Evaluation of Turbulence Models for Airflow and Heat Transfer Prediction in BIPV/T Systems Optimization

Abstract

Airflow patterns and convective heat transfer mechanisms in unglazed transpired solar collectors (UTCs) integrated with Photovoltaic-Thermal systems are crucial to their performance. Computational Fluid Dynamics (CFD) simulations can be a valuable tool for the design and analysis of these hybrid building-integrated solar energy systems while recent advances in CFD approaches and turbulence models provide a great potential for improving prediction accuracy. This study performs 3-dimensional steady Reynolds Averaged Navier-Stokes (RANS) CFD simulations and evaluates the performance of five turbulence closure models, potentially suitable for modeling UTCs in terms of accuracy and computing cost. These models include four two-equation models (Standard k-ɛ, Renormalization Group Methods k-ɛ, Realizable k-ɛ and Shear Stress Transport k-ω) and one Reynolds Stress Model. A flat UTC under free stream approaching flow conditions and a corrugated UTC subjected to a plane wall jet flow were considered. The predicted air velocity, air temperature, and turbulent kinetic energy were compared against experimental data from the literature and those obtained using a specially designed full-scale experimental set-up in a solar simulator. The results show that although the Reynolds Stress Model can provide more detailed flow features at an increased computational cost compared to other models, it does not necessarily result in better performance. Among the two- equation models, the Renormalization Group Methods k-ɛ has the best overall performance for both cases studied while the Standard k- ɛ and Shear Stress Transport k-ω models can also provide acceptable prediction accuracy. A BIPV/T system with two PV panel arrangements across a UTC under the same coverage was investigated using the CFD models developed in the present study. It was found that BIPV/T systems integrated with UTCs can result in electrical efficiency up to 1.2% higher, for the cases considered.