Defining ventilation boundary conditions for a greenhouse climate model

Abstract

Presently 10% of natural gas supplied to the Netherlands is used to maintain a stable climate and continuous electricity within horticultural greenhouses. As a result, technologies that reduce this energy consumption are in high demand. Theoretical models of heat flows in greenhouses can be used as a tool to increase the efficiency of these developments. This work seeks to improve such a tool by modeling the effects of various window opening angles and wind directions on the ventilation boundary condition for a greenhouse climate model. Using OpenFOAM, Computational Fluid Dynamics (CFD) simulations of various window opening angles and wind directions were run for both external and internal flow of a Venlo-type greenhouse. A thorough verification of the simulation results examined spatial convergence, temporal convergence, model implementation, iterative convergence, and consistency. The results of these simulations were deemed insufficient for a boundary analysis due to initial flow field errors. While the variable results could not be applied to a boundary condition analysis, the constant case (with 30 degree window openings and a zero degree azimuth angle) was used to reproduce the internal flow field of the greenhouse. The resulting model contained concentrated error at windows where fixed velocity values are not prescribed, correcting for continuity. This boundary condition is a first step towards more accurate internal greenhouse flow simulations of ventilation. Further, methods for generating a ventilation boundary condition using verified variable simulation results are discussed for future use.