modelHeater_T

Heater with prescribed outlet temperature

Extends from IBPSA.Fluid.HeatExchangers.BaseClasses.PartialPrescribedOutlet.

Information

Model for an ideal heater that controls its outlet temperature to a prescribed outlet temperature.

This model forces the outlet temperature at port_b to be no lower than the temperature of the input signal TSet, subject to optional limits on the capacity. By default, the model has unlimited heating capacity.

The output signal Q_flow is the heat added to the medium if the mass flow rate is from port_a to port_b. If the flow is reversed, then Q_flow=0.

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

If the parameter energyDynamics is different from Modelica.Fluid.Types.Dynamics.SteadyState, the component models the dynamic response using a first order differential equation. The time constant of the component is equal to the parameter tau. This time constant is adjusted based on the mass flow rate using

τeff = τ |ṁ| ⁄ ṁnom

where τeff is the effective time constant for the given mass flow rate ṁ and τ is the time constant at the nominal mass flow rate ṁnom. This type of dynamics is equal to the dynamics that a completely mixed control volume would have.

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

For a similar model that is a sensible cooling device, use IBPSA.Fluid.HeatExchangers.SensibleCooler_T. For a model that uses a control signal u ∈ [0, 1] and multiplies this with the nominal heating or cooling power, use IBPSA.Fluid.HeatExchangers.HeaterCooler_u

Limitations

If the flow is from port_b to port_a, then the enthalpy of the medium is not affected by this model.

Validation

The model has been validated against the analytical solution in the examples IBPSA.Fluid.HeatExchangers.Validation.PrescribedOutlet and IBPSA.Fluid.HeatExchangers.Validation.PrescribedOutlet_dynamic.

Parameters

TypeNameDefaultDescription
Modelica.SIunits.HeatFlowRateQMax_flowModelica.Constants.infMaximum heat flow rate for heating (positive)
Initialization
Modelica.SIunits.TemperatureT_startMedium.T_defaultStart value of temperature
Dynamics › Equations
Modelica.Fluid.Types.DynamicsenergyDynamicsModelica.Fluid.Types.Dynamics.SteadyStateType of energy balance: dynamic (3 initialization options) or steady state

Components

TypeNameDefaultDescription
Modelica.Blocks.Interfaces.RealInputTSetSet point temperature of the fluid that leaves port_b
Modelica.Blocks.Interfaces.RealOutputQ_flowHeat flow rate added to the fluid (if flow is from port_a to port_b)

Revisions

  • September 10, 2018, by Michael Wetter:
    Corrected missing propagation of initial conditions.
    This is for IBPSA, #1016.
  • May 3, 2017, by Michael Wetter:
    First implementation.
    This is for IBPSA, #763.