The ENVI-met Suite program Spaces makes it possible to digitize your raster-based model area directly in the program or optimize the model area previously created in Monde or other programs.

Initial Settings

As a first step after starting the program, you should, similar to most other ENVI-met Suite programs, pick the project will be working in. This way, the project-own materials will be available if you are using a project database.

When creating a new area, you are first prompted to set your Model Location. This is important as the local radiation during the simulation is calculated depending on the position on the earth. Please make sure to correctly adapt this setting.

The Model Geometry allows you to define the amount x, y, and z grids and their respective resolutions. It also gives you the option to use Splitting and/or Telescoping, two options which are further described here. Splitting allows for a better resolution towards the ground of the simulation area, leading to more accurate results here. Telescoping makes it possible to reach a higher overall height of the model area without adding too many z grids. The telescoping should only start at a height higher or equal to your highest building, so that the buildings are still gridded correctly.

Finding the right Vertical Gridding

Most ENVI-met studies want to analyze outdoor thermal comfort near the surface. Thus, a higher resolution is needed. As a rule of thumb, model area should at least be twice the height of the highest building. However, if larger buildings (e.g. 100 m height) are also included in the model area, we would need 100 Z cells in a 2 m resolution to accurately represent our model area and still get an output for the height of 1 m. We now have several solutions to decrease the amount of Z cells to still simulate in a reasonable amount of time:

Solution A: We use the telescoping option to stretch cells that are not in our scope, i.e. starting above highest building height, we will only stretch air cells. The stretching factor is then applied to the size of each previous cell: cell sizes thus quickly increase. Thereby, the needed model area height is achieved with less Z cells. Back to our example: With a telescoping factor of 20 % and a starting height of 60 m, we now only need 45 cells instead of 100 cells to reach more than 200 m in model area height.

Solution B: We use the splitting option that splits the lowest grid cell near the ground into 5 cells. While the especially interesting cells near the surface are now available in high resolution, the default vertical resolution can now be modified to a rather coarse value such as 5 m. Back to our example: With splitting activated and a 5 m resolution, we now only need 41 cells to reach more than 200 m in model area height and we still have output heights in high resolution near the surface (e.g. in 1.5 m height).

Solution C: We use a combination of telescoping and splitting with a 5 m vertical resolution and the telescoping settings described in Solution A. We now only need 22 cells to reach more than 200 m in model area height. However, since we saved that many Z cells now, we could try to improve the stability even further and thus add some more Z cells to receive more free air cells above the highest building. We could also consider to decrease vertical resolution to 3 or 4 m again or choose a higher starting height for telescoping / use a lower telescoping factor. We strongly recommend to check those settings before you start digitizing your model area in de-tail. 3D information will be lost, if you need to reconvert from 3D mode to 2.5D in the end because vertical gridding needs to be changed. Use the “Model Inspector” found in Tools tab in Spaces to find the perfect vertical resolution for your model area.

Model borders

Model areas should have a few cells at every model border where no building cells are digitized. Terrain, soil profiles, plants should still be digitized correctly. This recommendation should be fol-lowed to avoid a blocking / channeling of the wind flow at the borders which may cause large instabilities and crashes. How much open space is needed depends on the building density and building heights. As a rule of thumb, distance between model border and the first building should be half the size of the building height. That commonly leads to around 4-8 cells of open space at each border.

Soil profiles in Terrain / DEM

Soil profiles are only visually covered by terrain Spaces but are still correctly used in the simulation.

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