  Linear programming is used as a standard tool for optimising unit commitment
or power flows in energy supply systems. For heat supply systems, however, it
faces a relevant limitation: For them, energy yield depends on the output
temperature, thus both quantities would have to be optimised simultaneously and
the resulting problem is quadratic. As a solution, we describe a method working
with discrete temperature levels. This paper presents mathematical models of
various technologies and displays their potential in a case study focused on
integrated residential heat and electricity supply. It is shown that the
technique yields reasonable results including the choice of operational
temperatures.
