.Buildings.Fluid.HydronicConfigurations.ActiveNetworks.Decoupling .Buildings.Fluid.HydronicConfigurations.ActiveNetworks.DecouplingThis configuration (see schematic below) is used for variable flow primary and consumer circuits where the consumer circuit has the same supply temperature set point as the primary circuit. The fixed bypass prevents the primary pressure differential from being transmitted to the consumer circuit. This allows a proper operation of the terminal control valves on the consumer side when the primary pressure differential is either too low or too high or varying too much. The self-acting Δp control valve maintains a nearly constant bypass mass flow rate, set by default to 5% of the consumer circuit design mass flow rate.
The following table presents the main characteristics of this configuration.
| Primary circuit | Variable flow |
| Secondary (consumer) circuit | Variable flow |
| Typical applications |
Same consumer circuit supply temperature set point as primary circuit (Otherwise use either this model in conjunction with Buildings.Fluid.HydronicConfigurations.PassiveNetworks.SingleMixing, or Buildings.Fluid.HydronicConfigurations.ActiveNetworks.InjectionTwoWay) Primary pressure differential either too low or too high or varying too much such as in DHC systems |
| Non-recommended applications |
Heating systems with condensing boilers due to the recirculating primary flow rate (Since the recirculating primary flow rate is controlled to a nearly constant value, this configuration is used in DHC systems.) |
| Built-in valve control options | Self-acting Δp control valve with a proportional band of ±20% around the pressure differential set point |
|
Control valve selection (See the nomenclature in the schematic.) |
β = ΔpA-B /
(Δp1 + ΔpA-J)
≈ ΔpA-B / Δp1 The valve is sized with a pressure drop of Δp1 / 2 for a mass flow rate 5 to 10% higher than m2_flow_nominal.
|
| Balancing requirement |
The design pressure drop of the bypass balancing valve
dpBal3_nominal is typically around 10 kPa
for a mass flow rate of m1_flow_nominal-m2_flow_nominal.
No primary balancing valve is needed in addition to the self-acting
Δp control valve.(For an actuated control valve with external controls, the same balancing requirements as for Buildings.Fluid.HydronicConfigurations.ActiveNetworks.InjectionTwoWay hold. No bypass balancing valve is needed.) |
|
Lumped flow resistance includes (With the setting use_lumFloRes=true.)
|
Control valve val and primary balancing valve res1
|
The P-controller used in the model mimics a self-acting Δp control valve with a proportional band of ±20% around the pressure differential set point. This set point corresponds to the design pressure drop of the bypass balancing valve. Note that this configuration yields a nearly constant bypass mass flow rate, as opposed to a constant percentage of the consumer circuit mass flow rate provided by a control based on the return temperature upstream and downstream of the bypass. However, as illustrated in Buildings.Fluid.HydronicConfigurations.ActiveNetworks.Examples.DecouplingTemperature the latter control logic is flawed at low load, and the primary mass flow rate potentially maxed out. Since there is no standard strategy to counteract that effect, the configuration with built-in controls based on return temperature is not included in this package.
The specific built-in control option implemented in this model does not
depend on the actual function of the consumer circuit
(such as cooling, heating, or change-over).
Therefore, the model remains the same whatever the value
assigned to the parameter typCtl except if
None (no built-in controls) is selected.
In that latter case only, no built-in controls are included and the user
must connect a control signal to modulate the valve.
For consumer circuits with a different supply temperature set point, this configuration is sometimes used in conjunction with Buildings.Fluid.HydronicConfigurations.PassiveNetworks.SingleMixing, see the example Buildings.Fluid.HydronicConfigurations.ActiveNetworks.Examples.DecouplingMixing.