Uncoupled urban canopy models replace the full-fledged atmospheric representation with a computationally light equivalent that is used to optimize designs of urban layout. This type of model can be forced by boundary conditions that are directly measured or derived from an off-line meso-scale simulation. More often, it is driven, indirectly, by conditions measured at a nearby rural weather station (e.g., airport) via a hyper-simplified representation of the momentum/energy exchanges between the urban canopy layer and the surrounding atmosphere.
The urban canopy model represents the real urban geometry as an equivalent regularized arrangement of buildings and streets that is based on the average morphological parameters of the actual urban area. The thermal interactions to be considered here take place mainly in the urban canyon air, as it is in contact with the built-up areas as well as the free atmosphere above the canopy. To represent these interactions, a dynamic thermal network lumped-parameter model is used. This model provides compley physical modelst o capture aerodynamic and evapotranspiration. The simulation runs for every hour of a standard year. The main outcomes are average building energy use and urban heat island intensity.
Two main categories of uncoupled urban canopy models exist: single-layer and multilayer. The single-layer model focuses on the overall exchange of heat, momentum, and moisture with the atmosphere right above the urban canopy. Constant air temperature and humidity are assumed in the canyon. The multi-layer model is typically parameterized in terms of the horizontally averaged flow and scalar transport. This approach allows a higher resolution of atmospheric processes, but it incurs a greater computational cost.