modelWetCoilCounterFlow

Counterflow coil with discretization along the flow paths and humidity condensation

Extends from Buildings.Fluid.HeatExchangers.DryCoilCounterFlow.

Information

Model of a discretized coil with water vapor condensation. The coil consists of two flow paths which are, at the design flow direction, in opposite direction to model a counterflow heat exchanger. The flow paths are discretized into nEle elements. Each element is modeled by an instance of Buildings.Fluid.HeatExchangers.BaseClasses.HexElementLatent. Each element has a state variable for the metal.

The convective heat transfer coefficients can, for each fluid individually, be computed as a function of the flow rate and/or the temperature, or assigned to a constant. This computation is done using an instance of Buildings.Fluid.HeatExchangers.BaseClasses.HADryCoil.

In this model, the water (or liquid) flow path needs to be connected to port_a1 and port_b1, and the air flow path needs to be connected to the other two ports.

The mass transfer from the fluid 2 to the metal is computed using a similarity law between heat and mass transfer, as implemented by the model Buildings.Fluid.HeatExchangers.BaseClasses.MassExchange.

This model can only be used with medium models that implement the function enthalpyOfLiquid and that contain an integer variable Water whose value is the element number where the water vapor is stored in the species concentration vector. Examples for such media are Buildings.Media.Air and Modelica.Media.Air.MoistAir.

To model this coil for conditions without humidity condensation, use the model Buildings.Fluid.HeatExchangers.DryCoilCounterFlow instead of this model.

Parameters

TypeNameDefaultDescription
Booleansimplify_mWat_flowtrueSet to true to cause port_a.m_flow + port_b.m_flow = 0 even if mWat_flow is non-zero. Used only if Medium.nX > 1

Components

TypeNameDefaultDescription
Modelica.Units.SI.HeatFlowRateQSen2_flowQ2_flow - QLat2_flowSensible heat input into air stream (negative if air is cooled)
Modelica.Units.SI.HeatFlowRateQLat2_flowBuildings.Utilities.Psychrometrics.Constants.h_fg*mWat_flowLatent heat input into air (negative if air is dehumidified)
RealSHRQSen2_flow/noEvent(if (Q2_flow > 1E-6 or Q2_flow < -1E-6) then Q2_flow else 1)Sensible to total heat ratio
Modelica.Units.SI.MassFlowRatemWat_flowsum(ele[i].vol2.mWat_flow for i in 1:nEle)Water flow rate

Revisions

  • July 5, 2022, by Antoine Gautier:
    Restored the addition of heat to mas.T in Buildings.Fluid.HeatExchangers.BaseClasses.HexElementLatent.
    This is for #3065.
  • May 26, 2022, by Michael Wetter:
    Removed addition of heat to mas.T in Buildings.Fluid.HeatExchangers.BaseClasses.HexElementLatent to correct latent heat exchange calculation.
    This is for #3027.
  • March 12, 2021, by Michael Wetter:
    Removed final declaration in redeclaration.
    This is for #2392.
  • May 1, 2020, by Michael Wetter:
    Added constant simplify_mWat_flow.
    This is for #1920.
  • October 19, 2018, by Kino:
    Changed model to use a replaceable model as this allows translation in OpenModelica.
    This is for #1258.
  • April 14, 2017, by David Blum:
    Added heat of condensation to coil surface heat balance and removed it from the air stream. This gives higher coil surface temperature and avoids overestimating the latent heat ratio that was observed in the previous implementation. The code change was in Buildings.Fluid.HeatExchangers.BaseClasses.HexElementLatent.
    This is for #711.
  • April 11, 2017, by Michael Wetter:
    Changed computation of QLat_flow to be consistent with how it is computed in Buildings.Fluid.HeatExchangers.BaseClasses.HexElementLatent.
    Moved variable assignments out of equation section to avoid mixing textual and graphical modeling in equation section.
  • November 8, 2016, by Michael Wetter:
    Removed wrong usage of each keyword.
  • July 29, 2016, by Michael Wetter:
    Redeclared Medium2 to be Modelica.Media.Interfaces.PartialCondensingGases because it is used in vol2 and because the model calls Medium2.enthalpyOfCondensingGas, which requires the medium to extend from this subclass.
    This is for issue 547.
  • February 2, 2012, by Michael Wetter:
    Corrected error in assignment of dp2_nominal in the base class. The previous assignment caused a pressure drop in all except one element, instead of the opposite. This caused too high a flow resistance of the heat exchanger.
  • May 27, 2010, by Michael Wetter:
    First implementation.