Thank you again for your expertise, it is always appreciated.

So the flaws are:
  a) distance is too large between slab and floor surface above
  b) a lack of direct contact for the heat to conduct to the upper surface
  c) inability using a heat-pump to produce high temperature water
  d) issue of insulation, unknown thickness/placement for optimum efficiency

I can adjust the distance by design to make the slab closer to the floor surface.  If the floor has no openings is one situation where you rely on simple radiation from the slab.  (like tubes suspended below a floor at 40 to 60deg C.) But you think that a slab at 40-60deg C (entire surface area below a floor) vs tubes spaced 8" oc.  That the slab would radiate much more than the pipes simply because of surface area--if that is a factor.  So narrowing the distance would make the idea a workable option.

The lack of contact is a problem--normal floors here are a multiple variety of woods but this is the finish of choice.  So direct contact is difficult to achieve without a lot of special preparation work.  Wood is easier to walk on than concrete because it absorbs some of the impact shock while walking etc.  Tile, linoleum, stone...all make great choices for floor heating but that would be a very hard sell--at least here.

Heat pumps here can produce water at temperatures up to 194 deg F with an ambient temperature of 14 deg F.  (small publication "ECO-CUTE-CO2 Heat Pump Water Heater-in Japan" authored by Mr. Takehiro Maruyama of Lawrence Berkeley National Laboratory.  If you surf the internet under this title--you can read the little brochure.  I do not know if these units are available in the USA but they have been developed in a partnership between TEPCO (Tokyo Electric Power Company) and a variety of manufacturers.  I do not know all of them but I have seen Panasonic (National), and Daiken in operation and they are everything that they are promoted to be.  The problem is that they are very expensive--retailing for around $8000 per unit.  Wholesale is quite a bit less but still pricy.  If you want to test one, I could probably locate one and arrange for shipment to the USA... I guess that payment would be something that would have to be arranged.  Also, I do not know if there are any restrictions on exporting these units--I cannot see why.  They are available in 200V/100V 50 HZ and 60 HZ configurations.  Japan is split between these two different electrical supplies.  (So "c" is not a problem--except for cost), It would be a very green solution instead of using LPG or kerosene boilers.  These are much cheaper though.

Finally, the insulation has to be decided.  The entire design for the foundation would probably change to have an additional slab being poured after the initial foundation was completed.  Perimeter insulation installed, interior level raised, EPS base installed, tubing laid and finally a second slab poured.  Still easier than tubing installed in a sandwitch above the floor.  And an advantage of using the slab as "time battery".

Electrical rates (2008):  0700-1000  $.21/kwh
                                      1000-1700  $.26/kwh, (summer) $.31/kwh
                                      1700-2300  $.21/kwh
                                      2300-0700  $.07/kwh

This is a special rate for plans utilizing storage type of heat, ECO-Cute water heating, Area Storage Heaters (with special bricks inside) etc.  This is cheaper for persons who are away from the home during the daytime hour but questionable when someone works from home--- The non-controlled rate is probably $.23/kwh.

This is my reasoning for trying to use the slab heat as a "time battery" (your words), and hopefully use an ECO-Cute as the heat source, controlled time @$.07/kwh.  This depends on the Utility accepting my design as equivalent to the Area Storage Heaters (chikku-netsu) units.  This is still a big IF!

The other design using the electrical elements can be viewed at a sight: http://www.enertec.co.jp, all the information is in Japanese but maybe you could use somekind of translation tool to get an approximate translation into English.  I think that the information can be followed even without a translation.  I saw the brochure the first time yesterday.  Just interesting---a similar design as my initial premise but using electrical elements instead.  Please let me know what you think.  My friend has had it in operation for about 5 years now--he said that he would do it again if he built again.  There is a big plus to that design because of some kind of a rebate from the gov't or TEPCO?? I do not know from whom--but it amounts to around $98 per month indefinitely.  His initial installation would be paid back in 10 yrs with this alone.

Your final line is right on target.  The second part: finding a real engineer is like pulling teeth, I have met a lot and there are many around here--basically because of the automobile industry in this area.  However, most of the ones that I have met have their head in a bubble or cloud or... and they are great if you stay inside their bubble.  But few can grasp anything outside that sphere.  I would rather someone point me in the right direction ---where to find the formulas to crunch OR find someone with similar interests to massage the issue to find the best results.  I would believe and trust someone who has worked with these systems over a degree anytime.  I build homes for a living and can do every aspect of the project--from design through completion.  I do not build a lot of houses but the few I build are built well.  I never have to be ashamed to meet a previous customer or present them with a bill for my services.   I guess you can consider me a carpenter by trade but there are many things that interest me --it all has to do with finding a better way to live economically.  It keeps me thinking younger even though I am not.

You have given me a lot to think about--thank you for that.  Please continue to give good advice.