The combined heat and power system introduces a higher efficiency in energy conversion and consumption. By exploiting the flexibility of district heating systems (DHSs), the joint operation of heat and power systems can improve the overall system flexibility, reduce renewable energy curtailment, and decrease system operating costs. In a typical DHS, the heat exchange station (HES) is a key component which can help adjust the heat distribution among heat loads. In this paper, a joint hourly commitment of generation units and HESs is proposed. The DHS model is presented in which thermal storage and inertia of pipelines and heat loads are characterized. In addition, an approximation is applied to the HES model, making the overall joint commitment problem tractable. Numerical simulations are carried out, which demonstrate that the proposed joint commitment solution can introduce additional benefits in reducing wind power curtailment and system operation cost.