Internal Loads & Ventilation

Overview

Internal loads and air exchange of a zone are generated from the assigned usage profile. The solver uses three models for this: the internal loads model (heat), the internal moisture loads model (only with the moisture balance enabled) and the natural ventilation model.

Internal heat loads

The model knows the load types persons, electrical equipment and lighting. Each load type can be parameterized as constant or controlled via schedules (model types Constant/Scheduled; from the usage-profile sub-models, VICUS generally generates schedule-controlled loads per square meter of net floor area).

Each load is split into a convective and a radiant part via its convective fraction:

$$\dot{Q}_{\mathrm{conv}} = f_{\mathrm{conv}}\cdot\dot{Q}, \qquad \dot{Q}_{\mathrm{rad}} = (1-f_{\mathrm{conv}})\cdot\dot{Q}$$

The convective shares enter the room energy balance directly (ConvectivePersonHeatLoad, ConvectiveEquipmentHeatLoad, ConvectiveLightingHeatLoad). The radiant shares (RadiantPersonHeatLoad, RadiantEquipmentHeatLoad, RadiantLightingHeatLoad) are distributed onto the room-enclosing construction surfaces and act there like absorbed radiation. For equipment and lighting, the electrical powers EquipmentElectricalPower, LightingElectricalPower and TotalElectricalPower are additionally available as outputs.

Internal moisture loads

With the moisture balance enabled, the moisture loads model generates per zone a moisture mass flow (MoistureLoad [kg/s], constant or schedule-controlled as a load per floor area) as well as the associated enthalpy flow (MoistureEnthalpyFlux [W], sensible and latent heat), both of which enter the room balance.

Natural ventilation and infiltration

The ventilation model represents the outdoor air exchange of the zone. The ventilation heat flow results from the air change rate $n$ [1/h] and the zone volume $V$:

$$\dot{Q}_{\mathrm{ventilation}} = \rho_{\mathrm{air}}\, c_{\mathrm{air}}\, V \cdot n \cdot (T_{\mathrm{outdoor}} - T_{\mathrm{room}})$$

Four model types are available (the choice results from the infiltration and ventilation sub-models of the usage profile):

Model type	Behavior
Constant	Constant air change rate (infiltration only)
Scheduled	Schedule-controlled air change rate
ScheduledWithBaseACR	Schedule-controlled base air change (infiltration) plus additional, schedule-controlled increased air change (window ventilation). The additional air change acts only when the room temperature leaves the comfort range (VentilationMinAirTemperature/VentilationMaxAirTemperature), the outdoor air temperature supports a return into the comfort range (e.g. cooler outdoor air during overheating) and the wind speed is below MaxWindSpeed
ScheduledWithBaseACRDynamicTLimit	As above, but with schedule-controlled minimum/maximum temperature limits; this model type is generated for controlled window ventilation from the usage profile

With the moisture balance enabled, the ventilation additionally transports moisture: the moisture mass flow (VentilationMoistureMassFlux [kg/s]) is formed from the difference between outdoor and room air humidity, and the heat flow is supplemented by the enthalpy share of the water vapor.

Result quantities per zone: VentilationRate [1/h], VentilationHeatFlux [W] (visible in the room balance as VentilationHeatLoad) and, if applicable, VentilationMoistureMassFlux.