Location - Maryville, TN; House - Constructed 1954; ~1200 SF; Crawl space; wood floors with asphalt paper underlayment over 6" slotted boards.

I am going to try to simplify my situation.  For various reasons I am planning to pour a concrete slab in my crawl space and create a closed, conditioned crawl space.  As part of this I am planning to add radiant tubing in the slab attached to a solar water heater.  This would be "free" heat that would be stored in the slab during the day and distributed all night.  Additional heat would be air source heat pump.

Also, I have read that the asphalt paper will emit a smell at temps above 85 deg.  Anyone expericened that?

Given that I will insulate the space and the slab along with a radiant barrier under the slab and a crawl space height of three feet six inches to the subfloor does this sound like a useful thing to do?

Also, how do I decide what size solar system I need?  I think I would need to determine the heat storage ability of the slab size I will have, but I am not sure how to do that.

Any comments and all advice will be appreciated.

asphalt paper can make smell, yes.

Radiant barrier under the slab is a waste of time and money. use real insulation, rigid foam only.

You are likely to be able to utilize heat stored in water far more easily and effectively in this case, and I find it unlikely that you've got a solar array that is so massive you need this much concrete to store its heat. I would skip this entire idea, insulate your first floor, and use a solar tank for DHW preheat and maybe to dump heat inside the house itself, not in a slab.

If you're going to condition the crawlspace, ok, but I wouldn't really think an "active" storage system in the concrete would be very effective for much.