Integrating urban energy simulation in a parametric environment: a Grasshopper interface for CitySim

The increasing popularity of parametric design tools goes hand in hand with the use of building performance simulation (BPS) tools from the early design phase. However, current methods require a significant computational time and a high number of parameters as input, as they are based on traditional BPS tools conceived for detailed building design phase. Their application to the urban scale is hence difficult. As an alternative to the existing approaches, we developed an interface to CitySim, a validated building simulation tool adapted to urban scale assessments, bundled as a plug-in for Grasshopper, a popular parametric design platform. On the one hand, CitySim allows faster simulations and requires fewer parameters than traditional BPS tools, as it is based on algorithms providing a good trade-off between the simulations requirements and their accuracy at the urban scale; on the other hand, Grasshopper allows the easy manipulation of building masses and energy simulation parameters through semi-automated parametric workflows. In this paper, we present a preliminary version of the developed plug-in and a typical design workflow for the simulation and visualization of building performance at the neighbourhood scale. We conclude by discussing its scalability to larger urban areas using 3D geodata as input and the coupling with Computational Fluid Dynamics (CFD) simulations and optimization algorithms.