In this paper, a procedure aiming to integrate a detailed description of a multi-source thermal production system in a microgrid framework is proposed. The approach involves electric energy production and consumption as well. In particular, a bottom-up engineering viewpoint is adopted, involving energy flows interesting user buildings and mass flow rates and temperatures in the thermal supply facility. Different heating production systems, such as CHPs, boilers and solar thermal devices, are considered, as well as heat exchangers, thermal storage and pipe network. The proposed model is therefore embedded in the day-ahead energy management procedure of the microgrid. The optimal operation plan is evaluated by minimizing operation and emission costs over a daily horizon, satisfying electric demand and thermal comfort requirements. Tests are carried out on a model of the experimental microgrid system built at Electric Power System laboratory of Politecnico di Bari.