Starting the Simulation
Set the simulation period, start or test-initialize the simulation, stop a running run, resume instead of restarting, inspect the log file, and detailed settings such as threads and solver message level
Overview
The Start of the simulation start panel is embedded on the Dynamic Simulation page of the simulation view (button 
Simulation in the left toolbar, F10). On start-up, the VICUS project is automatically converted into a NANDRAD solver project (see Overview of calculation models) and the NANDRAD solver is run.
Simulation period
| Field | Meaning |
|---|---|
| Start date: | Start time in the format dd.mm.yyyy hh:mm:ss (incl. start year) |
| End date: | End time; must be after the start date |
| Duration: | Simulation duration with a selectable unit; changing the duration shifts the end date |
The three fields are coupled: if the start date is set after the end date, VICUS Buildings automatically corrects the end date based on the entered duration (a year as a fallback). The default for new projects is a full year.
Buttons
Start simulation — converts the project, runs the pre-checks (see below), and starts the solver. During the computation, the panel shows a progress bar and status (“Simulation running…”); with 
Stop running simulation it is aborted.
Test initialization — starts the solver with --test-init: the project is only read in and initialized, without time integration. This allows input errors to be found quickly; the log file then opens automatically. The note in the panel reads: “Before running the simulation, you should test the initialization to detect input errors.”
Export FMU… (Shift+F4) — generates the NANDRAD project and starts the FMU generator, see FMU Export & Co-Simulation.
Open simulation log file… — displays the file <ProjectName>/log/screenlog.txtfrom the last run or the last test initialization. In case of errors (“An error occurred during the simulation or initialization.”), the log opens automatically.
Resume or restart
If the project’s result directory already exists, the Start solver dialog asks (“The working/output directory for this project already exists.”):
Restart — starts from the beginning; the subfolders resultsandlog(as well asvar/fmus) are removed beforehand (checkbox Delete result directory before starting the simulation). Theinputfolder with cached shading files is retained.
Continue — resumes an interrupted computation with the solver option --restartfrom the last output time.
Pre-checks at start-up
Before the actual solver start, VICUS Buildings performs several consistency checks:
- Project saved? Unsaved projects must be saved first (“The project must be saved before the simulation can be started.”).
- Long-wave radiation consistent? If long-wave radiation exchange is defined as a boundary condition only on some of the interior surfaces, the start aborts with the error message “Inconsistent long-wave radiation configuration” and lists the surfaces without a long-wave boundary condition. Either all interior boundary conditions must define long-wave radiation — or none.
- View factors up to date? If long-wave radiation exchange is used on interior surfaces, VICUS Buildings automatically recomputes the view factors as soon as their stored geometry hash is missing or outdated (progress indicator; if the calculation fails, the start is aborted with an error message including details).
- Interior wall couplings present? If no single component instance couples two surfaces, even though a building contains several rooms, the dialog “No interior wall couplings” warns: without connected interior components, no heat exchange takes place between rooms via the building structure. The simulation can be started anyway; for connecting, see Interior walls & component links.
- Shading factors up to date? If the project has changed since the last shading calculation (hash comparison), the warning “Shading factors outdated” appears with the options Recalculate…, Continue anyway, and Cancel. See Calculating shading factors.
- Path length — project paths that are too long and would exceed the limit for output file paths on Windows are reported before start-up.
For projects with a heat network, network checks are added (ground-coupling time step, controlled pumps without a limiting polynomial, simultaneity data).
Error handling during project generation
If the conversion into the NANDRAD format fails (e.g. missing climate file, missing component assignments), the dialog “Error during NANDRAD project generation” shows all collected error messages in detail; the simulation does not start.
Detailed settings
The collapsible Detailed settings section contains the command-line solver options:
| Option | Command line | Meaning |
|---|---|---|
| Solver message level: | --verbosity-level=<0..3> | Message scope: Minimum, Normal (default), Detailed, Very detailed |
| Number of parallel threads: | -p=<n> | 1–64 threads; empty = “automatic (with OMP_NUM_THREADS, if set)”. Should not exceed the number of physical CPU cores |
| Write statistics for every internal solution step | --step-stats | Solver statistics per integration step for performance analyses |
| Terminal emulator: | — | Linux only: None (background process), XTerm, Gnome Terminal, Konsole. With a terminal, the solver continues to run as a stand-alone process, even if VICUS Buildings is closed |
| Close console window after simulation ends | -x | Windows only |
| Copy command line to clipboard | — | Copies the full solver call, e.g. for batch runs |
Good to know:
After major model changes, first run a test initialization: it takes only seconds and reports the same input errors that would otherwise only occur at simulation start. In addition, it generates the list of available output quantities, which is needed for the manual output definition.