Abstract
This paper presents a methodology for the development of an empirical equation which can provide the air mass flow rate imposed by single-sided wind-driven ventilation of a room, as a function of external wind speed and direction, using the results from Computational Fluid Dynamics (CFD) simulations. The proposed methodology is useful for a wide spectrum of applications, in which no access to experimental data or conduction of several CFD runs is possible, deriving a simple expression of natural ventilation rate, which can be further used for energy analysis of complicated building geometries in 0-D models or in object-oriented software codes. The developed computational model simulates a building, which belongs to Rheinisch-Westfälische Technische Hochschule (RWTH, Aachen University, Aachen, Germany) and its surrounding environment. A tilted window represents the opening that allows the ventilation of the adjacent room with fresh air. The derived data from the CFD simulations for the air mass flow were fitted with a Gaussian function in order to achieve the development of an empirical equation. The numerical simulations have been conducted using the Ansys Fluent v15.0® software package. In this work, the k-w Shear Stress Transport (SST) model was implemented for the simulation of turbulence, while the Boussinesq approximation was used for the simulation of the buoyancy forces. The coefficient of determination R2 of the curve is in the range of 0.84–0.95, depending on the wind speed. This function can provide the mass flow rate through the open window of the investigated building and subsequently the ventilation rate of the adjacent room in air speed range from 2.5 m/s to 16 m/s without the necessity of further numerical simulations.
Highlights
Nowadays, natural ventilation of a building is critical in order to reduce energy consumption for space conditioning
This paper presents a simple, versatile methodology for the development of an empirical equation, which can provide the air mass flow rate imposed by single-sided wind-driven ventilation of a room, as a function of external wind speed and direction, using the results from Computational Fluid Dynamics (CFD) simulations
K-w SST turbulence model and Boussinesq approximation have been used for the simulation of turbulence and buoyancy forces, respectively
Summary
Natural ventilation of a building is critical in order to reduce energy consumption for space conditioning (cooling and ventilation). The expression of airflow rate is a function of window and building geometry, opening angle, wind incident angle and speed These semi-empirical models are based on the previously analytical model and on pressure coefficients. Compared to other six empirical correlations [12,13,18,19,20,22], this model performs well due to the fact that the other models calculate the ventilation rates with average errors ranging from 12.9% to 46.1% This model takes into account the impact of both positive and negative buoyancy forces along with outside air pressure on natural ventilation through a single opening in contrast with the other models available. Even if the obtained correlation is not general and can only be used for this specific window type and this specific building envelope, the methodology is generic and can be followed in all cases
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