.Buildings.Fluid.HydronicConfigurations.ActiveNetworks.InjectionThreeWay .Buildings.Fluid.HydronicConfigurations.ActiveNetworks.InjectionThreeWayThis configuration (see schematic below) is used for constant flow primary and consumer circuits where the consumer circuit has a different supply temperature set point, either at design conditions or varying during operation. Although this configuration may theoretically still be used if the primary and secondary design temperatures are equal, it loses its main advantage which is that the control valve can be sized for a lower flow rate and can therefore be smaller. The fixed bypass ensures a consumer circuit operation hydronically decoupled from the primary side and the control valve position.
The following table presents the main characteristics of this configuration.
| Primary circuit | Constant flow |
| Secondary (consumer) circuit | Constant flow |
| Typical applications |
Consumer circuit supply temperature different from primary circuit such
as underfloor heating systems (Otherwise use Buildings.Fluid.HydronicConfigurations.ActiveNetworks.Decoupling) Primary pressure differential either too low or too high or varying too much |
| Non-recommended applications |
DHC systems due to the significant recirculating primary flow rate at low load Heating systems with condensing boilers for the same reason |
| Built-in valve control options |
Supply temperature Return temperature |
|
Control valve selection |
β
= ΔpA-AB / ΔpJ-AB
≈ 1 Sizing is only based on a minimum pressure drop of 3 kPa at design flow rate ṁ1, design (see below). |
| Balancing requirement |
The three-way valve should be fully open at design conditions.dpBal3_nominal=dp1_nominal-dpValve_nominal
for the primary design flow rate
ṁ1, design = ṁ2, design *
(T2, sup, design - T2, ret, design) /
(T1, sup, design - T2, ret, design)
|
|
Lumped flow resistances include (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.) |
The reduced flow through the control valve due to the intermediary bypass allows selecting a smaller valve for the same design pressure drop. The pressure drop through the control valve is compensated by the primary pump, reducing the secondary pump head.
The balancing procedure should ensure that the three-way valve is fully open at design conditions. Oversizing the primary balancing valve (yielding a lower pressure drop) is not detrimental to the consumer circuit operation: the control valve compensates by working at a lower opening fraction on average. However, the primary circuit operation is degraded with a lower ΔT and a higher mass flow rate. See Buildings.Fluid.HydronicConfigurations.ActiveNetworks.Examples.InjectionThreeWay for a numerical illustration of those effects.