Buildings.Fluid.Storage

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Buildings.Fluid.Storage

Package with thermal energy storage models

Information

This package contains thermal energy storage models.

Extends from Modelica.Icons.VariantsPackage (Icon for package containing variants).

Package Content

Name	Description
ExpansionVessel	Pressure expansion vessel with fixed gas cushion
Stratified	Model of a stratified tank for thermal energy storage
StratifiedEnhanced	Stratified tank model with enhanced discretization
StratifiedEnhancedInternalHex	A model of a water storage tank with a secondary loop and intenral heat exchanger
Examples	Collection of models that illustrate model use and test models
BaseClasses	Package with base classes for Buildings.Fluid.Storage

Buildings.Fluid.Storage.ExpansionVessel

Pressure expansion vessel with fixed gas cushion

Information

This is a model of a pressure expansion vessel. The vessel has a fixed total volume. A fraction of the volume is occupied by a fixed mass of gas, and the other fraction is occupied by the liquid that flows through the port. The pressure p in the vessel is

 VGas0 * p_start = (VTot-VLiquid) * p

where VGas0 is the initial volume occupied by the gas, p_start is the initial pressure, VTot is the total volume of the vessel and VLiquid is the amount of liquid in the vessel.

Optionally, a heat port can be activated by setting use_HeatTransfer=true. This heat port connects directly to the liquid. The gas does not participate in the energy balance.

The expansion vessel needs to be used in closed loops that contain water to set a reference pressure and, for liquids where the density is modeled as a function of temperature, to allow for the thermal expansion of the liquid.

Note that alternatively, the model Buildings.Fluid.Sources.FixedBoundary may be used to set a reference pressure. The main difference between these two models is that in this model, there is an energy and mass balance for the volume. In contrast, for Buildings.Fluid.Sources.FixedBoundary, any mass flow rate that flows out of the model will be at a user-specified temperature. Therefore, Buildings.Fluid.Sources.FixedBoundary leads to smaller systems of equations, which may result in faster simulation.

Extends from Buildings.Fluid.Interfaces.LumpedVolumeDeclarations (Declarations for lumped volumes).

Parameters

Type Name Default Description

replaceable package Medium PartialMedium Medium in the component

Volume VTot Total volume of vessel (water and gas side) [m3]

Volume VGas0 VTot/2 Initial volume of gas [m3]

Pressure pMax 5E5 Maximum pressure before simulation stops with an error [Pa]

Dynamics

Equations

Dynamics energyDynamics Modelica.Fluid.Types.Dynamic... Formulation of energy balance

Dynamics massDynamics energyDynamics Formulation of mass balance

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.)

Type	Name	Default	Description
replaceable package Medium	PartialMedium	Medium in the component
Volume	VTot		Total volume of vessel (water and gas side) [m3]
Volume	VGas0	VTot/2	Initial volume of gas [m3]
Pressure	pMax	5E5	Maximum pressure before simulation stops with an error [Pa]
Dynamics
Equations
Dynamics	energyDynamics	Modelica.Fluid.Types.Dynamic...	Formulation of energy balance
Dynamics	massDynamics	energyDynamics	Formulation of mass balance
Initialization
AbsolutePressure	p_start	Medium.p_default	Start value of pressure [Pa]
Temperature	T_start	Medium.T_default	Start value of temperature [K]
MassFraction	X_start[Medium.nX]	Medium.X_default	Start value of mass fractions m_i/m [kg/kg]
ExtraProperty	C_start[Medium.nC]	fill(0, Medium.nC)	Start value of trace substances
ExtraProperty	C_nominal[Medium.nC]	fill(1E-2, Medium.nC)	Nominal value of trace substances. (Set to typical order of magnitude.)

Connectors

Type Name Description

FluidPort_a port_a Fluid port

Type	Name	Description
FluidPort_a	port_a	Fluid port

Modelica definition

model ExpansionVessel 
  "Pressure expansion vessel with fixed gas cushion"
 extends Buildings.Fluid.Interfaces.LumpedVolumeDeclarations;
 parameter Modelica.SIunits.Volume VTot 
    "Total volume of vessel (water and gas side)";
 parameter Modelica.SIunits.Volume VGas0 = VTot/2 "Initial volume of gas";

//////////////////////////////////////////////////////////////
  Modelica.Fluid.Interfaces.FluidPort_a port_a(
    redeclare package Medium = Medium) "Fluid port";

  parameter Modelica.SIunits.Pressure pMax = 5E5 
    "Maximum pressure before simulation stops with an error";

 Modelica.SIunits.Volume VLiq "Volume of liquid in the vessel";
  // We set m(start=(VTot-VGas0)*1000, stateSelect=StateSelect.always)
  // since the mass accumulated in the volume should be a state.
  // This often leads to smaller systems of equations.
protected 
  Buildings.Fluid.Interfaces.ConservationEquation vol(
    redeclare final package Medium = Medium,
    m(start=(VTot-VGas0)*1000, stateSelect=StateSelect.always),
    final nPorts=1,
    final energyDynamics=energyDynamics,
    final massDynamics=massDynamics,
    final p_start=p_start,
    final T_start=T_start,
    final X_start=X_start,
    final C_start=C_start,
    final C_nominal=C_nominal,
    final fluidVolume = VLiq) 
    "Model for mass and energy balance of water in expansion vessel";
  Modelica.Blocks.Sources.Constant heaInp(final k=0) 
    "Block to set heat input into volume";

  Modelica.Blocks.Sources.Constant masExc(final k=0) 
    "Block to set mass exchange in volume";
equation 
  assert(port_a.p < pMax, "Pressure exceeds maximum pressure.\n" +
       "You may need to increase VTot of the ExpansionVessel.");

  // Water content and pressure
  port_a.p * (VTot-VLiq) = p_start * VGas0;

  connect(heaInp.y, vol.Q_flow);
  connect(port_a, vol.ports[1]);
  connect(masExc.y, vol.mWat_flow);
end ExpansionVessel;

Buildings.Fluid.Storage.Stratified

Model of a stratified tank for thermal energy storage

Information

This is a model of a stratified storage tank. The tank uses several volumes to model the stratification. Heat conduction is modeled between the volumes through the fluid, and between the volumes and the ambient. The port heaPorVol may be used to connect a temperature sensor that measures the fluid temperature of an individual volume. It may also be used to add heat to individual volumes.

The tank has nSeg fluid volumes. The top volume has the index 1. Thus, to add a heating element to the bottom element, connect a heat input to heaPorVol[nSeg].

The heat ports outside the tank insulation can be used to specify an ambient temperature. Leave these ports unconnected to force adiabatic boundary conditions. Note, however, that all heat conduction elements through the tank wall (but not the top and bottom) are connected to the heat port heaPorSid. Thus, not connecting heaPorSid means an adiabatic boundary condition in the sense that heaPorSid.Q_flow = 0. This, however, still allows heat to flow through the tank walls, modelled by conWal, from one fluid volume to another one.

For a model with enhanced stratification, use Buildings.Fluid.Storage.StratifiedEnhanced.

Extends from Buildings.Fluid.Interfaces.PartialTwoPortInterface (Partial model transporting fluid between two ports without storing mass or energy).

Parameters

Type	Name	Default	Description
replaceable package Medium	PartialMedium	Medium in the component
Volume	VTan		Tank volume [m3]
Length	hTan		Height of tank (without insulation) [m]
Length	dIns		Thickness of insulation [m]
ThermalConductivity	kIns	0.04	Specific heat conductivity of insulation [W/(m.K)]
Integer	nSeg	2	Number of volume segments
Time	tau	1	Time constant for mixing due to temperature inversion [s]
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*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
Dynamics
Equations
Dynamics	energyDynamics	system.energyDynamics	Formulation of energy balance
Dynamics	massDynamics	energyDynamics	Formulation of mass balance
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

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)

replaceable package Medium

HeatPort_a heaPorVol[nSeg] Heat port of fluid volumes

HeatPort_a heaPorSid Heat port tank side (outside insulation)

HeatPort_a heaPorTop Heat port tank top (outside insulation)

HeatPort_a heaPorBot Heat port tank bottom (outside insulation). Leave unconnected for adiabatic condition

output RealOutput Ql_flow Heat loss of tank (positive if heat flows from tank to ambient)

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)
replaceable package Medium
HeatPort_a	heaPorVol[nSeg]	Heat port of fluid volumes
HeatPort_a	heaPorSid	Heat port tank side (outside insulation)
HeatPort_a	heaPorTop	Heat port tank top (outside insulation)
HeatPort_a	heaPorBot	Heat port tank bottom (outside insulation). Leave unconnected for adiabatic condition
output RealOutput	Ql_flow	Heat loss of tank (positive if heat flows from tank to ambient)

Modelica definition

model Stratified 
  "Model of a stratified tank for thermal energy storage"
  extends Buildings.Fluid.Interfaces.PartialTwoPortInterface(
      showDesignFlowDirection=false);

  replaceable package Medium =
      Modelica.Media.Interfaces.PartialSimpleMedium;
  import Modelica.Fluid.Types;
  import Modelica.Fluid.Types.Dynamics;
  parameter Modelica.SIunits.Volume VTan "Tank volume";
  parameter Modelica.SIunits.Length hTan "Height of tank (without insulation)";
  parameter Modelica.SIunits.Length dIns "Thickness of insulation";
  parameter Modelica.SIunits.ThermalConductivity kIns = 0.04 
    "Specific heat conductivity of insulation";
  parameter Integer nSeg(min=2) = 2 "Number of volume segments";

  ////////////////////////////////////////////////////////////////////
  // Assumptions
  parameter Types.Dynamics energyDynamics=system.energyDynamics 
    "Formulation of energy balance";
  parameter Types.Dynamics massDynamics=energyDynamics 
    "Formulation of mass balance";

  // Initialization
  parameter Medium.AbsolutePressure p_start = Medium.p_default 
    "Start value of pressure";
  parameter Medium.Temperature T_start=Medium.T_default 
    "Start value of temperature";
  parameter Medium.MassFraction X_start[Medium.nX] = Medium.X_default 
    "Start value of mass fractions m_i/m";
  parameter Medium.ExtraProperty C_start[Medium.nC](
       quantity=Medium.extraPropertiesNames)=fill(0, Medium.nC) 
    "Start value of trace substances";

  ////////////////////////////////////////////////////////////////////

  MixingVolumes.MixingVolume[nSeg] vol(
    redeclare each package Medium = Medium,
    each energyDynamics=energyDynamics,
    each massDynamics=massDynamics,
    each p_start=p_start,
    each T_start=T_start,
    each X_start=X_start,
    each C_start=C_start,
    each V=VTan/nSeg,
    each nPorts=nPorts,
    each m_flow_nominal = m_flow_nominal) "Tank segment";
  Sensors.EnthalpyFlowRate hA_flow(redeclare package Medium = Medium,
      m_flow_nominal=m_flow_nominal) "Enthalpy flow rate at port a";
  Sensors.EnthalpyFlowRate[nSeg-1] hVol_flow(redeclare package Medium = Medium,
      each m_flow_nominal=m_flow_nominal);
  Sensors.EnthalpyFlowRate hB_flow(redeclare package Medium = Medium,
      m_flow_nominal=m_flow_nominal) "Enthalpy flow rate at port b";
  BaseClasses.Buoyancy buo(
    redeclare package Medium = Medium,
    V=VTan,
    nSeg=nSeg,
    tau=tau) "Model to prevent unstable tank stratification";
  parameter Modelica.SIunits.Time tau=1 
    "Time constant for mixing due to temperature inversion";
  Modelica.Thermal.HeatTransfer.Components.ThermalConductor[
                                                 nSeg - 1] conFlu(each G=
        conFluSeg) "Thermal conductance in fluid between the segments";
  Modelica.Thermal.HeatTransfer.Components.ThermalConductor[
                                                 nSeg] conWal(
     each G=2*Modelica.Constants.pi*kIns*hSeg/Modelica.Math.log((rTan+dIns)/rTan)) 
    "Thermal conductance through tank wall";
  Modelica.Thermal.HeatTransfer.Components.ThermalConductor conTop(
     G=conTopSeg) "Thermal conductance through tank top";
  Modelica.Thermal.HeatTransfer.Components.ThermalConductor conBot(
     G=conTopSeg) "Thermal conductance through tank bottom";
  Modelica.Thermal.HeatTransfer.Interfaces.HeatPort_a[nSeg] heaPorVol 
    "Heat port of fluid volumes";
  Modelica.Thermal.HeatTransfer.Interfaces.HeatPort_a heaPorSid 
    "Heat port tank side (outside insulation)";
  Modelica.Thermal.HeatTransfer.Sensors.HeatFlowSensor heaFloSid[
                                                         nSeg] 
    "Heat flow at wall of tank (outside insulation)";
  Modelica.Thermal.HeatTransfer.Interfaces.HeatPort_a heaPorTop 
    "Heat port tank top (outside insulation)";
  Modelica.Thermal.HeatTransfer.Sensors.HeatFlowSensor heaFloTop 
    "Heat flow at top of tank (outside insulation)";
  Modelica.Thermal.HeatTransfer.Interfaces.HeatPort_a heaPorBot 
    "Heat port tank bottom (outside insulation). Leave unconnected for adiabatic condition";
  Modelica.Thermal.HeatTransfer.Sensors.HeatFlowSensor heaFloBot 
    "Heat flow at bottom of tank (outside insulation)";
  Modelica.Blocks.Interfaces.RealOutput Ql_flow 
    "Heat loss of tank (positive if heat flows from tank to ambient)";

protected 
  constant Integer nPorts = 2 "Number of ports of volume";
  parameter Modelica.SIunits.Length hSeg = hTan / nSeg 
    "Height of a tank segment";
  parameter Modelica.SIunits.Area ATan = VTan/hTan 
    "Tank cross-sectional area (without insulation)";
  parameter Modelica.SIunits.Length rTan = sqrt(ATan/Modelica.Constants.pi) 
    "Tank diameter (without insulation)";
  parameter Modelica.SIunits.ThermalConductance conFluSeg = ATan*Medium.lambda_const/hSeg 
    "Thermal conductance between fluid volumes";
  parameter Modelica.SIunits.ThermalConductance conTopSeg = ATan*kIns/dIns 
    "Thermal conductance from center of top (or bottom) volume through tank insulation at top (or bottom)";

protected 
  Modelica.Blocks.Routing.Multiplex3 mul(
    n1=1,
    n2=nSeg,
    n3=1);
  Modelica.Blocks.Math.Sum sum1(nin=nSeg + 2);
public 
  Modelica.Thermal.HeatTransfer.Components.ThermalCollector theCol(m=nSeg) 
    "Connector to assign multiple heat ports to one heat port";
equation 
  connect(hA_flow.port_b, vol[1].ports[1]);
  connect(vol[nSeg].ports[2], hB_flow.port_a);
  connect(hB_flow.port_b, port_b);
  for i in 1:(nSeg-1) loop

  connect(vol[i].ports[2], hVol_flow[i].port_a);
  connect(hVol_flow[i].port_b, vol[i+1].ports[1]);
  end for;
  connect(port_a, hA_flow.port_a);
  connect(buo.heatPort, vol.heatPort);
  for i in 1:nSeg-1 loop
  // heat conduction between fluid nodes
     connect(vol[i].heatPort, conFlu[i].port_a);
    connect(vol[i+1].heatPort, conFlu[i].port_b);
  end for;
  connect(vol[1].heatPort, conTop.port_a);
  connect(vol.heatPort, conWal.port_a);
  connect(conBot.port_a, vol[nSeg].heatPort);
  connect(vol.heatPort, heaPorVol);
  connect(conWal.port_b, heaFloSid.port_a);
  for i in 1:nSeg loop

  end for;

  connect(conTop.port_b, heaFloTop.port_a);
  connect(conBot.port_b, heaFloBot.port_a);
  connect(heaFloTop.port_b, heaPorTop);
  connect(heaFloBot.port_b, heaPorBot);
  connect(heaFloTop.Q_flow, mul.u1[1]);
  connect(heaFloSid.Q_flow, mul.u2);
  connect(heaFloBot.Q_flow, mul.u3[1]);
  connect(mul.y, sum1.u);
  connect(sum1.y, Ql_flow);
  connect(heaFloSid.port_b, theCol.port_a);
  connect(theCol.port_b, heaPorSid);
end Stratified;

Buildings.Fluid.Storage.StratifiedEnhanced

Stratified tank model with enhanced discretization

Information

This is a model of a stratified storage tank for thermal energy storage. The model is identical to Buildings.Fluid.Storage.Stratified, except that it adds a correction that reduces the numerical dissipation. The correction uses a third order upwind scheme to compute the outlet temperatures of the segments in the tank. This model is implemented in Buildings.Fluid.Storage.BaseClasses.ThirdOrderStratifier.

Limitations

The model requires at least 4 fluid segments. Hence, set nSeg to 4 or higher.

Extends from Stratified (Model of a stratified tank for thermal energy storage).

Parameters

Type	Name	Default	Description
replaceable package Medium	PartialMedium	Medium in the component
Volume	VTan		Tank volume [m3]
Length	hTan		Height of tank (without insulation) [m]
Length	dIns		Thickness of insulation [m]
ThermalConductivity	kIns	0.04	Specific heat conductivity of insulation [W/(m.K)]
Integer	nSeg	4	Number of volume segments
Time	tau	1	Time constant for mixing due to temperature inversion [s]
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*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
Dynamics
Equations
Dynamics	energyDynamics	system.energyDynamics	Formulation of energy balance
Dynamics	massDynamics	energyDynamics	Formulation of mass balance
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

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 heaPorVol[nSeg] Heat port of fluid volumes

HeatPort_a heaPorSid Heat port tank side (outside insulation)

HeatPort_a heaPorTop Heat port tank top (outside insulation)

HeatPort_a heaPorBot Heat port tank bottom (outside insulation). Leave unconnected for adiabatic condition

output RealOutput Ql_flow Heat loss of tank (positive if heat flows from tank to ambient)

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	heaPorVol[nSeg]	Heat port of fluid volumes
HeatPort_a	heaPorSid	Heat port tank side (outside insulation)
HeatPort_a	heaPorTop	Heat port tank top (outside insulation)
HeatPort_a	heaPorBot	Heat port tank bottom (outside insulation). Leave unconnected for adiabatic condition
output RealOutput	Ql_flow	Heat loss of tank (positive if heat flows from tank to ambient)

Modelica definition

model StratifiedEnhanced 
  "Stratified tank model with enhanced discretization"
  extends Stratified(nSeg=4, nPorts=3, vol(each prescribedHeatFlowRate=true));
  BaseClasses.ThirdOrderStratifier str(
    redeclare package Medium = Medium,
    nSeg=nSeg,
    m_flow_small=m_flow_small) "Model to reduce numerical dissipation";
  Modelica.Blocks.Sources.RealExpression mTan_flow(y=port_a.m_flow) 
    "Mass flow rate at port a";
equation 
  connect(vol[1:nSeg].ports[3], str.fluidPort[2:nSeg+1]);
  connect(hA_flow.H_flow, str.H_flow[1]);
  connect(hVol_flow[1:nSeg-1].H_flow, str.H_flow[2:nSeg]);
  connect(hB_flow.H_flow, str.H_flow[nSeg + 1]);
  connect(str.heatPort, vol.heatPort);
  connect(port_a, str.fluidPort[1]);
  connect(port_b, str.fluidPort[nSeg + 2]);
  connect(mTan_flow.y, str.m_flow);
end StratifiedEnhanced;

Buildings.Fluid.Storage.StratifiedEnhancedInternalHex

A model of a water storage tank with a secondary loop and intenral heat exchanger

Information

This model is an extension of Buildings.Fluid.Storage.StratifiedEnhanced.

The modifications consist of adding a heat exchanger ( Buildings.Fluid.Storage.BaseClasses.IndirectTankHeatExchanger) and fluid ports to connect to the heat exchanger. The modifications allow to run a fluid through the tank causing heat transfer to the stored fluid. A typical example is a storage tank in a solar hot water system.

The heat exchanger model assumes flow through the inside of a helical coil heat exchanger, and stagnant fluid on the outside. Parameters are used to describe the heat transfer on the inside of the heat exchanger at nominal conditions, and geometry of the outside of the heat exchanger. This information is used to compute an hA-value for each side of the coil. Convection calculations are then performed to identify heat transfer between the heat transfer fluid and the fluid in the tank.

Default values describing the heat exchanger are taken from the documentation for a Vitocell 100-B, 300 L tank.

Extends from StratifiedEnhanced (Stratified tank model with enhanced discretization).

Parameters

Type Name Default Description

replaceable package Medium PartialMedium Medium in the component

Volume VTan Tank volume [m3]

Length hTan Height of tank (without insulation) [m]

Length dIns Thickness of insulation [m]

ThermalConductivity kIns 0.04 Specific heat conductivity of insulation [W/(m.K)]

Integer nSeg 4 Number of volume segments

Time tau 1 Time constant for mixing due to temperature inversion [s]

Integer topHexSeg integer(ceil(hexTopHeight/se... Segment the top of the heat exchanger is located in

Integer botHexSeg integer(hexBotHeight/segHeig... Segment the bottom of the heat exchanger is located in

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]

Heat exchanger

replaceable package MediumHex Modelica.Media.Interfaces.Pa... Medium in the heat exchanger loop

Height hexTopHeight Height of the top of the heat exchanger [m]

Height hexBotHeight Height of the bottom of the heat exchanger [m]

Integer hexSegMult 2 Number of heat exchanger segments in each tank segment

HeatCapacity CHex 25.163 Capacitance of the heat exchanger [J/K]

HeatFlowRate Q_flow_nominal Heat transfer at nominal conditions [W]

Temperature TTan_nominal Temperature of fluid inside the tank at nominal heat transfer conditions [K]

Temperature THex_nominal Temperature of fluid inside the heat exchanger at nominal heat transfer conditions [K]

Real r_nominal 0.5 Ratio between coil inside and outside convective heat transfer at nominal heat transfer conditions

MassFlowRate mHex_flow_nominal Nominal mass flow rate through the heat exchanger [kg/s]

Diameter dExtHex 0.025 Exterior diameter of the heat exchanger pipe [m]

Pressure dpHex_nominal 2500 Pressure drop across the heat exchanger at nominal conditions [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*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

Dynamics

Equations

Dynamics energyDynamics system.energyDynamics Formulation of energy balance

Dynamics massDynamics energyDynamics Formulation of mass balance

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

Dynamics heat exchanger

Equations

Dynamics energyDynamicsHex Modelica.Fluid.Types.Dynamic... Formulation of energy balance

Dynamics massDynamicsHex energyDynamicsHex Formulation of mass balance

Flow resistance heat exchanger

Boolean computeFlowResistance true =true, compute flow resistance. Set to false to assume no friction

Boolean from_dp false = true, use m_flow = f(dp) else dp = f(m_flow)

Boolean linearizeFlowResistance false = true, use linear relation between m_flow and dp for any flow rate

Real deltaM 0.1 Fraction of nominal flow rate where flow transitions to laminar

Type	Name	Default	Description
replaceable package Medium	PartialMedium	Medium in the component
Volume	VTan		Tank volume [m3]
Length	hTan		Height of tank (without insulation) [m]
Length	dIns		Thickness of insulation [m]
ThermalConductivity	kIns	0.04	Specific heat conductivity of insulation [W/(m.K)]
Integer	nSeg	4	Number of volume segments
Time	tau	1	Time constant for mixing due to temperature inversion [s]
Integer	topHexSeg	integer(ceil(hexTopHeight/se...	Segment the top of the heat exchanger is located in
Integer	botHexSeg	integer(hexBotHeight/segHeig...	Segment the bottom of the heat exchanger is located in
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]
Heat exchanger
replaceable package MediumHex	Modelica.Media.Interfaces.Pa...	Medium in the heat exchanger loop
Height	hexTopHeight		Height of the top of the heat exchanger [m]
Height	hexBotHeight		Height of the bottom of the heat exchanger [m]
Integer	hexSegMult	2	Number of heat exchanger segments in each tank segment
HeatCapacity	CHex	25.163	Capacitance of the heat exchanger [J/K]
HeatFlowRate	Q_flow_nominal		Heat transfer at nominal conditions [W]
Temperature	TTan_nominal		Temperature of fluid inside the tank at nominal heat transfer conditions [K]
Temperature	THex_nominal		Temperature of fluid inside the heat exchanger at nominal heat transfer conditions [K]
Real	r_nominal	0.5	Ratio between coil inside and outside convective heat transfer at nominal heat transfer conditions
MassFlowRate	mHex_flow_nominal		Nominal mass flow rate through the heat exchanger [kg/s]
Diameter	dExtHex	0.025	Exterior diameter of the heat exchanger pipe [m]
Pressure	dpHex_nominal	2500	Pressure drop across the heat exchanger at nominal conditions [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*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
Dynamics
Equations
Dynamics	energyDynamics	system.energyDynamics	Formulation of energy balance
Dynamics	massDynamics	energyDynamics	Formulation of mass balance
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
Dynamics heat exchanger
Equations
Dynamics	energyDynamicsHex	Modelica.Fluid.Types.Dynamic...	Formulation of energy balance
Dynamics	massDynamicsHex	energyDynamicsHex	Formulation of mass balance
Flow resistance heat exchanger
Boolean	computeFlowResistance	true	=true, compute flow resistance. Set to false to assume no friction
Boolean	from_dp	false	= true, use m_flow = f(dp) else dp = f(m_flow)
Boolean	linearizeFlowResistance	false	= true, use linear relation between m_flow and dp for any flow rate
Real	deltaM	0.1	Fraction of nominal flow rate where flow transitions to laminar

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 heaPorVol[nSeg] Heat port of fluid volumes

HeatPort_a heaPorSid Heat port tank side (outside insulation)

HeatPort_a heaPorTop Heat port tank top (outside insulation)

HeatPort_a heaPorBot Heat port tank bottom (outside insulation). Leave unconnected for adiabatic condition

output RealOutput Ql_flow Heat loss of tank (positive if heat flows from tank to ambient)

FluidPort_a port_a1 Heat exchanger inlet

FluidPort_b port_b1 Heat exchanger outlet

Heat exchanger

replaceable package MediumHex Medium in the heat exchanger loop

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	heaPorVol[nSeg]	Heat port of fluid volumes
HeatPort_a	heaPorSid	Heat port tank side (outside insulation)
HeatPort_a	heaPorTop	Heat port tank top (outside insulation)
HeatPort_a	heaPorBot	Heat port tank bottom (outside insulation). Leave unconnected for adiabatic condition
output RealOutput	Ql_flow	Heat loss of tank (positive if heat flows from tank to ambient)
FluidPort_a	port_a1	Heat exchanger inlet
FluidPort_b	port_b1	Heat exchanger outlet
Heat exchanger
replaceable package MediumHex	Medium in the heat exchanger loop

Modelica definition

model StratifiedEnhancedInternalHex 
  "A model of a water storage tank with a secondary loop and intenral heat exchanger"
  extends StratifiedEnhanced;

  replaceable package MediumHex =
      Modelica.Media.Interfaces.PartialMedium 
    "Medium in the heat exchanger loop";

  parameter Modelica.SIunits.Height hexTopHeight 
    "Height of the top of the heat exchanger";

  parameter Modelica.SIunits.Height hexBotHeight 
    "Height of the bottom of the heat exchanger";

  parameter Integer hexSegMult = 2 
    "Number of heat exchanger segments in each tank segment";

  parameter Modelica.SIunits.HeatCapacity CHex = 25.163 
    "Capacitance of the heat exchanger";

  parameter Modelica.SIunits.HeatFlowRate Q_flow_nominal 
    "Heat transfer at nominal conditions";
  parameter Modelica.SIunits.Temperature TTan_nominal 
    "Temperature of fluid inside the tank at nominal heat transfer conditions";
  parameter Modelica.SIunits.Temperature THex_nominal 
    "Temperature of fluid inside the heat exchanger at nominal heat transfer conditions";
  parameter Real r_nominal(min=0, max=1)=0.5 
    "Ratio between coil inside and outside convective heat transfer at nominal heat transfer conditions";

  parameter Modelica.SIunits.MassFlowRate mHex_flow_nominal 
    "Nominal mass flow rate through the heat exchanger";

  parameter Modelica.SIunits.Diameter dExtHex = 0.025 
    "Exterior diameter of the heat exchanger pipe";

  parameter Modelica.SIunits.Pressure dpHex_nominal(displayUnit="Pa") = 2500 
    "Pressure drop across the heat exchanger at nominal conditions";

  parameter Modelica.Fluid.Types.Dynamics energyDynamicsHex=Modelica.Fluid.Types.Dynamics.DynamicFreeInitial 
    "Formulation of energy balance";
  parameter Modelica.Fluid.Types.Dynamics massDynamicsHex=energyDynamicsHex 
    "Formulation of mass balance";

  parameter Integer topHexSeg = integer(ceil(hexTopHeight/segHeight)) 
    "Segment the top of the heat exchanger is located in";

  parameter Integer botHexSeg = integer(hexBotHeight/segHeight) 
    "Segment the bottom of the heat exchanger is located in";

  parameter Boolean computeFlowResistance=true 
    "=true, compute flow resistance. Set to false to assume no friction";
  parameter Boolean from_dp=false 
    "= true, use m_flow = f(dp) else dp = f(m_flow)";
  parameter Boolean linearizeFlowResistance=false 
    "= true, use linear relation between m_flow and dp for any flow rate";

  parameter Real deltaM=0.1 
    "Fraction of nominal flow rate where flow transitions to laminar";

  Modelica.Fluid.Interfaces.FluidPort_a port_a1(
    redeclare package Medium =MediumHex) "Heat exchanger inlet";
  Modelica.Fluid.Interfaces.FluidPort_b port_b1(
     redeclare package Medium = MediumHex) "Heat exchanger outlet";

  BaseClasses.IndirectTankHeatExchanger indTanHex(
    final nSeg=nSegHex,
    final CHex=CHex,
    final volHexFlu=volHexFlu,
    final Q_flow_nominal=Q_flow_nominal,
    final TTan_nominal=TTan_nominal,
    final THex_nominal=THex_nominal,
    final r_nominal=r_nominal,
    final dExtHex=dExtHex,
    redeclare final package Medium = Medium,
    redeclare final package MediumHex = MediumHex,
    final dp_nominal=dpHex_nominal,
    final m_flow_nominal=mHex_flow_nominal,
    final energyDynamics=energyDynamicsHex,
    final massDynamics=massDynamicsHex,
    m_flow_small=1e-4*abs(mHex_flow_nominal),
    final computeFlowResistance=computeFlowResistance,
    from_dp=from_dp,
    linearizeFlowResistance=linearizeFlowResistance,
    deltaM=deltaM) "Heat exchanger inside the tank";

protected 
  parameter Modelica.SIunits.Height segHeight = hTan/nSeg 
    "Height of each tank segment (relative to bottom of same segment)";

  parameter Modelica.SIunits.Volume volHexFlu = 0.25 * Modelica.Constants.pi * dExtHex 
    "Volume of the heat exchanger";

  parameter Integer nSegHex = (topHexSeg - botHexSeg + 1)*hexSegMult 
    "Number of segments in the heat exchanger";

  parameter Integer nSegHexTan = topHexSeg - botHexSeg + 1 
    "Number of tank segments the heat exchanger resides in";

equation 
   for j in 1:nSegHexTan loop
     for i in 1:hexSegMult loop
     connect(indTanHex.port[(j-1)*hexSegMult+i], heaPorVol[nSeg-j+1]);
     end for;
   end for;
  connect(port_a1, indTanHex.port_a);
  connect(indTanHex.port_b, port_b1);

end StratifiedEnhancedInternalHex;

Automatically generated Wed Feb 12 08:17:08 2014.