Simulation of urban microclimate with uhiSolver:software validation using simplifed material data

Background:Increasing urbanization as well as global warming requires an investigation of the infuence of diferent construction methods and ground surfaces on the urban heat island efect(UHI efect).The extent of the infuence of the urban structure,the building materials used and their surfaces on the UHI efect can be signifcantly reduced already in the planning phase using a designated OpenFOAM-based solver“uhiSolver”.Results:In the frst part of this research work,it is shown that inner building details and components can be neglected while still obtaining sufciently accurate results.For this purpose,the building model was divided into two layers:a surface layer without mass,where the interaction with radiation takes place,and a component layer,which contains all relevant components and cavities of the building represented with mass-averaged material properties.It has become apparent that the three parameters—albedo,heat capacity and thermal resistance—which have a decisive infuence on the interaction,have diferent efects on the component temperatures and the surface temperatures.In the second part of this research work,dynamic 3D computational fuid dynamics(CFD)simulations are performed with uhiSolver for a residential block in Vienna.Comparing the simulation results with measurement data collected on site,it is shown that the simplifed assumption of homogeneous material data for building bodies provides very good results for the validation case investigated.However,the infuence of the greening measures in the courtyard of the residential block on the air temperature is found to be negligible.Furthermore,it was observed that due to locally higher radiation density,lower air velocities and higher air humidity,the apparent temperature in the courtyard is sometimes perceived to be higher than in the adjacent streets,despite the lower air temperature.Conclusions:Simplifying the modeling process of the uhiSolver software by reducing the model complexity helps to reduce manual work for setting up appropriate boundary conditions of buildings.Compared to market competitors,good results are obtained for the validation case Kandlgasse presented in this research work,despite the simplifcations proposed.Thus,uhiSolver can be used as a robust analytical tool for urban planning.

Investigation of typical residential block typologies and their impact on pedestrianlevel microclimate in summers in Nanjing, China

The morphology of urban residential blocks in China,which is strictly affected by regulations,can potentially improve or deteriorate microclimates.This paper first proposes a framework for identifying typical residential block typologies using Nanjing as an example.A thorough investigation,consisting of 114 samples,was conducted,and 18 typical residential block typologies were summarized.Second,3D non-isothermal numerical simulations were performed on the hottest days of summer using the ENVI-met.The effect of morphological indices on the microclimate at the pedestrian level was explored using statistical methods and a novel graphic method named m-SpaceMate.The results revealed a strong correlation between the urban heat island intensity(UHII),mean radiation temperature,and universal thermal climate index(UTCI)and floor area ratio(FAR),as well as between wind velocity(U)and building coverage ratio(BCR).A significant increase in FAR(by approximately 1.0)can result in a low UTCI that was driven by MRT and shading conditions.Six-floor blocks,with FAR between 1.8 and 2.1,had a better overall thermal environment(except for lower U)than that of 11-floor blocks.When considering a similar BCR,blocks with slab-type buildings tended to have a U that was higher by approximately 30%.