Buildings.Fluid.Movers.BaseClasses

Information

Package Content

Name	Description
Characteristics	Functions for fan or pump characteristics
assertPositiveDifference
FlowMachine	Fan or pump with ideally controlled mass flow rate or pressure difference
PartialFlowMachine	Base model for fans or pumps

Buildings.Fluid.Movers.BaseClasses.assertPositiveDifference

Information

Inputs

Type	Name	Default	Description
Pressure	p		[Pa]
Pressure	p_sat		[Pa]
String	message

Outputs

Type	Name	Description
Pressure	dp	[Pa]

Modelica definition

function assertPositiveDifference
  extends Modelica.Icons.Function;
  input Modelica.SIunits.Pressure p;
  input Modelica.SIunits.Pressure p_sat;
  input String message;
  output Modelica.SIunits.Pressure dp;
algorithm 
  dp := p - p_sat;
  assert(p >= p_sat, message);
end assertPositiveDifference;

Buildings.Fluid.Movers.BaseClasses.FlowMachine

Information

This model describes a fan or pump (or a group of nParallel fans/pumps) with ideally controlled mass flow rate or pressure.

Nominal values are used to predefine an exemplary fan or pump characteristics and to define the operation of the fan/pump. The input connectors m_flow_set or dp_set can optionally be enabled to provide time varying set points.

Use this model if the fan or pump characteristics is of secondary interest. The actual characteristics can be configured later on for the appropriate rotational speed N. Then the model can be replaced with Buildings.Fluid.Movers.FlowMachine_y or Buildings.Fluid.Movers.FlowMachine_N_rpm or

Extends from Buildings.Fluid.Movers.BaseClasses.PartialFlowMachine (Base model for fans or pumps).

Parameters

Type	Name	Default	Description
replaceable package Medium		PartialMedium	Medium in the component
AbsolutePressure	p_a_nominal	system.p_start	Nominal inlet pressure for predefined fan or pump characteristics [Pa]
AbsolutePressure	dp_set_nominal	1000	Nominal total pressure difference, fixed if not control_m_flow and not use_dp_set [Pa]
MassFlowRate	m_flow_nominal		Nominal mass flow rate, fixed if control_m_flow and not use_m_flow_set [kg/s]
Boolean	control_m_flow	true	= false to control outlet pressure port_b.p instead of m_flow
Boolean	use_m_flow_set	false	= true to use input signal m_flow_set instead of m_flow_nominal
Boolean	use_dp_set	false	= true to use input signal dp_set instead of dp_set_nominal
Characteristics
Integer	nParallel	1	Number of fans or pumps in parallel
replaceable function flowCharacteristic		Characteristics.quadraticFlo...	Total pressure vs. V_flow characteristic at nominal speed
AngularVelocity_rpm	N_nominal	1500	Nominal rotational speed for flow characteristic [1/min]
Density	rho_nominal	Medium.density_pTX(Medium.p_...	Nominal fluid density [kg/m3]
Boolean	use_powerCharacteristic	false	Use powerCharacteristic (vs. efficiencyCharacteristic)
replaceable function powerCharacteristic		Characteristics.quadraticPow...	Power consumption vs. V_flow at nominal speed and density
replaceable function efficiencyCharacteristic		Characteristics.constantEffi...	Efficiency vs. V_flow at nominal speed and density
Assumptions
Boolean	allowFlowReversal	system.allowFlowReversal	= true to allow flow reversal, false restricts to design direction (port_a -> port_b)
Boolean	checkValve	false	= true to prevent reverse flow
Volume	V	0	Volume inside the pump [m3]
Dynamics
Dynamics	energyDynamics	Modelica.Fluid.Types.Dynamic...	Formulation of energy balance
Dynamics	massDynamics	energyDynamics	Formulation of mass balance
Heat transfer
Boolean	use_HeatTransfer	false	= true to use a HeatTransfer model, e.g. for a housing
replaceable model HeatTransfer		IdealHeatTransfer	Wall heat transfer
Initialization
AbsolutePressure	p_a_start	system.p_start	Guess value for inlet pressure [Pa]
AbsolutePressure	p_b_start	p_a_start	Guess value for outlet pressure [Pa]
MassFlowRate	m_flow_start	1	Guess value of m_flow = port_a.m_flow [kg/s]
Boolean	use_T_start	true	= true, use T_start, otherwise h_start
Temperature	T_start	if use_T_start then system.T...	Start value of temperature [K]
SpecificEnthalpy	h_start	if use_T_start then Medium.s...	Start value of specific enthalpy [J/kg]
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
Advanced
Diagnostics
Boolean	show_NPSHa	false	= true to compute Net Positive Suction Head available

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)
HeatPort_a	heatPort
input RealInput	m_flow_set	Prescribed mass flow rate
input RealInput	dp_set	Prescribed outlet pressure
Characteristics
replaceable function flowCharacteristic		Total pressure vs. V_flow characteristic at nominal speed

Modelica definition

model FlowMachine 
  "Fan or pump with ideally controlled mass flow rate or pressure difference"
  import Modelica.SIunits.Conversions.NonSIunits.AngularVelocity_rpm;
  extends Buildings.Fluid.Movers.BaseClasses.PartialFlowMachine(
    N_nominal=1500,
    N(start=N_nominal),
    redeclare replaceable function flowCharacteristic = 
        Characteristics.quadraticFlow (V_flow_nominal={0,V_flow_op,1.5*
            V_flow_op}, dp_nominal={2*dp_op,dp_op,0}));

  // nominal values
  parameter Medium.AbsolutePressure p_a_nominal(displayUnit="Pa") = system.p_start 
    "Nominal inlet pressure for predefined fan or pump characteristics";
  parameter Medium.AbsolutePressure dp_set_nominal(displayUnit="Pa") = 1000 
    "Nominal total pressure difference, fixed if not control_m_flow and not use_dp_set";
  parameter Medium.MassFlowRate m_flow_nominal 
    "Nominal mass flow rate, fixed if control_m_flow and not use_m_flow_set";

  // what to control
  parameter Boolean control_m_flow = true 
    "= false to control outlet pressure port_b.p instead of m_flow";
  parameter Boolean use_m_flow_set = false 
    "= true to use input signal m_flow_set instead of m_flow_nominal";
  parameter Boolean use_dp_set = false 
    "= true to use input signal dp_set instead of dp_set_nominal";

  // exemplary characteristics
  final parameter Modelica.SIunits.VolumeFlowRate V_flow_op=m_flow_nominal/
      rho_nominal "operational volume flow rate according to nominal values";
  final parameter Modelica.SIunits.AbsolutePressure dp_op=dp_set_nominal 
    "operational fan or pump total pressure according to nominal values";

  Modelica.Blocks.Interfaces.RealInput m_flow_set if use_m_flow_set 
    "Prescribed mass flow rate";
  Modelica.Blocks.Interfaces.RealInput dp_set if use_dp_set 
    "Prescribed outlet pressure";

protected 
  Modelica.Blocks.Interfaces.RealInput m_flow_set_internal 
    "Needed to connect to conditional connector";
  Modelica.Blocks.Interfaces.RealInput dp_set_internal 
    "Needed to connect to conditional connector";
equation 
  // Ideal control
  if control_m_flow then
    m_flow = m_flow_set_internal;
  else
    dp = dp_set_internal;
  end if;

  // Internal connector value when use_m_flow_set = false
  if not use_m_flow_set then
    m_flow_set_internal = m_flow_nominal;
  end if;
  if not use_dp_set then
    dp_set_internal = dp_set_nominal;
  end if;
  connect(m_flow_set, m_flow_set_internal);
  connect(dp_set, dp_set_internal);
  assert(dp_set_internal >= 0, "dp_set cannot be negative. Obtained dp_set = " + realString(dp_set_internal));

end FlowMachine;

Buildings.Fluid.Movers.BaseClasses.PartialFlowMachine

Information

This is the base model for fans and pumps.

The model is similar to Modelica.Fluid.Machines.BaseClasses.PartialPump, except for the parameterization which has been changed so that the model is also applicable for fans. See the revision notes of this model for details.

The model describes a fan or pump, or a group of nParallel identical fans or pumps. The model is based on the theory of kinematic similarity: the fan or pump characteristics are given for nominal operating conditions (rotational speed and fluid density), and then adapted to actual operating condition, according to the similarity equations.

Fan or pump characteristics

The nominal hydraulic characteristic (total pressure vs. volume flow rate) is given by the the replaceable function flowCharacteristic.

The fan or pump energy balance can be specified in two alternative ways:

• use_powerCharacteristic = false (default option): the replaceable function efficiencyCharacteristic (efficiency vs. volume flow rate in nominal conditions) is used to determine the efficiency, and then the power consumption. The default is a constant efficiency of 0.8.
• use_powerCharacteristic = true: the replaceable function powerCharacteristic (power consumption vs. volume flow rate in nominal conditions) is used to determine the power consumption, and then the efficiency. Use powerCharacteristic to specify a non-zero power consumption for zero flow rate.

Several functions are provided in the package Characteristics to specify the characteristics as a function of some operating points at nominal conditions.

Depending on the value of the checkValve parameter, the model either supports reverse flow conditions, or includes a built-in check valve to avoid flow reversal.

It is possible to take into account the heat capacity of the fluid inside the fan or pump by specifying its volume V; this is necessary to avoid singularities in the computation of the outlet enthalpy in case of zero flow rate. If zero flow rate conditions are always avoided, this dynamic effect can be neglected by leaving the default value V = 0, thus avoiding a fast state variable in the model.

Dynamics options

Steady-state mass and energy balances are assumed per default, neglecting the holdup of fluid in the fan or pump. Dynamic mass and energy balance can be used by setting the corresponding dynamic parameters. This might be desirable if the fan or pump is assembled together with valves before port_a and behind port_b. If both valves are closed, then the fluid is useful to define the thermodynamic state and in particular the absolute pressure in the fan or pump. Note that the flowCharacteristic only specifies a pressure difference.

Heat transfer

The boolean paramter use_HeatTransfer can be set to true if heat exchanged with the environment should be taken into account or to model a housing. This might be desirable if a fan or pump with realistic powerCharacteristic for zero flow operates while a valve prevents fluid flow.

Diagnostics of Cavitation

The boolean parameter show_NPSHa can set true to compute the Net Positive Suction Head available and check for cavitation, provided a two-phase medium model is used.

Extends from Modelica.Fluid.Interfaces.PartialTwoPort (Partial component with two ports), Modelica.Fluid.Interfaces.PartialLumpedVolume (Lumped volume with mass and energy balance).

Parameters

Type	Name	Default	Description
replaceable package Medium		PartialMedium	Medium in the component
Volume	fluidVolume	V	Volume [m3]
Characteristics
Integer	nParallel	1	Number of fans or pumps in parallel
AngularVelocity_rpm	N_nominal	1500	Nominal rotational speed for flow characteristic [1/min]
Density	rho_nominal	Medium.density_pTX(Medium.p_...	Nominal fluid density [kg/m3]
Boolean	use_powerCharacteristic	false	Use powerCharacteristic (vs. efficiencyCharacteristic)
Assumptions
Boolean	allowFlowReversal	system.allowFlowReversal	= true to allow flow reversal, false restricts to design direction (port_a -> port_b)
Boolean	checkValve	false	= true to prevent reverse flow
Volume	V	0	Volume inside the pump [m3]
Dynamics
Dynamics	energyDynamics	Modelica.Fluid.Types.Dynamic...	Formulation of energy balance
Dynamics	massDynamics	energyDynamics	Formulation of mass balance
Heat transfer
Boolean	use_HeatTransfer	false	= true to use a HeatTransfer model, e.g. for a housing
Initialization
AbsolutePressure	p_a_start	system.p_start	Guess value for inlet pressure [Pa]
AbsolutePressure	p_b_start	p_a_start	Guess value for outlet pressure [Pa]
MassFlowRate	m_flow_start	1	Guess value of m_flow = port_a.m_flow [kg/s]
AbsolutePressure	p_start	p_b_start	Start value of pressure [Pa]
Boolean	use_T_start	true	= true, use T_start, otherwise h_start
Temperature	T_start	if use_T_start then system.T...	Start value of temperature [K]
SpecificEnthalpy	h_start	if use_T_start then Medium.s...	Start value of specific enthalpy [J/kg]
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
Advanced
Diagnostics
Boolean	show_NPSHa	false	= true to compute Net Positive Suction Head available

Connectors

Type	Name	Description
HeatPort_a	heatPort

Modelica definition

partial model PartialFlowMachine "Base model for fans or pumps"
//    import Modelica.SIunits.Conversions.NonSIunits.*;
  import Modelica.Constants;

  extends Modelica.Fluid.Interfaces.PartialTwoPort(
    port_b_exposesState = energyDynamics<>Modelica.Fluid.Types.Dynamics.SteadyState or 
         massDynamics<>Modelica.Fluid.Types.Dynamics.SteadyState,
    port_a(
      p(start=p_a_start),
      m_flow(start = m_flow_start,
             min = if allowFlowReversal and not checkValve then -Constants.inf else 0)),
    port_b(
      p(start=p_b_start),
      m_flow(start = -m_flow_start,
             max = if allowFlowReversal and not checkValve then +Constants.inf else 0)));

  // Initialization
  parameter Medium.AbsolutePressure p_a_start=system.p_start 
    "Guess value for inlet pressure";
  parameter Medium.AbsolutePressure p_b_start=p_a_start 
    "Guess value for outlet pressure";
  parameter Medium.MassFlowRate m_flow_start = 1 
    "Guess value of m_flow = port_a.m_flow";

  // Characteristics
  parameter Integer nParallel(min=1) = 1 "Number of fans or pumps in parallel";
  replaceable function flowCharacteristic = 
      Characteristics.baseFlow 
    "Total pressure vs. V_flow characteristic at nominal speed";
  parameter Modelica.SIunits.Conversions.NonSIunits.AngularVelocity_rpm
    N_nominal = 1500 "Nominal rotational speed for flow characteristic";
  parameter Medium.Density rho_nominal = Medium.density_pTX(Medium.p_default, Medium.T_default, Medium.X_default) 
    "Nominal fluid density";
  parameter Boolean use_powerCharacteristic = false 
    "Use powerCharacteristic (vs. efficiencyCharacteristic)";
  replaceable function powerCharacteristic = 
        Characteristics.quadraticPower (
       V_flow_nominal={0,0,0},W_nominal={0,0,0}) 
    "Power consumption vs. V_flow at nominal speed and density";
  replaceable function efficiencyCharacteristic = 
    Characteristics.constantEfficiency(eta_nominal = 0.8) constrainedby 
    Characteristics.baseEfficiency 
    "Efficiency vs. V_flow at nominal speed and density";

  // Assumptions
  parameter Boolean checkValve=false "= true to prevent reverse flow";

  parameter Modelica.SIunits.Volume V=0 "Volume inside the pump";

  // Energy and mass balance
  extends Modelica.Fluid.Interfaces.PartialLumpedVolume(
      final fluidVolume = V,
      energyDynamics = Modelica.Fluid.Types.Dynamics.SteadyState,
      massDynamics = energyDynamics,
      final p_start = p_b_start);

  // Heat transfer through boundary, e.g. to add a housing
  parameter Boolean use_HeatTransfer = false 
    "= true to use a HeatTransfer model, e.g. for a housing";
  replaceable model HeatTransfer = 
      Modelica.Fluid.Vessels.BaseClasses.HeatTransfer.IdealHeatTransfer 
    constrainedby 
    Modelica.Fluid.Vessels.BaseClasses.HeatTransfer.PartialVesselHeatTransfer 
    "Wall heat transfer";
  HeatTransfer heatTransfer(
    redeclare final package Medium = Medium,
    final n=1,
    surfaceAreas={4*Modelica.Constants.pi*(3/4*V/Modelica.Constants.pi)^(2/3)},
    final states = {medium.state},
    final use_k = use_HeatTransfer);
  Modelica.Thermal.HeatTransfer.Interfaces.HeatPort_a heatPort if use_HeatTransfer;

  // Variables
//  final parameter Modelica.SIunits.Acceleration g=system.g;
//  Medium.Density rho = medium.d;
  Modelica.SIunits.Pressure dp(displayUnit="Pa")=port_b.p - port_a.p 
    "Pressure increase";
//  Modelica.SIunits.Height head=dp_pump/(medium.d*g) "Pump head";
  Modelica.SIunits.MassFlowRate m_flow=port_a.m_flow "Mass flow rate (total)";
  Modelica.SIunits.MassFlowRate m_flow_single=m_flow/nParallel 
    "Mass flow rate (single pump)";
  Modelica.SIunits.VolumeFlowRate V_flow=m_flow/medium.d 
    "Volume flow rate (total)";
  Modelica.SIunits.VolumeFlowRate V_flow_single(start=m_flow_start/rho_nominal/
          nParallel)=V_flow/nParallel "Volume flow rate (single pump)";
  Modelica.SIunits.Conversions.NonSIunits.AngularVelocity_rpm N(min=0, start = N_nominal) 
    "Shaft rotational speed";
  Modelica.SIunits.Power W_single "Power consumption (single fan or pump)";
  Modelica.SIunits.Power W_total=W_single*nParallel "Power consumption (total)";
  Real eta "Global efficiency";
  Real s(start = m_flow_start) 
    "Curvilinear abscissa for the flow curve in parametric form (either mass flow rate or total pressure)";

  // Diagnostics
  parameter Boolean show_NPSHa = false 
    "= true to compute Net Positive Suction Head available";
  Medium.ThermodynamicState state_a=
    Medium.setState_phX(port_a.p, inStream(port_a.h_outflow), inStream(port_a.Xi_outflow)) if 
       show_NPSHa "state for medium inflowing through port_a";
  Medium.Density rho_in = Medium.density(state_a) if show_NPSHa 
    "Liquid density at the inlet port_a";
  Modelica.SIunits.Length NPSHa=NPSPa/(rho_in*system.g) if show_NPSHa 
    "Net Positive Suction Head available";
  Modelica.SIunits.Pressure NPSPa=assertPositiveDifference(
        port_a.p,
        Medium.saturationPressure(Medium.temperature(state_a)),
        "Cavitation occurs at the pump inlet") if show_NPSHa 
    "Net Positive Suction Pressure available";
  Modelica.SIunits.Pressure NPDPa=assertPositiveDifference(
        port_b.p,
        Medium.saturationPressure(medium.T),
        "Cavitation occurs in the pump") if show_NPSHa 
    "Net Positive Discharge Pressure available";
  // constant Modelica.SIunits.Height unitHead=1;

protected 
  constant Modelica.SIunits.Pressure unitPressure=1;
  constant Modelica.SIunits.MassFlowRate unitMassFlowRate=1;

equation 
  // Flow equations
  if not checkValve then
    // Regular flow characteristics without check valve
    // With a replaceable function, Dymola 7.3 does not find the derivative function.
    // Support request: Dynasim #10872
    dp = (N/N_nominal)^2*flowCharacteristic(V_flow_single*(N_nominal/N));
    // With the statement below, Dymola 7.3 finds the derivative function
   // dp = (N/N_nominal)^2*Buildings.Fluid.Movers.BaseClasses.Characteristics.quadraticFlow(V_flow_nominal={0,1.8,3}, dp_nominal={1000,600,0},
   //  V_flow=V_flow_single*(N_nominal/N));
    s = 0;
  elseif s > 0 then
    // Flow characteristics when check valve is open
    dp = (N/N_nominal)^2*flowCharacteristic(V_flow_single*(N_nominal/N));
    V_flow_single = s*unitMassFlowRate/medium.d;
  else
    // Flow characteristics when check valve is closed
    dp = (N/N_nominal)^2*flowCharacteristic(0) - s*unitPressure;
    V_flow_single = 0;
  end if;

  // Power consumption
  if use_powerCharacteristic then
    W_single = (N/N_nominal)^3*(medium.d/rho_nominal)*powerCharacteristic(V_flow_single*(N_nominal/N));
    eta = dp*V_flow_single/W_single;
  else
    eta = efficiencyCharacteristic(V_flow_single*(N_nominal/N));
    W_single = dp*V_flow_single/eta;
  end if;

  // Energy balance
  Wb_flow = W_total;
  Qb_flow = heatTransfer.Q_flows[1];
  Hb_flow = port_a.m_flow*actualStream(port_a.h_outflow) +
            port_b.m_flow*actualStream(port_b.h_outflow);

  // Ports
  port_a.h_outflow = medium.h;
  port_b.h_outflow = medium.h;
  port_b.p = medium.p 
    "outlet pressure is equal to medium pressure, which includes Wb_flow";

  // Mass balance
  mb_flow = port_a.m_flow + port_b.m_flow;

  mbXi_flow = port_a.m_flow*actualStream(port_a.Xi_outflow) +
              port_b.m_flow*actualStream(port_b.Xi_outflow);
  port_a.Xi_outflow = medium.Xi;
  port_b.Xi_outflow = medium.Xi;

  mbC_flow = port_a.m_flow*actualStream(port_a.C_outflow) +
             port_b.m_flow*actualStream(port_b.C_outflow);
  port_a.C_outflow = C;
  port_b.C_outflow = C;

  connect(heatTransfer.heatPorts[1], heatPort);

end PartialFlowMachine;

Buildings.Fluid.Movers.BaseClasses.PartialFlowMachine.HeatTransfer

Parameters

Type	Name	Default	Description
Ambient
CoefficientOfHeatTransfer	k	0	Heat transfer coefficient to ambient [W/(m2.K)]
Temperature	T_ambient	system.T_ambient	Ambient temperature [K]
Internal Interface
replaceable package Medium		PartialMedium	Medium in the component
Integer	n	1	Number of heat transfer segments
Boolean	use_k	false	= true to use k value for thermal isolation

Connectors

Type	Name	Description
HeatPorts_a	heatPorts[n]	Heat port to component boundary

Modelica definition

replaceable model HeatTransfer = 
    Modelica.Fluid.Vessels.BaseClasses.HeatTransfer.IdealHeatTransfer 
  constrainedby 
  Modelica.Fluid.Vessels.BaseClasses.HeatTransfer.PartialVesselHeatTransfer 
  "Wall heat transfer";