Brine temperature varies over the heating season by up to 10 deg C. I really tried to verify the horizontal coil length and installation depth recommended by i

Brine temperature varies over the heating season by up to 10 deg C. I really tried to verify the horizontal coil length and installation depth recommended by installers from the first principles, but I had to give up, as there were just too many unknown inputs: the type of soil (thus, specific heat and heat conduction), water content (which varies over the year), received solar energy (shady/sunny).