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Annualized geo solar (AGS) for passive heating in cloudy, cold regions

Levi Meeuwenberg

Joined: Dec 08, 2011
Posts: 7
Hello! I've caught the live-off-the-land bug like you all and I just love learning how easy all the solutions are, and yet they're not mainstream at all.
Anyways, I did a search on here and didn't find anything about annualized geo solar. Does anyone have any experience with, or opinion of this design method.
You can read about it here:
It sounds very similar to "Passive Annual Heat Storage" (PAHS) but a simpler and cheaper way of implementing it.
I'll be "getting to work" in northern Michigan where there isn't much sun during the winter months so a standard passive solar design wont cut it. My plan is to
build a fully passive, sustainable, greenhouse with a 1000gal aquaponics system inside. Since I'll be raising tilapia fish, they don't like it when it gets too chilly
as it does most of the year in Mi. Ill also have a rocket mass heater as backup.
So this AGS system sounds like a dream come true but it's hard to find much info on it besides that one site. Or if there's any other building methods you're
aware of for my particular climate I'd love to hear about them.
Thanks! Keep up the great work.
Brian Knight

Joined: Nov 02, 2011
Posts: 554
Location: Asheville NC
Thanks for the interesting link Levi. Check out the insulating Thermal Mass post as it covers some of this stuff. I agree that the methods in the links seem too good to be true because I feel they are. There is no science or research to back anything up just some interesting theories. Think about it this way; if one could store water that was brought to the boiling point(water has more more storage capacity than dirt) below a home or greenhouse to the depth of 20', how long would you expect it to heat the home or greenhouse without any additional heating in a cold MI winter. The answer would depend on the Airtightness and Insulation levels of the structure above it (and the insulation surrounding heated water). Even built to Passiv haus standards, roughly R50 walls R70 roof for your area, I would expect the heat to be gone in about one to four weeks depending on the Delta T. There's a much more clever way of using the ground for heating and cooling; ground source heat pumps.

"If you want to save the environment, build a city worth living in." - Wendell Berry
C.J. Murray

Joined: Dec 02, 2011
Posts: 92
Location: 5,500 ft. desert. 13" annual precip.
It is hard to convey all which one thinks he knows in a few short sentences but I’ll do my best to state what I believe is correct. I’ll start by saying that in an endeavor such as is being considered the devil is in the details. And there are a lot of details which will affect the implementation and success of any solar harvesting project. Fossil fuels are like beating someone up to take what you want whereas solar harvesting is like talking a farmer into selling a piece of his land.

I think the concepts behind PAHS and AGS have merit but they are not fully fleshed out with details. It’s still a work in progress. Heck, we can hardly get conventional housing made which performs as it is supposed to let alone implement all the concepts of PAHS or AGS in a workable manner when needs can vary so widely. Having said that, we all need to be working toward proving or disproving the concepts.

The AGS design calls for a metal roof as a solar collector. Over the years I have built about 8,000 ft2 of greenhouse but I’ve never had a metal roof on any of them. lol. What will be used as a collector, the roof of an adjacent building? The Mica Peak AGS does not have a solar collector for its roof so I’m assuming the solar collector is the low building in front of the home. Also, is the greenhouse glazing going to have an insulation system of some type? Besides fish, what will be growing in the greenhouse in the winter, in other words, will all of the glazing need to be open to the sunshine during the winter days? Will the greenhouse be sunken into the earth like a Walipini greenhouse?
Mike Schroer

Joined: Jun 12, 2013
Posts: 18
I am also having trouble finding information on this concept. I would like to build a house with the AGS design to supplement the heating needs. I can find plenty of complicated math on thermal conductivity of different types of soil and the effects of moisture but I am having trouble figuring out how to size the thermal mass and at what depth the thermal mass should be to heated by the heat tubes. Designing for the time it takes for the heat to move through the system for an accurate six month delay is puzzeling me. I feel like the solar collector can be adjusted in size after building the house but the thermal storage under the house will be very difficult to change. Any ideas.
paul wheaton

Joined: Apr 01, 2005
Posts: 17395
Location: missoula, montana (zone 4)
It seems the don stephens web site is no more. But I did find this document of his.

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allen lumley

Joined: Mar 16, 2012
Posts: 3858
Location: Northern New York Zone4-5 the OUTER 'RONDACs percip 36''
Just recently I was scolded for speaking for other people than just myself so - this is my interpretation of what Rob Roy says on the subject, and I will leave the

''proven science'' found in his books for others to find and interpret .

That part of the below ground structure of a Wafati within its Umbrella- is exposed to a weather temperature of a climate much further south ! Because the ground
temperature less than 6' down is 55º year round That part of my house is wintering over in Lower Virginia or North Carolina where the Averaged Winter Air Temps
are 55º !

Now, part of the structure Is Not wintering over down South! We must super insulate that section and religiously watch construction and use techniques to guard
against bridging, poor installation jobs, and carelessness in use allowing cold air entry !

Air exchanges are important to protect the insulation from performance loss due to water vapor entrapment ! Bridging again.

But, and it is a Big But, with careful structure design we can gain and store both Solar Heat Gain (trombe walls) and add much of the heat energy produced by our
personal energy uses to the structure -not forgetting to add the 100 watts of energy we add just simply by being alive !

Again these are my interpretations of other peoples words, and I am not speaking for them, merely mentioning the source, and my interpretations !

For the Good of The Craft ! big AL

Success has a Thousand Fathers , Failure is an Orphan

Danette Cross

Joined: Feb 11, 2013
Posts: 31
Location: St. Ignatius, Montana, zone 5b
Permie guru geoff lawton has a new video out on this very topic. Geoff Lawton - Heating Your Glasshouse This is not a complex system, but just the basic 2nd law of thermodynamics and can be done on what ever scale your situation calls for. If you are going to dig a 3 foot footing for an attached lean-to type of greenhouse (which is what I am planning) then this could be a perfect system for here in Northwestern Montana. The concept is simple. And I don't think we get very far when we over think to the point of becoming paralized. If you have doubt, create a "heat cofin" or similar small structure. It simply becomes an economy of scale as in any good design. For example, Swales work. They work if they are small, or huge. They work. The system is simple, elegant and effective. So is AGS. Don't get wigged out on the physics (as I kept telling myself all through my undergrad!) and give it a shot. I found that working on the calculus and mechanics is sometimes best when I have a shovel in my hands, and not a calculator and pencil.
seth wheeler

Joined: Sep 23, 2015
Posts: 3
Great info. everyone. Danette, any progress on your project? I'm designing an attached AGS type greenhouse for a potential client right now and may be getting too caught up on the physics myself! but any further info. would be appreciated.
Danette Cross

Joined: Feb 11, 2013
Posts: 31
Location: St. Ignatius, Montana, zone 5b
We have a financial challenge and have been pretty much stopped cold on a lot of the work here. Now that winter is about to set in, I am just wanting to get my sheep and livestock guardian dogs through in good shape and go at it all again in the spring. sigh* Money always seems to be a challenge.
I agree. Here's the link:
subject: Annualized geo solar (AGS) for passive heating in cloudy, cold regions