modelMixingBox

Outside air mixing box with interlocked air dampers
Diagram of MixingBoxOpen the diagram
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Extends from Buildings.Fluid.Actuators.BaseClasses.ActuatorSignal (Partial model that implements the filtered opening for valves and dampers).

Information

Model of an outside air mixing box with exponential dampers. Set y=0 to close the outside air and exhaust air dampers. See Buildings.Fluid.Actuators.Dampers.Exponential for the description of the exponential damper model.

Parameters

TypeNameDefaultDescription
Booleanuse_deltaMtrueSet to true to use deltaM for turbulent transition, else ReC is used
RealdeltaM0.3Fraction of nominal mass flow rate where transition to turbulent occurs
BooleanroundDuctfalseSet to true for round duct, false for square cross section
RealReC4000Reynolds 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
BooleanallowFlowReversaltrue= false to simplify equations, assuming, but not enforcing, no flow reversal
Nominal condition
Modelica.Units.SI.MassFlowRatemOut_flow_nominalMass flow rate outside air damper
Modelica.Units.SI.PressureDifferencedpDamOut_nominalPressure drop of damper in outside air leg
Modelica.Units.SI.PressureDifferencedpFixOut_nominal0Pressure drop of duct and other resistances in outside air leg
Modelica.Units.SI.MassFlowRatemRec_flow_nominalMass flow rate recirculation air damper
Modelica.Units.SI.PressureDifferencedpDamRec_nominalPressure drop of damper in recirculation air leg
Modelica.Units.SI.PressureDifferencedpFixRec_nominal0Pressure drop of duct and other resistances in recirculation air leg
Modelica.Units.SI.MassFlowRatemExh_flow_nominalMass flow rate exhaust air damper
Modelica.Units.SI.PressureDifferencedpDamExh_nominalPressure drop of damper in exhaust air leg
Modelica.Units.SI.PressureDifferencedpFixExh_nominal0Pressure drop of duct and other resistances in exhaust air leg
Advanced
Booleanfrom_dptrue= true, use m_flow = f(dp) else dp = f(m_flow)
Booleanlinearizedfalse= true, use linear relation between m_flow and dp for any flow rate
Booleanuse_constant_densitytrueSet to true to use constant density for flow friction
Damper coefficients
Reala-1.51Coefficient a for damper characteristics
Realb0.105*90Coefficient b for damper characteristics
RealyL15/90Lower value for damper curve
RealyU55/90Upper value for damper curve
Realk10.45Flow coefficient for y=1, k1 = pressure drop divided by dynamic pressure
Reall0.0001Damper leakage, ratio of flow coefficients k(y=0)/k(y=1)

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_OutFluid connector a (positive design flow direction is from port_a to port_b)
Modelica.Fluid.Interfaces.FluidPort_bport_ExhFluid connector b (positive design flow direction is from port_a to port_b)
Modelica.Fluid.Interfaces.FluidPort_aport_RetFluid connector a (positive design flow direction is from port_a to port_b)
Modelica.Fluid.Interfaces.FluidPort_bport_SupFluid connector b (positive design flow direction is from port_a to port_b)

Components

TypeNameDefaultDescription
Buildings.Fluid.Actuators.Dampers.ExponentialdamOAOutdoor air damper
Buildings.Fluid.Actuators.Dampers.ExponentialdamExhExhaust air damper
Buildings.Fluid.Actuators.Dampers.ExponentialdamRecRecirculation air damper
Modelica.Blocks.Sources.ConstantuniUnity signal
Modelica.Blocks.Math.AddaddAdder

Contents

NameDescription
MediumMedium in the component

Revisions

  • February 7, 2025, by Jelger Jansen:
    Removed import statement. This is for IBPSA, #1961.
  • September 21, 2021, by Michael Wetter:
    Corrected typo in comments.
    This is for #1525.
  • June 10, 2021, by Michael Wetter:
    Changed implementation of the filter and changed the parameter order to a constant as most users need not change this value.
    This is for #1498.
  • December 23, 2019, by Antoine Gautier:
    Updated parameter bindings consistently with refactoring of Buildings.Fluid.Actuators.BaseClasses.PartialDamperExponential.
    This is for #1188.
  • January 18, 2019, by Jianjun Hu:
    Limited the media choice to moist air only. See #1050.
  • 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 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.
  • December 14, 2012 by Michael Wetter:
    Renamed protected parameters for consistency with the naming conventions.
  • 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 23, 2010 by Michael Wetter:
    First implementation.