Buildings.Fluid.Actuators.Dampers
Package with air damper models
Information
This package contains component models for air dampers. For motor models, see Buildings.Fluid.Actuators.Motors.Extends from Modelica.Icons.VariantsPackage (Icon for package containing variants).
Package Content
| Name | Description |
|---|---|
 Exponential
|
Air damper with exponential opening characteristics |
 MixingBox
|
Outside air mixing box with interlocked air dampers |
 MixingBoxMinimumFlow
|
Outside air mixing box with parallel damper for minimum outside air flow rate |
 PressureIndependent
|
Model for an air damper whose mass flow is proportional to the input signal |
 Examples
|
Collection of models that illustrate model use and test models |
| Validation
|
Collection of validation models |
Buildings.Fluid.Actuators.Dampers.Exponential
Air damper with exponential opening characteristics
Information
Model of two flow resistances in series:
- one resistance has a fixed flow coefficient;
- the other resistance represents a damper whose flow coefficient is an exponential function of the opening angle.
The lumped flow coefficient k(y) (function of the fractional opening y) is used to compute the mass flow rate versus pressure drop relation as:
ṁ = sign(Δp) k(y) √ Δp
with regularization near the origin.
For a description of the damper opening characteristics and typical parameter values, see the partial model Buildings.Fluid.Actuators.BaseClasses.PartialDamperExponential.
Extends from Buildings.Fluid.Actuators.BaseClasses.PartialDamperExponential (Partial model for air dampers with exponential opening characteristics).
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| replaceable package Medium | PartialMedium | Medium in the component | |
| Boolean | use_deltaM | true | Set to true to use deltaM for turbulent transition, else ReC is used |
| Real | deltaM | 0.3 | Fraction of nominal mass flow rate where transition to turbulent occurs |
| Boolean | roundDuct | false | Set to true for round duct, false for square cross section |
| Real | ReC | 4000 | Reynolds number where transition to turbulent starts |
| Nominal condition | |||
| MassFlowRate | m_flow_nominal | Nominal mass flow rate [kg/s] | |
| PressureDifference | dpDamper_nominal | Pressure drop of fully open damper at nominal mass flow rate [Pa] | |
| PressureDifference | dpFixed_nominal | 0 | Pressure drop of duct and resistances other than the damper in series, at nominal mass flow rate [Pa] |
| Assumptions | |||
| Boolean | allowFlowReversal | true | = false to simplify equations, assuming, but not enforcing, no flow reversal |
| Advanced | |||
| Diagnostics | |||
| Boolean | show_T | false | = true, if actual temperature at port is computed |
| 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 |
| Boolean | use_constant_density | true | Set to true to use constant density for flow friction |
| Dynamics | |||
| Filtered opening | |||
| Boolean | use_inputFilter | true | = true, if opening is filtered with a 2nd order CriticalDamping filter |
| Time | riseTime | 120 | Rise time of the filter (time to reach 99.6 % of an opening step) [s] |
| Integer | order | 2 | Order of filter |
| Init | init | Modelica.Blocks.Types.Init.I... | Type of initialization (no init/steady state/initial state/initial output) |
| Real | y_start | 1 | Initial value of output |
| Damper coefficients | |||
| Real | a | -1.51 | Coefficient a for damper characteristics [1] |
| Real | b | 0.105*90 | Coefficient b for damper characteristics [1] |
| Real | yL | 15/90 | Lower value for damper curve [1] |
| Real | yU | 55/90 | Upper value for damper curve [1] |
| Real | k1 | 0.45 | Loss coefficient for y=1 (pressure drop divided by dynamic pressure) [1] |
| Real | l | 0.0001 | Damper leakage, ratio of flow coefficients k(y=0)/k(y=1) |
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) |
| input RealInput | y | Actuator position (0: closed, 1: open) |
| output RealOutput | y_actual | Actual actuator position |
Modelica definition
model Exponential
"Air damper with exponential opening characteristics"
extends Buildings.Fluid.Actuators.BaseClasses.PartialDamperExponential;
equation
// Pressure drop calculation
if linearized then
m_flow*m_flow_nominal_pos = k^2*dp;
else
if homotopyInitialization then
if from_dp then
m_flow=homotopy(
actual=Buildings.Fluid.BaseClasses.FlowModels.basicFlowFunction_dp(
dp=dp, k=k,
m_flow_turbulent=m_flow_turbulent),
simplified= m_flow_nominal_pos*dp/max(Modelica.Constants.eps, dp_nominal_pos));
else
dp=homotopy(
actual=Buildings.Fluid.BaseClasses.FlowModels.basicFlowFunction_m_flow(
m_flow=m_flow, k=k,
m_flow_turbulent=m_flow_turbulent),
simplified=dp_nominal_pos*m_flow/m_flow_nominal_pos);
end if; // from_dp
else // do not use homotopy
if from_dp then
m_flow=Buildings.Fluid.BaseClasses.FlowModels.basicFlowFunction_dp(
dp=dp, k=k, m_flow_turbulent=m_flow_turbulent);
else
dp=Buildings.Fluid.BaseClasses.FlowModels.basicFlowFunction_m_flow(
m_flow=m_flow, k=k, m_flow_turbulent=m_flow_turbulent);
end if; // from_dp
end if; // homotopyInitialization
end if; // linearized
end Exponential;
Buildings.Fluid.Actuators.Dampers.MixingBox
Outside air mixing box with interlocked air dampers
Information
Model of an outside air mixing box with exponential dampers.
Set y=0 to close the outside air and exhaust air dampers.
See
Buildings.Fluid.Actuators.Dampers.Exponential
for the description of the exponential damper model.
Extends from Buildings.Fluid.Actuators.BaseClasses.ActuatorSignal (Partial model that implements the filtered opening for valves and dampers).
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| replaceable package Medium | Modelica.Media.Interfaces.Pa... | Medium in the component | |
| Boolean | use_deltaM | true | Set to true to use deltaM for turbulent transition, else ReC is used |
| Real | deltaM | 0.3 | Fraction of nominal mass flow rate where transition to turbulent occurs |
| Boolean | roundDuct | false | Set to true for round duct, false for square cross section |
| Real | ReC | 4000 | Reynolds number where transition to turbulent starts |
| Nominal condition | |||
| MassFlowRate | mOut_flow_nominal | Mass flow rate outside air damper [kg/s] | |
| PressureDifference | dpDamOut_nominal | Pressure drop of damper in outside air leg [Pa] | |
| PressureDifference | dpFixOut_nominal | 0 | Pressure drop of duct and other resistances in outside air leg [Pa] |
| MassFlowRate | mRec_flow_nominal | Mass flow rate recirculation air damper [kg/s] | |
| PressureDifference | dpDamRec_nominal | Pressure drop of damper in recirculation air leg [Pa] | |
| PressureDifference | dpFixRec_nominal | 0 | Pressure drop of duct and other resistances in recirculation air leg [Pa] |
| MassFlowRate | mExh_flow_nominal | Mass flow rate exhaust air damper [kg/s] | |
| PressureDifference | dpDamExh_nominal | Pressure drop of damper in exhaust air leg [Pa] | |
| PressureDifference | dpFixExh_nominal | 0 | Pressure drop of duct and other resistances in exhaust air leg [Pa] |
| Dynamics | |||
| Filtered opening | |||
| Boolean | use_inputFilter | true | = true, if opening is filtered with a 2nd order CriticalDamping filter |
| Time | riseTime | 120 | Rise time of the filter (time to reach 99.6 % of an opening step) [s] |
| Integer | order | 2 | Order of filter |
| Init | init | Modelica.Blocks.Types.Init.I... | Type of initialization (no init/steady state/initial state/initial output) |
| Real | y_start | 1 | Initial value of output |
| Assumptions | |||
| Boolean | allowFlowReversal | true | = false to simplify equations, assuming, but not enforcing, no flow reversal |
| Advanced | |||
| Boolean | from_dp | true | = 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 |
| Boolean | use_constant_density | true | Set to true to use constant density for flow friction |
| Damper coefficients | |||
| Real | a | -1.51 | Coefficient a for damper characteristics |
| Real | b | 0.105*90 | Coefficient b for damper characteristics |
| Real | yL | 15/90 | Lower value for damper curve |
| Real | yU | 55/90 | Upper value for damper curve |
| Real | k1 | 0.45 | Flow coefficient for y=1, k1 = pressure drop divided by dynamic pressure |
| Real | l | 0.0001 | Damper leakage, ratio of flow coefficients k(y=0)/k(y=1) |
Connectors
| Type | Name | Description |
|---|---|---|
| input RealInput | y | Actuator position (0: closed, 1: open) |
| output RealOutput | y_actual | Actual actuator position |
| replaceable package Medium | Medium in the component | |
| FluidPort_a | port_Out | Fluid connector a (positive design flow direction is from port_a to port_b) |
| FluidPort_b | port_Exh | Fluid connector b (positive design flow direction is from port_a to port_b) |
| FluidPort_a | port_Ret | Fluid connector a (positive design flow direction is from port_a to port_b) |
| FluidPort_b | port_Sup | Fluid connector b (positive design flow direction is from port_a to port_b) |
Modelica definition
model MixingBox "Outside air mixing box with interlocked air dampers"
extends Buildings.Fluid.Actuators.BaseClasses.ActuatorSignal;
replaceable package Medium =
Modelica.Media.Interfaces.PartialMedium "Medium in the component";
import Modelica.Constants;
parameter Boolean allowFlowReversal = true
"= false to simplify equations, assuming, but not enforcing, no flow reversal";
parameter Boolean use_deltaM = true
"Set to true to use deltaM for turbulent transition, else ReC is used";
parameter Real deltaM = 0.3
"Fraction of nominal mass flow rate where transition to turbulent occurs";
parameter Boolean roundDuct = false
"Set to true for round duct, false for square cross section";
parameter Real ReC=4000
"Reynolds number where transition to turbulent starts";
parameter Modelica.SIunits.MassFlowRate mOut_flow_nominal
"Mass flow rate outside air damper";
parameter Modelica.SIunits.PressureDifference dpDamOut_nominal(min=0, displayUnit="Pa")
"Pressure drop of damper in outside air leg";
parameter Modelica.SIunits.PressureDifference dpFixOut_nominal(min=0, displayUnit="Pa")=0
"Pressure drop of duct and other resistances in outside air leg";
parameter Modelica.SIunits.MassFlowRate mRec_flow_nominal
"Mass flow rate recirculation air damper";
parameter Modelica.SIunits.PressureDifference dpDamRec_nominal(min=0, displayUnit="Pa")
"Pressure drop of damper in recirculation air leg";
parameter Modelica.SIunits.PressureDifference dpFixRec_nominal(min=0, displayUnit="Pa")=0
"Pressure drop of duct and other resistances in recirculation air leg";
parameter Modelica.SIunits.MassFlowRate mExh_flow_nominal
"Mass flow rate exhaust air damper";
parameter Modelica.SIunits.PressureDifference dpDamExh_nominal(min=0, displayUnit="Pa")
"Pressure drop of damper in exhaust air leg";
parameter Modelica.SIunits.PressureDifference dpFixExh_nominal(min=0, displayUnit="Pa")=0
"Pressure drop of duct and other resistances in exhaust air leg";
parameter Boolean from_dp=true
"= true, use m_flow = f(dp) else dp = f(m_flow)";
parameter Boolean linearized=false
"= true, use linear relation between m_flow and dp for any flow rate";
parameter Boolean use_constant_density=true
"Set to true to use constant density for flow friction";
parameter Real a=-1.51 "Coefficient a for damper characteristics";
parameter Real b=0.105*90 "Coefficient b for damper characteristics";
parameter Real yL=15/90 "Lower value for damper curve";
parameter Real yU=55/90 "Upper value for damper curve";
parameter Real k1=0.45
"Flow coefficient for y=1, k1 = pressure drop divided by dynamic pressure";
parameter Real l(min=1e-10, max=1) = 0.0001
"Damper leakage, ratio of flow coefficients k(y=0)/k(y=1)";
Modelica.Fluid.Interfaces.FluidPort_a port_Out(redeclare package Medium =
Medium, m_flow(start=0, min=if allowFlowReversal then -Constants.inf else
0))
"Fluid connector a (positive design flow direction is from port_a to port_b)";
Modelica.Fluid.Interfaces.FluidPort_b port_Exh(redeclare package Medium =
Medium, m_flow(start=0, max=if allowFlowReversal then +Constants.inf else
0))
"Fluid connector b (positive design flow direction is from port_a to port_b)";
Modelica.Fluid.Interfaces.FluidPort_a port_Ret(redeclare package Medium =
Medium, m_flow(start=0, min=if allowFlowReversal then -Constants.inf else
0))
"Fluid connector a (positive design flow direction is from port_a to port_b)";
Modelica.Fluid.Interfaces.FluidPort_b port_Sup(redeclare package Medium =
Medium, m_flow(start=0, max=if allowFlowReversal then +Constants.inf else
0))
"Fluid connector b (positive design flow direction is from port_a to port_b)";
Buildings.Fluid.Actuators.Dampers.Exponential damOA(
redeclare final package Medium = Medium,
final m_flow_nominal=mOut_flow_nominal,
final dpDamper_nominal=dpDamOut_nominal,
final dpFixed_nominal=dpFixOut_nominal,
final from_dp=from_dp,
final linearized=linearized,
final use_deltaM=use_deltaM,
final deltaM=deltaM,
final roundDuct=roundDuct,
final ReC=ReC,
final a=a,
final b=b,
final yL=yL,
final yU=yU,
final l=l,
final k1=k1,
final use_constant_density=use_constant_density,
final allowFlowReversal=allowFlowReversal,
final use_inputFilter=false)
"Outdoor air damper";
Buildings.Fluid.Actuators.Dampers.Exponential damExh(
redeclare final package Medium = Medium,
final m_flow_nominal=mExh_flow_nominal,
final dpDamper_nominal=dpDamExh_nominal,
final dpFixed_nominal=dpFixExh_nominal,
final from_dp=from_dp,
final linearized=linearized,
final use_deltaM=use_deltaM,
final deltaM=deltaM,
final roundDuct=roundDuct,
final ReC=ReC,
final a=a,
final b=b,
final yL=yL,
final yU=yU,
final l=l,
final k1=k1,
final use_constant_density=use_constant_density,
final allowFlowReversal=allowFlowReversal,
final use_inputFilter=false)
"Exhaust air damper";
Buildings.Fluid.Actuators.Dampers.Exponential damRec(
redeclare final package Medium = Medium,
final m_flow_nominal=mRec_flow_nominal,
final dpDamper_nominal=dpDamRec_nominal,
final dpFixed_nominal=dpFixRec_nominal,
final from_dp=from_dp,
final linearized=linearized,
final use_deltaM=use_deltaM,
final deltaM=deltaM,
final roundDuct=roundDuct,
final ReC=ReC,
final a=a,
final b=b,
final yL=yL,
final yU=yU,
final l=l,
final k1=k1,
final use_constant_density=use_constant_density,
final allowFlowReversal=allowFlowReversal,
final use_inputFilter=false)
"Recirculation air damper";
Modelica.Blocks.Sources.Constant uni(k=1)
"Unity signal";
Modelica.Blocks.Math.Add add(k2=-1)
"Adder";
protected
parameter Medium.Density rho_default=Medium.density(sta_default)
"Density, used to compute fluid volume";
parameter Medium.ThermodynamicState sta_default=
Medium.setState_pTX(T=Medium.T_default, p=Medium.p_default, X=Medium.X_default)
"Default medium state";
equation
connect(uni.y, add.u1);
connect(add.y, damRec.y);
connect(damOA.port_a, port_Out);
connect(damExh.port_b, port_Exh);
connect(port_Sup, damOA.port_b);
connect(damRec.port_b, port_Sup);
connect(port_Ret, damExh.port_a);
connect(port_Ret, damRec.port_a);
connect(y_actual, add.u2);
connect(y_actual, damOA.y);
connect(y_actual, damExh.y);
end MixingBox;
Buildings.Fluid.Actuators.Dampers.MixingBoxMinimumFlow
Outside air mixing box with parallel damper for minimum outside air flow rate
Information
Model of an outside air mixing box with air dampers and a flow path for the minimum outside air flow rate.
If dp_nominalIncludesDamper=true, then the parameter dp_nominal
is equal to the pressure drop of the damper plus the fixed flow resistance at the nominal
flow rate.
If dp_nominalIncludesDamper=false, then dp_nominal
does not include the flow resistance of the air damper.
Extends from Buildings.Fluid.Actuators.Dampers.MixingBox (Outside air mixing box with interlocked air dampers).
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| replaceable package Medium | PartialMedium | Medium in the component | |
| Boolean | use_deltaM | true | Set to true to use deltaM for turbulent transition, else ReC is used |
| Real | deltaM | 0.3 | Fraction of nominal mass flow rate where transition to turbulent occurs |
| Boolean | roundDuct | false | Set to true for round duct, false for square cross section |
| Real | ReC | 4000 | Reynolds number where transition to turbulent starts |
| Nominal condition | |||
| MassFlowRate | mOut_flow_nominal | Mass flow rate outside air damper [kg/s] | |
| PressureDifference | dpDamOut_nominal | Pressure drop of damper in outside air leg [Pa] | |
| PressureDifference | dpFixOut_nominal | 0 | Pressure drop of duct and other resistances in outside air leg [Pa] |
| MassFlowRate | mRec_flow_nominal | Mass flow rate recirculation air damper [kg/s] | |
| PressureDifference | dpDamRec_nominal | Pressure drop of damper in recirculation air leg [Pa] | |
| PressureDifference | dpFixRec_nominal | 0 | Pressure drop of duct and other resistances in recirculation air leg [Pa] |
| MassFlowRate | mExh_flow_nominal | Mass flow rate exhaust air damper [kg/s] | |
| PressureDifference | dpDamExh_nominal | Pressure drop of damper in exhaust air leg [Pa] | |
| PressureDifference | dpFixExh_nominal | 0 | Pressure drop of duct and other resistances in exhaust air leg [Pa] |
| MassFlowRate | mOutMin_flow_nominal | Mass flow rate minimum outside air damper [kg/s] | |
| PressureDifference | dpDamOutMin_nominal | Pressure drop of damper in minimum outside air leg [Pa] | |
| PressureDifference | dpFixOutMin_nominal | 0 | Pressure drop of duct and other resistances in minimum outside air leg [Pa] |
| Dynamics | |||
| Filtered opening | |||
| Boolean | use_inputFilter | true | = true, if opening is filtered with a 2nd order CriticalDamping filter |
| Time | riseTime | 120 | Rise time of the filter (time to reach 99.6 % of an opening step) [s] |
| Integer | order | 2 | Order of filter |
| Init | init | Modelica.Blocks.Types.Init.I... | Type of initialization (no init/steady state/initial state/initial output) |
| Real | y_start | 1 | Initial value of output |
| Real | yOutMin_start | y_start | Initial value of signal for minimum outside air damper |
| Assumptions | |||
| Boolean | allowFlowReversal | true | = false to simplify equations, assuming, but not enforcing, no flow reversal |
| Advanced | |||
| Boolean | from_dp | true | = 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 |
| Boolean | use_constant_density | true | Set to true to use constant density for flow friction |
| Damper coefficients | |||
| Real | a | -1.51 | Coefficient a for damper characteristics |
| Real | b | 0.105*90 | Coefficient b for damper characteristics |
| Real | yL | 15/90 | Lower value for damper curve |
| Real | yU | 55/90 | Upper value for damper curve |
| Real | k1 | 0.45 | Flow coefficient for y=1, k1 = pressure drop divided by dynamic pressure |
| Real | l | 0.0001 | Damper leakage, ratio of flow coefficients k(y=0)/k(y=1) |
Connectors
| Type | Name | Description |
|---|---|---|
| input RealInput | y | Actuator position (0: closed, 1: open) |
| output RealOutput | y_actual | Actual actuator position |
| FluidPort_a | port_Out | Fluid connector a (positive design flow direction is from port_a to port_b) |
| FluidPort_b | port_Exh | Fluid connector b (positive design flow direction is from port_a to port_b) |
| FluidPort_a | port_Ret | Fluid connector a (positive design flow direction is from port_a to port_b) |
| FluidPort_b | port_Sup | Fluid connector b (positive design flow direction is from port_a to port_b) |
| FluidPort_a | port_OutMin | Fluid connector a (positive design flow direction is from port_a to port_b) |
| input RealInput | yOutMin | Damper position minimum outside air (0: closed, 1: open) |
| output RealOutput | yOutMin_actual | Actual valve position |
Modelica definition
model MixingBoxMinimumFlow
"Outside air mixing box with parallel damper for minimum outside air flow rate"
extends Buildings.Fluid.Actuators.Dampers.MixingBox;
import Modelica.Constants;
parameter Modelica.SIunits.MassFlowRate mOutMin_flow_nominal
"Mass flow rate minimum outside air damper";
parameter Modelica.SIunits.PressureDifference dpDamOutMin_nominal(
min=0, displayUnit="Pa")
"Pressure drop of damper in minimum outside air leg";
parameter Modelica.SIunits.PressureDifference dpFixOutMin_nominal(
min=0, displayUnit="Pa") = 0
"Pressure drop of duct and other resistances in minimum outside air leg";
parameter Real yOutMin_start=y_start
"Initial value of signal for minimum outside air damper";
Modelica.Fluid.Interfaces.FluidPort_a port_OutMin(redeclare package Medium =
Medium, m_flow(start=0, min=if allowFlowReversal then -Constants.inf else
0))
"Fluid connector a (positive design flow direction is from port_a to port_b)";
Modelica.Blocks.Interfaces.RealInput yOutMin
"Damper position minimum outside air (0: closed, 1: open)";
Modelica.Blocks.Interfaces.RealOutput yOutMin_actual "Actual valve position";
Buildings.Fluid.Actuators.Dampers.Exponential damOAMin(
redeclare final package Medium = Medium,
final from_dp=from_dp,
final linearized=linearized,
final use_deltaM=use_deltaM,
final deltaM=deltaM,
final roundDuct=roundDuct,
final ReC=ReC,
final a=a,
final b=b,
final yL=yL,
final yU=yU,
final k1=k1,
final l=l,
final use_constant_density=use_constant_density,
final allowFlowReversal=allowFlowReversal,
final m_flow_nominal=mOutMin_flow_nominal,
final dpDamper_nominal=dpDamOutMin_nominal,
final dpFixed_nominal=dpFixOutMin_nominal,
final use_inputFilter=false) "Damper for minimum outside air intake";
protected
Modelica.Blocks.Interfaces.RealOutput yOutMin_filtered if use_inputFilter
"Filtered damper position in the range 0..1";
Modelica.Blocks.Continuous.Filter filterOutMin(
order=2,
f_cut=5/(2*Modelica.Constants.pi*riseTime),
final init=init,
final y_start=yOutMin_start,
final analogFilter=Modelica.Blocks.Types.AnalogFilter.CriticalDamping,
final filterType=Modelica.Blocks.Types.FilterType.LowPass,
x(each stateSelect=StateSelect.always))
if use_inputFilter
"Second order filter to approximate valve opening time, and to improve numerics";
equation
connect(filterOutMin.y, yOutMin_filtered);
if use_inputFilter then
connect(yOutMin, filterOutMin.u);
connect(filterOutMin.y, yOutMin_actual);
else
connect(yOutMin, yOutMin_actual);
end if;
//////
connect(port_OutMin, damOAMin.port_a);
connect(damOAMin.port_b, port_Sup);
connect(yOutMin_actual, damOAMin.y);
end MixingBoxMinimumFlow;
Buildings.Fluid.Actuators.Dampers.PressureIndependent
Model for an air damper whose mass flow is proportional to the input signal
Information
Model for an air damper whose airflow is proportional to the input signal, assuming
that at y = 1, m_flow = m_flow_nominal. This is unless the pressure difference
dp is too low,
in which case a kDam = m_flow_nominal/sqrt(dp_nominal) characteristic is used.
The model is similar to Buildings.Fluid.Actuators.Valves.TwoWayPressureIndependent, except for adaptations for damper parameters. Please see that documentation for more information.
Computation of the damper opening
The fractional opening of the damper is computed by
- inverting the quadratic flow function to compute the flow coefficient from the flow rate and the pressure drop values (under the assumption of a turbulent flow regime);
- inverting the exponential characteristics to compute the fractional opening from the loss coefficient value (directly derived from the flow coefficient).
The quadratic interpolation used outside the exponential domain in the function Buildings.Fluid.Actuators.BaseClasses.exponentialDamper yields a local extremum. Therefore, the formal inversion of the function is not possible. A cubic spline is used instead to fit the inverse of the damper characteristics. The central domain of the characteritics having a monotonous exponential profile, its inverse can be properly approximated with three equidistant support points. However, the quadratic functions used outside of the exponential domain can have various profiles depending on the damper coefficients. Therefore, five linearly distributed support points are used on each side domain to ensure a good fit of the inverse.
Note that below a threshold value of the input control signal (fixed at 0.02), the fractional opening is forced to zero and no more related to the actual flow coefficient of the damper. This avoids steep transients of the computed opening while transitioning from reverse flow. This is to be considered as a modeling workaround (avoiding the introduction of an additional state variable) to prevent control chattering during shut off operation where the pressure difference at the damper boundaries can vary between slightly positive and negative values due to outdoor pressure variations.
Extends from Buildings.Fluid.Actuators.BaseClasses.PartialDamperExponential (Partial model for air dampers with exponential opening characteristics).
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| replaceable package Medium | PartialMedium | Medium in the component | |
| Boolean | use_deltaM | true | Set to true to use deltaM for turbulent transition, else ReC is used |
| Real | deltaM | 0.3 | Fraction of nominal mass flow rate where transition to turbulent occurs |
| Boolean | roundDuct | false | Set to true for round duct, false for square cross section |
| Real | ReC | 4000 | Reynolds number where transition to turbulent starts |
| Nominal condition | |||
| MassFlowRate | m_flow_nominal | Nominal mass flow rate [kg/s] | |
| PressureDifference | dpDamper_nominal | Pressure drop of fully open damper at nominal mass flow rate [Pa] | |
| PressureDifference | dpFixed_nominal | 0 | Pressure drop of duct and resistances other than the damper in series, at nominal mass flow rate [Pa] |
| Assumptions | |||
| Boolean | allowFlowReversal | true | = false to simplify equations, assuming, but not enforcing, no flow reversal |
| Advanced | |||
| Diagnostics | |||
| Boolean | show_T | false | = true, if actual temperature at port is computed |
| Boolean | from_dp | true | = 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 |
| Boolean | use_constant_density | true | Set to true to use constant density for flow friction |
| Real | l2 | 0.01 | Gain for mass flow increase if pressure is above nominal pressure [1] |
| Real | deltax | 0.02 | Transition interval for flow rate [1] |
| Dynamics | |||
| Filtered opening | |||
| Boolean | use_inputFilter | true | = true, if opening is filtered with a 2nd order CriticalDamping filter |
| Time | riseTime | 120 | Rise time of the filter (time to reach 99.6 % of an opening step) [s] |
| Integer | order | 2 | Order of filter |
| Init | init | Modelica.Blocks.Types.Init.I... | Type of initialization (no init/steady state/initial state/initial output) |
| Real | y_start | 1 | Initial value of output |
| Damper coefficients | |||
| Real | a | -1.51 | Coefficient a for damper characteristics [1] |
| Real | b | 0.105*90 | Coefficient b for damper characteristics [1] |
| Real | yL | 15/90 | Lower value for damper curve [1] |
| Real | yU | 55/90 | Upper value for damper curve [1] |
| Real | k1 | 0.45 | Loss coefficient for y=1 (pressure drop divided by dynamic pressure) [1] |
| Real | l | 0.0001 | Damper leakage, ratio of flow coefficients k(y=0)/k(y=1) |
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) |
| input RealInput | y | Actuator position (0: closed, 1: open) |
| output RealOutput | y_actual | Actual actuator position |
Modelica definition
model PressureIndependent
"Model for an air damper whose mass flow is proportional to the input signal"
extends Buildings.Fluid.Actuators.BaseClasses.PartialDamperExponential(
final linearized=false,
final casePreInd=true,
from_dp=true);
input Real phi = l + y_internal*(1 - l)
"Ratio actual to nominal mass flow rate of damper, phi=kDam(y)/kDam(y=1)";
parameter Real l2(unit="1", min=1e-10) = 0.01
"Gain for mass flow increase if pressure is above nominal pressure";
parameter Real deltax(unit="1", min=1E-5) = 0.02 "Transition interval for flow rate";
protected
Real kSquInv
"Square inverse of flow coefficient (damper plus fixed resistance)";
Real kDamSquInv
"Square inverse of flow coefficient (damper only)";
parameter Real y_min = 2E-2
"Minimum value of control signal before zeroing of the opening";
parameter Integer sizeSupSplBnd = 5
"Number of support points on each quadratic domain for spline interpolation";
parameter Integer sizeSupSpl = 2 * sizeSupSplBnd + 3
"Total number of support points for spline interpolation";
parameter Real[sizeSupSpl] ySupSpl_raw = cat(
1,
linspace(1, yU, sizeSupSplBnd),
{yU-1/3*(yU-yL), (yU+yL)/2, yU-2/3*(yU-yL)},
linspace(yL, 0, sizeSupSplBnd))
"y values of unsorted support points for spline interpolation";
parameter Real[sizeSupSpl] kSupSpl_raw = Buildings.Fluid.Actuators.BaseClasses.exponentialDamper(
y=ySupSpl_raw, a=a, b=b, cL=cL, cU=cU, yL=yL, yU=yU) .^ 2
"k values of unsorted support points for spline interpolation";
parameter Real[sizeSupSpl] ySupSpl(each fixed=false)
"y values of sorted support points for spline interpolation";
parameter Real[sizeSupSpl] kSupSpl(each fixed=false)
"k values of sorted support points for spline interpolation";
parameter Integer[sizeSupSpl] idx_sorted(each fixed=false)
"Indices of sorted support points";
parameter Real[sizeSupSpl] invSplDer(each fixed=false)
"Derivatives at support points for spline interpolation";
parameter Real coeff1 = l2/dpDamper_nominal*m_flow_nominal
"Parameter for avoiding unnecessary computations";
parameter Real coeff2 = 1/coeff1
"Parameter for avoiding unnecessary computations";
constant Real y2dd = 0
"Second derivative at second support point";
Modelica.SIunits.MassFlowRate m_flow_set
"Requested mass flow rate";
Modelica.SIunits.PressureDifference dp_min(displayUnit="Pa")
"Minimum pressure difference required for delivering requested mass flow rate";
Modelica.SIunits.PressureDifference dp_x, dp_x1, dp_x2, dp_y2, dp_y1
"Support points for interpolation flow functions";
Modelica.SIunits.MassFlowRate m_flow_x, m_flow_x1, m_flow_x2, m_flow_y2, m_flow_y1
"Support points for interpolation flow functions";
Modelica.SIunits.MassFlowRate m_flow_smooth
"Smooth interpolation result between two flow regimes";
Modelica.SIunits.PressureDifference dp_smooth
"Smooth interpolation result between two flow regimes";
Real y_actual_smooth(final unit="1")
"Fractional opening computed based on m_flow_smooth and dp";
function basicFlowFunction_dp_m_flow
"Inverse of flow function that computes that computes the square inverse of flow coefficient"
extends Modelica.Icons.Function;
input Modelica.SIunits.MassFlowRate m_flow
"Mass flow rate in design flow direction";
input Modelica.SIunits.PressureDifference dp
"Pressure difference between port_a and port_b (= port_a.p - port_b.p)";
input Modelica.SIunits.MassFlowRate m_flow_small
"Minimum value of mass flow rate guarding against k=(0)/sqrt(dp)";
input Modelica.SIunits.PressureDifference dp_small
"Minimum value of pressure drop guarding against k=m_flow/(0)";
output Real kSquInv
"Square inverse of flow coefficient";
protected
Modelica.SIunits.PressureDifference dpPos=
Buildings.Utilities.Math.Functions.smoothMax(dp, -dp, dp_small)
"Regularized absolute value of pressure drop";
Real mSqu_flow = Buildings.Utilities.Math.Functions.smoothMax(
m_flow^2, m_flow_small^2, m_flow_small^2)
"Regularized square value of mass flow rate";
algorithm
kSquInv := dpPos / mSqu_flow;
end basicFlowFunction_dp_m_flow;
function exponentialDamper_inv
"Inverse function of the exponential damper characteristics"
extends Modelica.Icons.Function;
input Real kTheta "Loss coefficient";
input Real[:] kSupSpl "k values of support points";
input Real[:] ySupSpl "y values of support points";
input Real[:] invSplDer "Derivatives at support points";
output Real y "Fractional opening";
protected
parameter Integer sizeSupSpl = size(kSupSpl, 1) "Number of spline support points";
Integer i "Integer to select data interval";
algorithm
i := 1;
for j in 2:sizeSupSpl loop
if kTheta <= kSupSpl[j] then
i := j;
break;
end if;
end for;
y := Buildings.Utilities.Math.Functions.smoothLimit(
Buildings.Utilities.Math.Functions.cubicHermiteLinearExtrapolation(
x=kTheta,
x1=kSupSpl[i - 1],
x2=kSupSpl[i],
y1=ySupSpl[i - 1],
y2=ySupSpl[i],
y1d=invSplDer[i - 1],
y2d=invSplDer[i]),
0,
1,
1E-3);
end exponentialDamper_inv;
initial equation
(kSupSpl, idx_sorted) = Modelica.Math.Vectors.sort(kSupSpl_raw, ascending=true);
ySupSpl = ySupSpl_raw[idx_sorted];
invSplDer = Buildings.Utilities.Math.Functions.splineDerivatives(x=kSupSpl, y=ySupSpl);
equation
// From TwoWayPressureIndependent valve model
m_flow_set = m_flow_nominal*phi;
dp_min = Buildings.Fluid.BaseClasses.FlowModels.basicFlowFunction_m_flow(
m_flow=m_flow_set,
k=kTotMax,
m_flow_turbulent=m_flow_turbulent);
if from_dp then
m_flow_x=0;
m_flow_x1=0;
m_flow_x2=0;
dp_y1=0;
dp_y2=0;
dp_smooth=0;
dp_x = dp-dp_min;
dp_x1 = -dp_x2;
dp_x2 = deltax*dp_min;
// min function ensures that m_flow_y1 does not increase further for dp_x > dp_x1
m_flow_y1 = Buildings.Fluid.BaseClasses.FlowModels.basicFlowFunction_dp(
dp=min(dp, dp_min+dp_x1),
k=kTotMax,
m_flow_turbulent=m_flow_turbulent);
// max function ensures that m_flow_y2 does not decrease further for dp_x < dp_x2
m_flow_y2 = m_flow_set + coeff1*max(dp_x,dp_x2);
m_flow_smooth = noEvent(smooth(2,
if dp_x <= dp_x1
then m_flow_y1
elseif dp_x >=dp_x2
then m_flow_y2
else Buildings.Utilities.Math.Functions.quinticHermite(
x=dp_x,
x1=dp_x1,
x2=dp_x2,
y1=m_flow_y1,
y2=m_flow_y2,
y1d= Buildings.Fluid.BaseClasses.FlowModels.basicFlowFunction_dp_der(
dp=dp_min + dp_x1,
k=kTotMax,
m_flow_turbulent=m_flow_turbulent,
dp_der=1),
y2d=coeff1,
y1dd=Buildings.Fluid.BaseClasses.FlowModels.basicFlowFunction_dp_der2(
dp=dp_min + dp_x1,
k=kTotMax,
m_flow_turbulent=m_flow_turbulent,
dp_der=1,
dp_der2=0),
y2dd=y2dd)));
else
dp_x=0;
dp_x1=0;
dp_x2=0;
m_flow_y1=0;
m_flow_y2=0;
m_flow_smooth=0;
m_flow_x = m_flow-m_flow_set;
m_flow_x1 = -m_flow_x2;
m_flow_x2 = deltax*m_flow_set;
// min function ensures that dp_y1 does not increase further for m_flow_x > m_flow_x1
dp_y1 = Buildings.Fluid.BaseClasses.FlowModels.basicFlowFunction_m_flow(
m_flow=min(m_flow, m_flow_set + m_flow_x1),
k=kTotMax,
m_flow_turbulent=m_flow_turbulent);
// max function ensures that dp_y2 does not decrease further for m_flow_x < m_flow_x2
dp_y2 = dp_min + coeff2*max(m_flow_x, m_flow_x2);
dp_smooth = noEvent(smooth(2,
if m_flow_x <= m_flow_x1
then dp_y1
elseif m_flow_x >=m_flow_x2
then dp_y2
else Buildings.Utilities.Math.Functions.quinticHermite(
x=m_flow_x,
x1=m_flow_x1,
x2=m_flow_x2,
y1=dp_y1,
y2=dp_y2,
y1d=Buildings.Fluid.BaseClasses.FlowModels.basicFlowFunction_m_flow_der(
m_flow=m_flow_set + m_flow_x1,
k=kTotMax,
m_flow_turbulent=m_flow_turbulent,
m_flow_der=1),
y2d=coeff2,
y1dd=Buildings.Fluid.BaseClasses.FlowModels.basicFlowFunction_m_flow_der2(
m_flow=m_flow_set + m_flow_x1,
k=kTotMax,
m_flow_turbulent=m_flow_turbulent,
m_flow_der=1,
m_flow_der2=0),
y2dd=y2dd)));
end if;
// Computation of damper opening
kSquInv = basicFlowFunction_dp_m_flow(
m_flow=m_flow,
dp=dp,
m_flow_small=1E-3*abs(m_flow_nominal),
dp_small=1E-4*dp_nominal_pos);
kDamSquInv = if dpFixed_nominal > Modelica.Constants.eps then
kSquInv - 1 / kFixed^2 else kSquInv;
// Use of regStep might no longer be needed when the leakage flow modeling is updated.
y_actual_smooth = Buildings.Utilities.Math.Functions.regStep(
x=y_internal - y_min,
y1=exponentialDamper_inv(
kTheta=kDamSquInv*2*rho*A^2, kSupSpl=kSupSpl, ySupSpl=ySupSpl, invSplDer=invSplDer),
y2=0,
x_small=1E-3);
// Homotopy transformation
if homotopyInitialization then
if from_dp then
m_flow=homotopy(actual=m_flow_smooth,
simplified=m_flow_nominal_pos*dp/dp_nominal_pos);
else
dp=homotopy(actual=dp_smooth,
simplified=dp_nominal_pos*m_flow/m_flow_nominal_pos);
end if;
y_actual = homotopy(
actual=y_actual_smooth,
simplified=y);
else
if from_dp then
m_flow=m_flow_smooth;
else
dp=dp_smooth;
end if;
y_actual = y_actual_smooth;
end if;
end PressureIndependent;