I'm designing an active/passive solar home in NW Indiana, and I would like some advice on whether my idea is feasible and worth further investigation, before I start with actual designs and heat loss calcs.  Thanks in advance for any help you guys might be able to provide.  Also, I can provide any additional details you may need.

Here are some of the design parameters of the home:
-All supplemental heating must either be LP or electric
-Will be built on a frost protected shallow foundation
-4" concrete slab on lower level
-OSB sheathed floor on second level, with 1/3 terra cotta tile and 2/3 laminate flooring
-Back of home will face south
-~3400 sqft lower level
     -there will be no living quarters on first floor
     -840 sqft north end will be a shop
     -1800 sqft middle section will be solar collector (air + thermal mass)
     -760 sqft south end will be greenhouse
          -this will house an aquaponics system, so several fish water tanks will help add
          thermal mass
-~1650 sqft living quarters on second level
     -living room, kitchen, and all beds except one will have south facing glazing
     -will be partially heated from passive thermosyphon from lower level greenhouse, and
     from south facing glazing


Concerns:
-I would like to use pex tubing to help distribute heat from the concrete pad in the greenhouse to the rest of the lower level slab for thermal storage and to heat the shop (I have included a rough sketch of the design to help illustrate the idea)
     -Will this be effective or not?
-Would it be worth the effort to build solar collectors on the trombe wall, and install radiant floor in the upper level with a sandwich/plate installation, to help heat in addition to the passive thermosyphon?
-Should I insulate the lower level slab, or use the earth as more storage since I am using solar?

I see my image is not showing. Any tricks for embedding images? If not, I will shrink the file size and attach it.  (EDIT: I got it.)

Naudi2u,

I will post the plans tomorrow to give you a better idea (the plans are still in the rough stage, however, and are not yet optimized for building materials, efficiency, etc.). The main reasons for the living area upstairs are as follows:
-the structure is being built as a large barn with an English gambrel roof
-the shop will be used to house an electrical business, so I would like to keep the living quarters away from the work area
-about 1/3 of the 1800 sqft will actually be garage area
-I need the space on the lower level for the aquaponics system and for general storage
-by having the living quarters on the second level, and by utilizing a gambrel roof, I have a simple way to superinsulate the walls

Also, the reason I am thinking about utilizing a trombe wall in the lower level is because it is a load bearing wall, so I figured "might as well pour it, and kill to birds with one stone". After thinking about it more today, though, I don't think it will work as planned, because it will be set too far back in the greenhouse area and will not get enough direct sun. I need to find my protractor and make sure. The upstairs will just utilize direct gain and the storage heat from the lower level.

Will you be able to get large enough overhangs for summer shading and still staying within the style of the gambrel roof?

I will wait for your plans before I make any concrete statements on it.

Here are the plans.  The greenhouse will be treated as a completely sealed off area from the rest of the structure, except for vents that can open and close.  I can also adjust the overhang on the shed roof that covers the back bedroom, to provide summer shading.

That helps some. Can you size them bigger I can't read the plan at all Never mind now they the right size

Looks good the plans help alot,

The pex layout in garage should be on the return of the loop to keep it from be cooled before reaching shop/basement.

My only other concern is the bedrooms. The main living ares have more glazing then the Master and North bedrooms. The south bedroom will receive the most passive per SQ ft , main living area next, master bed, and lastly the north bed room. Many passive designs try to equalize the glazing per sq ft to give equal temps.

With all that green house. I think you should not have a problem heating during the daytime, just minimize the heat loss at night.

Thanks for the tip on the garage pex, I completely overlooked that.

The bedrooms have been my main concern, also.  I'm not opposed to any active solar applications, I would just like to keep the overall system fairly simple.  One of my thoughts was using the pex on the second floor to help zone control the problem areas.  And my other thought was to use inline duct fans to pull air from the greenhouse to the cooler rooms, and have these controlled by thermostats, then, let the cooler air passively return through vents into the lower level.

I plan on building a system that will lower 2" XPS to cover the greenhouse windows during the night, to help insulate.

Do you mind explaining your thought process for the use of insulation under the lower level slab?  I know I don't want to waste energy heating the earth, but I know a little more thermal mass could help my situation.  Maybe, I should just lay the 2" XPS, then a 10-12" layer of crushed rock, and lay the slab on that.  If I went with this application, can I assume I would intertwine the pex throughout the layer of crushed rock?

I think that it is easy to add more mass after the fact, it is hard to add insulation under the slab after. I think that the slab/heatsink should be seperated from the ~55(here in wisconsin) earth temp.

The slab ABSOLUTELY needs to be insulated! (As does every other surface of that house!) That low-temp solar HW is too precious to spend/waste it on heating the earth beneath the house! Make it at least R12 (2.5" XPS) R20 would be better, but gets expensive, eh? (If you're going to be using a lot of XPS and can wait for the right deal, using recycled stuff is less than half the up-front cost. InsulationDepot.com will ship if it's a big enough lot, which it might be, since you're looking at several thousand board-feet. There may be others, or recyclers nearerer to you.)

As for running it on a thermosiphon- it can work but the relatively high-head of even a hundred feet of 1" PEX will likely kill it's efficiency & effectiveness in thermosiphon mode. Designing in DC pumps running directly off a PV panel will almost always be worth it.

Dana1,

I think I will insulate under the slab. The question I now have is whether I should insulate, backfill with 10-12" of crushed rock, then pour the slab, or just insulate and pour. I already contacted isulationdepot the other day (I'm just trying to figure out a way to use a 53' truckload of the stuff, lol). For those that insulate with 2" XPS on the outside of OSB sheathing on exterior walls, what do you do when it comes time to attach siding? Use 3-1/2" siding nails? Any thoughts are welcome.

Sorry, I wasn't very clear on the thermosyphon. I plan on using a passive thermosyphon for air exchange, and not water.

I've not seen siding attached directly over 2" XPS sheathing.  It might be done, but I suspect it wouldn't pass wind-loading standards with long nails.  What I have seen is 1/2" or 3/8" OSB over the XPS held in place with long screws (there's probably a minimum number of fasteners or fastener spacing & fastener type specified in some code somewhere), to which the drain plane & siding get attached.  This is fairly common in roofing structures as well.  Assembling it so that the OSB  & XPS seams are at least 6" apart makes and only overlap at 90 degree angles makes it a nearly perfect air-barrier as well.

As for the backfilling, crushed backfill over the insulation has little value (and crushed, as opposed to screenings would impart more damage to the XPS, no?) .  I'd think for radon & or drainage issues, select backfill should go UNDER the vapor-barrier & insulation layers.  XPS is a class-II vapor retarder, but where soil gases are an issue it's worth putting polyethylene sheeting (class-I vapor retarder) over the insulation as well. It's cheaper/easier to lay down some sheet than it is to seal all the seams.)  Installing passive radon abatement systems under slabs is becoming code for new construction in many parts of the US.  I'm not sure how much of an issue radon is in your area (it varies considerably with local geology), but it's cheap insurance even if not required by local code.  Where it IS code the minimum backfill depth & type, and location of vapor retarder in the stackup are specified.

If your thought was to use stone as thermal storage for the air thermosiphon, IIRC from back in the early '80s the in thermosiphoning systems the stone size & cross-sectional area of the flow path specified is usually pretty large 2-4" screenings, (never crushed stone.) Sub-1" screenings were used only in systems with powered air handlers (400-800 watts suckers!).  You get better heat-transfer out of the greater surface area of the smaller stone, but the air drag goes up considerably.