Local High-Resolution Outdoor Thermal Comfort Evaluation
Urban canyon CFD and Thermal Simulation Coupling
The last 20 years clearly show an increasing frequency of extreme weather events throughout the world. Climate change is particularly evident in larger cities, where the phenomenon is further amplified by the Urban Heat Island Effect (UHI) and has an increasing impact on the health of the inhabitants. Consequently, outdoor thermal comfort is an essential aspect of urban spaces and their sustainable development. Moreover, attractive public realm encourages people to engage in interpersonal exchange, thus making a significant contribution to the social stability of the city. Therefore, it is a big challenge and responsibility for the urban planner and researchers to analyze outdoor spaces and make them usable and enjoyable. Hence, appropriate instruments are needed to support planning processes.
As interest in outdoor thermal comfort grows and the demand for passively comfortable urban microclimates rises with global city growth, so does the desire to simulate and map these microclimates. Although there ar many tools for measuring indoor comfort in a detailed spatial and time resolution, there is a relative lack of outdoor comfort assessment methods with an equal degree of precision. Partly this can be explained by the difficulty in modeling all relevant external comfort variables that are usually less critical in indoor spaces. Outdoor environments have higher wind velocities and more complex wind flow patterns, thus requiring simulations on computational fluid dynamics (CFD).
As Transsolar Academy Fellow, I supported the work of Marion Hiller and Christian Frenzel, further developing the Transsolar Outdoor Comfort Toolset for assessing urban microclimates, transient heat flows, and thermal comfort in outdoor spaces. The goal was the improvement of simulation tools using the thermal simulation engine TRNSYS coupled with results from an urban canyon CFD using OpenFoam. The tools were implemented in Grasshopper 3D, a visual scripting environment for Rhinoceros, using plugins such TRNSlizard, Eddy3D, Ladybug Tools, and custom ghPython components.
I was also involved in testing the new Transsolar Outdoor Comfort Tool. Thus, I conducted a case study at the Bordeauxplatz in the city of Munich, Germany. The study involved performing multi-directional urban CFD simulations coupled with dynamic outdoor thermal simulations based on TRNLizard/TRNSYS. The results showed that in cold climates detailed outdoor comfort calculations using precalculated CFD results in thermal simulations differ significantly from simplified ones. Additionally, the results show that currently, UTCI does not accurately reflect thermal comfort difference due to increased wind speed in temperate and dry climates. Therefore, further analysis should compare UTCI against other outdoor comfort metrics such as PET and Out-SET. Considering these results, using detailed methods for assessing outdoor comfort provides a better base for decisions in urban planning.
With my improved knowledge of how to measure and improve thermal comfort conditions in urban spaces, I seek to influence the design and improvement of urban space design regulations in the tropics.
Mentors: Marion Hiller, Christian Frenzel
Pablo Arango – Colombia
Pablo studied architecture and urbanism with an emphasis on bioclimatic design, construction and BIM at the National University of Colombia (UNAL) in Medellin and achieved Summa Cum Laude in his Architecture Degree. He also volunteered in the SAVIA program through AIESEC Mexico, making an environmental awareness plan for the most polluted city in Mexico, Monterrey.