  We propose a comprehensive nonlinear ODE-based thermo-hydraulic model of a
district heating system featuring several heat producers, consumers and storage
devices which are interconnected through a distribution network of meshed
topology whose temperature dynamics are explicitly considered. Moreover, we
analyze the conditions under which the hydraulic and thermal subsystems of the
model exhibit shifted passivity properties. For the hydraulic subsystem, our
claims on passivity draw on the monotonicity of the vector field associated to
the DH system's flow dynamics, which mainly codifies viscous friction effects
on the system's pressures. For the temperature dynamics, we propose a storage
function based on the ectropy function of a thermodynamic system, recently used
in the passivity analysis of heat exchanger networks.
