modelSingleMixingOpenLoop

Information

This model illustrates the disturbance caused on the three-way valve operation by an induced negative pressure differential at the circuit boundaries. Two consumer circuits are connected to a primary loop by means of Buildings.Fluid.HydronicConfigurations.PassiveNetworks.SingleMixing. The primary loop is configured with a flow resistance that generates a negative pressure differential at the boundaries of the consumer circuits (representing for instance a boiler with a high pressure drop and no minimum flow requirement). Each consumer circuit is equipped with a circulation pump that is sized to cover the primary pressure differential. When the parameter is_bal is false no bypass balancing valve is considered. When this parameter is true a bypass balancing valve is considered with the same design pressure drop as the one in the primary loop. The pump design head remains unchanged whatever the value of the parameter is_bal. The model is configured in steady-state with open loop control. The load on each consumer circuit is constant. The control valve of the first circuit is modulated from fully open to fully closed position while the control valve of the remote circuit is kept fully open.

When the bypass is not balanced, the flow reverses in the primary branch when the valve opening is below 20% which means that the load cannot be served any more.

When the bypass is balanced, no flow reversal occurs and the mixing function of the three-way valve is preserved over its whole opening range.

Note that the setting of this model represents an oversized control valve with a low authority β = 0.14. Setting a higher valve design pressure drop to reach an authority close to 0.5 alleviates the risk of primary flow reversal and reduces the need for a bypass balancing valve.

Parameters

Components

Revisions

• June 30, 2022, by Antoine Gautier:
  First implementation.