modelHeatExchanger

District heat exchanger controller

Information

This block implements the control logic for the district heat exchanger, which realizes the interface between the building system and the district system.

The input signal u is yielded by the supervisory controller. The primary and secondary circuits are enabled to operate if this input signal is greater than zero and the return position of at least one isolation valve is greater than 90%. When enabled,

the secondary circuit is controlled based on the input signal u, which is mapped to modulate in sequence the mixing valve (from full bypass to closed bypass for a control signal varying between 0% and 30%) and the pump speed (from the minimum to the maximum value for a control signal varying between 30% and 100%), and
the primary pump speed (or valve opening) is directly modulated with the input signal u.

Note that the valve on the secondary side is needed to stabilize the control of the system when the secondary mass flow rate required to meet the heat or cold rejection demand is below the flow rate corresponding to the minimum pump speed.

Parameters

Type	Name	Default	Description
Buildings.DHC.ETS.Types.ConnectionConfiguration	conCon		District connection configuration
Real	spePum1Min	0.1	Heat exchanger primary pump minimum speed (fractional)
Real	spePum2Min	0.1	Heat exchanger secondary pump minimum speed (fractional)

Connectors

Type	Name	Description
Buildings.Controls.OBC.CDL.Interfaces.RealInput[2]	yValIso	Isolation valves return position (index 1 for condenser)
Buildings.Controls.OBC.CDL.Interfaces.RealOutput	y1	District heat exchanger primary control signal
Buildings.Controls.OBC.CDL.Interfaces.RealOutput	yPum2	District heat exchanger secondary pump control signal
Buildings.Controls.OBC.CDL.Interfaces.RealOutput	yVal2	District heat exchanger secondary valve control signal
Buildings.Controls.OBC.CDL.Interfaces.RealInput	u	Control signal for secondary side (from supervisory)

Components

Type	Name	Description
Buildings.Controls.OBC.CDL.Reals.Max	max1	Maximum between control signal and minimum speed or opening
Buildings.Controls.OBC.CDL.Reals.Switch	swiOff1	Output zero if not enabled
Buildings.Controls.OBC.CDL.Reals.Sources.Constant	min1	Minimum pump speed or actuator opening
Buildings.Controls.OBC.CDL.Reals.GreaterThreshold	greThr	Check for heat or cold rejection demand
Buildings.Controls.OBC.CDL.Logical.And	and2	At least one valve is open and HX circuit is enabled
Buildings.Controls.OBC.CDL.Reals.GreaterThreshold	heaRej	Heat rejection if condenser isolation valve is open
Buildings.Controls.OBC.CDL.Reals.GreaterThreshold	cooRej	Cold rejection if evaporator isolation valve is open
Buildings.Controls.OBC.CDL.Logical.Or	or1	At least one valve is open
Buildings.Controls.OBC.CDL.Reals.Sources.Constant	speMin	Minimum pump speed
Buildings.Controls.OBC.CDL.Reals.Switch	swiOff2	Output zero if not enabled
Buildings.Controls.OBC.CDL.Reals.Line	mapSpe	Mapping function for pump speed
Buildings.Controls.OBC.CDL.Reals.Sources.Constant	one	One
Buildings.Controls.OBC.CDL.Reals.Sources.Constant	zer	Zero
Buildings.Controls.OBC.CDL.Reals.Sources.Constant	hal	Control signal value for full opening of the valve
Buildings.Controls.OBC.CDL.Reals.Line	mapVal	Mapping function for valve opening

Revisions

November 14, 2025, by Michael Wetter:
Moved to Buildings.Obsolete.
This is for #4354.
July 14, 2021, by Antoine Gautier:
Updated the control logic.
This is for issue #2561.
July 31, 2020, by Antoine Gautier:
First implementation.