The renunciation of fossil energies and the associated large-scale deployment of variable renewable energy (VRE) sources provides special challenges for future electric power grids. To maintain the security of energy supply, an adjustment of the electrical energy demand to the energy production becomes increasingly important. Industrial plants are large energy consumers and therefore essential in stabilizing the power grid. Systems of the technical building services are particularly suitable for a more flexible use of the electricity consumption due to the usually high energy demand of these facilities and the independence from the production process. As a result, process reliability is not directly jeopardized. This paper introduces a model-based approach to evaluate energy flexibility of those supply systems already in the planning phase of factories. This enables a strategic planning to cover the useful energy demand of production machinery with the most flexible electrical power consumption possible.