Explicit simulations of the building heating and cooling loads at the district scale is hard to achieve because of their huge computational cost and the lack of relevant data at such an urban scale. A common solution to answer both problems is to simplify the model, usually resulting in a lower accuracy. This issue rises the following question: how to design a district energy model given computational limitations ? A specific modelling and simulation platform, called MoDEM (Modular District Energy Model), was developed to answer this question. The level of details of the model is modular in order to fit the available data or the available computational resources. For both cases, the impact of the assumptions can be evaluated as well as the loss of accuracy. To illustrate the possibilities offered by the platform, a district is taken as a use case. The results are discussed regarding the effects of various model adaptations on simulation outputs. The introduced methodology evidences the steps making it possible to reach explicit simulations of the energy load of a district and demonstrates the ability, and the limitations, of current tools.