Borehole heat exchangers (BHE) in connection with heat pumps and floor heating in many countries are becoming an alternative to conventional heating or cooling systems using fossil resources. They are one building block of the suite of alternative low-carbon, sustainable and renewable energy sources. Modeling is a convenient tool in order to understand and optimize the heat transfer between the technical system, consisting of borehole, pipes and grout, and the surrounding ground, which is crucial for the performance of the BHE. We describe how 1D model components for flow and heat transport in the technical part can be coupled with a 2D or 3D component for the ground. With appropriate borehole conductances so coupled model is capable to cope with laminar, turbulent and transitory conditions in the pipes.