# Advances in Simulating Radiative Transfer in Complex Environments
## 2 Model Description
### Proof-of-Concept Simulation  
The advancements of ENVI-met's new IVS module are evaluated by comparing the model results of a simulation featuring the old AVF concept against a simulation featuring the new IVS algorithm, respectively. The model results will first be compared against each other with regard to longwave and shortwave radiation patterns, MRT, and potential air temperatures for different heights and times during the day. Furthermore, the impact of simulating secondary radiative transfers using IVS is examined by comparing the thermal comfort index PET between the two simulations. In order to find the expected large differences in radiation budgets--and, thus, in the resulting microclimate conditions--between varying surface and building materials, the modeled area was chosen based on high spatial variability. The model area is located at the edge of Central Park in New York City, NY, USA featuring an additional high recognition value because of its iconic urban morphology surrounding the Columbus Circle. Varying building heights, differing materials such as glass, concrete, or brick and specific roof types such as roofs featuring greenery or cool (high-albedo) materials, which are common heat mitigation measures [49; 50], already show the heterogeneity of the model area. Furthermore, the great differences in surface materials (meadows, rocks, sand pitches, streets, and pavements) together with the dense tree vegetation in Central Park located in a model area's lower right will enable us to show the complexity in secondary radiative fluxes that can be modeled by the new IVS module. To show the large variety of building and surface materials, the different materials have been visualized by specific colors (Figure 2). Table 1 gives an overview on the parameters of these materials that are based on the Midrise Apartment Post 1980 Standard for American Housing in NYC [51]. Building footprints and street tree locations were retrieved from the NYC open data portal [52]. Surface and building materials as well as park trees were digitized based on aerial imagery. The meteorological boundary conditions were taken from an Energy Plus Weather File of NYC [53]. To resemble a hot summer day with clear sky conditions, July 21 st was selected as simulation date. The simulation has been run for 24 h. Figure 3 shows the meteorological conditions for the whole simulation period provided by the EPW-file. Figure 2: Example model area at the edge of Central Park in NYC modeled for the proof-of-concept simulations. Different colors indicate different material properties. Non-default ENVI-met database item properties are defined in Table 1. Grey facades/roofs indicate concrete walls and default roofs, respectively; blue transmissive facades indicate glass walls; red facades indicate brick walls; white roofs indicate cool roofs; green facades indicate default roofs with default greenery 01 NASS being applied; green surfaces indicate default open soil 0100 SL and default grass 0100 XX; black surfaces indicate default asphalt road 0100 ST; grey surfaces indicate default pavement 0100 PP; pink surfaces indicate basalt rock profile entirely filled with default 0000 BA soil; yellow surfaces indicate default sand profile 0100 SD. Figure 3: Meteorological boundary conditions for the proof-of-concept simulation depicting direct shortwave (black line), diffuse shortwave (dashed line), and longwave radiation (dotted line) (**a**) as well as potential air temperature (black line) and specific air humidity (dashed line) (**b**).