modelDryCoilDiscretized

Information

Model of a discretized coil with no water vapor condensation. The coil consists of nReg registers that are perpendicular to the air flow path. Each register consists of nPipPar parallel pipes, and each pipe can be divided into nPipSeg pipe segments along the pipe length. Thus, the smallest element of the coil consists of a pipe segment. Each pipe segment is modeled by an instance of Buildings.Fluid.HeatExchangers.BaseClasses.HexElementSensible. Each element has a state variable for the metal.

If the parameter energyDynamics is different from Modelica.Fluid.Types.Dynamics.SteadyState, then a mixing volume of length dl is added to the duct connection. This can help reducing the dimension of the nonlinear system of equations.

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 need to be connected to the other two ports.

To model humidity condensation, use the model Buildings.Fluid.HeatExchangers.WetCoilDiscretized instead of this model, as this model computes only sensible heat transfer.

Implementation

At very small flow rates, which may be caused when the fan is off but there is wind pressure on the building that entrains outside air through the HVAC system, large temperature differences could occur if diffusion were neglected. This model therefore approximates a small diffusion between the elements to have more uniform medium temperatures if the flow is near zero. The approximation is done using the heat conductors heaCon1 and heaCon2. As this is a rough approximation, neighboring elements are connected through these heat conduction elements, ignoring the actual geometrical configuration. Also, radiation between the coil surfaces on the air side is not modelled explicitly, but rather may be considered as approximated by these heat conductors.

Parameters

Connectors

Components

Revisions

• June 22, 2023 by Hongxiang Fu:
  Corrected the modification of hexReg[nReg].m2_flow_nominal.
  This is for #3441.
• November 4, 2017, by Michael wetter:
  Added approximation of diffusion.
  This is for Buildings, #1038.
• October 19, 2017, by Michael Wetter:
  Changed initialization of pressure from a constant to a parameter.
  This is for Buildings, issue 1013.
• September 8, 2017, by Michael Wetter:
  Changed computation of temperature used for hA calculation to avoid a state variable with small time constant for some model parameterizations.
  This is for Buildings, #678.
• September 17, 2016, by Michael Wetter:
  Corrected wrong annotation.
  This is for issue 557.
• February 5, 2015, by Michael Wetter:
  Changed initalize_p from a parameter to a constant. This is only required in finite volume models of heat exchangers (to avoid consistent but redundant initial conditions) and hence it should be set as a constant.
• August 10, 2014, by Michael Wetter:
  Removed parameter m1_flow_nominal, as this parameter is already declared in its base class Buildings.Fluid.Interfaces.PartialFourPortInterface. This change avoids an error in OpenModelica as the two declarations had a different value for the min attribute, which is not valid in Modelica.
  This change also reorganizes the order of the declaration of constants, parameters and models.
• July 3, 2014, by Michael Wetter:
  Added parameters initialize_p1 and initialize_p2. This is required to enable the coil models to initialize the pressure in the first volume, but not in the downstream volumes. Otherwise, the initial equations will be overdetermined, but consistent. This change was done to avoid a long information message that appears when translating models.
• June 29, 2014, by Michael Wetter:
  Removed parameter dl which is no longer needed.
• June 26, 2014, by Michael Wetter:
  Removed parameters energyDynamics1, energyDynamics2 and ductConnectionDynamics, and used instead of these parameters the new parameter energyDynamics. This was done as this complexity is not required.
• December 13, 2013, by Michael Wetter:
  Corrected wrong connection connect(hexReg[nReg].port_b1, pipMan_b.port_b) to connect(hexReg[nReg].port_a1, pipMan_b.port_b). This closes issue https://github.com/lbl-srg/modelica-buildings/issues/194, which caused the last register to have no liquid flow.
• October 8, 2010, by Michael Wetter:
  Set show_T=false to avoid state events near zero flow.
• March 24, 2011, by Michael Wetter:
  Replaced integer division nReg/2 by div(nReg,2) when instantiating an array of models as the former leads to a syntax error in Dymola 7.4 FD01.
• May 28, 2010, by Michael Wetter:
  Fixed bug in assigning pressure drops that led to too high a resistances.
• September 10, 2008, by Michael Wetter:
  Added additional parameters.
• September 9, 2008 by Michael Wetter:
  Propagated more parameters.
• August 12, 2008 by Michael Wetter:
  Introduced option to compute each medium using a steady state model or a dynamic model.
• March 25, 2008, by Michael Wetter:
  First implementation.