blockReliefFanGroup

Sequence for relief fans control for AHUs using actuated relief dampers with relief fan(s)

Information

Sequence for controlling relief fans and their dampers for AHUs using actuated relief dampers with relief fan(s). It is developed based on Section 5.16.9 of ASHRAE Guideline 36, May 2020.

All operating relief fans that serve a common or shared air volume shall be grouped and controlled as if they were one system, running at the same speed and using the same control loop, even if they are associated with different AHUs.
A relief fan shall be enabled when its associated supply fan is proven ON (u1SupFan=true), and shall be disabled otherwise.
Building static pressure (dpBui) shall be time averaged with a sliding 5-minute window and 15 second sampling rate (to dampen fluctuations). The average value shall be that displayed and used for control.
A P-only control loop maintains the building pressure at a set point (dpBuiSet) of 12 Pa (0.05 in. of water) with an output ranging from 0% to 100%. The loop is disabled and output set to zero when all fans in the relief system group are disabled.
Fan speed signal to all operating fans in the relief system group shall be the same and shall be equal to the PID signal but no less than the minimum speed. Except for Stage 0, discharge dampers of all relief fans shall be open only when fan is commanded ON.
1. Stage 0 (barometric relief). When relief system is enabled, and the control loop output is above 5%, open the motorized dampers to all relief fans serving the relief system group that are enabled; close the dampers when the loop output drops to 0% for 5 minutes.
2. Stage Up. When control loop is above minimum speed (relFanSpe_min) plus 15%, start stage-up timer. Each time the timer reaches 7 minutes, start the next relief fan (and open the associated damper) in the relief system group, per staging order, and reset the timer to 0. The timer is reset to 0 and frozen if control loop is below minimum speed plus 15%. Note, when staging from Stage 0 (no relief fans) to Stage 1 (one relief fan), the discharge dampers of all nonoperating relief fans must be closed.
3. Stage Down. When PID loop is below minimum speed (relFanSpe_min), start stage-down timer. Each time the timer reaches 5 minutes, shut off lag fan per staging order and reset the timer to 0. The timer is reset to 0 and frozen if PID loop rises above minimum speed or all fans are OFF. If all fans are OFF, go to Stage 0 (all dampers open and all fans OFF).
For fans in a Level 2 alarm and status is OFF, discharge damper shall be closed when is above Stage 0.

Parameters

Type	Name	Default	Description
Integer	nSupFan	2	Total number of AHU supply fans that are serving the same common space
Integer	nRelFan	4	Total number of relief fans that are serving the same common space
Real	relFanSpe_min	0.1	Relief fan minimum speed
Integer[nRelFan]	staVec	{2, 3, 1, 4}	Vector of the order for staging up relief fan, i.e. the 1st element means the 1st relief fan and its value showing its sequence when staging up
Integer[nRelFan,nSupFan]	relFanMat	{{1, 0}, {1, 0}, {0, 1}, {0, 1}}	Relief fan matrix with relief fan as row index and AHU supply fan as column index. It flags which relief fan is associated with which supply fan
Real	dpBuiSet	12	Building static pressure difference relative to ambient (positive to pressurize the building)
Pressure controller
Real	k	1	Gain, normalized using dpBuiSet
Advanced
Real	hys	0.005	Hysteresis for checking the controller output value

Connectors

Type	Name	Description
Buildings.Controls.OBC.CDL.Interfaces.BooleanInput[nSupFan]	u1SupFan	AHU supply fan proven on status
Buildings.Controls.OBC.CDL.Interfaces.RealInput	dpBui	Building static pressure difference, relative to ambient (positive if pressurized)
Buildings.Controls.OBC.CDL.Interfaces.IntegerInput[nRelFan]	uRelFanAla	Relief fan current alarm index
Buildings.Controls.OBC.CDL.Interfaces.BooleanInput[nRelFan]	u1RelFan	Relief fan proven on status
Buildings.Controls.OBC.CDL.Interfaces.RealOutput	yDpBui	Building static pressure difference, relative to ambient (positive if pressurized)
Buildings.Controls.OBC.CDL.Interfaces.RealOutput[nRelFan]	yRelFan	Relief fan commanded speed
Buildings.Controls.OBC.CDL.Interfaces.RealOutput[nRelFan]	yDam	Relief damper commanded position

Components

Type	Name	Description
Buildings.Controls.OBC.CDL.Reals.MatrixGain	enaRel	Vector of relief fans with the enabled one denoted by 1
Buildings.Controls.OBC.CDL.Conversions.BooleanToReal[nSupFan]	booToRea	Convert boolean to real
Buildings.Controls.OBC.CDL.Reals.MultiplyByParameter[nRelFan]	gai	Vector of enabling fan, along with its staging order
Buildings.Controls.OBC.CDL.Reals.MovingAverage	movMea	Average building static pressure measurement
Buildings.Controls.OBC.CDL.Reals.Divide	div1	Normalized the control error
Buildings.Controls.OBC.CDL.Reals.PID	conP	Building static pressure controller
Buildings.Controls.OBC.CDL.Logical.MultiOr	enaRelGro	Relief group enabling status
Buildings.Controls.OBC.CDL.Conversions.BooleanToReal	booToRea1	Convert boolean to real
Buildings.Controls.OBC.CDL.Reals.Multiply	pro	Set controller output to zero when the relief system is disabled
Buildings.Controls.OBC.CDL.Reals.GreaterThreshold	greThr	Check if the controller output is greater than threshold
Buildings.Controls.OBC.CDL.Logical.And	and2	Check if the controller output is greater than threshold and the relief system has been enabled
Buildings.Controls.OBC.CDL.Logical.Latch	lat	Enable damper
Buildings.Controls.OBC.CDL.Reals.LessThreshold	lesThr	Check if the controller output is near zero
Buildings.Controls.OBC.CDL.Logical.Timer	tim	Check if the controller output has been near zero for threshold time
Buildings.Controls.OBC.CDL.Routing.BooleanScalarReplicator	booRep	Boolean replicator
Buildings.Controls.OBC.CDL.Reals.GreaterThreshold[nRelFan]	greThr1	Check if a relief fan should be enabled
Buildings.Controls.OBC.CDL.Logical.And[nRelFan]	enaDam	Enable damper
Buildings.Controls.OBC.CDL.Reals.GreaterThreshold	greThr2	Check if the controller output is greater than minimum speed plus threshold
Buildings.Controls.OBC.CDL.Logical.Timer	upTim	Check if the controller output has been greater than threshold for sufficient long time
Buildings.Controls.OBC.CDL.Logical.Pre	pre	Break algebraic loop
Buildings.Controls.OBC.CDL.Conversions.BooleanToReal[nRelFan]	booToRea2	Convert boolean to real
Buildings.Controls.OBC.CDL.Reals.Subtract[nRelFan]	sub2	Identify relief fans that have been enabled but not yet operating
Buildings.Controls.OBC.CDL.Reals.Multiply[nRelFan]	pro1	List of standby fans, along with their staging order
Buildings.Controls.OBC.CDL.Reals.MultiMin	mulMin	Identify current order of staging
Buildings.Controls.OBC.CDL.Routing.RealScalarReplicator	reaRep	Replicate real number
Buildings.Controls.OBC.CDL.Reals.Subtract[nRelFan]	sub1	Identify next operating fan
Buildings.Controls.OBC.CDL.Reals.LessThreshold[nRelFan]	lesThr1	Check if the input is less than threshold
Buildings.Controls.OBC.CDL.Reals.AddParameter[nRelFan]	addPar	Add value to the input
Buildings.Controls.OBC.CDL.Reals.Switch[nRelFan]	swi	Switch input values
Buildings.Controls.OBC.CDL.Reals.Abs[nRelFan]	abs1	Find absolute value
Buildings.Controls.OBC.CDL.Reals.LessThreshold[nRelFan]	lesThr2	Identify next operating fan
Buildings.Controls.OBC.CDL.Logical.Or[nRelFan]	or2	Targeted vector of operating relief fan after one new fan being turned on
Buildings.Controls.OBC.CDL.Logical.Latch	lat2	Stage up next relief fan
Buildings.Controls.OBC.CDL.Reals.LessThreshold	lesThr3	Check if the controller output is less than minimum speed
Buildings.Controls.OBC.CDL.Logical.Timer	dowTim	Check if the controller output has been less than threshold for sufficient long time
Buildings.Controls.OBC.CDL.Logical.Pre	pre1	Break algebraic loop
Buildings.Controls.OBC.CDL.Reals.Multiply[nRelFan]	pro2	List of operating fans, along with their staging order
Buildings.Controls.OBC.CDL.Reals.AddParameter[nRelFan]	addPar1	Add value to the input
Buildings.Controls.OBC.CDL.Reals.LessThreshold[nRelFan]	lesThr4	Check if the input is less than threshold
Buildings.Controls.OBC.CDL.Reals.Switch[nRelFan]	swi1	Switch input values
Buildings.Controls.OBC.CDL.Reals.MultiMin	mulMin1	Minimum staging order of the running relief fans
Buildings.Controls.OBC.CDL.Reals.Subtract[nRelFan]	sub3	Identify next operating fan
Buildings.Controls.OBC.CDL.Reals.Abs[nRelFan]	abs2	Find absolute value
Buildings.Controls.OBC.CDL.Reals.LessThreshold[nRelFan]	lesThr5	Identify next fan to be off
Buildings.Controls.OBC.CDL.Routing.RealScalarReplicator	reaRep1	Replicate real number
Buildings.Controls.OBC.CDL.Logical.Xor[nRelFan]	xor	Vector of relief fan after one fan being turned off
Buildings.Controls.OBC.CDL.Conversions.BooleanToInteger[nRelFan]	booToInt	Convert boolean to integer
Buildings.Controls.OBC.CDL.Conversions.BooleanToInteger[nRelFan]	booToInt1	Convert boolean to integer
Buildings.Controls.OBC.CDL.Conversions.BooleanToInteger[nRelFan]	booToInt2	Convert boolean to integer
Buildings.Controls.OBC.CDL.Integers.Equal[nRelFan]	intEqu	Check if newly started fan has become proven on
Buildings.Controls.OBC.CDL.Logical.MultiAnd	mulAnd	Check if newly started fan has become proven on
Buildings.Controls.OBC.CDL.Integers.Equal[nRelFan]	intEqu1	Check if newly turned off fan has become off
Buildings.Controls.OBC.CDL.Logical.MultiAnd	mulAnd2	Check if newly turned off fan has become off
Buildings.Controls.OBC.CDL.Logical.Latch	lat1	Stage down lag fan
Buildings.Controls.OBC.CDL.Logical.Switch[nRelFan]	logSwi	Vector of relief fan status after staging up
Buildings.Controls.OBC.CDL.Routing.BooleanScalarReplicator	booRep1	Replicate boolean input
Buildings.Controls.OBC.CDL.Logical.Switch[nRelFan]	logSwi1	Vector of relief fan status after staging down
Buildings.Controls.OBC.CDL.Routing.BooleanScalarReplicator	booRep2	Replicate boolean input
Buildings.Controls.OBC.CDL.Conversions.BooleanToReal[nRelFan]	booToRea3	Convert boolean to real
Buildings.Controls.OBC.CDL.Reals.Limiter	lim	Limit the controller output
Buildings.Controls.OBC.CDL.Routing.RealScalarReplicator	reaRep2	Replicate real input
Buildings.Controls.OBC.CDL.Reals.Multiply[nRelFan]	pro3	Relief fan speed
Buildings.Controls.OBC.CDL.Logical.Switch[nRelFan]	logSwi2	Vector of relief fan status after staging up
Buildings.Controls.OBC.CDL.Reals.Sources.Constant	dpBuiSetPoi	Building pressure setpoint
Buildings.Controls.OBC.CDL.Reals.Sources.Constant	conOne	Constant one
Buildings.Controls.OBC.CDL.Reals.Sources.Constant	con	Zero fan speed when it is in stage 0
Buildings.Controls.OBC.CDL.Reals.Switch	swi2	Switch input values
Buildings.Controls.OBC.CDL.Logical.MultiOr	mulOr	Check if there is any relief fan enabled, but may not be running
Buildings.Controls.OBC.CDL.Conversions.BooleanToReal[nRelFan]	booToRea4	Convert boolean to real
Buildings.Controls.OBC.CDL.Logical.Not	not1	Logical not
Buildings.Controls.OBC.CDL.Logical.And	and1	Start timer, and reset to zero if the threshold time has passed
Buildings.Controls.OBC.CDL.Logical.And	and3	Start timer, and reset to zero if the threshold time has passed
Buildings.Controls.OBC.CDL.Logical.Not	not2	Logical not
Buildings.Controls.OBC.CDL.Integers.Equal[nRelFan]	intEqu2	Check if the relief fan is in level 2 alarm
Buildings.Controls.OBC.CDL.Integers.Sources.Constant[nRelFan]	conInt	Constant
Buildings.Controls.OBC.CDL.Logical.Not[nRelFan]	not3	Logical not
Buildings.Controls.OBC.CDL.Logical.And[nRelFan]	and4	Check if the relief fan is in level 2 alarm and it is proven off
Buildings.Controls.OBC.CDL.Conversions.BooleanToReal[nRelFan]	booToRea5	Convert boolean to real
Buildings.Controls.OBC.CDL.Reals.Multiply[nRelFan]	mul	Product of inputs
Buildings.Controls.OBC.CDL.Reals.GreaterThreshold[nRelFan]	greThr3	Check if the relief fan is enabled
Buildings.Controls.OBC.CDL.Logical.MultiAnd	mulAnd1	Check if all the fans are proven off
Buildings.Controls.OBC.CDL.Reals.Switch[nRelFan]	swi3	Switch input values
Buildings.Controls.OBC.CDL.Routing.BooleanScalarReplicator	booRep4	Replicate boolean input
Buildings.Controls.OBC.CDL.Logical.Switch[nRelFan]	logSwi3	Vector of relief fan status after staging down
Buildings.Controls.OBC.CDL.Logical.TrueDelay[nRelFan]	truDel	Delay true input
Buildings.Controls.OBC.CDL.Logical.MultiOr	mulOr1	Check if there is any fan is proven on
Buildings.Controls.OBC.CDL.Routing.BooleanScalarReplicator	booRep5	Replicate boolean input
Buildings.Controls.OBC.CDL.Logical.Not[nRelFan]	not5	Logical not
Buildings.Controls.OBC.CDL.Logical.Not[nRelFan]	not6	Logical not
Buildings.Controls.OBC.CDL.Logical.TrueDelay[nRelFan]	truDel1	Delay true input

Revisions

March 5, 2024, by Michael Wetter:
Corrected wrong use of displayUnit.
July 15, 2021, by Jianjun Hu:
First implementation.