Numerical simulations of district heating and cooling networks constitute a valuable tool for system design and optimization. This paper presents a novel thermo-hydraulic network model, which addresses particularly large 5th generation district heating and cooling (5GDHC) networks. We take into account the current flow regime for heat loss calculation, which significantly improves accuracy during zero mass flux compared to a widely used literature model. We demonstrate our model's capability on a real-world 5GDHC network with 6 km length and 180 distributed heat pumps. In contrast to existing models, we take into account the temperature dependency of the viscosity, which leads to a deviation of up to 65% in pressure drop in the given example. Yet, the performance of our implementation is considerably higher in comparison to simplified models of similar size that use generic equation solver, such as Modelica, as we avoid typical performance issues due to tight coupling and solution of large equation systems. The model is implemented using error-controlled, adaptive time step solver CVODE and made available as open-source project for reference and general usage.