Radiant floor is a good approach because the air temp can be considerably lower if the floor is warm, and besides, air is very leaky, particularly in a building with large openings like a shop has so all those heating $ go out the door. Radiation on the other hand can pretty much be contained with good interior lining. Are you planning to put in generous amounts of under-slab and perimeter rigid insulation? I read an article in Fine Homebuilding about the value of going with higher R-values on the perimeter insulation especially as that's apparently the route a relatively large proportion of heat takes, and the fact that for square footage, the perimeter is much less than the under-slab.

I like the idea of used conveyor belting, thanks for recommending it team. The fact that it's thin but robust, can easily be moved to where it's needed and even put out of the way when it's not needed, and that it still presents a flat surface ok for rolling shop equipment round on checks a lot of boxes.

For others that might be interested, passive solar and other building approaches that maximize "free" energy have a really good payback and become essentially free. It can make a huge difference in the running costs of all different types of buildings, not just houses. Number one ROI is insulation coupled with a tight envelope and air to air energy recovery to maintain air quality are the three no-brainers for a new build, and can often be retrofitted too. The first two are in the building code already so it's just a matter of how much insulation you want based on your zone, and of course the capability of the builder to construct it correctly, which is not as likely as it should be for a lot of builders.