Building Model Options
Building settings of the dynamic simulation: initial temperature and humidity, enable moisture balance, Perez radiation model, solar radiation distribution model with fractions, and selection of the simulated geometry
Overview
The building model options are located in the simulation view (button 
Simulation in the left toolbar, F10) on the Dynamic Simulation page (icon 
) in the Building settings tab. Alongside it are the tabs Network settings (only visible in district projects and only selectable if the project contains a heat network) and Performance options (see Solver options). Below the tabs, the start panel is embedded, see Starting the simulation.
All settings are stored undo-capably in the project’s simulation parameters and adopted unchanged during the NANDRAD export.
Initial conditions
| Field | Default value | Meaning |
|---|---|---|
| Initial temperature: | 20 °C | Initial temperature of all zones and constructions at the start of the simulation (allowed −50 … 150 °C) |
| Initial relative humidity: | 50 % | Initial value of the relative room air humidity; only active if the moisture balance is switched on |
Good to know:
Since all constructions start at the initial temperature, the model needs a settling time until realistic component temperatures have established. For annual evaluations, it is advisable to start the simulation a few weeks before the evaluation period, or to treat the first result interval as a settling phase.
Balance equations: moisture balance
The Enable moisture balancing checkbox enables a moisture balance of the room air in addition to the energy balance (NANDRAD flag EnableMoistureBalance). This computes the relative humidity, water vapor pressure, and absolute humidity per zone; ventilation then also transports moisture, and people release moisture into the room (see Room balance & room states and Internal loads & ventilation). Without the moisture balance enabled, the input field for the initial humidity is disabled.
Radiation model settings
Perez radiation model
The Use Perez radiation model checkbox enables the anisotropic diffuse radiation model according to Perez for the conversion of diffuse radiation onto inclined surfaces (NANDRAD flag PerezDiffuseRadiationModel at the location). Without this option, an isotropic sky model is used.
Shading calculation
The Shading calculation section (“Calculation of sunlight factors”) is embedded on this page; methods, quality levels, and output formats are described in Calculating shading factors.
Solar radiation distribution model
The Solar radiation distribution model: drop-down list determines how solar radiation entering through windows is distributed within the room:
- Distribution by area [AreaWeighted] (default) — the radiation is distributed proportionally to the surface areas onto the room-enclosing surfaces.
- Distribution by surface type [SurfaceTypeFactor] — the radiation is distributed according to user-defined fractions for floor, ceiling, and walls.
- Distribution based on zone-specific view factors [ViewFactor] — distribution based on pre-computed view factors.
In both of the first models, the fraction Percentage of solar radiation assigned directly to the room node: (default 10 %) is first added as a convective load directly to the room air. As a guideline, DIN EN ISO 13791 G.2 is given: “no furniture 0 % | little furnishing 10 % | extensive furnishing 20 %”.
Only in the “Distribution by surface type” model are the three surface fractions additionally editable (default values in parentheses):
- Percentage of solar radiation on surfaces assigned to the floor: (40 %)
- Percentage of solar radiation on surfaces assigned to floor/ceiling: (ceiling, 20 %)
- Percentage of solar radiation on surfaces assigned to walls: (30 %)
The three surface fractions plus the room-node fraction must together add up to 100 %; otherwise the error note “The sum of the radiation load fractions must equal 100 %.” appears and the simulation aborts during the parameter check.
Simulated geometry
The Simulated geometry option group controls which part of the model is exported into the solver project:
- Simulate the entire project (all buildings) — default; all rooms and surfaces are simulated.
- Simulate only selected geometry — only the objects currently selected in the 3D scene are exported. This setting also affects the embedded shading calculation (only selected surfaces).
Selecting individual building parts is suitable for detailed studies of individual rooms or storeys without changing the overall model; for object selection see Selection & visibility.
License note
If the license does not include dynamic simulation, the note “Your current license does not include the option for dynamic simulation. …” appears and the start panel is disabled.