.Buildings.Fluid.HydronicConfigurations.ActiveNetworks.Throttle .Buildings.Fluid.HydronicConfigurations.ActiveNetworks.ThrottleThis 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
|
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.
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_