Yes, you can use a solar loading model and a surface-to-surface radiation model together, and it’s actually the best way to capture heat effects in your calf hutch. The solar loading model calculates how sunlight directly heats the hutch surfaces, while the surface-to-surface radiation model figures out how those warmed surfaces exchange heat with each other. Using both means you’ll account for the sun’s energy coming in and the heat bouncing around between surfaces, which is important in both hot and cold conditions. If you add a cover on the exterior walls, include it in both models so it blocks and absorbs sunlight correctly and also participates in the heat exchange.@