Model that is used as a container for an HVAC system that is to be exported as an FMU and that serves a single zone.
To use this model as a container for an FMU, extend from this model, rather than instantiate it, and add your HVAC system. By extending from this model, the top-level signal connectors on the right stay at the top-level, and hence will be visible at the FMI interface. The example Buildings.Fluid.FMI.ExportContainers.Examples.FMUs.HVACZone shows how a simple HVAC system can be implemented and exported as an FMU. The example Buildings.Fluid.FMI.ExportContainers.Validation.RoomHVAC shows how such an FMU can be connected to a room model that has signal flow.
The conversion between the fluid ports and signal ports is done
in the HVAC adapter hvacAda.
This adapter has a vector of fluid ports called ports.
The supply and return air ducts, including any resistance model for the inlet
diffusor or exhaust grill, need to be connected to these ports.
Also, if a thermal zone has interzonal air exchange or air infiltration,
these flows need to be connected to ports.
This model outputs at the port fluPor the mass flow rate for
each flow that is connected to ports, together with its
temperature, water vapor mass fraction per total mass of the air (not per kg dry
air), and trace substances. These quantities are always as if the flow
enters the room, even if the flow is zero or negative.
If a medium has no moisture, e.g., if Medium.nXi=0, or
if it has no trace substances, e.g., if Medium.nC=0, then
the output signal for these properties are removed.
These quantities are always as if the flow
enters the room, even if the flow is zero or negative.
Thus, a thermal zone model that uses these signals to compute the
heat added by the HVAC system needs to implement an equation such as
Qsen = max(0, ṁsup) cp (Tsup - Tair,zon),
where
Qsen is the sensible heat flow rate added to the thermal zone,
ṁsup is the supply air mass flow rate from
the port fluPor (which is negative if it is an exhaust),
cp is the specific heat capacity at constant pressure,
Tsup is the supply air temperature and
Tair,zon is the zone air temperature.
Note that without the max(·, ·), the energy
balance would be wrong.
The input signals of this model are the zone radiative temperature.
The the zone air temperature,
the water vapor mass fraction per total mass of the air (unless Medium.nXi=0)
and trace substances (unless Medium.nC=0) are obtained from the connector
fluPor.backward.
The outflowing fluid stream(s) at the port ports will be at the
states obtained from fluPor.backward.
All fluid streams at port ports are at the same
pressure.
For convenience, the instance hvacAda also outputs the
properties obtained from fluPor.backward. These can be used
to connect a controller. The properties are available for each flow path in
fluPor.backward. For a thermal zone with mixed air, these are
all equal, while for a stratified room model, they can be different.
See Buildings.Fluid.FMI.ExportContainers.Examples.FMUs.HVACZone for a model that uses this model.
For models that multiple thermal zones connected to the HVAC system, use the model Buildings.Fluid.FMI.ExportContainers.HVACZones.
The mass flow rates at ports sum to zero, hence this
model conserves mass.
This model does not impose any pressure, other than setting the pressure
of all fluid connections to ports to be equal.
The reason is that setting a pressure can lead to non-physical system models,
for example if a mass flow rate is imposed and the HVAC system is connected
to a model that sets a pressure boundary condition such as
Buildings.Fluid.Sources.Outside.
Also, setting a pressure would make it impossible to use multiple instances
of this model (one for each thermal zone) and build in Modelica an airflow network
model with pressure driven mass flow rates.
The model has no pressure drop. Hence, the pressure drop
of an air diffuser or of an exhaust grill needs to be modelled
in models that are connected to ports.
| Name | Description |
|---|---|
| Medium | Medium in the component |