.BuildingSystems.Fluid.HeatExchangers.PrescribedOutlet

Information

Model that allows specifying the temperature and mass fraction of the fluid that leaves the model from port_b.

This model forces the outlet temperature at port_b to be equal to the temperature of the input signal TSet, subject to optional limits on the heating or cooling capacity QMax_flow ≥ 0 and QMin_flow ≤ 0. Similarly than for the temperature, this model also forces the outlet water mass fraction at port_b to be no lower than the input signal X_wSet, subject to optional limits on the maximum water vapor mass flow rate that is added, as described by the parameter mWatMax_flow. By default, the model has unlimited capacity, but control of temperature and humidity can be subject to capacity limits, or be disabled.

The output signal Q_flow is the heat added (for heating) or subtracted (for cooling) to the medium if the 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.

If the parameter energyDynamics is not equal to 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

τ_eff = τ |ṁ| ⁄ ṁ_nom

where τ_eff is the effective time constant for the given mass flow rate ṁ and τ is the time constant at the nominal mass flow rate ṁ_nom. 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. If no flow resistance is requested, set dp_nominal=0.

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

Limitations

This model only adds or removes heat or water vapor for the flow from port_a to port_b. The enthalpy of the reverse flow is not affected by this model.

If this model is used to cool air below the dew point temperature, the water mass fraction will not change.

Note that for use_TSet = false, the enthalpy of the leaving fluid will not be changed, even if moisture is added. The enthalpy added (or removed) by the change in humidity is neglected. To properly account for change in enthalpy due to humidification, use instead BuildingSystems.Fluid.Humidifiers.SprayAirWasher_X.

Validation

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

Revisions

• March 3, 2022, by Michael Wetter:
  Removed massDynamics.
  This is for issue 1542.
• May 3, 2017, by Michael Wetter:
  Updated protected model for #763.
• December 1, 2016, by Michael Wetter:
  Updated model as use_dh is no longer a parameter in the pressure drop model.
  This is for #480.
• November 11, 2014, by Michael Wetter:
  Revised implementation.
• March 19, 2014, by Christoph Nytsch-Geusen:
  First implementation.