This continous the discussion of "crawl space or not" but directs it to focus of the thermal mass underneath the house. The thermal mass underneath the house could be underneath a basement, underneath a stemwall, or underneath an elevated or non-elevated slab on grade.

As we all know, ICF is the greatest thing since sliced bread. But it only answers part of the question of how to build an energy efficient house. ICF walls by themselves only create a strong wall. In order to make the structure energy efficient, we must have a good base and a good lid (roof) on it.

How do you build a good base from which you can benefit year round? What if you could use the base as a transitional form of energy storage? Store the energy and retrieve when needed? Do you think this is possible? How would you go about forming an energy loop that would feed the base with energy and retrieve it at the same time?

I really think, and I have plans to do this, is to capture the energy(hot water) and store it in a 5k gallon insulated tank. This method has been done successfully, and I don't have to build using a non-standard technology. Of course, I'm talking about a Super Insulated structure.

are you talking about a 5 ton tank? how would you garner any additional energy other than the 50-55 degree Fahrenheit from mother earth?

Active Solar. Try a Google on Solar Harvest. A guy in Boulder, CO is doing a great job...

panelcrafters, I did check out the system. It has a 6000gallon tank. Impressive system, any idea of the cost? I e-mailed them and am waiting to hear back.

If you read some of the items on the site, I think that he gives out some info. But, I believe he pieced the system together with used components(collectors & tank) and custom built some others. He did start with a Super Insulated structure to lower the Heat Loss.

Aside from the idea of storing energy in water, which is good by the way, water has a bad habit to corrode things, unless you store it in a plastic tank, I like to explore the idea of staying natural and store the energy in mother earth for her to give back when I need it. There are certain calculations that are made in respect to depth and square footage that will determine how many feet of PEX tubing you would need to lay in order to heat the earth and retrieve the energy from the earth.

I was planning a slab with a frostwall.
What is more energy efficient slab, or crawl space?
I do not want a basement.

vic

vmg, there are different schools of thought on a crawl space. But when it comes to energy stored vs. energy wasted a crawl space will always loose out. So, in regards to energy efficiency, an energy efficient slab will always outdo a crawl space.

Thanks Manfred,

Is there soil type you would suggest that is better?

vic

THis system will work with any soil condition, but I would say the pex tubing is harder to place into clay. I prefer sand since energy will travel easier (quicker)through sand than it will through clay.

Does the kind of sand matter, and how much sand?

I'm in clay, lots of it.

Vic

Any sand is better than clay. Depth depends on the square footage of the slab, but needs to be 2-3 feet.

Manfred,

To address your original question/concept, the basic fundamentals of heat storage/transfer(thermodynamics) are the most important to learn about and keep in mind. I suggest research into passive solar heat storage, starting with the classic The Passive Solar Energy Book 1979 by Ed Mazria. It is old, but the physical laws of heat storage and transfer do not change, and this is a great book for your purposes.

That said, I will try to paraphrase(BRIEFLY!?!?) some things I have learned over the past 20 years of building/using passive solar mass storage in homes.

1. There is always a heat transfer occurring whenever there is a difference in temp. otherwise known as "delta T." between the heated material and some colder material.  If you put pex tubing into the ground under the slab and heat up the whole of the slab and ground under it, you will indeed create a very large mass that is warmer than normal(50 or 55 degF ground temp). This will take quite some time and create a large warm mass that will take a long time to cool down. BUT...this heat in the mass will ALWAYS be being transferred to the colder parts of the ground on the perimeter of your "heated" mass since there is a delta T. This heat loss will be very significant and will prevent the heated mass from achieving a high temp. that you want so you can "retrieve" heat at some later time.  It will also cost a lot of money if you are not using solar/wind/geo/etc. to generate the heat for the liquid in the pex tubing.  Your general idea is very good, it is merely lacking one major component: insulation.

2. A much more efficient way to store the heat in the slab is to place a layer of, for example, 2" Dow board insulation somewhere under the slab. By "somewhere under the slab" I mean that you could place some earth material that has a high heat storage capacity(you say you like the idea of sand, but you might research other materials in Mazria's book as well) on top of the insulation in a thickness of...2 to 12 inches or more, depending on a lot of factors that are too lengthy to discuss now.  What you will achieve is a significant mass of slab and earth that is now very well insulated from the "cold" ground below the Dow board and outside your ICF foundation walls. I would also recommend putting the pex in the slab since that is closest to where you need the heat. The delta T between the heated slab and the sand under it will insure that the sand will become heated as well.

3. IF you do as described in #2 above, you will have a very stable, warm mass that will provide very comfortable and CHEAP heated living space, BUT it will still not be a viable reservoir of excess heat that you described in your original post. To do that you would need the water tank that was also discussed, or some other storage medium that would most likely have a VERY long payback time and not be economical.  Money is best spent on insulation so that the heat that is generated is transferred as slowly as possible to the cold exterior surroundings. All discussions of efficient heating will start and end with the insulation!  I am soon to build my own ICF passive solar house and am contemplating using some extra Dow board insulation on the exterior of the ICF that will be below grade to better hold the heat inside, as well as under the slab.

Whew, what a babble...not very brief?!

Where are you located Manfred? Perhaps you should consider passive solar heating for the house as well as the radiant floor heat pex. I am very willing to discuss further any of these principles with you, but phone conversations are much more efficient. Call me if you wish: 307 290 0364. I live in NE Wyoming.

Hope this helps!

Dave

Dave, thank you for input. I am answering your suggestions, objections, difference of opinion in order of your punctuation:

1. I am aware of the delta T! If you would have followed the thread more closely you would have noticed the mentioning of a perimeter insulation slowing down the energy transfer from high load to low load. The liquid in the pex tubing is water, this is a cheap as you can get. This "heat circuit" is continously fed from the solar catch area on the roof, regardless of which climate zone you are living in.

2. Again if you follow the thread "crawl space or not" you will notice this "problem" having been solved already. The ground slab as well as the walls are being used as a thermal barrier between the "outside" and the "inside" thermal conditions. Therfore additional insulation between the ground slab and the earth is not required. The pex tubing, with its continous water temperature carrying equivalent in the slab, are the thermal barriers no further insulation is needed. Entropic degradation of energy between the slab and the ground underneath does not exist and is a phenomenon that is handled differently by this installation.

3. Water tank is a good start in thinking of capturing external energy but it has its definitive dissadvantage: Energy dissipation from a water storage tank is at a much greater rate than a sand storage tank. Your assumptions regarding a sand storage tank "not being a viable resservoir of excess heat" is incorrect. I refer to the discussions on "crawl space or not" having cited specific temperatures reached in different loops underneath the slab. The cost of this installation is negligable, or to be more blunt "cheap". I am not creating passive energy housing but "zero energy housing".

You have to keep an open mind about how simple it is to make an energy transfer into the perimeter walls a year round possibility. I do appreciate your constructive input.