modelHeaterCooler_u

Heater or cooler with prescribed heat flow rate

Extends from Buildings.Fluid.Interfaces.TwoPortHeatMassExchanger (Partial model transporting one fluid stream with storing mass or energy).

Information

Model for an ideal heater or cooler with prescribed heat flow rate to the medium.

This model adds heat in the amount of Q_flow = u Q_flow_nominal to the medium. The input signal u and the nominal heat flow rate Q_flow_nominal can be positive or negative. A positive value of Q_flow means heating, and negative means cooling.

The outlet conditions at port_a are not affected by this model, other than for a possible pressure difference due to flow friction.

Optionally, this model can have a flow resistance. Set dp_nominal = 0 to disable the flow friction calculation.

For a model that uses as an input the fluid temperature leaving at port_b, use Buildings.Fluid.HeatExchangers.PrescribedOutlet

Limitations

This model does not affect the humidity of the air. Therefore, if used to cool air below the dew point temperature, the water mass fraction will not change.

Validation

The model has been validated against the analytical solution in the example Buildings.Fluid.HeatExchangers.Validation.HeaterCooler_u.

Parameters

Type	Name	Default	Description
Boolean	homotopyInitialization (from TwoPortHeatMassExchanger)	true	= true, use homotopy method
Modelica.Units.SI.HeatFlowRate	Q_flow_nominal		Heat flow rate at u=1, positive for heating
Assumptions
Boolean	allowFlowReversal (from PartialTwoPort)	true	= false to simplify equations, assuming, but not enforcing, no flow reversal
Nominal condition
Modelica.Units.SI.MassFlowRate	m_flow_nominal (from PartialTwoPortInterface)		Nominal mass flow rate
Modelica.Units.SI.PressureDifference	dp_nominal (from TwoPortFlowResistanceParameters)		Pressure difference
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
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
Dynamics › Nominal condition
Modelica.Units.SI.Time	tau (from TwoPortHeatMassExchanger)	30	Time constant at nominal flow (if energyDynamics <> SteadyState)
Dynamics › Conservation equations
Modelica.Fluid.Types.Dynamics	energyDynamics (from TwoPortHeatMassExchanger)	Modelica.Fluid.Types.Dynamics.DynamicFreeInitial	Type of energy balance: dynamic (3 initialization options) or steady state
Initialization
Medium.AbsolutePressure	p_start (from TwoPortHeatMassExchanger)	Medium.p_default	Start value of pressure
Medium.Temperature	T_start (from TwoPortHeatMassExchanger)	Medium.T_default	Start value of temperature
Medium.MassFraction[Medium.nX]	X_start (from TwoPortHeatMassExchanger)	Medium.X_default	Start value of mass fractions m_i/m
Medium.ExtraProperty[Medium.nC]	C_start (from TwoPortHeatMassExchanger)	fill(0, Medium.nC)	Start value of trace substances

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.Blocks.Interfaces.RealInput	u	Control input
Modelica.Blocks.Interfaces.RealOutput	Q_flow	Heat added to the fluid

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.MixingVolumes.MixingVolume	vol (from TwoPortHeatMassExchanger)
Buildings.Fluid.FixedResistances.PressureDrop	preDro (from TwoPortHeatMassExchanger)		Flow resistance

Revisions

October 13, 2022, by Fabian Wuellhorst:
Added unit to instance gai.
This is for #1642.
March 7, 2022, by Michael Wetter:
Removed massDynamics.
This is for #1542.
November 3, 2016, by Michael Wetter:
Set preHea(final alpha=0) as this allows to simplify the system of equations.
This is for #570.
November 19, 2015, by Michael Wetter:
Removed assignment of parameter showDesignFlowDirection in extends statement. This is for #349.
May 6, 2015, by Michael Wetter:
Set prescribedHeatFlowRate=true. This is for issue #412.
May 1, 2015, by Marcus Fuchs:
Corrected typo in documentation.
November 12, 2014, by Michael Wetter:
Added output signal Q_flow so that it has the same output ports as Buildings.Fluid.HeatExchangers.Validation.PrescribedOutlet.
September 11, 2014, by Christoph Nytsch-Geusen:
Renaming class to HeaterCooler_u.
October 15, 2013, by Michael Wetter:
Redeclared the control volume to be final so that it does not show anymore in the parameter window.
July 11, 2011, by Michael Wetter:
Redeclared fluid volume as final. This prevents the fluid volume model to appear in the dialog window.
May 24, 2011, by Michael Wetter:
Changed base class to allow using the model as a dynamic or a steady-state model.
April 17, 2008, by Michael Wetter:
First implementation.