Paper Conference

Proceedings of Building Simulation 2021: 17th Conference of IBPSA


CFD-Based Analysis of the Discharge Coefficient for Buoyancy-Driven Ventilation in a Full-Scale Operational Building

Lup Wai Chew, Chen Chen, Catherine Gorlé
Stanford University, United States of America

Abstract: Natural ventilation can play a key role in reducing building energy consumption for ventilation and cooling. The ventilation rate across an opening can be characterized using a still-air discharge coefficient, Cd, which is often assumed to be constant for a given opening. We aim to evaluate this constant Cd assumption for the buoyancy-driven natural ventilation process in Stanford’s Y2E2 Building. Computational fluid dynamics (CFD) simulations, specifically large eddy simulations, are used to calculate the flow rate through each window and determine the corresponding Cd. The validated CFD results show that Cd decreases linearly with Reynolds number (Re, calculated based on the flow rate across the windows) when Re < 10,000 but stays constant around 0.51 when Re > 10,000. As a result, assuming a constant Cd to estimate natural ventilation rate can introduce significant errors. Widespread use of CFD would support a more accurate characterization of the dependency of Cd for Re for specific building geometries and support robust natural ventilation system design.
Keywords: CFD, large eddy simulation, full-scale building, flow rate
Pages: 3096 - 3102