The energy model of a building is a simulation in which a three-dimensional model of the real building is created. The model takes into account building materials, the construction of walls and partitions, as well as all energy-intensive systems present in the building, such as air conditioning, ventilation, heating and lighting. In addition, based on weather data such as temperature, wind speed and insolation, the response of the systems to external conditions is analyzed to maintain appropriate conditions inside the building, for example the right temperature. With a complete energy model, you can accurately map the actual energy consumption of a building and optimize system performance, making it possible to forecast future utility costs. In the case of existing buildings, the model is subject to calibration, i.e. adjustment of parameters to real consumption data, which allows to obtain compliance of the simulation with the actual results. Measuring the physical parameters of HVAC systems in an existing building is useful for determining the exact parameters of the model.