An important component of urban microclimate is the radiative heat transfer between the myriad elements that make up the urban fabric. While great progress has been made in developing radiation models for idealized urban spaces, operational simulations of fully resolved city-scale domains remain elusive. As a result, simplifications and assumptions must be made. Such compromises may limit utility, and reveal a need for new, scalable microclimate models. This paper presents a novel, physically-based, building-resolving radiation transfer model (QESRadiant) that utilizes ray tracing techniques accelerated with graphics processing units (GPUs). QESRadiant builds on computer graphics methods, incorporating approaches for global illumination and light transport. Tests show that our methods can rapidly simulate the radiation balance for millions of surfaces with unique shapes and properties using a single consumer-class workstation, requiring times on the order of several minutes. High-resolution (0.5m) street canyon radiation budgets are validated using field data covering nine months. The results show the model is able to predict radiative fluxes in the canyon with an overall average R2 of 0.77 and mean error of 14.5Wm-2. Solar radiation was extremely sensitive to geometric obstructions, demonstrating the need for high-quality field experiments that resolve urban details affecting the radiation balance.
Bibliographical noteFunding Information:
This material is based upon work supported by the National Science Foundation under the following Grant Nos.: 0828214 , 1134580 , 0828206 and 1133590 . We are grateful to all of the GEnUSiS project team members for their substantive contributions, particularly, Prof. Rob Stoll. We appreciate the development efforts by Daniel Alexander at the early stages of the project, for his contributions toward verifying view factors and the development of a simplified surface energy balance. Dr. David Schroeder was also of great help, in which the use of his visual analysis tools helped in the verification of QES models. We are indebted to Drs. Brian Offerle and Fredrik Lindberg and collaborators for providing us with the street canyon validation data (as well as key information about the data) from Gothenburg, Sweden. Finally we thank Dr. Michael Brown and Prof. Sue Grimmond for allowing us to use their sky view factor images and data from Salt Lake City. Appendix A
- Graphics processing units
- Heat transfer modeling
- Ray tracing
- Urban street canyon