Automating CFD to calculate ventilation rate of a naturally ventilate building

A well-controlled ventilation rate is essential to provide animals with good environment while minimizing heat losses as well as to assess environmental impact by emissions from livestock buildings. Therefore quantification of ventilation rate is crucial in terms of control of indoor air quality and emission of pollutants. Especially in naturally-ventilated (NV) buildings, measuring ventilation rate is more elusive because of dynamic and complex air flow patterns induced by natural wind. Computational fluid dynamics (CFD) simulation has been considered as a good method to quantify ventilation rate in NV buildings for design purposes because of its outstanding potential for analysing complex air flows. For its convenience in visualising air flow patterns, farmers and researchers have used simulation studies from CFD experts to predict ventilation performance before they build a new structure or modify the existing ventilation configuration. However, the skill of the modeller and understanding of the problem greatly influence the final results. Furthermore, hiring an expert for several simulation trials is costly and not practical. In this study, an automatic simulation tool using computational fluid dynamics (CFD) is being developed to predict the ventilation rate of NV buildings. OpenFOAM and ParaView were used for CFD simulation and visualisation respectively because they are free and open source software. The simulation tool was developed using Microsoft Visual Basic (VB) and Python to provide automation of general processes of CFD simulation, such as building geometry, meshing and computing, and the Graphical User Interface (GUI) for users. The GUI allows user to input structural specifications of building and ventilation openings and wind conditions, which are then used to build boundary conditions of the simulation model. Based on the input by the user, a computational domain with 16-sided polygon prism is built to realise 16 wind directions and filled with 3D meshes using the SnappyHexMesh technique. A steady-state solver is used to compute incompressible turbulent flows. A solver to calculate local mean age (LMA) and local mean residual-life-time (LMR) was also developed and included in the simulation tool to assess ventilation efficiency as post process. The simulated results are shown to the user by the visualization interface based on the Visualization Toolkit (VTK) source. In this study, the framework of the automatic simulation tool was completed. Using the simulation tool, farmers and researchers can easily simulate the ventilation process without any help from CFD experts but with the merit of ensuring a similar level of accuracy by the pre-developed procedures.status: publishe