blockUpEnd

Sequence for ending stage-up process

Information

Block that controls devices at the ending step of the chiller staging up process. This development is based on ASHRAE Guideline 36-2021, section 5.20.4.16, item f and g. These sections specify the controls of devices at the ending step of the staging up process.

For the stage-up process that does not require a smaller chiller being disabled and a larger chiller being enabled (uOnOff=false),

Start the next stage chiller (nexEnaChi) after the chilled water isolation valve is fully open (uEnaChiWatIsoVal=true). This is implemented in block enaChi. See Buildings.Controls.OBC.ASHRAE.G36.Plants.Chillers.Staging.Processes.Subsequences.EnableChiller for more descriptions.

For any stage change during which a smaller chiller is disabled and a larger chiller is enabled (uOnOff=true), after starting the next stage chiller specified above, do the following:

Wait 5 minutes (proOnTim) for the newly enabled chiller to prove that is operating correctly, then shut off the small chiller (nexDisChi). This is implemented in block enaChi. See Buildings.Controls.OBC.ASHRAE.G36.Plants.Chillers.Staging.Processes.Subsequences.EnableChiller for more descriptions.
When the controller of the smaller chiller being shut off indicates no request for chilled water flow (uChiWatReq=false), slowly close the chiller's chilled water isolation valve to avoid a sudden change in flow through other operating chillers. This is implemented in block disChiIsoVal. See Buildings.Controls.OBC.ASHRAE.G36.Plants.Chillers.Staging.Processes.Subsequences.CHWIsoVal for more descriptions.
When the controller of the smaller chiller being shut off indicates no request for condenser water flow (uConWatReq=false), disable the chiller's head pressure control loop. This is implemented in block disHeaCon. See Buildings.Controls.OBC.ASHRAE.G36.Plants.Chillers.Staging.Processes.Subsequences.HeadControl for more descriptions.
Change the minimum flow bypass setpoint to that appropriate for the new stage. This is implemented in block minChiWatSet. See Buildings.Controls.OBC.ASHRAE.G36.Plants.Chillers.MinimumFlowBypass.FlowSetpoint for more descriptions.
Block minBypSet will then check if the new chilled water flow setpoint has been achieved. See Buildings.Controls.OBC.ASHRAE.G36.Plants.Chillers.Staging.Processes.Subsequences.ResetMinBypass for more descriptions.

Parameters

Type	Name	Default	Description
Integer	nChi	2	Total number of chillers
Boolean	have_airCoo	false	True: the plant has air cooled chiller
Boolean	have_parChi	true	True: the plant has parallel chillers
Real	delStaCha	900	Hold period for each stage change
Enable next chiller
Real	proOnTim	300	Threshold time to check if newly enabled chiller being operated by more than 5 minutes
Chilled water isolation valve
Buildings.Controls.OBC.ASHRAE.G36.Plants.Chillers.Types.Actuator	chiIsoValTyp	Buildings.Controls.OBC.ASHRAE.G36.Plants.Chillers.Types.Actuator.Modulating	Chiller CHW isolation valve type
Boolean	have_twoPosEndSwiChiVal	false	True for chiller CHW isolation valves with end switch status feedback
Real	chaChiWatIsoTim		Time to slowly change isolation valve, should be determined in the field
Reset CHW minimum flow setpoint
Real	byPasSetTim		Time to slowly reset minimum bypass flow
Real[nChi]	minFloSet		Minimum chilled water flow through each chiller
Real[nChi]	maxFloSet		Maximum chilled water flow through each chiller
Reset bypass
Real	aftByPasSetTim	60	Time after minimum bypass flow being resetted to new setpoint

Connectors

Type	Name	Description
Buildings.Controls.OBC.CDL.Interfaces.IntegerInput	nexEnaChi	Index of next enabling chiller
Buildings.Controls.OBC.CDL.Interfaces.BooleanInput	uStaUp	Stage-up command
Buildings.Controls.OBC.CDL.Interfaces.BooleanInput	uEnaChiWatIsoVal	Status of chiller chilled water isolation valve control: true=enabled valve is fully open
Buildings.Controls.OBC.CDL.Interfaces.BooleanInput[nChi]	uChi	Chiller status: true=ON
Buildings.Controls.OBC.CDL.Interfaces.BooleanInput	uOnOff	Indicate if the stage require one chiller to be enabled while another is disabled
Buildings.Controls.OBC.CDL.Interfaces.IntegerInput	nexDisChi	Next disabling chiller when there is any stage up that need one chiller on and another off
Buildings.Controls.OBC.CDL.Interfaces.BooleanInput[nChi]	uChiWatReq	Chilled water request status for each chiller
Buildings.Controls.OBC.CDL.Interfaces.BooleanInput[nChi]	u1ChiWatIsoValOpe	Chiller chilled water isolation valve open end switch. True: the valve is fully open
Buildings.Controls.OBC.CDL.Interfaces.BooleanInput[nChi]	u1ChiWatIsoValClo	Chiller chilled water isolation valve close end switch. True: the valve is fully closed
Buildings.Controls.OBC.CDL.Interfaces.BooleanInput[nChi]	uConWatReq	Condenser water request status for each chiller
Buildings.Controls.OBC.CDL.Interfaces.BooleanInput[nChi]	uChiHeaCon	Chillers head pressure control status
Buildings.Controls.OBC.CDL.Interfaces.RealInput	VMinChiWat_setpoint	Minimum chiller water flow setpoint calculated from upstream process
Buildings.Controls.OBC.CDL.Interfaces.BooleanOutput[nChi]	yChi	Chiller enabling status
Buildings.Controls.OBC.CDL.Interfaces.BooleanOutput[nChi]	y1ChiWatIsoVal	Chiller chilled water isolation valve commanded on
Buildings.Controls.OBC.CDL.Interfaces.RealOutput[nChi]	yChiWatIsoVal	Chilled water isolation valve position setpoint
Buildings.Controls.OBC.CDL.Interfaces.BooleanOutput[nChi]	yChiHeaCon	Chiller head pressure control enabling status
Buildings.Controls.OBC.CDL.Interfaces.RealOutput	yChiWatMinSet	Chilled water minimum flow setpoint
Buildings.Controls.OBC.CDL.Interfaces.BooleanOutput	endStaTri	Staging end trigger

Revisions

September 22, 2019, by Jianjun Hu:
First implementation.