Fume hood stabilizing jet (FhStbJet11)

Overview

The application function "Fume hood stabilizing jet 11" (FhStbJet11) is used to monitor and control a fume hood stabilizing jet fan. The status of the stabilizing jet fan is shared with other AFs to determine exhaust volume setpoints and generate alarms. The stabilizing jet can be commanded by either the analog output FhStbJetVarSpd, or the binary output FhStbJetCmd (user choice during DXR configuration). The binary output FhStbJetFail represents the state of the stabilizing jet fan failure. The output is monitored by other modules to indicate a failure on the Operator Display Panel and adjust the fume hood exhaust airflow setpoint.

Main features:

Stabilizing jet fan control (AO or BO)
Stabilizing jet fan failure monitoring

Function

	Command or request (or related)
	Notification of condition or status, or availability
	Device mode
	Interlock (internal signal, not a BACnet object; see Interlocks section for additional information)

Stabilizing jet fan control: The stabilizing jet fan is turned on and off based on fume hood sash position, fume exhaust air volume flow. The fan is switched off when the analog output for fan speed control is set to 0. The fan is switched on when the analog output for fan speed control is set to the value provided by the hood manufacture.

Sash position control: The fan speed control output will be set to 0 when the sash position is less than SwiOffSshpFan. The fan speed control output will be set to FhStbJetVarSpd, when the sash position is greater than SwiOffSshpFan.

Exhaust air volume control: The fan speed control output will be set to 0 when the fume hood exhaust air volume falls below the value in SwiOffAflEhFan for longer than the time specified in DlyOffFanAirFl. The fan speed control output is set to FhStbJetVarSpd, when the fume hood exhaust airflow is greater than SwiOffAflEhFan plus HysAirFlEh.

Stabilizing jet fan monitoring: The stabilizing jet fan failure is a calculated binary value object.

A differential pressure switch is normally used to determine if the stabilizing jet fan is operating properly. The stabilizing jet fan failure will be off when the stabilizing jet fan is off or when the fan is turned on and the differential pressure switch closes before the alarm switch delay expires.

The stabilizing jet fan failure will be on when the fan is on, the alarm switch delay timer is expired, and the differential pressure switch is open.

Occasionally a differential pressure switch is not installed. The stabilizing jet alarm will always be off when the binary input for the differential pressure switch is not present.

Feature configuration

Feature selections for "Room HVAC coordination" are accessed via the Application configuration task in the Configuration component.

Feature (AF)	Feature description	Ref.
Monitoring fume hood stabilizing jet fan failure	None/Active	☑

Configuration

Parameters

Description	Parameter	Default value
Setpoint for stabilizing jet fan speed ▶ The speed signal to the stabilizing jet fan when the fan is operating. Set according to the fume hood manufactures instruction.	SpStbFanSpd	42 [%]
Switch-off sash position for stabilizing jet fan ▶ The stabilizing jet fan will be off when the sash is below this position. Set according to the fume hood manufactures instruction. Only used with FhSash15.	SwiOffSshpFan	4.0 [cm] 1.6 [in]
Switch-on sash position for stabilizing jet fan ▶ The stabilizing jet fan will be on when the sash is above this position. Set according to the fume hood manufactures instruction. Only used with FhSash15.	SwiOnSshpFan	8.0 [cm] 3.1 [in]
Switch-off area for stabilizing jet fan ▶ The stabilizing jet fan will be off when the face area is less than this value. Set according to the fume hood manufactures instruction. Only used with FhSash11…14.	SwiOffAreaFan	0.06 [m²] 0.65 [ft²]
Switch-on area for stabilizing jet fan ▶ The stabilizing jet fan will be on when the face area is greater than this value. Set according to the fume hood manufactures instruction. Only used with FhSash11…15.	SwiOnAreaFan	0.12 [m²] 1.29 [ft²]
Switch-off point for exhaust air volume flow for stabilizing jet fan ▶ The stabilizing jet fan will be turned off if FhAirFlEh < SwiOffAflEhFan for a time longer than DlyOffFanAirFl. Set according to the fume hood manufactures instruction.	SwiOffAflEhFan	150 [m³/h] 88.3 [ft³/min] 41.67 [l/s]
Hysteresis for exhaust air volume flow ▶ The stabilizing jet fan will be allowed to be turned on if FhAirFlEh > SwiOffAflEhFan + HysAirFlEh. Set according to the fume hood manufactures instruction.	HysAirFlEh	40 [m³/h] 23.5 [ft³/min] 11.11 [l/s]
Switch-off delay for stabilizing jet fan based on air volume flow ▶ The stabilizing jet fan will be turned off if FhAirFlEh < SwiOffAflEhFan for a time longer than DlyOffFanAirFl. Set according to the fume hood manufactures instruction. Setting to 0 will disable the time delay.	DlyOffFanAirFl	10 [s]
Switch-on time for stabilizing jet fan state before fan alarm ▶ The Stabilizer jet fan failure will be on if the stabilizer jet fan status is not on within TiOnStbFanAlm of the fan turning on.	TiOnStbFanAlm	15 [s]
Length unit ▶ Defined by selected engineering unit – do not change.	LngtUnit	[cm] [in]
Air volume flow unit ▶ Defined by selected engineering unit – do not change.	AirFlUnit	[m³/h] [ft³/min] [l/s]
Area unit ▶ Defined by selected engineering unit – do not change.	AreaUnit	[m²] [ft²]

Interface

Interface	Description	Type	Ref.	Owned by
FhStbJetVarSpd	Fume hood stabilizing jet fan variable speed	AO	◉	Room segment / Field device
FhStbJetCmd	Fume hood stabilizing jet fan command	BO	◉	Room segment / Field device
FhStbJetFanSta	Fume hood stabilizing jet fan state	BI	◉	Room segment / Field device
FhStbJetFail	Fume hood stabilizing jet fan failure	BCalcVal	●	-
FhStbJetFailm	Monitoring fume hood stabilizing jet fan failure	FtrSel	●	-

Engineering and commissioning

Optional.