modelDecoupling

Information

Summary

This 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.

Additional comments

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.

Parameters

Connectors

Components

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.