The model Buildings.ThermalZones.Detailed.MixedAir is a model of a room with completely mixed air. The room can have any number of constructions and surfaces that participate in the heat exchange through convection, conduction, infrared radiation and solar radiation.
A description of the model assumptions and the implemention and validation of this room model can be found in Wetter et al. (2011). Note that this paper describes a previous version of the room model. The equations have not changed. However, what is shown in Figure 2 in the paper has in this version of the model been integrated directly into what is shown in Figure 1.
The room models the following physical processes:
The next paragraphs describe how to instantiate a room model. To instantiate a room model,
Entering parameters may be easiest in a textual editor.
In the here presented example, we assume we made several instances of data records for the construction material by dragging them from the package Buildings.HeatTransfer.Data to create the following list of declarations:
Buildings.HeatTransfer.Data.OpaqueConstructions.Insulation100Concrete200 matLayExt "Construction material for exterior walls" annotation (Placement(transformation(extent={{-60,140},{-40,160}}))); Buildings.HeatTransfer.Data.OpaqueConstructions.Brick120 matLayPar "Construction material for partition walls" annotation (Placement(transformation(extent={{-20,140},{0,160}}))); Buildings.HeatTransfer.Data.OpaqueConstructions.Generic matLayRoo( material={ HeatTransfer.Data.Solids.InsulationBoard(x=0.2), HeatTransfer.Data.Solids.Concrete(x=0.2)}, final nLay=2) "Construction material for roof" annotation (Placement(transformation(extent={{20,140},{40,160}}))); Buildings.HeatTransfer.Data.OpaqueConstructions.Generic matLayFlo( material={ HeatTransfer.Data.Solids.Concrete(x=0.2), HeatTransfer.Data.Solids.InsulationBoard(x=0.1), HeatTransfer.Data.Solids.Concrete(x=0.05)}, final nLay=3) "Construction material for floor" annotation (Placement(transformation(extent={{60,140},{80,160}}))); Buildings.HeatTransfer.Data.GlazingSystems.DoubleClearAir13Clear glaSys( UFra=2, shade=Buildings.HeatTransfer.Data.Shades.Gray(), haveExteriorShade=false, haveInteriorShade=true) "Data record for the glazing system" annotation (Placement(transformation(extent={{100,140},{120,160}})));
Note that construction layers are assembled from the outside to
the room-side. Thus, the construction matLayRoo
has an
exterior insulation. This constructions can then be used in the
room model.
Before we explain how to declare and parametrize a room model, we explain the different models that can be used to compute heat transfer through the room enclosing surfaces and constructions. The room model Buildings.ThermalZones.Detailed.MixedAir contains the constructions shown in the table below. The first row of the table lists the name of the data record that is used by the user to assign the model parameters. The second row lists the name of the instance of the model that simulates the equations. The third column provides a reference to the class definition that implements the equations. The forth column describes the main applicability of the model.
Record name | Model instance name | Class name | Description of the model |
---|---|---|---|
datConExt | modConExt | Buildings.ThermalZones.Detailed.Constructions.Construction | Exterior constructions that have no window. |
datConExtWin | modConExtWin | Buildings.ThermalZones.Detailed.Constructions.ConstructionWithWindow | Exterior constructions that have a window. Each construction of
this type must have one window. Within the same room, all windows can either have an interior shade, an exterior shade or no shade. Each window has its own control signal for the shade. This signal is exposed by the port uSha , which has the same dimension as the number of
windows. The values for uSha must be between
0 and 1 . Set uSha=0 to open
the shade, and uSha=1 to close the shade.Windows can also have an overhang, side fins, both (overhang and sidefins) or no external shading device. |
datConPar | modConPar | Buildings.ThermalZones.Detailed.Constructions.Construction | Interior constructions such as partitions within a room. Both surfaces of this construction are inside the room model and participate in the infrared and solar radiation balance. Since the view factor between these surfaces is zero, there is no infrared radiation from one surface to the other of the same construction. |
datConBou | modConBou | Buildings.ThermalZones.Detailed.Constructions.Construction | Constructions that expose the other boundary conditions of the
other surface to the outside of this room model. The heat
conduction through these constructions is modeled in this room
model. The surface at the port opa_b is connected to
the models for convection, infrared and solar radiation exchange
with this room model and with the other surfaces of this room
model. The surface at the port opa_a is connected to
the port surf_conBou of this room model. This could be
used, for example, to model a floor inside this room and connect to
other side of this floor model to a model that computes heat
transfer in the soil. |
surBou | N/A | Buildings.HeatTransfer.Data.OpaqueSurfaces.Generic | Opaque surfaces of this room model whose heat transfer through
the construction is modeled outside of this room model. This object
is modeled using a data record that contains the area, solar and
infrared emissivities and surface tilt. The surface then
participates in the convection and radiation heat balance of the
room model. The heat flow rate and temperature of this surface are
exposed at the heat port surf_surBou . An application
of this object may be to connect the port surf_surBou
of this room model with the port surf_conBou of
another room model in order to couple two room models. Another
application would be to model a radiant ceiling outside of this
room model, and connect its surface to the port
surf_conBou in order for the radiant ceiling model to
participate in the heat balance of this room. |
With these constructions, we may define a room as follows:
Buildings.ThermalZones.Detailed.MixedAir roo( redeclare package Medium = MediumA, AFlo=6*4, hRoo=2.7, nConExt=2, datConExt(layers={matLayRoo, matLayExt}, A={6*4, 6*3}, til={Buildings.Types.Tilt.Ceiling, Buildings.Types.Tilt.Wall}, azi={Buildings.Types.Azimuth.S, Buildings.Types.Azimuth.W}), nConExtWin=nConExtWin, datConExtWin(layers={matLayExt}, A={4*3}, glaSys={glaSys}, hWin={2}, wWin={2}, fFra={0.1}, til={Buildings.Types.Tilt.Wall}, azi={Buildings.Types.Azimuth.S}), nConPar=1, datConPar(layers={matLayPar}, each A=10, each til=Buildings.Types.Tilt.Wall), nConBou=1, datConBou(layers={matLayFlo}, each A=6*4, each til=Buildings.Types.Tilt.Floor), nSurBou=1, surBou(each A=6*3, each absIR=0.9, each absSol=0.9, each til=Buildings.Types.Tilt.Wall), linearizeRadiation = true , energyDynamics=Modelica.Fluid.Types.Dynamics.FixedInitial, lat=0.73268921998722) "Room model" annotation (Placement(transformation(extent={{46,20},{86,60}})));
The following paragraphs explain the different declarations.
The statement
redeclare package Medium = MediumA, AFlo=20, V=20*2.5,
declares that the medium of the room air is set to
MediumA
, that the floor area is 20
m2 and that the room air volume is 20*2.5
m3. The floor area is used to scale the internal
heat gains, which are declared with units of W/m2
using the input signal qGai_flow
.
The next entries specify constructions and surfaces that participate in the heat exchange.
The entry
nConExt=2,
declares that there are two exterior constructions.
The lines
datConExt(layers={matLayRoo, matLayExt}, A={6*4, 6*3}, til={Buildings.Types.Tilt.Ceiling, Buildings.Types.Tilt.Wall}, azi={Buildings.Types.Azimuth.S, Buildings.Types.Azimuth.W}),
declare that the material layers in these constructions are set
the records matLayRoo
and matLayExt
. What
follows are the declarations for the surface area, the tilt of the
surface and the azimuth of the surfaces. Thus, the surface with
construction matLayExt
is 6*3 m2
large and it is a west-facing wall.
Next, the declaration
nConExtWin=nConExtWin, datConExtWin(layers={matLayExt}, A={4*3}, glaSys={glaSys}, hWin={2}, wWin={2}, fFra={0.1}, til={Buildings.Types.Tilt.Wall}, azi={Buildings.Types.Azimuth.S}),
declares the construction that contains a window. This
construction is built using the materials defined in the record
matLayExt
. Its total area, including the window, is
4*3 m2. The glazing system is built using the
construction defined in the record glaSys
. The window
area is hwin=2 m high and wwin=2
m wide. The ratio of frame to total glazing system area is
10%.
Optionally, each window can have an overhang, side fins or both. If the above window were to have an overhang of 2.5 m width that is centered above the window, and hence extends each side of the window by 0.25 m, and has a depth of 1 m and a gap between window and overhang of 0.1 m, then its declaration would be
ove(wL={0.25}, wR={0.25}, gap={0.1}, dep={1}),
This line can be placed below the declaration of
wWin
. This would instanciate the model Buildings.HeatTransfer.Windows.Overhang
to model the overhang. See this class for a picture of the above
dimensions.
If the window were to have side fins that are 2.5 m high, measured from the bottom of the windows, and hence extends 0.5 m above the window, are 1 m depth and are placed 0.1 m to the left and right of the window, then its declaration would be
sidFin(h={0.5}, gap={0.1}, dep={1}),
This would instanciate the model Buildings.HeatTransfer.Windows.SideFins to model the side fins. See this class for a picture of the above dimensions.
The lines
til={Buildings.Types.Tilt.Wall}, azi={Buildings.Types.Azimuth.S}),
declare that the construction is a wall that is south exposed.
Note that if the room were to have two windows, and one window
has side fins and the other window has an overhang, the following
declaration could be used, which sets the value of dep
to 0
for the non-present side fins or overhang,
respectively:
sidFin(h = {0.5, 0}, gap = {0.1, 0.0}, dep = {1, 0}), ove(wL = {0.0, 0.25}, wR = {0.0, 0.25}, gap = {0.0, 0.1}, dep = {0, 1}),
What follows is the declaration of the partition constructions, as declared by
nConPar=1, datConPar(layers={matLayPar}, each A=10, each til=Buildings.Types.Tilt.Wall),
Thus, there is one partition construction. Its area is 10 m2 for each surface, to form a total surface area inside this thermal zone of 20 m2.
Next, the declaration
nConBou=1, datConBou(layers={matLayFlo}, each A=6*4, each til=Buildings.Types.Tilt.Floor),
declares one construction whose other surface boundary condition
is exposed by this room model (through the heat port
surf_conBou
).
Note that by default, there is a temperature state at the
surface of this wall. Therefore, connecting to the heat port
surf_conBou
a prescribed temperature boundary
condition such as
Modelica.Thermal.HeatTransfer.Sources.PrescribedTemperature
would lead to an error and the model won't translate. The reason is
that both, the state defines the temperature at the surface, and
Modelica.Thermal.HeatTransfer.Sources.PrescribedTemperature
prescribes the value of this temperature, leading to an
overspecification. To avoid this, add between
surf_conBou
and the prescribed boundary condition a
thermal conductance such as
Modelica.Thermal.HeatTransfer.Components.ThermalConductor or a
thermal convection model such as Buildings.HeatTransfer.Convection.Exterior.
Alternatively, you could remove the state from the surface by
declaring
nConBou=1, datConBou(layers={matLayFlo}, each A=6*4, each til=Buildings.Types.Tilt.Floor, each stateAtSurface_a = false),
The declaration
nSurBou=1, surBou(each A=6*3, each absIR=0.9, each absSol=0.9, each til=Buildings.Types.Tilt.Wall),
is used to instantiate a model for a surface that is in this
room. The surface has an area of 6*3 m2,
absorptivity in the infrared and the solar spectrum of 0.9
and it is a wall. The room model will compute infrared radiative
heat exchange, solar radiative heat gains and infrared radiative
heat gains of this surface. The surface temperature and heat flow
rate are exposed by this room model at the heat port
surf_surBou
. A model builder may use this construct to
couple this room model to another room model that may model the
construction.
The declaration
linearizeRadiation = true,
causes the equations for radiative heat transfer to be linearized. This can reduce computing time at the expense of accuracy.
The declaration
energyDynamics=Modelica.Fluid.Types.Dynamics.FixedInitial,
is used to initialize the air volume inside the thermal zone.
Finally, the declaration
lat=0.73268921998722) "Room model"
sets the latitude of the building which needs to correspond with the latitude of the weather data file.
The model has a parameter use_C_flow
. If set to
true
, then an input connector C_flow
is
enabled, which allows adding trace substances to the room air. Note
that this requires a medium model that has trace substances
enabled. See the example Buildings.ThermalZones.Detailed.Examples.MixedAirCO2.
To connect two rooms, the model Buildings.HeatTransfer.Conduction.MultiLayer
can be connected to the ports surf_surBou
of the two
rooms. However, make sure to set stateAtSurface_a =
true
and stateAtSurface_b = true
in the
instance of the heat conduction model, as this allows to avoid a
nonlinear system of equation to compute the radiative heat
transfer, thereby leading to faster simulation. See
Buildings.ThermalZones.Detailed.Validation.BESTEST.Cases9xx.Case960
for an example.
By setting linearizeRadiation = false
, nonlinear
equations will be used to compute the infrared radiation exchange
among surfaces. This can lead to slower computation.
Michael
Wetter, Wangda Zuo and Thierry Stephane Nouidui.
Modeling of Heat Transfer in Rooms in the Modelica "Buildings"
Library.
Proc. of the 12th IBPSA Conference, p. 1096-1103. Sydney,
Australia, November 2011.