modelDualMixing

Dual mixing circuit

Extends from HydronicConfigurations.Interfaces.PartialHydronicConfiguration.

Information

Summary

This configuration (see schematic below) is used instead of Buildings.Fluid.HydronicConfigurations.PassiveNetworks.SingleMixing when the primary and secondary circuits have a different design supply temperature. Contrary to the single mixing circuit, the use of this configuration is restricted to constant flow secondary circuits due to the constraint on the fixed bypass pressure differential that must remain sufficiently high.

Schematic

The following table presents the main characteristics of this configuration.

Primary circuit	Variable flow
Secondary (consumer) circuit	Constant flow
Typical applications	Consumer circuit supply temperature different from primary circuit such as underfloor heating systems
Non-recommended applications	Applications where primary and secondary supply temperature must be equal as secondary flow recirculation cannot be avoided.
Built-in valve control options	Supply temperature
Control valve selection (See the nomenclature in the schematic.)	β = Δp_A-AB / Δp_K-L = Δp_A-AB / (Δp₁ + Δp_A-AB) The control valve is sized with a pressure drop equal to the maximum of Δp₁ and 3e3 Pa at ṁ_{1, design} (see below).
Balancing requirement	The three-way valve should be fully open at design conditions. `dpBal3_nominal=dpValve_nominal+dp1_nominal` for a design flow rate in the fixed bypass equal to: ṁ_{3, design} = ṁ_{2, design} - ṁ_{1, design} = ṁ_{2, design} (T_{1, sup, design} - T_{2, sup, design}) / (T_{1, sup, design} - T_{2, ret, design})* The primary design flow rate is: ṁ_{1, design} = ṁ_{2, design} (T_{2, sup, design} - T_{2, ret, design}) / (T_{1, sup, design} - T_{2, ret, design})*
Lumped flow resistance includes (With the setting `use_lumFloRes=true`.)	Control valve `val` only (So the option has no effect here: the balancing valves are always modeled as distinct flow resistances.)

Additional comments

The bypass balancing valve works together with the secondary pump to generate the pressure differential differential at the boundaries of the control valve. So it is paramount for proper operation of the consumer circuit that the bypass balancing valve generates enough pressure drop at its design flow rate ṁ_{3, design} otherwise the consumer circuit is starved with primary flow rate despite the control valve being fully open. So oversizing the bypass balancing valve (yielding a lower pressure drop) is detrimental to the consumer circuit operation. Undersizing the bypass balancing valve (yielding a lower pressure drop) does not disturb the secondary circuit operation as the control valve then compensates for the elevated pressure differential by working at a lower opening on average. However, the secondary pump head is increased and so is the electricity consumption. See Buildings.Fluid.HydronicConfigurations.PassiveNetworks.Examples.DualMixing for a numerical illustration of those effects.

The parameter dp1_nominal stands for the potential primary back pressure and must be provided as an absolute value. By default the secondary pump is parameterized with a design pressure rise equal to dp2_nominal + dpBal2_nominal + dpBal3_nominal.

Parameters

Type	Name	Default	Description
Real	n (from PartialHydronicConfiguration)	2	Flow exponent, n1=1 for laminar, n1=2 for turbulent
Movers.Data.Generic	perPum (from PartialHydronicConfiguration)
Configuration
Boolean	use_siz (from PartialHydronicConfiguration)	true	Set to true for built-in sizing of control valve and optional pump
Boolean	use_dp1 (from PartialHydronicConfiguration)		Set to true to enable dp1_nominal
Boolean	use_dp2 (from PartialHydronicConfiguration)		Set to true to enable dp2_nominal
Buildings.Fluid.HydronicConfigurations.Types.Valve	typVal (from PartialHydronicConfiguration)		Type of control valve
Boolean	have_typVar (from PartialHydronicConfiguration)	true	Set to true to enable the choice of the controlled variable
Nominal condition
Modelica.Units.SI.MassFlowRate	m1_flow_nominal (from PartialHydronicConfiguration)		Mass flow rate in primary circuit at design conditions
Modelica.Units.SI.MassFlowRate	m2_flow_nominal (from PartialHydronicConfiguration)		Mass flow rate in consumer circuit at design conditions
Modelica.Units.SI.PressureDifference	dp1_nominal (from PartialHydronicConfiguration)		Primary circuit pressure differential at design conditions
Modelica.Units.SI.PressureDifference	dp2_nominal (from PartialHydronicConfiguration)		Consumer circuit pressure differential at design conditions
Control valve
Buildings.Fluid.HydronicConfigurations.Types.ValveCharacteristic	typCha (from PartialHydronicConfiguration)	Buildings.Fluid.HydronicConfigurations.Types.ValveCharacteristic.EqualPercentage	Control valve characteristic
Modelica.Units.SI.PressureDifference	dpValve_nominal (from PartialHydronicConfiguration)		Control valve pressure drop at design conditions
Actuators.Valves.Data.Generic	flowCharacteristics (from PartialHydronicConfiguration)		Table with flow characteristics
Actuators.Valves.Data.Generic	flowCharacteristics1 (from PartialHydronicConfiguration)		Table with flow characteristics for direct flow path at port_1
Actuators.Valves.Data.Generic	flowCharacteristics3 (from PartialHydronicConfiguration)		Table with flow characteristics for bypass flow path at port_3
Pump
Buildings.Fluid.HydronicConfigurations.Types.Pump	typPum (from PartialHydronicConfiguration)	Buildings.Fluid.HydronicConfigurations.Types.Pump.VariableInput	Type of secondary pump
Buildings.Fluid.HydronicConfigurations.Types.PumpModel	typPumMod (from PartialHydronicConfiguration)	Buildings.Fluid.HydronicConfigurations.Types.PumpModel.Speed	Type of pump model
Modelica.Units.SI.MassFlowRate	mPum_flow_nominal (from PartialHydronicConfiguration)	m2_flow_nominal	Pump head at design conditions
Modelica.Units.SI.PressureDifference	dpPum_nominal (from PartialHydronicConfiguration)	dp2_nominal + dpBal2_nominal	Pump head at design conditions
Controls
Buildings.Fluid.HydronicConfigurations.Types.Control	typCtl (from PartialHydronicConfiguration)	Buildings.Fluid.HydronicConfigurations.Types.Control.None	Type of built-in controls
Buildings.Fluid.HydronicConfigurations.Types.ControlVariable	typVar (from PartialHydronicConfiguration)	Buildings.Fluid.HydronicConfigurations.Types.ControlVariable.SupplyTemperature	Controlled variable
Buildings.Controls.OBC.CDL.Types.SimpleController	controllerType (from PartialHydronicConfiguration)	Buildings.Controls.OBC.CDL.Types.SimpleController.PI	Type of controller
Real	k (from PartialHydronicConfiguration)	0.1	Gain of controller
Real	Ti (from PartialHydronicConfiguration)	120	Time constant of integrator block
Assumptions
Boolean	use_lumFloRes (from PartialHydronicConfiguration)	true	Set to true to use a lumped flow resistance when possible
Boolean	allowFlowReversal (from PartialHydronicConfiguration)	true	= false to simplify equations, assuming, but not enforcing, no flow reversal for medium 1
Balancing valves
Modelica.Units.SI.PressureDifference	dpBal1_nominal (from PartialHydronicConfiguration)	0	Primary balancing valve pressure drop at design conditions
Modelica.Units.SI.PressureDifference	dpBal2_nominal (from PartialHydronicConfiguration)	0	Secondary balancing valve pressure drop at design conditions
Modelica.Units.SI.PressureDifference	dpBal3_nominal (from PartialHydronicConfiguration)	0	Bypass balancing valve pressure drop at design conditions
Dynamics › Conservation equations
Modelica.Fluid.Types.Dynamics	energyDynamics (from PartialHydronicConfiguration)	Modelica.Fluid.Types.Dynamics.FixedInitial	Type of energy balance: dynamic (3 initialization options) or steady state
Advanced › Diagnostics
Boolean	show_T (from PartialHydronicConfiguration)	false	= true, if actual temperature at port is computed

Connectors

Type	Name	Description
Modelica.Fluid.Interfaces.FluidPort_a	port_a1 (from PartialHydronicConfiguration)	Primary supply port
Modelica.Fluid.Interfaces.FluidPort_b	port_b1 (from PartialHydronicConfiguration)	Primary return port
Modelica.Fluid.Interfaces.FluidPort_a	port_a2 (from PartialHydronicConfiguration)	Secondary return port
Modelica.Fluid.Interfaces.FluidPort_b	port_b2 (from PartialHydronicConfiguration)	Secondary supply port
Buildings.Controls.OBC.CDL.Interfaces.RealInput	yVal (from PartialHydronicConfiguration)	Valve control signal
Buildings.Controls.OBC.CDL.Interfaces.RealInput	set (from PartialHydronicConfiguration)	Set point
Buildings.Controls.OBC.CDL.Interfaces.RealInput	yPum (from PartialHydronicConfiguration)	Pump control signal (variable speed)
Buildings.Controls.OBC.CDL.Interfaces.IntegerInput	mode (from PartialHydronicConfiguration)	Operating mode
Buildings.Controls.OBC.CDL.Interfaces.RealOutput	yVal_actual (from PartialHydronicConfiguration)	Valve position feedback
Buildings.Controls.OBC.CDL.Interfaces.RealOutput	yPum_actual (from PartialHydronicConfiguration)	Actual pump input value that is used for computations
Buildings.Controls.OBC.CDL.Interfaces.RealOutput	PPum (from PartialHydronicConfiguration)	Pump electrical power

Components

Type	Name	Default	Description
Medium.MassFlowRate	m1_flow (from PartialHydronicConfiguration)	port_a1.m_flow	Mass flow rate from port_a1 to port_b1 (m1_flow > 0 is design flow direction)
Modelica.Units.SI.PressureDifference	dp1 (from PartialHydronicConfiguration)	port_a1.p - port_b1.p	Pressure difference between port_a1 and port_b1
Medium.MassFlowRate	m2_flow (from PartialHydronicConfiguration)	port_a2.m_flow	Mass flow rate from port_a2 to port_b2 (m2_flow > 0 is design flow direction)
Modelica.Units.SI.PressureDifference	dp2 (from PartialHydronicConfiguration)	port_a2.p - port_b2.p	Pressure difference between port_a2 and port_b2
Medium.ThermodynamicState	sta_a1 (from PartialHydronicConfiguration)	if allowFlowReversal then Medium.setState_phX(port_a1.p, noEvent(actualStream(port_a1.h_outflow)), noEvent(actualStream(port_a1.Xi_outflow))) else Medium.setState_phX(port_a1.p, inStream(port_a1.h_outflow), inStream(port_a1.Xi_outflow))	Medium properties in port_a1
Medium.ThermodynamicState	sta_b1 (from PartialHydronicConfiguration)	if allowFlowReversal then Medium.setState_phX(port_b1.p, noEvent(actualStream(port_b1.h_outflow)), noEvent(actualStream(port_b1.Xi_outflow))) else Medium.setState_phX(port_b1.p, port_b1.h_outflow, port_b1.Xi_outflow)	Medium properties in port_b1
Medium.ThermodynamicState	sta_a2 (from PartialHydronicConfiguration)	if allowFlowReversal then Medium.setState_phX(port_a2.p, noEvent(actualStream(port_a2.h_outflow)), noEvent(actualStream(port_a2.Xi_outflow))) else Medium.setState_phX(port_a2.p, inStream(port_a2.h_outflow), inStream(port_a2.Xi_outflow))	Medium properties in port_a2
Medium.ThermodynamicState	sta_b2 (from PartialHydronicConfiguration)	if allowFlowReversal then Medium.setState_phX(port_b2.p, noEvent(actualStream(port_b2.h_outflow)), noEvent(actualStream(port_b2.Xi_outflow))) else Medium.setState_phX(port_b2.p, port_b2.h_outflow, port_b2.Xi_outflow)	Medium properties in port_b2
Buildings.Fluid.HydronicConfigurations.Components.ThreeWayValve	val		Control valve
FixedResistances.Junction	jun		Junction
FixedResistances.PressureDrop	res2		Secondary balancing valve
Buildings.Fluid.HydronicConfigurations.Components.Pump	pum		Pump
Sensors.TemperatureTwoPort	T2Sup		Consumer circuit supply temperature sensor
FixedResistances.Junction	junBypSup		Junction
FixedResistances.Junction	junBypRet		Junction
Sensors.TemperatureTwoPort	T2Ret		Consumer circuit return temperature sensor
Buildings.Controls.OBC.CDL.Integers.GreaterThreshold	isEna		Returns true if enabled
Controls.PIDWithOperatingMode	ctl		Controller
FixedResistances.PressureDrop	res3		Bypass balancing valve

Revisions

June 17, 2026, by Michael Wetter:
Updated implementation to allow a flow coefficient n that is different from 2. This allows use of the model for not fully turbulent flow.
This is for Buildings, #4620.
June 30, 2022, by Antoine Gautier:
First implementation.