The task of the FLECS project is the development of a database for the Environmental Control System (ECS). Each component of the ECS is related to one model block. In general the description of the ECS is correlated to the description of an air/gas distribution network. The model blocks correspond to a physical model. The inner structure of the models is built up as universal as possible considering thermodynamic and fluid mechanic basics. Generalized volume elements consider water vapor, CO2 content and free water, condensation and evaporation processes, incompressible and compressible flow conditions. Further elements: Nodes, heat transfer elements, steady state and dynamical heat exchangers, specialized flow resistances like compressors and turbines, vapor compression cycle systems.