modelThrottle
Throttle circuit
Extends from Fluid.HydronicConfigurations.Interfaces.PartialHydronicConfiguration.
Information
This configuration (see schematic below) is used for variable flow primary and consumer circuits that have the same supply temperature set point.
The following table presents the main characteristics of this configuration.
| Primary circuit | Constant flow |
| Secondary (consumer) circuit | Variable flow |
| Typical applications |
Single heating or cooling coil served by a variable flow circuit DHC system energy transfer station with intermediary heat exchanger |
| Non-recommended applications | |
| Built-in valve control options | No built-in controls |
| Control valve selection |
β = ΔpA-B /
Δp1 =
ΔpA-B /
(ΔpA-B + Δp2 + ΔpB-b1) The valve is sized with a pressure drop equal to the one of the consumer circuit and of the primary balancing valve (if any) at design flow rate, yielding an authority of 0.5. |
| Balancing requirement | No strict requirements: see additional comments below. |
|
Lumped flow resistances include (With the setting use_lumFloRes=true.)
|
Control valve val,
whole consumer circuit between b2 and a2and primary balancing valve res1
|
Additional comments
Some authors such as Taylor (2002, 2017) claim that variable flow circuits with variable speed pumps and terminal units with two-valves should not be balanced. The reason is that the circuit can only be balanced at one operating point. At partial load, if remote consumers have a low demand while the consumers closest to the pump have a high demand, the latter ones will experience a flow shortage due to the balancing valve that generates too much pressure drop for the lower available pressure differential due to the lower pump speed. In addition, there is no clear balancing procedure when a load diversity factor is taken into account. The example Buildings.Fluid.HydronicConfigurations.ActiveNetworks.Examples.ThrottleOpenLoop allows drawing similar conclusions.
References
Taylor, S. T., 2002. Balancing variable flow hydronic systems. ASHRAE Journal. URL: https://tayloreng.egnyte.com/dl/CZVS52ZTVB/ASHRAE_Journal_-_Balancing_Variable_Flow_Hydronic_Systems.pdf_
Taylor, S. T., 2017. Doubling down on not balancing variable flow hydronic systems. ASHRAE Journal. URL: https://tayloreng.egnyte.com/dl/W8sfOOuoni/ASHRAE_Journal_-_Doubling-Down_on_NOT_Balancing_Variable_Flow_Hydronic_Systems.pdf_
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
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.TwoWayValve | val | Control valve | |
| Buildings.Fluid.FixedResistances.PressureDrop | res1 | Primary balancing valve |
Revisions
-
June 17, 2026, by Michael Wetter:
Updated implementation to allow a flow coefficientnthat is different from2. This allows use of the model for not fully turbulent flow.
This is for Buildings, #4620. -
June 30, 2022, by Antoine Gautier:
First implementation.