Buildings.Fluid.BaseClasses
Package with base classes for Buildings.Fluid
Information
This package contains base classes that are used to construct the models in Buildings.Fluid.
Extends from Modelica.Icons.BasesPackage (Icon for packages containing base classes).
Package Content
| Name | Description |
|---|---|
 ActuatorFilter
|
Filter used for actuators of valves, dampers and movers |
 IndexMassFraction
|
Computes the index of a substance in the mass fraction vector Xi |
 MassFlowRateMultiplier
|
Model that multiplies the mass flow rate |
 PartialResistance
|
Partial model for a hydraulic resistance |
 PartialThreeWayResistance
|
Flow splitter with partial resistance model at each port |
 FlowModels
|
Flow models for pressure drop calculations |
 Validation
|
Collection of validation models |
Buildings.Fluid.BaseClasses.ActuatorFilter
Filter used for actuators of valves, dampers and movers
Information
This block implements a filter that is used to approximate the actuators of valves, dampers and fans.
Implementation
The implementation is based on
Modelica.Blocks.Continuous.CriticalDamping.
It differs from that model in that the internal state of the filter s
is transformed using x = u_nominal*s.
It turns out that this transformation leads to smaller system of nonlinear equations if u_nominal ≠ 0, see
IBPSA, #1498
for a discussion.
Extends from Modelica.Blocks.Interfaces.SISO (Single Input Single Output continuous control block).
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Frequency | f | Cut-off frequency [Hz] | |
| Boolean | normalized | true | = true, if amplitude at f_cut is 3 dB, otherwise unmodified filter |
| Real | u_nominal | 1 | Magnitude of input |
| Initialization | |||
| Init | initType | Modelica.Blocks.Types.Init.N... | Type of initialization (1: no init, 2: steady state, 3: initial state, 4: initial output) |
| Real | x_start[n] | zeros(n) | Initial or guess values of states |
| Real | y_start | 0.0 | Initial value of output (remaining states are in steady state) |
Connectors
| Type | Name | Description |
|---|---|---|
| input RealInput | u | Connector of Real input signal |
| output RealOutput | y | Connector of Real output signal |
Modelica definition
block ActuatorFilter
"Filter used for actuators of valves, dampers and movers"
import Modelica.Blocks.Types.Init;
extends Modelica.Blocks.Interfaces.SISO;
constant Integer n=2 "Order of filter";
parameter Modelica.Units.SI.Frequency f(start=1) "Cut-off frequency";
parameter Boolean normalized = true
"= true, if amplitude at f_cut is 3 dB, otherwise unmodified filter";
parameter Modelica.Blocks.Types.Init initType=Modelica.Blocks.Types.Init.NoInit
"Type of initialization (1: no init, 2: steady state, 3: initial state, 4: initial output)";
parameter Real x_start[n]=zeros(n) "Initial or guess values of states";
parameter Real y_start=0.0
"Initial value of output (remaining states are in steady state)";
parameter Real u_nominal = 1 "Magnitude of input";
Real x[n](each final stateSelect=StateSelect.never) = u_nom*s
"Transformed filter states";
protected
final parameter Real u_nom = if abs(u_nominal-1) < 1E-12 then 1-1E-12 else u_nominal
"Magnitude of input (set to a value different from 1 to avoid elimination by symbolic processing)";
parameter Real alpha=if normalized then sqrt(2^(1/n) - 1) else 1.0
"Frequency correction factor for normalized filter";
parameter Real w_u=2*Modelica.Constants.pi*f/alpha/u_nom;
Real s[n](start=x_start/u_nom) "Filter states";
initial equation
if initType == Init.SteadyState then
der(s) = zeros(n);
elseif initType == Init.InitialState then
s = x_start/u_nom;
elseif initType == Init.InitialOutput then
y = y_start;
der(s[1:n - 1]) = zeros(n - 1);
end if;
equation
der(s[1]) = (u - u_nom*s[1])*w_u;
for i in 2:n loop
der(s[i]) = (u_nom*s[i - 1] - u_nom*s[i])*w_u;
end for;
y =u_nom*s[n];
end ActuatorFilter;
Buildings.Fluid.BaseClasses.IndexMassFraction
Computes the index of a substance in the mass fraction vector Xi
Information
This block computes the index that the subtance with name
substanceName has in the mass fraction vector X.
If the medium model has no component called substanceName,
then the block writes an error message and terminates the simulation.
This block is used for example to obtain the index of the subtance 'water' to obtain the water vapor concentration, or to measure any other mass fraction.
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| replaceable package Medium | Modelica.Media.Interfaces.Pa... | Medium model | |
| String | substanceName | "" | Name of species substance |
Connectors
| Type | Name | Description |
|---|---|---|
| replaceable package Medium | Medium model | |
Modelica definition
block IndexMassFraction
"Computes the index of a substance in the mass fraction vector Xi"
replaceable package Medium =
Modelica.Media.Interfaces.PartialCondensingGases "Medium model";
parameter String substanceName="" "Name of species substance";
protected
parameter Integer i_x = sum(
if Modelica.Utilities.Strings.isEqual(string1=Medium.substanceNames[i],
string2=substanceName,
caseSensitive=false) then i else 0
for i in 1:Medium.nXi) "Index of substance";
initial equation
assert(i_x > 0, "Substance '" + substanceName + "' is not present in medium '"
+ Medium.mediumName + "'.\n"
+ "Change medium model to one that has '" + substanceName + "' as a substance.");
end IndexMassFraction;
Buildings.Fluid.BaseClasses.MassFlowRateMultiplier
Model that multiplies the mass flow rate
Information
This model multiplies the mass flow rate so that
0 = port_b.m_flow + k * port_a.m_flow.
The specific enthalpy, the species concentration and the trace substance concentration remain unchanged. Therefore, this model does not conserve mass or energy. It is used in Buildings.Fluid.Geothermal.Borefields.BaseClasses.PartialBorefield and also in the Buildings library to avoid having to instantiate circuits in parallel, with each having the same mass flow rate and temperatures.
Extends from Buildings.Fluid.Interfaces.PartialTwoPort (Partial component with two ports).
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| replaceable package Medium | PartialMedium | Medium in the component | |
| Real | k | Gain for mass flow rate | |
| Assumptions | |||
| Boolean | allowFlowReversal | true | = false to simplify equations, assuming, but not enforcing, no flow reversal |
Connectors
| Type | Name | Description |
|---|---|---|
| FluidPort_a | port_a | Fluid connector a (positive design flow direction is from port_a to port_b) |
| FluidPort_b | port_b | Fluid connector b (positive design flow direction is from port_a to port_b) |
Modelica definition
model MassFlowRateMultiplier "Model that multiplies the mass flow rate"
extends Buildings.Fluid.Interfaces.PartialTwoPort;
parameter Real k "Gain for mass flow rate";
initial equation
assert(k > Modelica.Constants.small or -k < -Modelica.Constants.small,
"Gain must not be zero. Received k = " + String(k));
equation
// Pressure drop in design flow direction
port_a.p = port_b.p;
// Mass balance (mass is not conserved by this model!)
port_b.m_flow = -k*port_a.m_flow;
// Specific enthalpy flow rate
port_a.h_outflow = inStream(port_b.h_outflow);
port_b.h_outflow = inStream(port_a.h_outflow);
// Transport of substances
port_a.Xi_outflow = inStream(port_b.Xi_outflow);
port_b.Xi_outflow = inStream(port_a.Xi_outflow);
port_a.C_outflow = inStream(port_b.C_outflow);
port_b.C_outflow = inStream(port_a.C_outflow);
end MassFlowRateMultiplier;
Buildings.Fluid.BaseClasses.PartialResistance
Partial model for a hydraulic resistance
Information
Partial model for a flow resistance, possible with variable flow coefficient.
Models that extend this class need to implement an equation that relates
m_flow and dp, and they need to assign the parameter
m_flow_turbulent.
See for example Buildings.Fluid.FixedResistances.PressureDrop for a model that extends this base class.
Extends from Buildings.Fluid.Interfaces.PartialTwoPortInterface (Partial model transporting fluid between two ports without storing mass or energy).
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| replaceable package Medium | PartialMedium | Medium in the component | |
| MassFlowRate | m_flow_turbulent | Turbulent flow if |m_flow| >= m_flow_turbulent [kg/s] | |
| Nominal condition | |||
| MassFlowRate | m_flow_nominal | Nominal mass flow rate [kg/s] | |
| PressureDifference | dp_nominal | Pressure drop at nominal mass flow rate [Pa] | |
| Assumptions | |||
| Boolean | allowFlowReversal | true | = false to simplify equations, assuming, but not enforcing, no flow reversal |
| Advanced | |||
| MassFlowRate | m_flow_small | 1E-4*abs(m_flow_nominal) | Small mass flow rate for regularization of zero flow [kg/s] |
| Boolean | from_dp | false | = true, use m_flow = f(dp) else dp = f(m_flow) |
| Boolean | linearized | false | = true, use linear relation between m_flow and dp for any flow rate |
| Diagnostics | |||
| Boolean | show_T | false | = true, if actual temperature at port is computed |
Connectors
| Type | Name | Description |
|---|---|---|
| FluidPort_a | port_a | Fluid connector a (positive design flow direction is from port_a to port_b) |
| FluidPort_b | port_b | Fluid connector b (positive design flow direction is from port_a to port_b) |
Modelica definition
partial model PartialResistance "Partial model for a hydraulic resistance"
extends Buildings.Fluid.Interfaces.PartialTwoPortInterface(
show_T=false,
dp(nominal=if dp_nominal_pos > Modelica.Constants.eps
then dp_nominal_pos else 1),
m_flow(
nominal=if m_flow_nominal_pos > Modelica.Constants.eps
then m_flow_nominal_pos else 1),
final m_flow_small = 1E-4*abs(m_flow_nominal));
constant Boolean homotopyInitialization = true "= true, use homotopy method";
parameter Boolean from_dp = false
"= true, use m_flow = f(dp) else dp = f(m_flow)";
parameter Modelica.Units.SI.PressureDifference dp_nominal(displayUnit="Pa")
"Pressure drop at nominal mass flow rate";
parameter Boolean linearized = false
"= true, use linear relation between m_flow and dp for any flow rate";
parameter Modelica.Units.SI.MassFlowRate m_flow_turbulent(min=0)
"Turbulent flow if |m_flow| >= m_flow_turbulent";
protected
parameter Medium.ThermodynamicState sta_default=
Medium.setState_pTX(T=Medium.T_default, p=Medium.p_default, X=Medium.X_default);
parameter Modelica.Units.SI.DynamicViscosity eta_default=
Medium.dynamicViscosity(sta_default)
"Dynamic viscosity, used to compute transition to turbulent flow regime";
final parameter Modelica.Units.SI.MassFlowRate m_flow_nominal_pos=abs(
m_flow_nominal) "Absolute value of nominal flow rate";
final parameter Modelica.Units.SI.PressureDifference dp_nominal_pos(
displayUnit="Pa") = abs(dp_nominal)
"Absolute value of nominal pressure difference";
initial equation
assert(homotopyInitialization, "In " + getInstanceName() +
": The constant homotopyInitialization has been modified from its default value. This constant will be removed in future releases.",
level = AssertionLevel.warning);
equation
// Isenthalpic state transformation (no storage and no loss of energy)
port_a.h_outflow = if allowFlowReversal then inStream(port_b.h_outflow) else Medium.h_default;
port_b.h_outflow = inStream(port_a.h_outflow);
// Mass balance (no storage)
port_a.m_flow + port_b.m_flow = 0;
// Transport of substances
port_a.Xi_outflow = if allowFlowReversal then inStream(port_b.Xi_outflow) else Medium.X_default[1:Medium.nXi];
port_b.Xi_outflow = inStream(port_a.Xi_outflow);
port_a.C_outflow = if allowFlowReversal then inStream(port_b.C_outflow) else zeros(Medium.nC);
port_b.C_outflow = inStream(port_a.C_outflow);
end PartialResistance;
Buildings.Fluid.BaseClasses.PartialThreeWayResistance
Flow splitter with partial resistance model at each port
Information
Partial model for flow resistances with three ports such as a flow mixer/splitter or a three way valve.
If energyDynamics ≠ Modelica.Fluid.Types.Dynamics.SteadyState,
then at the junction of the three flows,
a mixing volume will be present. This will introduce a dynamic energy and momentum
balance, which often breaks algebraic loops.
The time constant of the mixing volume is determined by the parameter tau.
Extends from Buildings.Fluid.Interfaces.LumpedVolumeDeclarations (Declarations for lumped volumes).
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| replaceable package Medium | PartialMedium | Medium in the component | |
| PartialTwoPortInterface | res1 | redeclare Buildings.Fluid.In... | Partial model, to be replaced with a fluid component |
| PartialTwoPortInterface | res2 | redeclare Buildings.Fluid.In... | Partial model, to be replaced with a fluid component |
| PartialTwoPortInterface | res3 | redeclare Buildings.Fluid.In... | Partial model, to be replaced with a fluid component |
| Dynamics | |||
| Conservation equations | |||
| Dynamics | energyDynamics | Modelica.Fluid.Types.Dynamic... | Type of energy balance: dynamic (3 initialization options) or steady state |
| MassFlowRate | mDyn_flow_nominal | Nominal mass flow rate for dynamic momentum and energy balance [kg/s] | |
| Real | mSenFac | 1 | Factor for scaling the sensible thermal mass of the volume |
| Nominal condition | |||
| Time | tau | 10 | Time constant at nominal flow for dynamic energy and momentum balance [s] |
| Advanced | |||
| Dynamics | |||
| Dynamics | massDynamics | energyDynamics | Type of mass balance: dynamic (3 initialization options) or steady state, must be steady state if energyDynamics is steady state |
| Boolean | from_dp | true | = true, use m_flow = f(dp) else dp = f(m_flow) |
| PortFlowDirection | portFlowDirection_1 | Modelica.Fluid.Types.PortFlo... | Flow direction for port_1 |
| PortFlowDirection | portFlowDirection_2 | Modelica.Fluid.Types.PortFlo... | Flow direction for port_2 |
| PortFlowDirection | portFlowDirection_3 | Modelica.Fluid.Types.PortFlo... | Flow direction for port_3 |
| Boolean | verifyFlowReversal | false | =true, to assert that the flow does not reverse when portFlowDirection_* does not equal Bidirectional |
| MassFlowRate | m_flow_small | Small mass flow rate for checking flow reversal [kg/s] | |
| Initialization | |||
| AbsolutePressure | p_start | Medium.p_default | Start value of pressure [Pa] |
| Temperature | T_start | Medium.T_default | Start value of temperature [K] |
| MassFraction | X_start[Medium.nX] | Medium.X_default | Start value of mass fractions m_i/m [kg/kg] |
| ExtraProperty | C_start[Medium.nC] | fill(0, Medium.nC) | Start value of trace substances |
| ExtraProperty | C_nominal[Medium.nC] | fill(1E-2, Medium.nC) | Nominal value of trace substances. (Set to typical order of magnitude.) |
Connectors
| Type | Name | Description |
|---|---|---|
| FluidPort_a | port_1 | First port, typically inlet |
| FluidPort_b | port_2 | Second port, typically outlet |
| FluidPort_a | port_3 | Third port, can be either inlet or outlet |
Modelica definition
partial model PartialThreeWayResistance
"Flow splitter with partial resistance model at each port"
extends Buildings.Fluid.Interfaces.LumpedVolumeDeclarations(
final massDynamics=energyDynamics,
final mSenFac=1);
Modelica.Fluid.Interfaces.FluidPort_a port_1(
redeclare package Medium = Medium,
h_outflow(start=Medium.h_default, nominal=Medium.h_default),
m_flow(min=if (portFlowDirection_1 == Modelica.Fluid.Types.PortFlowDirection.Entering) then 0.0 else -Modelica.Constants.inf,
max=if (portFlowDirection_1== Modelica.Fluid.Types.PortFlowDirection.Leaving) then 0.0 else Modelica.Constants.inf))
"First port, typically inlet";
Modelica.Fluid.Interfaces.FluidPort_b port_2(
redeclare package Medium = Medium,
h_outflow(start=Medium.h_default, nominal=Medium.h_default),
m_flow(min=if (portFlowDirection_2 == Modelica.Fluid.Types.PortFlowDirection.Entering) then 0.0 else -Modelica.Constants.inf,
max=if (portFlowDirection_2 == Modelica.Fluid.Types.PortFlowDirection.Leaving) then 0.0 else Modelica.Constants.inf))
"Second port, typically outlet";
Modelica.Fluid.Interfaces.FluidPort_a port_3(
redeclare package Medium=Medium,
h_outflow(start=Medium.h_default, nominal=Medium.h_default),
m_flow(min=if (portFlowDirection_3==Modelica.Fluid.Types.PortFlowDirection.Entering) then 0.0 else -Modelica.Constants.inf,
max=if (portFlowDirection_3==Modelica.Fluid.Types.PortFlowDirection.Leaving) then 0.0 else Modelica.Constants.inf))
"Third port, can be either inlet or outlet";
parameter Modelica.Units.SI.Time tau=10
"Time constant at nominal flow for dynamic energy and momentum balance";
parameter Modelica.Units.SI.MassFlowRate mDyn_flow_nominal
"Nominal mass flow rate for dynamic momentum and energy balance";
parameter Boolean from_dp = true
"= true, use m_flow = f(dp) else dp = f(m_flow)";
parameter Modelica.Fluid.Types.PortFlowDirection portFlowDirection_1=Modelica.Fluid.Types.PortFlowDirection.Bidirectional
"Flow direction for port_1";
parameter Modelica.Fluid.Types.PortFlowDirection portFlowDirection_2=Modelica.Fluid.Types.PortFlowDirection.Bidirectional
"Flow direction for port_2";
parameter Modelica.Fluid.Types.PortFlowDirection portFlowDirection_3=Modelica.Fluid.Types.PortFlowDirection.Bidirectional
"Flow direction for port_3";
parameter Boolean verifyFlowReversal = false
"=true, to assert that the flow does not reverse when portFlowDirection_* does not equal Bidirectional";
parameter Modelica.Units.SI.MassFlowRate m_flow_small
"Small mass flow rate for checking flow reversal";
replaceable Buildings.Fluid.Interfaces.PartialTwoPortInterface res1
constrainedby Buildings.Fluid.Interfaces.PartialTwoPortInterface(
redeclare final package Medium = Medium,
allowFlowReversal=portFlowDirection_1 == Modelica.Fluid.Types.PortFlowDirection.Bidirectional)
"Partial model, to be replaced with a fluid component";
replaceable Buildings.Fluid.Interfaces.PartialTwoPortInterface res2
constrainedby Buildings.Fluid.Interfaces.PartialTwoPortInterface(
redeclare final package Medium = Medium,
allowFlowReversal=portFlowDirection_2 == Modelica.Fluid.Types.PortFlowDirection.Bidirectional)
"Partial model, to be replaced with a fluid component";
replaceable Buildings.Fluid.Interfaces.PartialTwoPortInterface res3
constrainedby Buildings.Fluid.Interfaces.PartialTwoPortInterface(
redeclare final package Medium = Medium,
allowFlowReversal=portFlowDirection_3 == Modelica.Fluid.Types.PortFlowDirection.Bidirectional)
"Partial model, to be replaced with a fluid component";
Buildings.Fluid.Delays.DelayFirstOrder vol(
redeclare final package Medium = Medium,
final nPorts=3,
final tau=tau,
final m_flow_nominal=mDyn_flow_nominal,
final energyDynamics=energyDynamics,
final p_start=p_start,
final T_start=T_start,
final X_start=X_start,
final C_start=C_start,
final allowFlowReversal=true,
final prescribedHeatFlowRate=false)
if have_controlVolume "Fluid volume to break algebraic loop";
protected
parameter Boolean have_controlVolume=
energyDynamics <> Modelica.Fluid.Types.Dynamics.SteadyState
"Boolean flag used to remove conditional components";
Modelica.Fluid.Interfaces.FluidPort_a port_internal(
redeclare package Medium = Medium) if not have_controlVolume
"Internal dummy port for easier connection of conditional connections";
initial equation
assert(portFlowDirection_1<>Modelica.Fluid.Types.PortFlowDirection.Leaving or
portFlowDirection_2<>Modelica.Fluid.Types.PortFlowDirection.Leaving or
portFlowDirection_3<>Modelica.Fluid.Types.PortFlowDirection.Leaving,
"In " + getInstanceName() + ": All ports are configured to
Modelica.Fluid.Types.PortFlowDirection.Leaving, which is non-physical.");
assert(portFlowDirection_1<>Modelica.Fluid.Types.PortFlowDirection.Entering or
portFlowDirection_2<>Modelica.Fluid.Types.PortFlowDirection.Entering or
portFlowDirection_3<>Modelica.Fluid.Types.PortFlowDirection.Entering,
"In " + getInstanceName() + ": All ports are configured to
Modelica.Fluid.Types.PortFlowDirection.Entering, which is non-physical.");
equation
if verifyFlowReversal then
if portFlowDirection_1==Modelica.Fluid.Types.PortFlowDirection.Entering then
assert(port_1.m_flow> -m_flow_small,
"In " + getInstanceName() + ":
Flow is leaving port_1 despite portFlowDirection_1=PortFlowDirection.Entering, since m_flow=" +
String(port_1.m_flow) + "<-"+String(m_flow_small));
end if;
if portFlowDirection_1==Modelica.Fluid.Types.PortFlowDirection.Leaving then
assert(port_1.m_flow< m_flow_small,
"In " + getInstanceName() + ":
Flow is entering port_1 despite portFlowDirection_1=PortFlowDirection.Leaving, since m_flow=" +
String(port_1.m_flow) + ">"+String(m_flow_small));
end if;
if portFlowDirection_2==Modelica.Fluid.Types.PortFlowDirection.Entering then
assert(port_2.m_flow> -m_flow_small,
"In " + getInstanceName() + ":
Flow is leaving port_2 despite portFlowDirection_2=PortFlowDirection.Entering, since m_flow=" +
String(port_2.m_flow) + "<-"+String(m_flow_small));
end if;
if portFlowDirection_2==Modelica.Fluid.Types.PortFlowDirection.Leaving then
assert(port_2.m_flow< m_flow_small,
"In " + getInstanceName() + ":
Flow is entering port_2 despite portFlowDirection_2=PortFlowDirection.Leaving, since m_flow=" +
String(port_2.m_flow) + ">"+String(m_flow_small));
end if;
if portFlowDirection_3==Modelica.Fluid.Types.PortFlowDirection.Entering then
assert(port_3.m_flow> -m_flow_small,
"In " + getInstanceName() + ":
Flow is leaving port_3 despite portFlowDirection_3=PortFlowDirection.Entering, since m_flow=" +
String(port_3.m_flow) + "<-"+String(m_flow_small));
end if;
if portFlowDirection_3==Modelica.Fluid.Types.PortFlowDirection.Leaving then
assert(port_3.m_flow< m_flow_small,
"In " + getInstanceName() + ":
Flow is entering port_3 despite portFlowDirection_3=PortFlowDirection.Leaving, since m_flow=" +
String(port_3.m_flow) + ">"+String(m_flow_small));
end if;
end if;
if portFlowDirection_1==Modelica.Fluid.Types.PortFlowDirection.Leaving then
if not have_controlVolume then
connect(res1.port_a, port_internal);
else
connect(res1.port_a, vol.ports[1]);
end if;
connect(port_1, res1.port_b);
else
if not have_controlVolume then
connect(res1.port_b, port_internal);
else
connect(res1.port_b, vol.ports[1]);
end if;
connect(port_1, res1.port_a);
end if;
if portFlowDirection_2==Modelica.Fluid.Types.PortFlowDirection.Leaving then
if not have_controlVolume then
connect(res2.port_a, port_internal);
else
connect(res2.port_a, vol.ports[2]);
end if;
connect(port_2, res2.port_b);
else
if not have_controlVolume then
connect(res2.port_b, port_internal);
else
connect(res2.port_b, vol.ports[2]);
end if;
connect(port_2, res2.port_a);
end if;
if portFlowDirection_3==Modelica.Fluid.Types.PortFlowDirection.Leaving then
if not have_controlVolume then
connect(res3.port_a, port_internal);
else
connect(res3.port_a, vol.ports[3]);
end if;
connect(port_3, res3.port_b);
else
if not have_controlVolume then
connect(res3.port_b, port_internal);
else
connect(res3.port_b, vol.ports[3]);
end if;
connect(port_3, res3.port_a);
end if;
end PartialThreeWayResistance;