modelMixingBoxMinimumFlow

Outside air mixing box with parallel damper for minimum outside air flow rate
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Extends from Buildings.Fluid.Actuators.Dampers.MixingBox (Outside air mixing box with interlocked air dampers).

Information

Model of an outside air mixing box with air dampers and a flow path for the minimum outside air flow rate.

If dp_nominalIncludesDamper=true, then the parameter dp_nominal is equal to the pressure drop of the damper plus the fixed flow resistance at the nominal flow rate. If dp_nominalIncludesDamper=false, then dp_nominal does not include the flow resistance of the air damper.

Parameters

TypeNameDefaultDescription
Booleanuse_deltaM (from MixingBox)trueSet to true to use deltaM for turbulent transition, else ReC is used
RealdeltaM (from MixingBox)0.3Fraction of nominal mass flow rate where transition to turbulent occurs
BooleanroundDuct (from MixingBox)falseSet to true for round duct, false for square cross section
RealReC (from MixingBox)4000Reynolds number where transition to turbulence starts
Dynamics › Actuator position
Booleanuse_strokeTime (from ActuatorSignal)trueSet to true to continuously open and close valve using strokeTime
Modelica.Units.SI.TimestrokeTime (from ActuatorSignal)120Time needed to fully open or close actuator
Modelica.Blocks.Types.Initinit (from ActuatorSignal)Modelica.Blocks.Types.Init.InitialOutputType of initialization (no init/steady state/initial state/initial output)
Realy_start (from ActuatorSignal)1Initial position of actuator
Assumptions
BooleanallowFlowReversal (from MixingBox)true= false to simplify equations, assuming, but not enforcing, no flow reversal
Nominal condition
Modelica.Units.SI.MassFlowRatemOut_flow_nominal (from MixingBox)Mass flow rate outside air damper
Modelica.Units.SI.PressureDifferencedpDamOut_nominal (from MixingBox)Pressure drop of damper in outside air leg
Modelica.Units.SI.PressureDifferencedpFixOut_nominal (from MixingBox)0Pressure drop of duct and other resistances in outside air leg
Modelica.Units.SI.MassFlowRatemRec_flow_nominal (from MixingBox)Mass flow rate recirculation air damper
Modelica.Units.SI.PressureDifferencedpDamRec_nominal (from MixingBox)Pressure drop of damper in recirculation air leg
Modelica.Units.SI.PressureDifferencedpFixRec_nominal (from MixingBox)0Pressure drop of duct and other resistances in recirculation air leg
Modelica.Units.SI.MassFlowRatemExh_flow_nominal (from MixingBox)Mass flow rate exhaust air damper
Modelica.Units.SI.PressureDifferencedpDamExh_nominal (from MixingBox)Pressure drop of damper in exhaust air leg
Modelica.Units.SI.PressureDifferencedpFixExh_nominal (from MixingBox)0Pressure drop of duct and other resistances in exhaust air leg
Modelica.Units.SI.MassFlowRatemOutMin_flow_nominalMass flow rate minimum outside air damper
Modelica.Units.SI.PressureDifferencedpDamOutMin_nominalPressure drop of damper in minimum outside air leg
Modelica.Units.SI.PressureDifferencedpFixOutMin_nominal0Pressure drop of duct and other resistances in minimum outside air leg
Advanced
Booleanfrom_dp (from MixingBox)true= true, use m_flow = f(dp) else dp = f(m_flow)
Booleanlinearized (from MixingBox)false= true, use linear relation between m_flow and dp for any flow rate
Booleanuse_constant_density (from MixingBox)trueSet to true to use constant density for flow friction
Damper coefficients
Reala (from MixingBox)-1.51Coefficient a for damper characteristics
Realb (from MixingBox)0.105*90Coefficient b for damper characteristics
RealyL (from MixingBox)15/90Lower value for damper curve
RealyU (from MixingBox)55/90Upper value for damper curve
Realk1 (from MixingBox)0.45Flow coefficient for y=1, k1 = pressure drop divided by dynamic pressure
Reall (from MixingBox)0.0001Damper leakage, ratio of flow coefficients k(y=0)/k(y=1)
Dynamics › Time needed to open or close valve
RealyOutMin_starty_startInitial value of signal for minimum outside air damper

Connectors

TypeNameDefaultDescription
Modelica.Blocks.Interfaces.RealInputy (from ActuatorSignal)Actuator position (0: closed, 1: open)
Modelica.Blocks.Interfaces.RealOutputy_actual (from ActuatorSignal)Actual actuator position
Modelica.Fluid.Interfaces.FluidPort_aport_Out (from MixingBox)Fluid connector a (positive design flow direction is from port_a to port_b)
Modelica.Fluid.Interfaces.FluidPort_bport_Exh (from MixingBox)Fluid connector b (positive design flow direction is from port_a to port_b)
Modelica.Fluid.Interfaces.FluidPort_aport_Ret (from MixingBox)Fluid connector a (positive design flow direction is from port_a to port_b)
Modelica.Fluid.Interfaces.FluidPort_bport_Sup (from MixingBox)Fluid connector b (positive design flow direction is from port_a to port_b)
Modelica.Fluid.Interfaces.FluidPort_aport_OutMinFluid connector a (positive design flow direction is from port_a to port_b)
Modelica.Blocks.Interfaces.RealInputyOutMinDamper position minimum outside air (0: closed, 1: open)
Modelica.Blocks.Interfaces.RealOutputyOutMin_actualActual valve position

Components

TypeNameDefaultDescription
Buildings.Fluid.Actuators.Dampers.ExponentialdamOA (from MixingBox)Outdoor air damper
Buildings.Fluid.Actuators.Dampers.ExponentialdamExh (from MixingBox)Exhaust air damper
Buildings.Fluid.Actuators.Dampers.ExponentialdamRec (from MixingBox)Recirculation air damper
Modelica.Blocks.Sources.Constantuni (from MixingBox)Unity signal
Modelica.Blocks.Math.Addadd (from MixingBox)Adder
Buildings.Fluid.Actuators.Dampers.ExponentialdamOAMinDamper for minimum outside air intake

Revisions

  • September 11, 2024, by Michael Wetter:
    Renamed parameters to use_strokeTime and strokeTime, and updated actuator model.
  • June 10, 2021, by Michael Wetter:
    Changed implementation of the filter.
    This is for consistency with the changes done in #1498.
  • February 26, 2020, by Antoine Gautier:
    Updated parameter bindings consistently with refactoring of Buildings.Fluid.Actuators.BaseClasses.PartialDamperExponential.
    This is for #1188.
  • March 24, 2017, by Michael Wetter:
    Renamed filteredInput to use_inputFilter.
    This is for #665.
  • March 22, 2017, by Michael Wetter:
    Removed the assignments of AOut, AExh, AOutMin and ARec as these are done in the damper instance using a final assignment of the parameter. This allows scaling the model with m_flow_nominal, which is generally known in the flow leg, and v_nominal, for which a default value can be specified.
    This is for #544.
  • January 22, 2016, by Michael Wetter:
    Corrected type declaration of pressure difference. This is for #404.
  • February 14, 2012 by Michael Wetter:
    Added filter to approximate the travel time of the actuator.
  • February 3, 2012, by Michael Wetter:
    Removed assignment of m_flow_small as it is no longer used in its base class.
  • February 24, 2010 by Michael Wetter:
    Changed implementation of flow resistance. Instead of using a fixed resistance and a damper model in series, only one model is used that internally adds these two resistances. This leads to smaller systems of nonlinear equations. This new implementation extends Buildings.Fluid.Actuators.Dampers.MixingBox.
  • July 20, 2007 by Michael Wetter:
    First implementation.