimney so the warm air travels up to the top where its drawn into the inlet duct.


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RE: Subterranean Heating/Cooling System

NOTE: We hit the limit for number of posts in a single thread. Continued in Subterranean Heating/Cooling System - Continued.

Waterstar, good news about the water pipe.

I have been trying different layouts on paper. Below is my latest draft showing a single level of pipes. There are two systems for each greenhouse, one for the internal heat sink and one for the outside. The outside system is intended for greenhouse cooling when the inside heat sink has reached capacity. Both return the air to the original greenhouse. The intake plenums are now in the north corners farthest from the doors.

The outside systems each have a single exit from the greenhouse through the lowest level of the greenhouse foundation wall and two return entries. There will be underground plenums on each side of the holes in the foundation wall to facilitate tubing attachments at the different levels. We are planning on using plastic totes for the underground plenums. Estimated tube lengths is 16 feet. 6x16=96 feet.

The inside systems will have three tubes on each level with a tube under each growing bed and one under the walkway. These will continue into the central shed area and loop back to exit on the north side of the greenhouse near the door. Since the foundation wall under the greenhouse doors does not need to support much, multiple levels can have sideways blocks. Estimated tube lengths is 22 feet. 9x22=198 feet.

96 + 198 = 294 feet of tubing per greenhouse. The estimate from the SHCS calculator was 120 feet of 4" tubing for each greenhouse. I will use 4" for the outside systems and maybe 3" for the inside since the space is limited and the length is exceeded.

The pipe levels for the east and west greenhouses will probably be offset by 6 inches in the central shed area. However, there are three places where the pipes for a single greenhouse cross. Should I put an air block between the pipes where the pipes are too close? How close is too close?

Thanks in advance for your feedback.
Anna
NOTE: We hit the limit for number of posts in a single thread. Continued in Subterranean Heating/Cooling System - Continued.

This post was edited by Annalog on Thu, Apr 3, 14 at 7:27


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