Anyone interested in modeling how much heating or cooling capacity is needed for a shop or building structure, you should try to find the SlantFin software.
You put all the construction details in (wall type, thickness, window surface areas, glass type, etc etc), and it tells you how much heating/cooling capacity is needed based on loss to the outside. Doesnt account for equipment or people, but VERY useful to size your furnace or A/C, and validated by a large empirical database.
I think they quit supporting the software a while back, but you should still be able to find a copy floating around.