modelVariableSpeed

Variable speed DX cooling coil

Extends from Buildings.Fluid.DXSystems.Cooling.BaseClasses.PartialDXCoolingCoil (Partial model for DX cooling coil).

Information

This model can be used to simulate an air source DX cooling coil with continuously variable speed compressors. The control input is the speed ratio. The coil will switch off if the speed ratio is below a minimum value.

See Buildings.Fluid.DXSystems.Cooling.UsersGuide for an explanation of the model.

Parameters

Type	Name	Default	Description
Buildings.Fluid.DXSystems.Cooling.AirSource.Data.Generic.DXCoil	datCoi (from EssentialParameters)		Performance data
Boolean	homotopyInitialization (from TwoPortHeatMassExchanger)	true	= true, use homotopy method
Boolean	use_mCon_flow (from PartialDXCoil)		Set to true to enable connector for the condenser mass flow rate
Real	minSpeRat		Minimum speed ratio
Real	speRatDeaBan	0.05	Deadband for minimum speed ratio
Assumptions
Boolean	allowFlowReversal (from PartialTwoPort)	true	= false to simplify equations, assuming, but not enforcing, no flow reversal
Nominal condition
Modelica.Units.SI.MassFlowRate	m_flow_nominal (from PartialTwoPortInterface)		Nominal mass flow rate
Modelica.Units.SI.PressureDifference	dp_nominal (from TwoPortFlowResistanceParameters)		Pressure difference
Advanced
Modelica.Units.SI.MassFlowRate	m_flow_small (from PartialTwoPortInterface)	1E-4*abs(m_flow_nominal)	Small mass flow rate for regularization of zero flow
Advanced › Diagnostics
Boolean	show_T (from PartialTwoPortInterface)	false	= true, if actual temperature at port is computed
Flow resistance
Boolean	computeFlowResistance (from TwoPortFlowResistanceParameters)	true	=true, compute flow resistance. Set to false to assume no friction
Boolean	from_dp (from TwoPortFlowResistanceParameters)	false	= true, use m_flow = f(dp) else dp = f(m_flow)
Real	n (from TwoPortFlowResistanceParameters)	2	Flow exponent, n=1 for laminar, n=2 for turbulent
Boolean	linearizeFlowResistance (from TwoPortFlowResistanceParameters)	false	= true, use linear relation between m_flow and dp for any flow rate
Real	deltaM (from TwoPortFlowResistanceParameters)	0.1	Fraction of nominal flow rate where flow transitions to laminar
Dynamics › Nominal condition
Modelica.Units.SI.Time	tau (from TwoPortHeatMassExchanger)	30	Time constant at nominal flow (if energyDynamics <> SteadyState)
Dynamics › Conservation equations
Modelica.Fluid.Types.Dynamics	energyDynamics (from TwoPortHeatMassExchanger)	Modelica.Fluid.Types.Dynamics.DynamicFreeInitial	Type of energy balance: dynamic (3 initialization options) or steady state
Initialization
Medium.AbsolutePressure	p_start (from TwoPortHeatMassExchanger)	Medium.p_default	Start value of pressure
Medium.Temperature	T_start (from TwoPortHeatMassExchanger)	Medium.T_default	Start value of temperature
Medium.MassFraction[Medium.nX]	X_start (from TwoPortHeatMassExchanger)	Medium.X_default	Start value of mass fractions m_i/m
Medium.ExtraProperty[Medium.nC]	C_start (from TwoPortHeatMassExchanger)	fill(0, Medium.nC)	Start value of trace substances
Dynamics › Moisture balance
Boolean	computeReevaporation (from PartialDXCoil)	true	Set to true to compute reevaporation of water that accumulated on coil

Connectors

Type	Name	Description
Modelica.Fluid.Interfaces.FluidPort_a	port_a (from PartialTwoPort)	Fluid connector a (positive design flow direction is from port_a to port_b)
Modelica.Fluid.Interfaces.FluidPort_b	port_b (from PartialTwoPort)	Fluid connector b (positive design flow direction is from port_a to port_b)
Modelica.Blocks.Interfaces.RealInput	TOut (from PartialDXCoil)	Outside air dry bulb temperature for an air cooled condenser or wetbulb temperature for an evaporative cooled condenser
Modelica.Blocks.Interfaces.RealInput	mCon_flow (from PartialDXCoil)	Water mass flow rate for condenser
Modelica.Blocks.Interfaces.RealOutput	P (from PartialDXCoil)	Electrical power consumed by the unit
Modelica.Blocks.Interfaces.RealOutput	QSen_flow (from PartialDXCoil)	Sensible heat flow rate
Modelica.Blocks.Interfaces.RealOutput	QLat_flow (from PartialDXCoolingCoil)	Latent heat flow rate
Modelica.Blocks.Interfaces.RealInput	speRat	Speed ratio

Components

Type	Name	Default	Description
Modelica.Units.SI.MassFlowRate	m_flow (from PartialTwoPortInterface)	port_a.m_flow	Mass flow rate from port_a to port_b (m_flow > 0 is design flow direction)
Modelica.Units.SI.PressureDifference	dp (from PartialTwoPortInterface)	port_a.p - port_b.p	Pressure difference between port_a and port_b
Medium.ThermodynamicState	sta_a (from PartialTwoPortInterface)	if allowFlowReversal then Medium.setState_phX(port_a.p, noEvent(actualStream(port_a.h_outflow)), noEvent(actualStream(port_a.Xi_outflow))) else Medium.setState_phX(port_a.p, noEvent(inStream(port_a.h_outflow)), noEvent(inStream(port_a.Xi_outflow)))	Medium properties in port_a
Medium.ThermodynamicState	sta_b (from PartialTwoPortInterface)	if allowFlowReversal then Medium.setState_phX(port_b.p, noEvent(actualStream(port_b.h_outflow)), noEvent(actualStream(port_b.Xi_outflow))) else Medium.setState_phX(port_b.p, noEvent(port_b.h_outflow), noEvent(port_b.Xi_outflow))	Medium properties in port_b
Buildings.Fluid.MixingVolumes.MixingVolume	vol (from TwoPortHeatMassExchanger)
Buildings.Fluid.FixedResistances.PressureDrop	preDro (from TwoPortHeatMassExchanger)		Flow resistance
Buildings.Fluid.DXSystems.Cooling.BaseClasses.PartialCoilInterface	dxCoi (from PartialDXCoil)
Buildings.Fluid.DXSystems.Cooling.BaseClasses.Evaporation	watVapEva (from PartialDXCoolingCoil)		Model that computes evaporation of water that accumulated on the coil surface

Revisions

November 26, 2025, by Michael Wetter:
Updated redeclare and replaceable statements.
This is for issue 4421.
March 19, 2023 by Xing Lu and Karthik Devaprasad:
Renamed class to VariableSpeedDXCooling to differentiate it from DX heating coils.
Updated connect statement to reflect name change of instance from dxCoo to dxCoi.
Updated formatting.
March 7, 2022, by Michael Wetter:
Set final massDynamics=energyDynamics.
This is for #1542.
July 28, 2012 by Kaustubh Phalak:
First implementation.