Buildings.Fluid.HydronicConfigurations.PassiveNetworks.Examples

Example models

Information

This package contains examples for the use of models that can be found in Buildings.Fluid.HydronicConfigurations.PassiveNetworks.

Extends from Modelica.Icons.ExamplesPackage (Icon for packages containing runnable examples).

Package Content

Name	Description
DualMixing	Model illustrating the operation of a dual mixing circuit
SingleMixing	Model illustrating the operation of single mixing circuits
SingleMixingOpenLoop	Model illustrating the operation of single mixing circuits with primary back pressure
BaseClasses	Package with base classes

Buildings.Fluid.HydronicConfigurations.PassiveNetworks.Examples.DualMixing

Model illustrating the operation of a dual mixing circuit

Information

This model represents a heating system where the configuration Buildings.Fluid.HydronicConfigurations.PassiveNetworks.DualMixing serves as the interface between a variable flow primary circuit and a constant flow secondary circuit. The secondary supply temperature is constant and lower than the primary circuit.

The fixed bypass of the dual mixing circuit is balanced at design conditions if kSizBal=1. Selecting a lower value such as kSizBal=0.6 illustrates the operation with an oversized balancing valve, yielding a lower pressure drop. One can observe that the secondary supply temperature set point cannot be met despite the control valve being fully open. The secondary distribution pump operates with sufficient head as the design flow rate is met in the consumer circuit. This is the low pressure differential at the boundaries of the control valve due to the oversized balancing valve that creates the primary flow shortage and prevents from serving the load properly.

Extends from BaseClasses.PartialPassivePrimary (Partial model of passive primary network).

Parameters

Modelica definition

Buildings.Fluid.HydronicConfigurations.PassiveNetworks.Examples.SingleMixing

Model illustrating the operation of single mixing circuits

Information

This model represents a change-over system where the configuration Buildings.Fluid.HydronicConfigurations.PassiveNetworks.SingleMixing serves as the interface between a variable flow primary circuit at constant supply temperature and two consumer circuits: the first one is a constant flow circuit, the second one is a variable flow circuit. For each circuit, the secondary supply temperature is reset with an open loop, representing for instance a reset logic based on the outdoor air temperature. The pump model for the second circuit is an ideal Δp-controlled model, its input being computed to mimic the tracking of a pressure differential at the boundaries of the terminal unit.

Extends from BaseClasses.PartialPassivePrimary (Partial model of passive primary network).

Parameters

Modelica definition

Buildings.Fluid.HydronicConfigurations.PassiveNetworks.Examples.SingleMixingOpenLoop

Model illustrating the operation of single mixing circuits with primary back pressure

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.

Extends from BaseClasses.PartialPassivePrimary (Partial model of passive primary network).

Parameters

Modelica definition