We're still in the design phase, and plan to have a pro design a radiant system for our home.  It will be a 36'x75' home, situated with a long side facing directly south.  Lots of glazing will provide heat to the south half of an insulated slab on grade.  I'm curious about the interaction of the hot water and the half of the slab with solar input.  The floorplan has large, open areas that span the full width of the house (north to south).  I think we need three zones: master suite/sitting area (runs N to S full width), living/kitchen (runs N to S full width), and everything else (2nd and 3rd BR, utility, sewing, laundry, chopped up into small spaces).  I know that the circuit lengths will need to be balanced, and there will be other considerations, but I'd like to hear your thoughts.

It seems to me there are three ways to approach this:

1.  A north-side zone and and south-side zone, with separate in-slab temperature sensors.  I'd expect that the north side would demand more hot water than the south side on sunny days.  Might end up doubling the number of zones.

2. Allow the 3 zones to follow the floorplan, and run the width of the house.  Hot water would enter the zone at the north side, hopefully losing more energy into the cooler half of the slab.

3. Allow the 3 zones to follow the floorplan, but supply the heated water to the south side of the zone.  Excess energy from the south side would be moved to the cooler north side.

I can see pros and cons for each.  Any thoughts or experience out there?  Which option would you use?

Rick

circuits lengths do NOT have to be balanced if your manifolds have flow meters, and I think it's much more important to have room loop isolation than "balanced circuit lengths".

you zone rooms, not sides of houses, though you might zone two rooms on different sides of the house separately for solar gain issues. if a room is open north and south, the south will most likely heat the whole room, it'll just be warmER in the direct sunlight.

I have a home set up as you have described in option 1 and it works very well. On sunny winter days the south zone is almost always off. The north zone cycles to maintain temp there. After sun down, the windows that allowed the solar gain during the day allow for more heat loss and the south zone is on frequently but that doesn't overheat the north area.
Jerry