blockController

Head pressure controller for plants with headered condenser water pumps

Information

Block that generates control signals for chiller head pressure control, according to ASHRAE Guideline 36-2021, section 5.20.10 head pressure control.

Note that if a plant has the waterside economizer, the condenser water pump must be variable speed.

This sequence contains three subsequences:

First, if the head pressure control signal uHeaPreCon is not available from the chiller controller. The signal will be generated by block chiHeaPreLoo. See Buildings.Controls.OBC.ASHRAE.G36.Plants.Chillers.HeadPressure.Subsequences.ControlLoop for a description.
If the chiller plant does not have the waterside economizer, block noWSE will be used for controlling maximum cooling tower speed setpoint yMaxTowSpeSet and, whether the plant has the constant speed condenser water pump or not, resetting head pressure control valve position yHeaPreConVal when have_fixSpeConWatPum=true, or resetting condenser water pump speed yConWatPumSpeSet when have_fixSpeConWatPum=false. See Buildings.Controls.OBC.ASHRAE.G36.Plants.Chillers.HeadPressure.Subsequences.MappingWithoutWSE for a description.
If the chiller plant has the waterside economizer, block withWSE will be used for specifying yMaxTowSpeSet, yHeaPreConVal and condenser water pump speed yConWatPumSpeSet. See Buildings.Controls.OBC.ASHRAE.G36.Plants.Chillers.HeadPressure.Subsequences.MappingWithWSE for a description.

Type	Name	Default	Description
Plant
Boolean	have_chiHeaPreCon	false	Flag indicating if there is head pressure control signal from chiller controller
Boolean	have_WSE	true	True if the plant has waterside economizer. When the plant has waterside economizer, the condenser water pump speed must be variable
Boolean	have_fixSpeConWatPum	false	Flag indicating if the plant has fixed speed condenser water pumps
Setpoints
Real	minTowSpe	0.1	Minimum cooling tower fan speed
Real	minConWatPumSpe	0.1	Minimum condenser water pump speed
Real	minHeaPreValPos	0.1	Minimum head pressure control valve position
Loop signal
Real	minChiLif	10	Minimum allowable lift at minimum load for chiller
Loop signal › PID controller
Buildings.Controls.OBC.CDL.Types.SimpleController	controllerType	Buildings.Controls.OBC.CDL.Types.SimpleController.PI	Type of controller
Real	k	1	Gain of controller
Real	Ti	0.5	Time constant of integrator block
Real	Td	0.5	Time constant of derivative block

Type	Name	Description
Buildings.Controls.OBC.CDL.Interfaces.BooleanInput	uChiHeaCon	Enabling chillers head pressure control: true = ON, false = OFF
Buildings.Controls.OBC.CDL.Interfaces.RealInput	TConWatRet	Measured condenser water return temperature (condenser leaving)
Buildings.Controls.OBC.CDL.Interfaces.RealInput	TChiWatSup	Measured chilled water supply temperature
Buildings.Controls.OBC.CDL.Interfaces.RealInput	desConWatPumSpe	Design condenser water pump speed for current stage
Buildings.Controls.OBC.CDL.Interfaces.BooleanInput	uWSE	Status of water side economizer: true = ON, false = OFF
Buildings.Controls.OBC.CDL.Interfaces.RealInput	uHeaPreCon	Chiller head pressure control loop signal from chiller controller
Buildings.Controls.OBC.CDL.Interfaces.RealOutput	yMaxTowSpeSet	Maximum cooling tower speed setpoint
Buildings.Controls.OBC.CDL.Interfaces.RealOutput	yHeaPreConVal	Head pressure control valve position
Buildings.Controls.OBC.CDL.Interfaces.RealOutput	yConWatPumSpeSet	Condenser water pump speed setpoint

Type	Name	Description
Buildings.Controls.OBC.ASHRAE.G36.Plants.Chillers.HeadPressure.Subsequences.ControlLoop	chiHeaPreLoo	Generate chiller head pressure control loop signal
Buildings.Controls.OBC.ASHRAE.G36.Plants.Chillers.HeadPressure.Subsequences.MappingWithoutWSE	noWSE	Controlling equipments for plants without waterside economizer
Buildings.Controls.OBC.ASHRAE.G36.Plants.Chillers.HeadPressure.Subsequences.MappingWithWSE	withWSE	Controlling equipments for plants with waterside economizer