modelIndirectTankHeatExchanger

Heat exchanger typically submerged in a fluid with a second fluid circulating through it

Extends from Buildings.Fluid.Interfaces.TwoPortFlowResistanceParameters (Parameters for flow resistance for models with two ports), Buildings.Fluid.Interfaces.LumpedVolumeDeclarations (Declarations for lumped volumes), Buildings.Fluid.Interfaces.PartialTwoPortInterface (Partial model with two ports and declaration of quantities that are used by many models).

Information

This model is a heat exchanger with a moving fluid on one side and a stagnant fluid on the other. It is intended for use when a heat exchanger is submerged in a stagnant fluid. For example, the heat exchanger in a storage tank which is part of a solar thermal system.

This component models the fluid in the heat exchanger, convection between the fluid and the heat exchanger, and convection from the heat exchanger to the surrounding fluid.

The model is based on Buildings.Fluid.HeatExchangers.BaseClasses.HACoilInside and Buildings.Fluid.HeatExchangers.BaseClasses.HANaturalCylinder.

The fluid ports are intended to be connected to a circulated heat transfer fluid while the heat port is intended to be connected to a stagnant fluid.

Parameters

Type	Name	Default	Description
Boolean	homotopyInitialization	true	= true, use homotopy method
Integer	nSeg		Number of segments in the heat exchanger
Modelica.Units.SI.HeatCapacity	CHex		Capacitance of the heat exchanger
Modelica.Units.SI.Volume	volHexFlu		Volume of heat transfer fluid in the heat exchanger
Modelica.Units.SI.ThermalConductance	UA_nominal	abs(Q_flow_nominal/(THex_nominal - TTan_nominal))	Nominal UA value for the heat exchanger
Modelica.Units.SI.Diameter	dExtHex		Exterior diameter of the heat exchanger pipe
Flow resistance
Boolean	computeFlowResistance (from TwoPortFlowResistanceParameters)	true	=true, compute flow resistance. Set to false to assume no friction
Boolean	from_dp (from TwoPortFlowResistanceParameters)	false	= true, use m_flow = f(dp) else dp = f(m_flow)
Real	n (from TwoPortFlowResistanceParameters)	2	Flow exponent, n=1 for laminar, n=2 for turbulent
Boolean	linearizeFlowResistance (from TwoPortFlowResistanceParameters)	false	= true, use linear relation between m_flow and dp for any flow rate
Real	deltaM (from TwoPortFlowResistanceParameters)	0.1	Fraction of nominal flow rate where flow transitions to laminar
Nominal condition
Modelica.Units.SI.PressureDifference	dp_nominal (from TwoPortFlowResistanceParameters)		Pressure difference
Modelica.Units.SI.MassFlowRate	m_flow_nominal (from PartialTwoPortInterface)		Nominal mass flow rate
Dynamics › Conservation equations
Modelica.Fluid.Types.Dynamics	energyDynamics (from LumpedVolumeDeclarations)	Modelica.Fluid.Types.Dynamics.DynamicFreeInitial	Type of energy balance: dynamic (3 initialization options) or steady state
Modelica.Fluid.Types.Dynamics	substanceDynamics (from LumpedVolumeDeclarations)	energyDynamics	Type of independent mass fraction balance: dynamic (3 initialization options) or steady state
Modelica.Fluid.Types.Dynamics	traceDynamics (from LumpedVolumeDeclarations)	energyDynamics	Type of trace substance balance: dynamic (3 initialization options) or steady state
Modelica.Fluid.Types.Dynamics	energyDynamicsSolid	energyDynamics	Formulation of energy balance for heat exchanger solid mass
Advanced › Dynamics
Modelica.Fluid.Types.Dynamics	massDynamics (from LumpedVolumeDeclarations)	energyDynamics	Type of mass balance: dynamic (3 initialization options) or steady state, must be steady state if energyDynamics is steady state
Initialization
Medium.AbsolutePressure	p_start (from LumpedVolumeDeclarations)	Medium.p_default	Start value of pressure
Medium.Temperature	T_start (from LumpedVolumeDeclarations)	Medium.T_default	Start value of temperature
Medium.MassFraction[Medium.nX]	X_start (from LumpedVolumeDeclarations)	Medium.X_default	Start value of mass fractions m_i/m
Medium.ExtraProperty[Medium.nC]	C_start (from LumpedVolumeDeclarations)	fill(0, Medium.nC)	Start value of trace substances
Medium.ExtraProperty[Medium.nC]	C_nominal (from LumpedVolumeDeclarations)	fill(1E-2, Medium.nC)	Nominal value of trace substances. (Set to typical order of magnitude.)
Dynamics
Real	mSenFac (from LumpedVolumeDeclarations)	1	Factor for scaling the sensible thermal mass of the volume
Assumptions
Boolean	allowFlowReversal (from PartialTwoPort)	true	= false to simplify equations, assuming, but not enforcing, no flow reversal
Advanced
Modelica.Units.SI.MassFlowRate	m_flow_small (from PartialTwoPortInterface)	1E-4*abs(m_flow_nominal)	Small mass flow rate for regularization of zero flow
Advanced › Diagnostics
Boolean	show_T (from PartialTwoPortInterface)	false	= true, if actual temperature at port is computed
General › Nominal condition
Modelica.Units.SI.HeatFlowRate	Q_flow_nominal		Heat transfer at nominal conditions
Modelica.Units.SI.Temperature	TTan_nominal		Temperature of fluid inside the tank at UA_nominal
Modelica.Units.SI.Temperature	THex_nominal		Temperature of fluid inside the heat exchanger at UA_nominal
Real	r_nominal	0.5	Ratio between coil inside and outside convective heat transfer
Advanced › Modeling detail
Boolean	hA_flowDependent	true	Set to false to make the convective heat coefficient calculation of the fluid inside the coil independent of mass flow rate
Boolean	hA_temperatureDependent	true	Set to false to make the convective heat coefficient calculation of the fluid inside the coil independent of temperature

Connectors

Type	Name	Description
Modelica.Fluid.Interfaces.FluidPort_a	port_a (from PartialTwoPort)	Fluid connector a (positive design flow direction is from port_a to port_b)
Modelica.Fluid.Interfaces.FluidPort_b	port_b (from PartialTwoPort)	Fluid connector b (positive design flow direction is from port_a to port_b)
Modelica.Thermal.HeatTransfer.Interfaces.HeatPort_a[nSeg]	port	Heat port connected to water inside the tank

Components

Type	Name	Default	Description
Modelica.Units.SI.MassFlowRate	m_flow (from PartialTwoPortInterface)	port_a.m_flow	Mass flow rate from port_a to port_b (m_flow > 0 is design flow direction)
Modelica.Units.SI.PressureDifference	dp (from PartialTwoPortInterface)	port_a.p - port_b.p	Pressure difference between port_a and port_b
Medium.ThermodynamicState	sta_a (from PartialTwoPortInterface)	if allowFlowReversal then Medium.setState_phX(port_a.p, noEvent(actualStream(port_a.h_outflow)), noEvent(actualStream(port_a.Xi_outflow))) else Medium.setState_phX(port_a.p, noEvent(inStream(port_a.h_outflow)), noEvent(inStream(port_a.Xi_outflow)))	Medium properties in port_a
Medium.ThermodynamicState	sta_b (from PartialTwoPortInterface)	if allowFlowReversal then Medium.setState_phX(port_b.p, noEvent(actualStream(port_b.h_outflow)), noEvent(actualStream(port_b.Xi_outflow))) else Medium.setState_phX(port_b.p, noEvent(port_b.h_outflow), noEvent(port_b.Xi_outflow))	Medium properties in port_b
Buildings.Fluid.FixedResistances.PressureDrop	res		Calculates the flow resistance and pressure drop through the heat exchanger
Buildings.Fluid.MixingVolumes.MixingVolume[nSeg]	vol		Heat exchanger fluid
Modelica.Thermal.HeatTransfer.Components.HeatCapacitor[nSeg]	cap		Thermal mass of the heat exchanger

Name	Description
MediumHex	Heat transfer fluid flowing through the heat exchanger
MediumTan	Heat transfer fluid inside the tank

Revisions

June 17, 2026, by Michael Wetter:
Updated implementation to allow a flow coefficient n that is different from 2. This allows use of the model for not fully turbulent flow.
This is for Buildings, #4620.
March 7, 2022, by Michael Wetter:
Set final massDynamics=energyDynamics.
This is for #1542.
April 9, 2021, by Michael Wetter:
Corrected placement of each keyword.
See Buildings, PR #2440.
April 14, 2020, by Michael Wetter:
Changed homotopyInitialization to a constant.
This is for IBPSA, #1341.
June 7, 2018 by Filip Jorissen:
Copied model from Buildings and update the model accordingly. This is for #314.
January 7, 2016, by Filip Jorissen:
Propagated flowDependent and temperatureDependent in hAPipIns. This is for issue #454.
September 24, 2015 by Michael Wetter:
Set fixed attribute in cap.T to avoid unspecified initial conditions.
July 2, 2015, by Michael Wetter:
Set prescribedHeatFlowRate=false in control volume.
July 1, 2015, by Filip Jorissen:
Added parameter energyDynamicsSolid. This is for #434.
March 28, 2015, by Filip Jorissen:
Propagated allowFlowReversal.
August 29, 2014, by Michael Wetter:
Introduced MediumTan for the tank medium, and assigned Medium to be equal to MediumHex. This is to correct issue #271.
June 18, 2014, by Michael Wetter:
Set initial equations for cap, and renamed this instance from Cap to cap. This was done to avoid a warning during translation, and to comply with the coding convention.
October 8, 2013, by Michael Wetter:
Removed parameter show_V_flow.
January 29, 2013, by Peter Grant:
First implementation.