Buildings.Fluid.Movers

Package Content

Name	Description
Examples	Collection of models that illustrate model use and test models
FlowMachinePolynomial	Pump or fan with head and efficiency declared by a non-dimensional polynomial

Buildings.Fluid.Movers.FlowMachinePolynomial

Information

This is a model of a flow machine (pump or fan).

The normalized pressure difference is computed using a function of the normalized mass flow rate. The function is a polynomial for which a user needs to supply the coefficients and two values that determine for what flow rate the polynomial is linearly extended.

Parameters

Type	Name	Default	Description
replaceable package Medium		PartialMedium	Medium in the component
Length	D		Diameter [m]
Real	a[:]		Polynomial coefficients for pressure=p(mNor_flow)
Real	b[:]		Polynomial coefficients for etaSha=p(mNor_flow)
Real	mNorMin_flow		Lowest valid normalized mass flow rate
Real	mNorMax_flow		Highest valid normalized mass flow rate
Real	scaM_flow	1	Factor used to scale the mass flow rate of the fan (used for quickly adjusting fan size)
Real	scaDp	1	Factor used to scale the pressure increase of the fan (used for quickly adjusting fan size)
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]
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*m_flow_nominal	Small mass flow rate for regularization of zero flow [kg/s]
Diagnostics
Boolean	show_V_flow	true	= true, if volume flow rate at inflowing port is computed
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]

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	N_in	Prescribed rotational speed

Modelica definition

model FlowMachinePolynomial 
  "Pump or fan with head and efficiency declared by a non-dimensional polynomial"
  extends Buildings.Fluid.Interfaces.PartialStaticTwoPortInterface;


  Modelica.Blocks.Interfaces.RealInput N_in "Prescribed rotational speed";

  parameter Modelica.SIunits.Length D "Diameter";
  parameter Real[:] a "Polynomial coefficients for pressure=p(mNor_flow)";
  parameter Real[:] b "Polynomial coefficients for etaSha=p(mNor_flow)";
  parameter Real mNorMin_flow "Lowest valid normalized mass flow rate";
  parameter Real mNorMax_flow "Highest valid normalized mass flow rate";
  parameter Real scaM_flow = 1 
    "Factor used to scale the mass flow rate of the fan (used for quickly adjusting fan size)";
  parameter Real scaDp = 1 
    "Factor used to scale the pressure increase of the fan (used for quickly adjusting fan size)";

  Real pNor(min=0) "Normalized pressure";
  Real mNor_flow(start=mNorMax_flow) "Normalized mass flow rate";
  Real etaSha(min=0, max=1) "Efficiency, flow work divided by shaft power";
  Modelica.SIunits.Power PSha "Power input at shaft";

  Medium.Density den "Medium density";
protected 
  parameter Real pNorMin1(fixed=false) 
    "Normalized pressure, used to test slope of polynomial outside [xMin, xMax]";
  parameter Real pNorMin2(fixed=false) 
    "Normalized pressure, used to test slope of polynomial outside [xMin, xMax]";
  parameter Real pNorMax1(fixed=false) 
    "Normalized pressure, used to test slope of polynomial outside [xMin, xMax]";
  parameter Real pNorMax2(fixed=false) 
    "Normalized pressure, used to test slope of polynomial outside [xMin, xMax]";

initial equation 
 // check slope of polynomial outside the domain [mNorMin_flow, mNorMax_flow]
 pNorMin1 = Buildings.Fluid.Utilities.extendedPolynomial(
                                        c=a, x=mNorMin_flow/2, xMin=mNorMin_flow, xMax=mNorMax_flow);
 pNorMin2 = Buildings.Fluid.Utilities.extendedPolynomial(
                                        c=a, x=mNorMin_flow, xMin=mNorMin_flow, xMax=mNorMax_flow);
 pNorMax1 = Buildings.Fluid.Utilities.extendedPolynomial(
                                        c=a, x=mNorMax_flow, xMin=mNorMin_flow, xMax=mNorMax_flow);
 pNorMax2 = Buildings.Fluid.Utilities.extendedPolynomial(
                                        c=a, x=mNorMax_flow*2, xMin=mNorMin_flow, xMax=mNorMax_flow);
 assert(pNorMin1>pNorMin2,
    "Slope of pump pressure polynomial is non-negative for mNor_flow < mNorMin_flow. Check parameter a.");
 assert(pNorMax1>pNorMax2,
    "Slope of pump pressure polynomial is non-negative for mNorMax_flow < mNor_flow. Check parameter a.");

equation 
  den = Medium.density(sta_a);
  -dp = scaDp     * pNor      * den * D*D   * N_in * N_in;
  m_flow = scaM_flow * mNor_flow * den * D*D*D * N_in;
  pNor = Buildings.Fluid.Utilities.extendedPolynomial(
                                        c=a, x=mNor_flow, xMin=mNorMin_flow, xMax=mNorMax_flow);
  etaSha = max(0.1, Buildings.Fluid.Utilities.polynomial(
                                                      c=b, x=mNor_flow));
  etaSha * PSha = -dp * m_flow / den; // dp<0 and m_flow>0 for normal operation

  // Energy balance (no storage, no heat loss/gain)
  PSha = -m_flow*(port_a.h_outflow-inStream(port_b.h_outflow));
  PSha = m_flow*(port_b.h_outflow-inStream(port_a.h_outflow));

  // Mass balance (no storage)
  port_a.m_flow + port_b.m_flow = 0;

  // Transport of substances
  port_a.Xi_outflow = inStream(port_b.Xi_outflow);
  port_b.Xi_outflow = inStream(port_a.Xi_outflow);

  port_a.C_outflow = inStream(port_b.C_outflow);
  port_b.C_outflow = inStream(port_a.C_outflow);

end FlowMachinePolynomial;