Overview of Calculation Models

Overview

The dynamic simulation is computed by the NANDRAD solver, a stand-alone computation core for thermal building and plant simulation. When starting the simulation, VICUS Buildings automatically translates the graphical building model into a NANDRAD project; the solver then solves the coupled system of equations made up of room balances, component heat conduction, and load/plant models with adaptive time step control (see Solver options).

This chapter documents the physical models as a reference. The subpages:

• Room balance & room states
• Construction heat conduction
• Window model
• Internal loads & ventilation
• Ideal heating/cooling, thermostat & surface heating

Model list

Model	Short description
Room states	Converts the balanced energy (and moisture) of each zone into air temperature, relative humidity, vapor pressure
Room balance	Sums all heat and moisture flows into the zone and provides the time derivatives for the integrator
Construction states	1D heat conduction through components, finite-volume discretization of the layers
Construction balance	Boundary fluxes of the components: heat transfer, short- and long-wave radiation, loads of the active layer
Window	Heat transmission through glazing, frame, and glazing bars; solar transmission with angle-dependent SHGC and shading
Internal loads	Person, equipment, and lighting loads, split into convective and radiative fractions
Internal moisture loads	Moisture release into the zone; only with moisture balance enabled
Natural ventilation	Infiltration and (controlled) window ventilation as air change of the zone
Thermostat	Control signals for heating and cooling from setpoint and actual temperature
Ideal heating/cooling	Ideal convective heating/cooling power following the thermostat signal, limited by maximum outputs
Ideal surface heating	Heating/cooling load directly in the active layer of a construction
Ideal pipe register	Surface heating with mass flow, supply temperature, and heat transfer in the pipe register
Shading control	Radiation-threshold-based control of the solar shading (with hysteresis)
Thermal comfort	Operative room temperature from air and area-weighted surface temperatures
Climate loads	Solar position, short- and long-wave radiation onto arbitrarily oriented/inclined surfaces from the climate file
Room radiation loads	Sum of the solar window loads per zone as the basis for radiation distribution
Heat load summation	Sums the heat loads of several zones, e.g. for coupling to heat networks
Constant zone	Zone with a prescribed temperature as a boundary condition (not balanced)

Added to this are the network/plant models of the hydraulic network (VICUS Districts) as well as infrastructure models (schedules, controllers, output management, FMI interface). There is no stand-alone ground model for buildings — ground-contacting components receive their boundary condition via the boundary condition definition.

Mapping the VICUS model to NANDRAD

At start-up, the project generator translates the following model components (in this order; errors are collected and shown as a detailed message):

1. Simulation, solver, and location parameters — directly from the pages Climate & Location, Model options, and Solver options. In addition, five default radiation sensors are created (horizontal, north/east/south/west).
2. Schedules — all referenced schedules from the usage profiles, with a uniqueness check of the IDs.
3. Zones — each room becomes a NANDRAD zone with volume, area, and additional heat capacity.
4. Controlled shadings — from the solar shading controls of the rooms (Assigning solar shading).
5. Construction instances, constructions, and materials — from surfaces, component assignments, and windows, including embedded objects (windows/doors) and boundary conditions.
6. Ideal surface heating systems — from the surface heating assignments, possibly with generated supply networks for supply systems.
7. Zone template models — per room, internal loads, ventilation, thermostat, and ideal heating/cooling from the assigned usage profile.
8. Shading factors file — pre-computed shading factors are adopted with object references rewritten to NANDRAD IDs.
9. Network model — in district projects, the active heat network.
10. Outputs — grids and definitions from the Outputs page.

For the DIN 4108-2 verification, the same generator automatically creates project variants with standard-compliant boundary conditions.