New build ideas - sunken greenhouse for underfloor heating... thoughts?

Hi y'all,

Anyone tried this take on AGS before? Digging out a metre deep to sink a greenhouse - using the spoil as a thermal battery, blowing hot air from the greenhouse into it via heat tubes?

The house would be a straw bale job to insulate the battery, the corridor to the north of the house should act as a cold sink and would be good for food storage etc...

Not sure whether or not to insulate on top of the mound in the house to limit the heat it will give off, could be too much!

Would love to hear any thoughts.













Sean

I like it.

Would you use a powered fan to blow the greenhouse air through or would you use a trombe wall style passive system?

Another thing I was wondering about and didn't see in the drawings was if you have plans for forming the large "umbrella" that is a big part of the AGS system or some other means of separating the soil used as the "thermal battery" from the rest of the earth.

Sean Kettle : You need to consider more than the foot print of the dwellings - as drawn you Potentially have a Greenhouse setting in a Cold sink!

A pond no deeper than a foot placed in front of the greenhouse would help here increase both solar energy and act as a temperature buffer ! greatly !

For the Good of the Cause ! Big AL

Thanks for your replies Michael and Big Al!

I like it.

Would you use a powered fan to blow the greenhouse air through or would you use a trombe wall style passive system?

Another thing I was wondering about and didn't see in the drawings was if you have plans for forming the large "umbrella" that is a big part of the AGS system or some other means of separating the soil used as the "thermal battery" from the rest of the earth.

I was thinking of using a powered fan but I like the idea of doing it passively with a trombe wall. I will look into it.

I think I would have to put down a layer of insulation and some epdm before piling on the battery. The soil heated in PAHS houses doesn't tend to be insulated underneath, but as this will be above ground I think it would be necessary.

Sean Kettle : You need to consider more than the foot print of the dwellings - as drawn you Potentially have a Greenhouse setting in a Cold sink!

A pond no deeper than a foot placed in front of the greenhouse would help here increase both solar energy and act as a temperature buffer ! greatly !

For the Good of the Cause ! Big AL

I had thought about a shallow pond running the length of the greenhouse - as part of an aquaponic system, you bring up a good point and another reason for one. I could also install a grey-water reed bed system along the front. Exciting stuff!

I've been playing about with this idea a bit more, here's where I'm at:

To insulate the soil that's being used as the thermal mass from the ground and to prevent any moisture sapping the heat away I would first put down a layer of glasscrete/limecrete (see here)



I would then pile on and compact the spoil, and top off with an earthern or limecrete floor.



This would all be done within a lime mortared stem wall that would be built initially.



Timber frame and greenhouse...



Green roof and then straw bales...



I've sunk the corridor down a meter so I can split it into two floors - the lower would be an ideal root cellar.









Regarding drainage and stopping water getting into this basement - I've been thinking of digging out a Mike Oehler style uphill patio. Or I could use his PSP technique to keep the ground water out? I'm wary that whatever liner used will fail over time...

Would love to hear any thoughts at all on all this!

Any pointers regarding how to deal with the water table and hydrostatic pressure where I've dug out for the basement and greenhouse would be greatly appreciated... are big french drains the key here?

I'm not sure what the water table is like on the site, but as it is in a spring catchment area I imagine it rises pretty high. Will dig a test pit when I can.

I'm working out whether a greenhouse under the barn is do-able in this area.
The land has many fresh water springs and is also very well drained, I'm thinking of manure storage under the critters in the greenhouse will heat the water and the air nicely if I can achieve proper ventilation and humidity control.
Of course eventually that organic compost will be used in the greenhouse if all goes well.

Barn is yet to be built, my dream is to make it all efficient to work in and pleasing to be in--including a breezeway from garage to barn in case one wishes to avid the weather somedays all together.
We get deep dark and cold winters here for a minimum of six months, so it's very important the space be comfortable to work in.
Heck I even add another floor for living space above the animals, I had a lovely apartment over a working barn once, and would totally do it again.

Thoughts or ideas or very welcome, this is not part of my natural skill set!

susan vita wrote:I'm working out whether a greenhouse under the barn is do-able in this area.
The land has many fresh water springs and is also very well drained, I'm thinking of manure storage under the critters in the greenhouse will heat the water and the air nicely if I can achieve proper ventilation and humidity control.
Of course eventually that organic compost will be used in the greenhouse if all goes well.

Barn is yet to be built, my dream is to make it all efficient to work in and pleasing to be in--including a breezeway from garage to barn in case one wishes to avid the weather somedays all together.
We get deep dark and cold winters here for a minimum of six months, so it's very important the space be comfortable to work in.
Heck I even add another floor for living space above the animals, I had a lovely apartment over a working barn once, and would totally do it again.

Thoughts or ideas or very welcome, this is not part of my natural skill set!

Hi Susan,

Is your idea to shovel the manure from the barn down into a greenhouse that's lower than it? Using the heat given off from decomposition to keep the edge off things?

Maybe you could combine this approach with some pig-aerators?

Yup, that kind of gravity fed system using pigs and hens where appropriate.
I need to read up on round barns--the one at Shelburne Museum in Vermont is a great example.
My goal is to incorporate a greenhouse on the lowest level, earth bermed on three sides, glass on the south. That manure produces such heat, I know I can figure out a way to capture it .

Maybe even add fish someday...!

Sean,

I think this is a very cool variation on the traditional concept.

I can see a few problems with your sketch though. First, the tube is way too long as you have in your sketch (assuming you have a normally sized house). It will severely diminish air flow given that length. Besides, it's not generally needed -- you can get complete heat transfer (between the air and soil) with a shorter length. Usually earth to air heat exchangers use multiple sections of pipes with multiple fans to get more airflow.

Article you may find helpful: http://www.ceresgs.com/#!10-Dos-and-Donts-for-Designing-a-Ground-to-Air-Heat-Transfer-system/cf3k/55131f4c0cf2aa18115c5439

I don't know how to deal with the high water table, but that should be a major point of concern.

Lindsey
ceres greenhouses

susan vita wrote:Yup, that kind of gravity fed system using pigs and hens where appropriate.
I need to read up on round barns--the one at Shelburne Museum in Vermont is a great example.
My goal is to incorporate a greenhouse on the lowest level, earth bermed on three sides, glass on the south. That manure produces such heat, I know I can figure out a way to capture it .

Maybe even add fish someday...!

Sounds great Susan, I'm sure you'll make it work had a google for those round barns, they look amazing.

Lindsey Schiller wrote:Sean,

I think this is a very cool variation on the traditional concept.

I can see a few problems with your sketch though. First, the tube is way too long as you have in your sketch (assuming you have a normally sized house). It will severely diminish air flow given that length. Besides, it's not generally needed -- you can get complete heat transfer (between the air and soil) with a shorter length. Usually earth to air heat exchangers use multiple sections of pipes with multiple fans to get more airflow.

Article you may find helpful: http://www.ceresgs.com/#!10-Dos-and-Donts-for-Designing-a-Ground-to-Air-Heat-Transfer-system/cf3k/55131f4c0cf2aa18115c5439

I don't know how to deal with the high water table, but that should be a major point of concern.

Lindsey
ceres greenhouses

Hi Lindsey, it's encouraging to hear that you like it.

Thanks for the pointers, I really appreciate it. I hadn't researched the layout of the earth tube or anything - I just stuck it in there to demonstrate the concept.

Your greenhouses and GAHT systems look fantastic - I see you use perforated drain tile with a sleeve as your heat tubes, that makes a lot of sense.

I'm going to stop thinking about the water table for now, I'll soon find out if it's a problem once I get a pit dug...

Going to throw out another variation - a passive version based on Michael's suggestion of using a trombe wall style system...

I've sunk the stem wall and thermal mass down another metre for this to work.



Envelope of foam glass, to insulate the mass from the stem wall...



Thermal mass...



Stem wall...



Greenhouse et al...



Not so sure about this - could convection do the job for me here without the need for fans? Heat enters at the top of the tubes, cools and exits out of the bottom..?

Sean,

Heat always rises so it will enter low, rise and be exhausted top. I would speculate extremely low air flow rates, if they are detectable at all. My speculation. Cold air will take the natural convection route - straight up, still within the greenhouse -- unless there is a huge temperature differential creating a chimney effect (draft) within the mass. I would presume not nearly enough. So I'd advise sticking to something closer to a conventional trombe wall if going the passive route. Doing that on multiple levels... I'll leave that to others comments.

Lindsey

Lindsey Schiller wrote:Sean,

Heat always rises so it will enter low, rise and be exhausted top. I would speculate extremely low air flow rates, if they are detectable at all. My speculation. Cold air will take the natural convection route - straight up, still within the greenhouse -- unless there is a huge temperature differential creating a chimney effect (draft) within the mass. I would presume not nearly enough. So I'd advise sticking to something closer to a conventional trombe wall if going the passive route. Doing that on multiple levels... I'll leave that to others comments.

Lindsey

Thanks for your speculation! I'm not convinced it would function properly either. Not sure how I could get a conventional trombe wall to work in this set-up - will focus on a GAHT system for now.

Another idea for passive heating - again, having a network of earth tubes in the thermal mass - hooked up to a chimney on the north side that would go up and out of the house.

Could this provide the draw needed? Any thoughts on whether the mass would absorb any noticeable heat or would it simply blow out of the chimney? I'll post another mock-up when I get time

Edit: something like this -

Once-through passive heating will not work for you - throwing away all the heat generated and replacing it with 100% outside air doesn't make sense. You need a recirculating flow if you are using air.

A thermal mass that is underfloor will absolutely need some circulating tubes (air or water or...) to get the heat into its back end. A passive system would require the mass to be more vertical, like a thick trombe wall. You could put gaps in it for direct south view from the living space.

Glenn Herbert wrote:Once-through passive heating will not work for you - throwing away all the heat generated and replacing it with 100% outside air doesn't make sense. You need a recirculating flow if you are using air.

A thermal mass that is underfloor will absolutely need some circulating tubes (air or water or...) to get the heat into its back end. A passive system would require the mass to be more vertical, like a thick trombe wall. You could put gaps in it for direct south view from the living space.

Recirculating flow is the key eh! That makes sense, thanks Glenn I will stick to the original idea.

Maybe you can plant a bunch of thirsty plants heavily around the area. Maybe a willow. I've heard the drink lots of water. Just an idea though. Or corugated pipes and a crock might do some work. Instead of plastic sheeting also a thicker shield would maybe be better.

Dan Mangan wrote:Maybe you can plant a bunch of thirsty plants heavily around the area. Maybe a willow. I've heard the drink lots of water. Just an idea though. Or corugated pipes and a crock might do some work. Instead of plastic sheeting also a thicker shield would maybe be better.

Thanks Dan, I'll be planting plenty of willow about the place What do you mean by a thicker shield?