This package contains base classes that are used to construct the models in Buildings.Fluid.Movers.
Extends from Modelica.Icons.BasesPackage (Icon for packages containing base classes).Name | Description |
---|---|
Characteristics | Functions for fan or pump characteristics |
ControlledFlowMachine | Partial model for fan or pump with ideally controlled mass flow rate or head as input signal |
PrescribedFlowMachine | Partial model for fan or pump with speed (y or Nrpm) as input signal |
PartialFlowMachine | Partial model to interface fan or pump models with the medium |
IdealSource | Base class for pressure and mass flow source with optional power input |
PowerInterface | Partial model to compute power draw and heat dissipation of fans and pumps |
FlowMachineInterface | Partial model with performance curves for fans or pumps |
This model describes a fan or pump that takes as an input the head or the mass flow rate.
Extends from Buildings.Fluid.Movers.BaseClasses.PartialFlowMachine (Partial model to interface fan or pump models with the medium), Buildings.Fluid.Movers.BaseClasses.PowerInterface (Partial model to compute power draw and heat dissipation of fans and pumps).
Type | Name | Default | Description |
---|---|---|---|
replaceable package Medium | PartialMedium | Medium in the component | |
Boolean | addPowerToMedium | true | Set to false to avoid any power (=heat and flow work) being added to medium (may give simpler equations) |
Density | rho_default | Medium.density(sta_default) | Fluid density at medium default state [kg/m3] |
Boolean | control_m_flow | = false to control head instead of m_flow | |
Nominal condition | |||
MassFlowRate | m_flow_nominal | Nominal mass flow rate [kg/s] | |
Initialization | |||
MassFlowRate | m_flow.start | 0 | Mass flow rate from port_a to port_b (m_flow > 0 is design flow direction) [kg/s] |
Pressure | dp.start | 0 | Pressure difference between port_a and port_b [Pa] |
Characteristics | |||
Boolean | use_powerCharacteristic | false | Use powerCharacteristic (vs. efficiencyCharacteristic) |
Boolean | motorCooledByFluid | true | If true, then motor heat is added to fluid stream |
efficiencyParameters | motorEfficiency | Normalized volume flow rate vs. efficiency | |
efficiencyParameters | hydraulicEfficiency | Normalized volume flow rate vs. efficiency | |
Dynamics | |||
Equations | |||
Dynamics | energyDynamics | Modelica.Fluid.Types.Dynamic... | Formulation of energy balance |
Dynamics | massDynamics | energyDynamics | Formulation of mass balance |
Boolean | dynamicBalance | true | Set to true to use a dynamic balance, which often leads to smaller systems of equations |
Nominal condition | |||
Time | tau | 1 | Time constant of fluid volume for nominal flow, used if dynamicBalance=true [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.) |
Assumptions | |||
Boolean | allowFlowReversal | system.allowFlowReversal | = true to allow flow reversal, false restricts to design direction (port_a -> port_b) |
Advanced | |||
MassFlowRate | m_flow_small | 1E-4*abs(m_flow_nominal) | Small mass flow rate for regularization of zero flow [kg/s] |
Boolean | homotopyInitialization | true | = true, use homotopy method |
Diagnostics | |||
Boolean | show_T | false | = true, if actual temperature at port is computed |
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) |
HeatPort_a | heatPort | Heat dissipation to environment |
output RealOutput | P | Electrical power consumed [W] |
model ControlledFlowMachine "Partial model for fan or pump with ideally controlled mass flow rate or head as input signal" extends Buildings.Fluid.Movers.BaseClasses.PartialFlowMachine( preSou(final control_m_flow=control_m_flow)); extends Buildings.Fluid.Movers.BaseClasses.PowerInterface( final use_powerCharacteristic = false, final rho_default = Medium.density(sta_default)); import cha = Buildings.Fluid.Movers.BaseClasses.Characteristics; // parameter Modelica.SIunits.MassFlowRate m_flow_nominal // "Nominal mass flow rate, used as flow rate if control_m_flow"; // parameter Modelica.SIunits.MassFlowRate m_flow_max = m_flow_nominal // "Maximum mass flow rate (at zero head)"; // what to control constant Boolean control_m_flow "= false to control head instead of m_flow"; Real r_V(start=1) "Ratio V_flow/V_flow_max = V_flow/V_flow(dp=0, N=N_nominal)"; protected final parameter Medium.AbsolutePressure p_a_default(displayUnit="Pa") = Medium.p_default "Nominal inlet pressure for predefined fan or pump characteristics"; parameter Medium.ThermodynamicState sta_default = Medium.setState_pTX( T=Medium.T_default, p=Medium.p_default, X=Medium.X_default[1:Medium.nXi]) "Default medium state";Modelica.Blocks.Sources.RealExpression PToMedium_flow(y=Q_flow + WFlo) if addPowerToMedium "Heat and work input into medium"; initial equation V_flow_max=m_flow_nominal/rho_default; equation r_V = VMachine_flow/V_flow_max; etaHyd = cha.efficiency(data=hydraulicEfficiency, r_V=r_V, d=hydDer); etaMot = cha.efficiency(data=motorEfficiency, r_V=r_V, d=motDer); dpMachine = -dp; VMachine_flow = -port_b.m_flow/rho_in; // To compute the electrical power, we set a lower bound for eta to avoid // a division by zero. P = WFlo / Buildings.Utilities.Math.Functions.smoothMax(x1=eta, x2=1E-5, deltaX=1E-6);connect(PToMedium_flow.y, prePow.Q_flow); end ControlledFlowMachine;
This is the base model for fans and pumps that take as
input a control signal in the form of the pump speed Nrpm
or the normalized pump speed y=Nrpm/N_nominal
.
Type | Name | Default | Description |
---|---|---|---|
Density | rho_default | Medium.density_pTX(p=Medium.... | Fluid density at medium default state [kg/m3] |
replaceable package Medium | PartialMedium | Medium in the component | |
Boolean | addPowerToMedium | true | Set to false to avoid any power (=heat and flow work) being added to medium (may give simpler equations) |
Characteristics | |||
Boolean | use_powerCharacteristic | false | Use powerCharacteristic (vs. efficiencyCharacteristic) |
Boolean | motorCooledByFluid | true | If true, then motor heat is added to fluid stream |
efficiencyParameters | motorEfficiency | Normalized volume flow rate vs. efficiency | |
efficiencyParameters | hydraulicEfficiency | Normalized volume flow rate vs. efficiency | |
AngularVelocity_rpm | N_nominal | 1500 | Nominal rotational speed for flow characteristic [1/min] |
flowParameters | pressure | Volume flow rate vs. total pressure rise | |
powerParameters | power | Volume flow rate vs. electrical power consumption | |
Initialization | |||
Real | r_V.start | 1 | Ratio V_flow/V_flow_max [1] |
MassFlowRate | m_flow.start | 0 | Mass flow rate from port_a to port_b (m_flow > 0 is design flow direction) [kg/s] |
Pressure | dp.start | 0 | Pressure difference between port_a and port_b [Pa] |
Nominal condition | |||
MassFlowRate | m_flow_nominal | max(pressure.V_flow)*rho_def... | Nominal mass flow rate [kg/s] |
Advanced | |||
Boolean | homotopyInitialization | true | = true, use homotopy method |
MassFlowRate | m_flow_small | 1E-4*abs(m_flow_nominal) | Small mass flow rate for regularization of zero flow [kg/s] |
Diagnostics | |||
Boolean | show_T | false | = true, if actual temperature at port is computed |
Dynamics | |||
Filtered speed | |||
Boolean | filteredSpeed | true | = true, if speed is filtered with a 2nd order CriticalDamping filter |
Time | riseTime | 30 | Rise time of the filter (time to reach 99.6 % of the speed) [s] |
Init | init | Modelica.Blocks.Types.Init.I... | Type of initialization (no init/steady state/initial state/initial output) |
Real | N_start | 0 | Initial value of speed |
Equations | |||
Dynamics | energyDynamics | Modelica.Fluid.Types.Dynamic... | Formulation of energy balance |
Dynamics | massDynamics | energyDynamics | Formulation of mass balance |
Boolean | dynamicBalance | true | Set to true to use a dynamic balance, which often leads to smaller systems of equations |
Nominal condition | |||
Time | tau | 1 | Time constant of fluid volume for nominal flow, used if dynamicBalance=true [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.) |
Assumptions | |||
Boolean | allowFlowReversal | system.allowFlowReversal | = true to allow flow reversal, false restricts to design direction (port_a -> port_b) |
Type | Name | Description |
---|---|---|
output RealOutput | P | Electrical power consumed [W] |
output RealOutput | N_actual | [1/min] |
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) |
HeatPort_a | heatPort | Heat dissipation to environment |
partial model PrescribedFlowMachine "Partial model for fan or pump with speed (y or Nrpm) as input signal" extends Buildings.Fluid.Movers.BaseClasses.FlowMachineInterface( V_flow_max(start=V_flow_nominal), final rho_default = Medium.density_pTX( p=Medium.p_default, T=Medium.T_default, X=Medium.X_default)); extends Buildings.Fluid.Movers.BaseClasses.PartialFlowMachine( final m_flow_nominal = max(pressure.V_flow)*rho_default, preSou(final control_m_flow=false)); // Modelsprotected Modelica.Blocks.Sources.RealExpression dpMac(y=-dpMachine) "Pressure drop of the pump or fan"; Modelica.Blocks.Sources.RealExpression PToMedium_flow(y=Q_flow + WFlo) if addPowerToMedium "Heat and work input into medium"; equation VMachine_flow = -port_b.m_flow/rho; rho = rho_in;connect(preSou.dp_in, dpMac.y); connect(PToMedium_flow.y, prePow.Q_flow); end PrescribedFlowMachine;
This is the base model for fans and pumps. It provides an interface between the equations that compute head and power consumption, and the implementation of the energy and pressure balance of the fluid.
Depending on the value of
the parameter dynamicBalance
, the fluid volume
is computed using a dynamic balance or a steady-state balance.
The parameter addPowerToMedium
determines whether
any power is added to the fluid. The default is addPowerToMedium=true
,
and hence the outlet enthalpy is higher than the inlet enthalpy if the
flow device is operating.
The setting addPowerToMedium=false
is physically incorrect
(since the flow work, the flow friction and the fan heat do not increase
the enthalpy of the medium), but this setting does in some cases lead to simpler equations
and more robust simulation, in particular if the mass flow is equal to zero.
Type | Name | Default | Description |
---|---|---|---|
replaceable package Medium | PartialMedium | Medium in the component | |
Boolean | addPowerToMedium | true | Set to false to avoid any power (=heat and flow work) being added to medium (may give simpler equations) |
Nominal condition | |||
MassFlowRate | m_flow_nominal | Nominal mass flow rate [kg/s] | |
Initialization | |||
MassFlowRate | m_flow.start | 0 | Mass flow rate from port_a to port_b (m_flow > 0 is design flow direction) [kg/s] |
Pressure | dp.start | 0 | Pressure difference between port_a and port_b [Pa] |
Dynamics | |||
Equations | |||
Dynamics | energyDynamics | Modelica.Fluid.Types.Dynamic... | Formulation of energy balance |
Dynamics | massDynamics | energyDynamics | Formulation of mass balance |
Boolean | dynamicBalance | true | Set to true to use a dynamic balance, which often leads to smaller systems of equations |
Nominal condition | |||
Time | tau | 1 | Time constant of fluid volume for nominal flow, used if dynamicBalance=true [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.) |
Assumptions | |||
Boolean | allowFlowReversal | system.allowFlowReversal | = true to allow flow reversal, false restricts to design direction (port_a -> port_b) |
Advanced | |||
MassFlowRate | m_flow_small | 1E-4*abs(m_flow_nominal) | Small mass flow rate for regularization of zero flow [kg/s] |
Boolean | homotopyInitialization | true | = true, use homotopy method |
Diagnostics | |||
Boolean | show_T | false | = true, if actual temperature at port is computed |
Type | Name | Description |
---|---|---|
HeatPort_a | heatPort | Heat dissipation to environment |
partial model PartialFlowMachine "Partial model to interface fan or pump models with the medium" extends Buildings.Fluid.Interfaces.LumpedVolumeDeclarations; import Modelica.Constants; extends Buildings.Fluid.Interfaces.PartialTwoPortInterface(show_T=false, port_a( h_outflow(start=h_outflow_start), final m_flow(min = if allowFlowReversal then -Constants.inf else 0)), port_b( h_outflow(start=h_outflow_start), p(start=p_start), final m_flow(max = if allowFlowReversal then +Constants.inf else 0)), final showDesignFlowDirection=false);Delays.DelayFirstOrder vol( redeclare package Medium = Medium, tau=tau, energyDynamics=if dynamicBalance then energyDynamics else Modelica.Fluid.Types.Dynamics.SteadyState, massDynamics=if dynamicBalance then massDynamics else Modelica.Fluid.Types.Dynamics.SteadyState, T_start=T_start, X_start=X_start, C_start=C_start, m_flow_nominal=m_flow_nominal, p_start=p_start, prescribedHeatFlowRate=true, allowFlowReversal=allowFlowReversal, nPorts=2) "Fluid volume for dynamic model"; parameter Boolean dynamicBalance = true "Set to true to use a dynamic balance, which often leads to smaller systems of equations"; parameter Boolean addPowerToMedium=true "Set to false to avoid any power (=heat and flow work) being added to medium (may give simpler equations)"; parameter Modelica.SIunits.Time tau=1 "Time constant of fluid volume for nominal flow, used if dynamicBalance=true"; // ModelsModelica.Thermal.HeatTransfer.Interfaces.HeatPort_a heatPort "Heat dissipation to environment"; protected Modelica.SIunits.Density rho_in "Density of inflowing fluid";Buildings.Fluid.Movers.BaseClasses.IdealSource preSou( redeclare package Medium = Medium, allowFlowReversal=allowFlowReversal) "Pressure source"; Buildings.HeatTransfer.Sources.PrescribedHeatFlow prePow if addPowerToMedium "Prescribed power (=heat and flow work) flow for dynamic model"; parameter Medium.ThermodynamicState sta_start=Medium.setState_pTX( T=T_start, p=p_start, X=X_start) "Medium state at start values"; parameter Modelica.SIunits.SpecificEnthalpy h_outflow_start = Medium.specificEnthalpy(sta_start) "Start value for outflowing enthalpy"; equation // For computing the density, we assume that the fan operates in the design flow direction. rho_in = Medium.density( Medium.setState_phX(port_a.p, inStream(port_a.h_outflow), inStream(port_a.Xi_outflow)));connect(prePow.port, vol.heatPort); connect(vol.heatPort, heatPort); connect(port_a, vol.ports[1]); connect(vol.ports[2], preSou.port_a); connect(preSou.port_b, port_b); end PartialFlowMachine;
Model of a fictious pipe that is used as a base class for a pressure source or to prescribe a mass flow rate.
Note that for fans and pumps with dynamic balance, both the heat and the flow work are added to the volume of air or water. This simplifies the equations compared to adding heat to the volume, and flow work to this model.
Extends from Modelica.Fluid.Interfaces.PartialTwoPortTransport (Partial element transporting fluid between two ports without storage of mass or energy).
Type | Name | Default | Description |
---|---|---|---|
replaceable package Medium | PartialMedium | Medium in the component | |
Boolean | control_m_flow | = false to control dp instead of m_flow | |
Assumptions | |||
Boolean | allowFlowReversal | system.allowFlowReversal | = true to allow flow reversal, false restricts to design direction (port_a -> port_b) |
Advanced | |||
AbsolutePressure | dp_start | 0.01*system.p_start | Guess value of dp = port_a.p - port_b.p [Pa] |
MassFlowRate | m_flow_start | system.m_flow_start | Guess value of m_flow = port_a.m_flow [kg/s] |
MassFlowRate | m_flow_small | system.m_flow_small | Small mass flow rate for regularization of zero flow [kg/s] |
Diagnostics | |||
Boolean | show_T | false | = true, if temperatures at port_a and port_b are computed |
Boolean | show_V_flow | true | = true, if volume flow rate at inflowing port is computed |
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 | m_flow_in | Prescribed mass flow rate |
input RealInput | dp_in | Prescribed outlet pressure |
model IdealSource "Base class for pressure and mass flow source with optional power input" extends Modelica.Fluid.Interfaces.PartialTwoPortTransport(show_T=false); // what to control parameter Boolean control_m_flow "= false to control dp instead of m_flow";Modelica.Blocks.Interfaces.RealInput m_flow_in if control_m_flow "Prescribed mass flow rate"; Modelica.Blocks.Interfaces.RealInput dp_in if not control_m_flow "Prescribed outlet pressure"; protected Modelica.Blocks.Interfaces.RealInput m_flow_internal "Needed to connect to conditional connector"; Modelica.Blocks.Interfaces.RealInput dp_internal "Needed to connect to conditional connector"; equation // Ideal control if control_m_flow then m_flow = m_flow_internal; dp_internal = 0; else dp = dp_internal; m_flow_internal = 0; end if; connect(dp_internal, dp_in); connect(m_flow_internal, m_flow_in); // Energy balance (no storage) port_a.h_outflow = inStream(port_b.h_outflow); port_b.h_outflow = inStream(port_a.h_outflow);end IdealSource;
This is an interface that implements the functions to compute the power draw and the heat dissipation of fans and pumps. It is used by the model Buildings.Fluid.Movers.BaseClasses.FlowMachineInterface.
Models that extend this model need to provide an implementation of
WFlo = eta * P
.
This equation is not implemented in this model to allow other models
to properly guard against division by zero.
Type | Name | Default | Description |
---|---|---|---|
Density | rho_default | Fluid density at medium default state [kg/m3] | |
Characteristics | |||
Boolean | use_powerCharacteristic | false | Use powerCharacteristic (vs. efficiencyCharacteristic) |
Boolean | motorCooledByFluid | true | If true, then motor heat is added to fluid stream |
efficiencyParameters | motorEfficiency | Normalized volume flow rate vs. efficiency | |
efficiencyParameters | hydraulicEfficiency | Normalized volume flow rate vs. efficiency | |
Advanced | |||
Boolean | homotopyInitialization | true | = true, use homotopy method |
Type | Name | Description |
---|---|---|
output RealOutput | P | Electrical power consumed [W] |
partial model PowerInterface "Partial model to compute power draw and heat dissipation of fans and pumps" import Modelica.Constants; parameter Boolean use_powerCharacteristic = false "Use powerCharacteristic (vs. efficiencyCharacteristic)"; parameter Boolean motorCooledByFluid = true "If true, then motor heat is added to fluid stream"; parameter Boolean homotopyInitialization = true "= true, use homotopy method";parameter Buildings.Fluid.Movers.BaseClasses.Characteristics.efficiencyParameters motorEfficiency(r_V={1}, eta={0.7}) "Normalized volume flow rate vs. efficiency"; parameter Buildings.Fluid.Movers.BaseClasses.Characteristics.efficiencyParameters hydraulicEfficiency(r_V={1}, eta={0.7}) "Normalized volume flow rate vs. efficiency"; parameter Modelica.SIunits.Density rho_default "Fluid density at medium default state";Modelica.Blocks.Interfaces.RealOutput P(quantity="Modelica.SIunits.Power", unit="W") "Electrical power consumed"; Modelica.SIunits.Power WHyd "Hydraulic power input (converted to flow work and heat)"; Modelica.SIunits.Power WFlo "Flow work"; Modelica.SIunits.HeatFlowRate Q_flow "Heat input from fan or pump to medium"; Real eta(min=0, max=1) "Global efficiency"; Real etaHyd(min=0, max=1) "Hydraulic efficiency"; Real etaMot(min=0, max=1) "Motor efficiency"; Modelica.SIunits.Pressure dpMachine(displayUnit="Pa") "Pressure increase"; Modelica.SIunits.VolumeFlowRate VMachine_flow "Volume flow rate"; protected parameter Modelica.SIunits.VolumeFlowRate V_flow_max(fixed=false) "Maximum volume flow rate, used for smoothing"; //Modelica.SIunits.HeatFlowRate QThe_flow "Heat input into the medium"; parameter Modelica.SIunits.VolumeFlowRate delta_V_flow = 1E-3*V_flow_max "Factor used for setting heat input into medium to zero at very small flows"; final parameter Real motDer[size(motorEfficiency.r_V, 1)](each fixed=false) "Coefficients for polynomial of pressure vs. flow rate"; final parameter Real hydDer[size(hydraulicEfficiency.r_V,1)](each fixed=false) "Coefficients for polynomial of pressure vs. flow rate"; Modelica.SIunits.HeatFlowRate QThe_flow "Heat input from fan or pump to medium"; initial algorithm // Compute derivatives for cubic spline motDer := if use_powerCharacteristic then zeros(size(motorEfficiency.r_V, 1)) elseif ( size(motorEfficiency.r_V, 1) == 1) then {0} else Buildings.Utilities.Math.Functions.splineDerivatives( x=motorEfficiency.r_V, y=motorEfficiency.eta, ensureMonotonicity=Buildings.Utilities.Math.Functions.isMonotonic(x=motorEfficiency.eta, strict=false)); hydDer := if use_powerCharacteristic then zeros(size(hydraulicEfficiency.r_V, 1)) elseif ( size(hydraulicEfficiency.r_V, 1) == 1) then {0} else Buildings.Utilities.Math.Functions.splineDerivatives( x=hydraulicEfficiency.r_V, y=hydraulicEfficiency.eta); equation eta = etaHyd * etaMot; // WFlo = eta * P; // Flow work WFlo = dpMachine*VMachine_flow; // Hydraulic power (transmitted by shaft), etaHyd = WFlo/WHyd etaHyd * WHyd = WFlo; // Heat input into medium QThe_flow + WFlo = if motorCooledByFluid then P else WHyd; // At m_flow = 0, the solver may still obtain positive values for QThe_flow. // The next statement sets the heat input into the medium to zero for very small flow rates. if homotopyInitialization then Q_flow = homotopy(actual=Buildings.Utilities.Math.Functions.spliceFunction(pos=QThe_flow, neg=0, x=noEvent(abs(VMachine_flow))-2*delta_V_flow, deltax=delta_V_flow), simplified=0); else Q_flow = Buildings.Utilities.Math.Functions.spliceFunction(pos=QThe_flow, neg=0, x=noEvent(abs(VMachine_flow))-2*delta_V_flow, deltax=delta_V_flow); end if;end PowerInterface;
This is an interface that implements the functions to compute the head, power draw and efficiency of fans and pumps. It is used by the model PrescribedFlowMachine.
The nominal hydraulic characteristic (volume flow rate versus total pressure) is given by a set of data points. A cubic hermite spline with linear extrapolation is used to compute the performance at other operating points.
The fan or pump energy balance can be specified in two alternative ways:
use_powerCharacteristic = false
, then the data points for
normalized volume flow rate versus efficiency is used to determine the efficiency,
and then the power consumption. The default is a constant efficiency of 0.8.
use_powerCharacteristic = true
, then the data points for
normalized volume flow rate versus power consumption
is used to determine the power consumption, and then the efficiency
is computed based on the actual power consumption and the flow work.
For numerical reasons, the user-provided data points for volume flow rate versus pressure rise are modified to add a fan internal flow resistance. Because this flow resistance is subtracted during the simulation when computing the fan pressure rise, the model reproduces the exact points that were provided by the user.
Also for numerical reasons, the pressure rise at zero flow rate and
the flow rate at zero pressure rise is added to the user-provided data,
unless the user already provides these data points.
Since Modelica 3.2 does not allow dynamic memory allocation, this
implementation required the use of three different arrays for the
situation where no additional point is added, where one additional
point is added and where two additional points are added.
The parameter curve
causes the correct data record
to be used during the simulation.
Type | Name | Default | Description |
---|---|---|---|
Density | rho_default | Fluid density at medium default state [kg/m3] | |
Characteristics | |||
Boolean | use_powerCharacteristic | false | Use powerCharacteristic (vs. efficiencyCharacteristic) |
Boolean | motorCooledByFluid | true | If true, then motor heat is added to fluid stream |
efficiencyParameters | motorEfficiency | Normalized volume flow rate vs. efficiency | |
efficiencyParameters | hydraulicEfficiency | Normalized volume flow rate vs. efficiency | |
AngularVelocity_rpm | N_nominal | 1500 | Nominal rotational speed for flow characteristic [1/min] |
flowParameters | pressure | Volume flow rate vs. total pressure rise | |
powerParameters | power | Volume flow rate vs. electrical power consumption | |
Advanced | |||
Boolean | homotopyInitialization | true | = true, use homotopy method |
Dynamics | |||
Filtered speed | |||
Boolean | filteredSpeed | true | = true, if speed is filtered with a 2nd order CriticalDamping filter |
Time | riseTime | 30 | Rise time of the filter (time to reach 99.6 % of the speed) [s] |
Init | init | Modelica.Blocks.Types.Init.I... | Type of initialization (no init/steady state/initial state/initial output) |
Real | N_start | 0 | Initial value of speed |
Type | Name | Description |
---|---|---|
output RealOutput | P | Electrical power consumed [W] |
output RealOutput | N_actual | [1/min] |
partial model FlowMachineInterface "Partial model with performance curves for fans or pumps" extends Buildings.Fluid.Movers.BaseClasses.PowerInterface( VMachine_flow(nominal=V_flow_nominal, start=V_flow_nominal), V_flow_max(nominal=V_flow_nominal, start=V_flow_nominal)); import Modelica.Constants; import cha = Buildings.Fluid.Movers.BaseClasses.Characteristics; parameter Modelica.SIunits.Conversions.NonSIunits.AngularVelocity_rpm N_nominal = 1500 "Nominal rotational speed for flow characteristic"; final parameter Modelica.SIunits.VolumeFlowRate V_flow_nominal= pressure.V_flow[size(pressure.V_flow,1)] "Nominal volume flow rate, used for homotopy";parameter Buildings.Fluid.Movers.BaseClasses.Characteristics.flowParameters pressure "Volume flow rate vs. total pressure rise"; parameter Buildings.Fluid.Movers.BaseClasses.Characteristics.powerParameters power "Volume flow rate vs. electrical power consumption"; parameter Boolean homotopyInitialization = true "= true, use homotopy method"; // Classes used to implement the filtered speed parameter Boolean filteredSpeed=true "= true, if speed is filtered with a 2nd order CriticalDamping filter"; parameter Modelica.SIunits.Time riseTime=30 "Rise time of the filter (time to reach 99.6 % of the speed)"; parameter Modelica.Blocks.Types.Init init=Modelica.Blocks.Types.Init.InitialOutput "Type of initialization (no init/steady state/initial state/initial output)"; parameter Real N_start=0 "Initial value of speed"; // SpeedModelica.Blocks.Interfaces.RealOutput N_actual(min=0, max=N_nominal, final quantity="AngularVelocity", final unit="1/min", nominal=N_nominal); // "Shaft rotational speed in rpm"; Real r_N(min=0, start=N_start/N_nominal, unit="1") "Ratio N_actual/N_nominal"; Real r_V(start=1, unit="1") "Ratio V_flow/V_flow_max";protected Modelica.Blocks.Interfaces.RealOutput N_filtered(min=0, start=N_start, max=N_nominal) if filteredSpeed "Filtered speed in the range 0..N_nominal"; Modelica.Blocks.Continuous.Filter filter( order=2, f_cut=5/(2*Modelica.Constants.pi*riseTime), final init=init, final y_start=N_start, x(each stateSelect=StateSelect.always), u_nominal=N_nominal, u(final quantity="AngularVelocity", final unit="1/min", nominal=N_nominal), y(final quantity="AngularVelocity", final unit="1/min", nominal=N_nominal), final analogFilter=Modelica.Blocks.Types.AnalogFilter.CriticalDamping, final filterType=Modelica.Blocks.Types.FilterType.LowPass) if filteredSpeed "Second order filter to approximate valve opening time, and to improve numerics"; parameter Modelica.SIunits.VolumeFlowRate VDelta_flow(fixed=false, start=delta*V_flow_nominal) "Small volume flow rate"; parameter Modelica.SIunits.Pressure dpDelta(fixed=false, start=100) "Small pressure"; parameter Real delta = 0.05 "Small value used to transition to other fan curve"; parameter Real cBar[2](each fixed=false) "Coefficients for linear approximation of pressure vs. flow rate"; parameter Modelica.SIunits.Pressure dpMax(min=0, fixed=false); parameter Real kRes(min=0, unit="kg/(s.m4)", fixed=false) "Coefficient for internal pressure drop of fan or pump"; parameter Integer curve(min=1, max=3, fixed=false) "Flag, used to pick the right representatio of the fan or pump pressure curve"; parameter Integer nOri = size(pressure.V_flow,1) "Number of data points for pressure curve"; parameter Buildings.Fluid.Movers.BaseClasses.Characteristics.flowParametersInternal pCur1( final n = nOri, V_flow(each fixed=false), dp(each fixed=false)) "Volume flow rate vs. total pressure rise with correction for pump resistance added"; parameter Buildings.Fluid.Movers.BaseClasses.Characteristics.flowParametersInternal pCur2( final n = nOri + 1, V_flow(each fixed=false), dp(each fixed=false)) "Volume flow rate vs. total pressure rise with correction for pump resistance added"; parameter Buildings.Fluid.Movers.BaseClasses.Characteristics.flowParametersInternal pCur3( final n = nOri + 2, V_flow(each fixed=false), dp(each fixed=false)) "Volume flow rate vs. total pressure rise with correction for pump resistance added"; parameter Real preDer1[nOri](each fixed=false) "Derivatives of flow rate vs. pressure at the support points"; parameter Real preDer2[nOri+1](each fixed=false) "Derivatives of flow rate vs. pressure at the support points"; parameter Real preDer3[nOri+2](each fixed=false) "Derivatives of flow rate vs. pressure at the support points"; parameter Real powDer[size(power.V_flow,1)]= if use_powerCharacteristic then Buildings.Utilities.Math.Functions.splineDerivatives( x=power.V_flow, y=power.P, ensureMonotonicity=Buildings.Utilities.Math.Functions.isMonotonic(x=power.P, strict=false)) else zeros(size(power.V_flow,1)) "Coefficients for polynomial of pressure vs. flow rate"; parameter Boolean haveMinimumDecrease(fixed=false) "Flag used for reporting"; parameter Boolean haveDPMax(fixed=false) "Flag, true if user specified data that contain dpMax"; parameter Boolean haveVMax(fixed=false) "Flag, true if user specified data that contain V_flow_max"; // Variables Modelica.SIunits.Density rho "Medium density";function getPerformanceDataAsString input Buildings.Fluid.Movers.BaseClasses.Characteristics.flowParameters pressure "Performance data"; input Real derivative[:](unit="kg/(s.m4)") "Derivative"; input Integer minimumLength = 6 "Minimum width of result"; input Integer significantDigits = 6 "Number of significant digits"; output String str "String representation"; algorithm str :=""; for i in 1:size(derivative, 1) loop str :=str + " V_flow[" + String(i) + "]=" + String( pressure.V_flow[i], minimumLength=minimumLength, significantDigits=significantDigits) + "\t" + "dp[" + String(i) + "]=" + String( pressure.dp[i], minimumLength=minimumLength, significantDigits=significantDigits) + "\tResulting derivative dp/dV_flow = " + String( derivative[i], minimumLength=minimumLength, significantDigits=significantDigits) + "\n"; end for; end getPerformanceDataAsString ;function getArrayAsString input Real array[:] "Array to be printed"; input String varName "Variable name"; input Integer minimumLength = 6 "Minimum width of result"; input Integer significantDigits = 6 "Number of significant digits"; output String str "String representation"; algorithm str :=""; for i in 1:size(array, 1) loop str :=str + " " + varName + "[" + String(i) + "]=" + String( array[i], minimumLength=minimumLength, significantDigits=significantDigits) + "\n"; end for; end getArrayAsString ; initial algorithm // Check validity of data assert(size(pressure.V_flow, 1) > 1, "Must have at least two data points for pressure.V_flow."); assert(Buildings.Utilities.Math.Functions.isMonotonic(x=pressure.V_flow, strict=true) and pressure.V_flow[1] > -Modelica.Constants.eps, "The volume flow rate for the fan pressure rise must be a strictly decreasing sequence with the first element being non-zero. The following performance data have been entered: " + getArrayAsString(pressure.V_flow, "pressure.V_flow")); // Check if V_flow_max or dpMax are provided by user haveVMax :=(abs(pressure.dp[nOri]) < Modelica.Constants.eps); haveDPMax :=(abs(pressure.V_flow[1]) < Modelica.Constants.eps); // Assign V_flow_max and dpMax if haveVMax then V_flow_max :=pressure.V_flow[nOri]; else assert((pressure.V_flow[nOri]-pressure.V_flow[nOri-1])/((pressure.dp[nOri]-pressure.dp[nOri-1]))<0, "The last two pressure points for the fan or pump performance curve must be decreasing. You need to set more reasonable parameters. Received " + getArrayAsString(pressure.dp, "dp")); V_flow_max :=pressure.V_flow[nOri] - (pressure.V_flow[nOri] - pressure.V_flow[ nOri - 1])/((pressure.dp[nOri] - pressure.dp[nOri - 1]))*pressure.dp[nOri]; end if; if haveDPMax then dpMax :=pressure.dp[1]; else dpMax :=pressure.dp[1] - ((pressure.dp[2] - pressure.dp[1])/(pressure.V_flow[ 2] - pressure.V_flow[1]))*pressure.V_flow[1]; end if; // Check if minimum decrease condition is satisfied haveMinimumDecrease :=true; kRes :=dpMax/V_flow_max*delta^2/10; for i in 1:nOri-1 loop if ((pressure.dp[i+1]-pressure.dp[i])/(pressure.V_flow[i+1]-pressure.V_flow[i]) >= -kRes) then haveMinimumDecrease :=false; end if; end for; // Write warning if the volumetric flow rate versus pressure curve does not satisfy // the minimum decrease condition if (not haveMinimumDecrease) then Modelica.Utilities.Streams.print(" Warning: ======== It is recommended that the volume flow rate versus pressure relation of the fan or pump satisfies the minimum decrease condition (pressure.dp[i+1]-pressure.dp[i]) d[i] = ----------------------------------------- < " + String(-kRes) + " (pressure.V_flow[i+1]-pressure.V_flow[i]) is " + getArrayAsString({(pressure.dp[i+1]-pressure.dp[i])/(pressure.V_flow[i+1]-pressure.V_flow[i]) for i in 1:nOri-1}, "d") + " Otherwise, a solution to the equations may not exist if the fan or pump speed is reduced. In this situation, the solver will fail due to non-convergence and the simulation stops."); end if; // Correction for flow resistance of pump or fan // Case 1: if (haveVMax and haveDPMax) or (nOri == 2) then // ----- Curve 1 curve :=1; // V_flow_max and dpMax are provided by the user, or we only have two data points for i in 1:nOri loop pCur1.dp[i] :=pressure.dp[i] + pressure.V_flow[i] * kRes; pCur1.V_flow[i] := pressure.V_flow[i]; end for; pCur2.V_flow := zeros(nOri + 1); pCur2.dp := zeros(nOri + 1); pCur3.V_flow := zeros(nOri + 2); pCur3.dp := zeros(nOri + 2); preDer1:=Buildings.Utilities.Math.Functions.splineDerivatives(x=pCur1.V_flow, y=pCur1.dp); preDer2:=zeros(nOri+1); preDer3:=zeros(nOri+2); // Equation to compute dpDelta dpDelta :=cha.pressure( data=pCur1, V_flow=0, r_N=delta, VDelta_flow=0, dpDelta=0, V_flow_max=Modelica.Constants.eps, dpMax=0, delta=0, d=preDer1, cBar=zeros(2), kRes= kRes); // Equation to compute VDelta_flow. By the affinity laws, the volume flow rate is proportional to the speed. VDelta_flow :=V_flow_max*delta; // Linear equations to determine cBar // Conditions for r_N=delta, V_flow = VDelta_flow // Conditions for r_N=delta, V_flow = 0 cBar[1] :=cha.pressure( data=pCur1, V_flow=0, r_N=delta, VDelta_flow=0, dpDelta=0, V_flow_max=Modelica.Constants.eps, dpMax=0, delta=0, d=preDer1, cBar=zeros(2), kRes= kRes) * (1-delta)/delta^2; cBar[2] :=((cha.pressure( data=pCur1, V_flow=VDelta_flow, r_N=delta, VDelta_flow=0, dpDelta=0, V_flow_max=Modelica.Constants.eps, dpMax=0, delta=0, d=preDer1, cBar=zeros(2), kRes= kRes) - delta*dpDelta)/delta^2 - cBar[1])/VDelta_flow; elseif haveVMax or haveDPMax then // ----- Curve 2 curve :=2; // V_flow_max or dpMax is provided by the user, but not both if haveVMax then pCur2.V_flow[1] := 0; pCur2.dp[1] := dpMax; for i in 1:nOri loop pCur2.dp[i+1] :=pressure.dp[i] + pressure.V_flow[i] * kRes; pCur2.V_flow[i+1] := pressure.dp[i]; end for; else for i in 1:nOri loop pCur2.dp[i] :=pressure.dp[i] + pressure.V_flow[i] * kRes; pCur2.V_flow[i] := pressure.V_flow[i]; end for; pCur2.V_flow[nOri+1] := V_flow_max; pCur2.dp[nOri+1] := 0; end if; pCur1.V_flow := zeros(nOri); pCur1.dp := zeros(nOri); pCur3.V_flow := zeros(nOri + 2); pCur3.dp := zeros(nOri + 2); preDer1:=zeros(nOri); preDer2:=Buildings.Utilities.Math.Functions.splineDerivatives(x=pCur2.V_flow, y=pCur2.dp); preDer3:=zeros(nOri+2); // Equation to compute dpDelta dpDelta :=cha.pressure( data=pCur2, V_flow=0, r_N=delta, VDelta_flow=0, dpDelta=0, V_flow_max=Modelica.Constants.eps, dpMax=0, delta=0, d=preDer2, cBar=zeros(2), kRes= kRes); // Equation to compute VDelta_flow. By the affinity laws, the volume flow rate is proportional to the speed. VDelta_flow :=V_flow_max*delta; // Linear equations to determine cBar // Conditions for r_N=delta, V_flow = VDelta_flow // Conditions for r_N=delta, V_flow = 0 cBar[1] :=cha.pressure( data=pCur2, V_flow=0, r_N=delta, VDelta_flow=0, dpDelta=0, V_flow_max=Modelica.Constants.eps, dpMax=0, delta=0, d=preDer2, cBar=zeros(2), kRes= kRes) * (1-delta)/delta^2; cBar[2] :=((cha.pressure( data=pCur2, V_flow=VDelta_flow, r_N=delta, VDelta_flow=0, dpDelta=0, V_flow_max=Modelica.Constants.eps, dpMax=0, delta=0, d=preDer2, cBar=zeros(2), kRes= kRes) - delta*dpDelta)/delta^2 - cBar[1])/VDelta_flow; else // ----- Curve 3 curve :=3; // Neither V_flow_max nor dpMax are provided by the user pCur3.V_flow[1] := 0; pCur3.dp[1] := dpMax; for i in 1:nOri loop pCur3.dp[i+1] :=pressure.dp[i] + pressure.V_flow[i] * kRes; pCur3.V_flow[i+1] := pressure.V_flow[i]; end for; pCur3.V_flow[nOri+2] := V_flow_max; pCur3.dp[nOri+2] := 0; pCur1.V_flow := zeros(nOri); pCur1.dp := zeros(nOri); pCur2.V_flow := zeros(nOri + 1); pCur2.dp := zeros(nOri + 1); preDer1:=zeros(nOri); preDer2:=zeros(nOri+1); preDer3:=Buildings.Utilities.Math.Functions.splineDerivatives(x=pCur3.V_flow, y=pCur3.dp); // Equation to compute dpDelta dpDelta :=cha.pressure( data=pCur3, V_flow=0, r_N=delta, VDelta_flow=0, dpDelta=0, V_flow_max=Modelica.Constants.eps, dpMax=0, delta=0, d=preDer3, cBar=zeros(2), kRes= kRes); // Equation to compute VDelta_flow. By the affinity laws, the volume flow rate is proportional to the speed. VDelta_flow :=V_flow_max*delta; // Linear equations to determine cBar // Conditions for r_N=delta, V_flow = VDelta_flow // Conditions for r_N=delta, V_flow = 0 cBar[1] :=cha.pressure( data=pCur3, V_flow=0, r_N=delta, VDelta_flow=0, dpDelta=0, V_flow_max=Modelica.Constants.eps, dpMax=0, delta=0, d=preDer3, cBar=zeros(2), kRes= kRes) * (1-delta)/delta^2; cBar[2] :=((cha.pressure( data=pCur3, V_flow=VDelta_flow, r_N=delta, VDelta_flow=0, dpDelta=0, V_flow_max=Modelica.Constants.eps, dpMax=0, delta=0, d=preDer3, cBar=zeros(2), kRes= kRes) - delta*dpDelta)/delta^2 - cBar[1])/VDelta_flow; end if; equation // Hydraulic equations r_N = N_actual/N_nominal; r_V = VMachine_flow/V_flow_max; // For the homotopy method, we approximate dpMachine by an equation // that is linear in VMachine_flow, and that goes linearly to 0 as r_N goes to 0. // The three branches below are identical, except that we pass either // pCur1, pCur2 or pCur3, and preDer1, preDer2 or preDer3 if (curve == 1) then if homotopyInitialization then dpMachine = homotopy(actual=cha.pressure(data=pCur1, V_flow=VMachine_flow, r_N=r_N, VDelta_flow=VDelta_flow, dpDelta=dpDelta, V_flow_max=V_flow_max, dpMax=dpMax, delta=delta, d=preDer1, cBar=cBar, kRes=kRes), simplified=r_N* (cha.pressure(data=pCur1, V_flow=V_flow_nominal, r_N=1, VDelta_flow=VDelta_flow, dpDelta=dpDelta, V_flow_max=V_flow_max, dpMax=dpMax, delta=delta, d=preDer1, cBar=cBar, kRes=kRes) +(VMachine_flow-V_flow_nominal)* (cha.pressure(data=pCur1, V_flow=(1+delta)*V_flow_nominal, r_N=1, VDelta_flow=VDelta_flow, dpDelta=dpDelta, V_flow_max=V_flow_max, dpMax=dpMax, delta=delta, d=preDer1, cBar=cBar, kRes=kRes) -cha.pressure(data=pCur1, V_flow=(1-delta)*V_flow_nominal, r_N=1, VDelta_flow=VDelta_flow, dpDelta=dpDelta, V_flow_max=V_flow_max, dpMax=dpMax, delta=delta, d=preDer1, cBar=cBar, kRes=kRes)) /(2*delta*V_flow_nominal))); else dpMachine = cha.pressure(data=pCur1, V_flow=VMachine_flow, r_N=r_N, VDelta_flow=VDelta_flow, dpDelta=dpDelta, V_flow_max=V_flow_max, dpMax=dpMax, delta=delta, d=preDer1, cBar=cBar, kRes=kRes); end if; // end of computation for this branch elseif (curve == 2) then if homotopyInitialization then dpMachine = homotopy(actual=cha.pressure(data=pCur2, V_flow=VMachine_flow, r_N=r_N, VDelta_flow=VDelta_flow, dpDelta=dpDelta, V_flow_max=V_flow_max, dpMax=dpMax, delta=delta, d=preDer2, cBar=cBar, kRes=kRes), simplified=r_N* (cha.pressure(data=pCur2, V_flow=V_flow_nominal, r_N=1, VDelta_flow=VDelta_flow, dpDelta=dpDelta, V_flow_max=V_flow_max, dpMax=dpMax, delta=delta, d=preDer2, cBar=cBar, kRes=kRes) +(VMachine_flow-V_flow_nominal)* (cha.pressure(data=pCur2, V_flow=(1+delta)*V_flow_nominal, r_N=1, VDelta_flow=VDelta_flow, dpDelta=dpDelta, V_flow_max=V_flow_max, dpMax=dpMax, delta=delta, d=preDer2, cBar=cBar, kRes=kRes) -cha.pressure(data=pCur2, V_flow=(1-delta)*V_flow_nominal, r_N=1, VDelta_flow=VDelta_flow, dpDelta=dpDelta, V_flow_max=V_flow_max, dpMax=dpMax, delta=delta, d=preDer2, cBar=cBar, kRes=kRes)) /(2*delta*V_flow_nominal))); else dpMachine = cha.pressure(data=pCur2, V_flow=VMachine_flow, r_N=r_N, VDelta_flow=VDelta_flow, dpDelta=dpDelta, V_flow_max=V_flow_max, dpMax=dpMax, delta=delta, d=preDer2, cBar=cBar, kRes=kRes); end if; // end of computation for this branch else if homotopyInitialization then dpMachine = homotopy(actual=cha.pressure(data=pCur3, V_flow=VMachine_flow, r_N=r_N, VDelta_flow=VDelta_flow, dpDelta=dpDelta, V_flow_max=V_flow_max, dpMax=dpMax, delta=delta, d=preDer3, cBar=cBar, kRes=kRes), simplified=r_N* (cha.pressure(data=pCur3, V_flow=V_flow_nominal, r_N=1, VDelta_flow=VDelta_flow, dpDelta=dpDelta, V_flow_max=V_flow_max, dpMax=dpMax, delta=delta, d=preDer3, cBar=cBar, kRes=kRes) +(VMachine_flow-V_flow_nominal)* (cha.pressure(data=pCur3, V_flow=(1+delta)*V_flow_nominal, r_N=1, VDelta_flow=VDelta_flow, dpDelta=dpDelta, V_flow_max=V_flow_max, dpMax=dpMax, delta=delta, d=preDer3, cBar=cBar, kRes=kRes) -cha.pressure(data=pCur3, V_flow=(1-delta)*V_flow_nominal, r_N=1, VDelta_flow=VDelta_flow, dpDelta=dpDelta, V_flow_max=V_flow_max, dpMax=dpMax, delta=delta, d=preDer3, cBar=cBar, kRes=kRes)) /(2*delta*V_flow_nominal))); else dpMachine = cha.pressure(data=pCur3, V_flow=VMachine_flow, r_N=r_N, VDelta_flow=VDelta_flow, dpDelta=dpDelta, V_flow_max=V_flow_max, dpMax=dpMax, delta=delta, d=preDer3, cBar=cBar, kRes=kRes); end if; // end of computation for this branch end if; // Power consumption if use_powerCharacteristic then // For the homotopy, we want P/V_flow to be bounded as V_flow -> 0 to avoid a very high medium // temperature near zero flow. if homotopyInitialization then P = homotopy(actual=cha.power(data=power, V_flow=VMachine_flow, r_N=r_N, d=powDer), simplified=VMachine_flow/V_flow_nominal* cha.power(data=power, V_flow=V_flow_nominal, r_N=1, d=powDer)); else P = (rho/rho_default)*cha.power(data=power, V_flow=VMachine_flow, r_N=r_N, d=powDer); end if; // To compute the efficiency, we set a lower bound on the electricity consumption. // This is needed because WFlo can be close to zero when P is zero, thereby // causing a division by zero. // Earlier versions of the model computed WFlo = eta * P, but this caused // a division by zero. eta = WFlo / Buildings.Utilities.Math.Functions.smoothMax(x1=P, x2=1E-5, deltaX=1E-6); // In this configuration, we only now the total power consumption. // Because nothing is known about etaMot versus etaHyd, we set etaHyd=1. This will // cause etaMot=eta, because eta=etaHyd*etaMot. // Earlier versions used etaMot=sqrt(eta), but as eta->0, this function has // and infinite derivative. etaHyd = 1; else if homotopyInitialization then etaHyd = homotopy(actual=cha.efficiency(data=hydraulicEfficiency, r_V=r_V, d=hydDer), simplified=cha.efficiency(data=hydraulicEfficiency, r_V=1, d=hydDer)); etaMot = homotopy(actual=cha.efficiency(data=motorEfficiency, r_V=r_V, d=motDer), simplified=cha.efficiency(data=motorEfficiency, r_V=1, d=motDer)); else etaHyd = cha.efficiency(data=hydraulicEfficiency, r_V=r_V, d=hydDer); etaMot = cha.efficiency(data=motorEfficiency, r_V=r_V, d=motDer); end if; // To compute the electrical power, we set a lower bound for eta to avoid // a division by zero. P = WFlo / Buildings.Utilities.Math.Functions.smoothMax(x1=eta, x2=1E-5, deltaX=1E-6); end if;end FlowMachineInterface;