Sorry for not being clear, no you would mix the sand with the portland cement and H20, you in essence are making a non structural concrete, it would be cost effective next to gyp crete as the thickness you are looking for is only 3/4, the 1x4 sleepers are your skrete guides, fill not quite to the top. With all the voids filled in the sand by the cement binder you have a medium that lets the heat store and transfer more efficiently. 1,600 sq ft is a large area,if my math is close about 100 cubic ft of material so think 4 yards of sand and #40 50 pound bags of portland cement, (5 sack mix ), water and a wheel barrel.......
RHT floor panel is a ply wood panel system similar to quick track or Stadler panel at about 50% less cost. we offer it on our site http://www.blueridgecompany.com/radiant/hydronic/527/rht-floor-panel-system . There is photos there. It runs about $2.50 sq foot for all the material including pipe and manifold system.
Dan |