Fume hood exhaust air setpoint, linear sash position and face velocity sensor (FhSpEh15)

Overview

The application function "Fume hood exhaust setpoint 15, face velocity and linear sash position" (FhSpEh15) is used to determine the exhaust volume setpoint based on a combination of a linear relationship with the fume hood sash position and face velocity sensor. Each one is used to separately calculate a value for the exhaust flow setpoint. The larger value is the effective exhaust flow setpoint.

This AF does not have any outputs associated with physical devices.The primary analog outputs of this AF are the calculated value objects:

Exhaust volume setpoint (FhSpAirFlEh), also present on chart output pin
Relative exhaust volume setpoint (FhSpAirFlRelEh), also present on chart output pin
Face velocity setpoint (FhSpVFace)
Calculated effective face velocity (FhVFaceEff)

Main features:

Exhaust volume setpoint
Calculated face velocity

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)

Exhaust setpoint selection: The exhaust setpoint selection (FhSpSelEh) is a configurable multistate process value:

Off
Auto
Setpoint 1
Setpoint 2
Setpoint 3

FhSpSelEh can be adjusted from the ODP when the setpoint adjustment features on the ODP are activated.

The application monitors the multistate calculated value object, exhaust air setpoint selection input value (FhSpSelEh), that is connected to the ODP. The application will write the current state of the exhaust setpoint selection on two multistate process value objects, exhaust air setpoint selection to ODP (SpSelEhOdpCol) and present exhaust air setpoint selection (PrSpSelEhCol).

A configuration extension parameter determines the value for the manual setpoints; SpOff, setpoint 1, setpoint 2, and setpoint 3. Other parameters configure the units for each of the manual setpoints.

Unit options	Enumeration value
m/s	74
ft/min	77
%	98
ft³/min	84
l/s	87
m³/h	135

If a velocity setpoint is selected (m/s or ft/min), the manual setpoint will be used to calculate the exhaust airflow setpoint based on the sash face area.
If % is selected, the resulting manual setpoint will be a percentage of the current auto setpoint.
If an airflow setpoint is selected (ft³/min, l/s, or m³/h), the resulting manual setpoint will be set equal to the value.

Setpoint 1, Setpoint 2, and Setpoint 3 will be limited by the minimum exhaust airflow setpoint, the Off setpoint will be allowed to be set to 0.

A manual setpoint of Off, Setpoint 1, Setpoint 2, or Setpoint 3 received from the ODP updates the value of the FhSpSelEh and sets the priority to 13. A setpoint of Auto received from the ODP will relinquish priority 13 for FhSpSelEh and update the value to priority 15.

The manual setpoint is set to Auto based on a change of FhOpMod and RlqManSpSelEh. The manual setpoint can be released when FhOpMod changes to Off or to Low air volume flow. The manual setpoint will not be released if the setpoint is configured to trigger emergency purge.

ManOpLockCnf defines when the ODP will be locked based on FhOpMod. The user setpoint selection will be locked by setting the priority of Fume hood exhaust setpoint selection (FhSpSelEh) to 12. The priority is passed down to SpSelEhOdp and PrSpSelEh.

FhSpSelEh Present priority	Exhaust setpoint selection to ODP	Present exhaust air setpoint selection
<13	12	12
13	13	13
>13	15	15

SpSelEhLoAirFl defines how FhSpSelEh will be set when the FhOpMod changes to low air volume flow.

When the configuration extension item is set to disabled, no action is taken.
If the configuration extension item is set to off, setpoint 1, setpoint 2, or setpoint 3, the exhaust setpoint selection will be set to that value.
The FhSpSelEh will return to Auto when the FhOpMod changes to Control.

Emergency purge: If the configuration extension item is set to off, setpoint 1, setpoint 2, or setpoint 3 and the exhaust setpoint selection is set to that value, SpEmgPrg is turned on.

Note:

The QMX3.P88 fume hood operating display does not have a specific button for emergency purge. The configuration extension item EmgPrgCnf allows one of the manual setpoints to be used to activate emergency purge.

Exhaust airflow effective minimum: The exhaust airflow effective minimum can be affected by the FhOpMod and the exhaust airflow request from the room.

When there is no request from the room and the FhOpMod is control, the exhaust airflow effective minimum will be set equal to the EhAirFlMin.

When there is no request from the room, the FhOpMod is low air volume flow and the FhUcdAflEhMin is not equal to zero, the FhAflMinEffEh will be set equal to FhUcdAflEhMin.

If there is no request from the room, the FhOpMod is low air volume flow and FhUcdAflEhMin is equal to zero, the FhAflMinEffEh will be set equal to EhAirFlMin.

Face velocity setpoint: When a manual setpoint (Sp1, Sp2 or Sp3) is active through the exhaust air setpoint selection and configured for velocity (m/s or ft/min), then the FhSpVFace will be set equal to the value of that manual setpoint.

When a manual setpoint is not active and the FhOpMod is set to Low airflow for a time longer than switch delay to unoccupied setpoint (DlyOnSpUcd ), the FhSpVFace is set equal to the FhUcdSpVFace, otherwise it is set equal to FhOcdSpVFace.

When the fume hood operating mode (FhOpMod) is set to fire, the face velocity setpoint will be set at priority 2 based on the SpEhFire.

When the FhOpMod is set to emergency or open, the face velocity setpoint will be set at priority 2 based on the SpEmgPrg.

Exhaust airflow setpoint: A velocity sensor and a linaer relationship between the sash position and the effective minimum and maximum exhaust airflow setpoints are used to separately calculate a value for the exhaust flow setpoint.

When the fume hood operating mode is set to Control, the exhaust setpoint selection is Auto, and the balancing state is not balancing, the exhaust airflow setpoint (FhSpAirFlEh) will be set equal to the larger of the linear setpoint and setpoint calculated from the face velocity sensor.

The priority for the exhaust airflow setpoint is set based on the priority of the fume hood operating mode object.

Fume hood operating mode present priority	Exhaust volume setpoint priority
1-3	2
4-6	5
7-15	15

Face velocity control: The application reads a sensor called a “face velocity sensor” or “through-the-wall sensor” to measure an air velocity that represents the face velocity (FhVFace). The velocity averaged over the open face area of the hood may differ significantly from the velocity measured through the sensor. The application includes a configurable conversion to calculate a representative face velocity from the sensed velocity, a configurable filter constant and a correction factor are involved to convert the raw measured face velocity to the effective face velocity (FhVFaceEff). The effective face velocity is set to valid only when FhVFaceis valid.

This application applies a cascade feedback loop to drive the calculated face velocity to the face velocity setpoint. The face velocity loop is the outer loop, calculating the setpoint of the exhaust flow inner loop. The outer loop outputs 0-100% representing exhaust airflow setpoint from minimum to maximum, and then converts the percentage value to airflow volumetric value, this value is further compared with the linear exhaust flow setpoint calculated from sash position to choose whichever is greater for exhaust damper modulating (inner loop of cascade control).

The loop must not be allowed to wind up when the exhaust volume setpoint is not being controlled by the loop.

Emergency alarm exhaust volume setpoint: The emergency purge exhaust setpoint (SpEmgPrg) is a configuration extension, entered as a percentage of setpoint. (see Configuration)

Fire: The fire exhaust setpoint (SpEhFire) is a configuration extension, entered as a percentage of setpoint. (see Configuration)

Stabilizing jet feature: The stabilizing jet failure setpoint is a configuration extension item that is entered in airflow units. When the stabilizing jet failure input indicates there is a problem with the stabilizing jet fan then the setpoint determined by the sash position will be increased by the amount in the configuration extension item. The stabilizing jet alarm does not affect the face velocity setpoint.

Decommission exhaust volume setpoint: When the fume hood operating mode is set to Off then FhSpAirFlEh will be set to 0.

Balancing mode exhaust volume setpoint: If the balancing command (VavEhBalCmd) is set to Balancing, the exhaust airflow setpoint (FhSpAirFlEh) is determined by the Balancing Mode (VavEhBalMod).

Relative setpoint: The relative airflow setpoint for the fume hood is a calculated analog value that is normalized as a percentage of the exhaust airflow setpoint based on the nominal (rated) value for the fume hood airflow, where 100% equals nominal and the relative value will not be limited to 100%.

Energy efficiency indication: If a manual setpoint is selected that results in a higher exhaust airflow setpoint than the auto setpoint, the setpoint AF notifies the ODP to set the energy efficiency indicator (green leaf) (EeiRstInCol) to Poor (2).

If the balancing command (VavEhBalCmd) is Balancing or the fume hood operating mode (FhOpMod) is Fire, Emergency purge, or Open, the energy efficiency indicator (green leaf) is set to Undefined (1).

If none of the above conditions exist, the energy efficiency indicator (green leaf) will be set to Good (4).

If the energy efficiency indicator reset button (REeiRstIn) is pressed when the high manual setpoint indicator is on, the manual setpoint will be released and the auto setpoint will be used.

Configuration

Objects

Description	Object	Type	Default value
Fume hood unoccupied face velocity setpoint	FhUcdSpVFace	ACnfVal	0.41 [m/s] 80.0 [ft/min]
Fume hood occupied face velocity setpoint	FhOcdSpVFace	ACnfVal	0.41 [m/s] 80.0 [ft/min)
Fume hood unoccupied minimum exhaust air volume flow	FhUcdAflEhMin	ACnfVal	0 [m³/h] 0.0 [ft³/min] 0.00 [l/s]
Fume hood exhaust manual air volume flow setpoint	FhSpAirFlManEh	ACnfVal	5 [m³/h] 2.9 [ft³/min] 1.39 [l/s]

Parameters

Description	Parameter	Default value
Sash position for maximum exhaust air volume setpoint ▶ Set per job specifications.	SshpSpAflMax	48.0 [cm] 18.9 [in]
Sash position for minimum exhaust air volume setpoint ▶ Set per job specifications.	SshpSpAflMin	2.0 [cm] 0.8 [in]
Maximum exhaust air volume setpoint based on sash position ▶ Fume hood maximum airflow limit, as specified by the fume hood manufacturer, that is associated with fully open sash position. Consult the fume hood manufacturer's product specifications for airflow values.	SpAirFlMaxSshp	100 [m³/h] 58.9 [ft³/min] 27.78 [l/s]
Minimum exhaust air volume setpoint based on sash position ▶ Fume hood minimum airflow limit, as specified by the fume hood manufacturer, that is associated with fully closed sash position. Consult the fume hood manufacturer's product specifications for airflow values.	SpAirFlMinSshp	50 [m³/h] 29.4 [ft³/min] 13.89 [l/s]
Emergency purge setpoint ▶ When EmgPrgCnf is set to disabled (1) and a manual setpoint is selected, no action is taken. When FhEmgPrg is active, the exhaust airflow setpoint will be multiplied by the emergency setpoint percentage. When the fume hood operating mode is set to Emergency and the balancing state is not balancing, FhSpAirFlEh is calculated occupied face velocity setpoint and is limited by the minimum exhaust airflow. (The maximum of the output of the face velocity controller, a calculated value based on sash position, and exhaust airflow minimum are used for the exhaust volume setpoint.) On fume hoods with face velocity sensors the face velocity setpoint is also multiplied by the emergency setpoint percentage. Select the setpoint to be used when FhEmgPrg is active. 1:Disabled 2:Off 3:Setpoint 1 4:Setpoint 2 5:Setpoint 3	SpEmgPrg	150 [%]
Fire exhaust setpoint ▶ When FhFire is active the exhaust airflow setpoint will be multiplied by the fire setpoint percentage. On fume hoods with face velocity sensors the face velocity setpoint is also multiplied by the fire setpoint percentage. When the fume hood operating mode is set to Fire and the balancing state is not balancing, FhSpAirFlEh is calculated using the occupied face velocity setpoint and limited by the minimum exhaust airflow setpoint.	SpEhFire	50 [%]
Added air volume flow during stabilizing jet failure ▶ The exhaust air flow setpoint will be increased by this amount while the stabilizing jet failure is active.	AddAflStbFail	200 [m³/h] 117.7 [ft³/min] 55.56 [l/s]
Time for increasing exhaust air volume flow setpoint ▶ Optional rate limiting feature – the time to increase the exhaust airflow setpoint from 0 to maximum (nominal). Leaving at 0 disables the feature.	TiIcrSpAirFlEh	0 [s]
Time for decreasing exhaust air volume flow setpoint ▶ Optional rate limiting feature – the time to decrease the exhaust air flow setpoint from maximum (nominal) to 0. Leaving at 0 disables the feature.	TiDcrSpAirFlEh	0 [s]
Attenuation filter face velocity ▶ Used to stabilize readings from the through-the-wall face velocity sensor. Setting to 0 disables the feature	AtnFltVFace	2 [s]
Switch-on delay to unoccupied setpoint ▶ Programmable time delay when FhOpMod changes from control to low air volume flow and switches to unoccupied setpoint(s). Leaving at 0 disables the delay.	DlyOnSpUcd	30 [s]
Minimum air volume flow setpoint by room request ▶ Setpoint value higher than the minimum fume hood exhaust setpoint, used when the fume hood exhaust airflow is at minimum and the room requests additional airflow.	SpAirFlMinReq	0 [m³/h] 0.0 [ft³/min] 0.00 [l/s]
Unit for setpoint off 1:m/s 2:ft/min 3:ft³/min 4:l/s 5:% 6:m³/h	SpOffUnit	5:%
Setpoint off	SpOff	100
Unit for setpoint 1 Enumeration see SpOffUnit	Sp1Unit	5:%
Setpoint 1	Sp1	100
Unit for setpoint 2 Enumeration see SpOffUnit	Sp2Unit	5:%
Setpoint 2	Sp2	100
Unit for setpoint 3 Enumeration see SpOffUnit	Sp3Unit	5:%
Setpoint 3	Sp3	100
Emergency purge configuration ▶ Used to simulate an Emergency Max button on the P88 ODP. Example: If EmgPrgCnf = setpoint 3 and the operator selects setpoint 3 from the ODP the value in SP3 will be ignored and the fume hood will react the same as if the emergency purge button was pressed on the P87 ODP. 1:Disabled 2:Off 3:Setpoint 1 4:Setpoint 2 5:Setpoint 3	EmgPrgCnf	1:Disabled
Exhaust setpoint selection on low air volume flow ▶ This allows one of the manual setpoints (off, Setpoint 1, Setpoint 2, Setpoint 3) to be used when FhOpMod = low air volume flow. The selected setpoint will be used instead of the unoccupied setpoint(s). Enumeration see EmgPrgCnf	SpSelEhLoAirFl	1:Disabled
Relinquish manual mode on exhaust setpoint selection ▶ Manual setpoints will be released and setpoint selection will return to Auto when FhOpMod = RlqManSpSelEh value. The manual setpoint will not be released if the setpoint is configured for emergency purge. 1:None 2:Off 3:Off and low air volume flow	RlqManSpSelEh	2:Off
Manual operation lock configuration ▶ The option for manual setpoint selection from the ODP will be disabled when FhOpMod = the setting for ManOpLockCnf. Enumeration see RlqManSpSelEh	ManOpLockCnf	2:Off
Retain manual setpoint after power failure ▶ When ManSpAfPwrFail is set to Yes, a fume hood exhaust airflow setpoint that was manually selected at the ODP (Setpoint 1, 2, 3, or Off) will persist after a power failure. 0:No 1:Yes	ManSpAfPwrFail	0:No
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]

Interface

Interface		Description	Type	Ref.	Owned by
FhVFace		Fume hood face velocity	AI	◉	Room segment / Field device
FhSpAirFlEh		Fume hood exhaust air volume flow setpoint	APrcVal	●	-
FhSpAirFlRelEh		Fume hood exhaust setpoint for relative air volume flow	ACalcVal	●	-
FhSpVFace		Fume hood face velocity setpoint	APrcVal	●	-
FhSpSelEh		Fume hood exhaust air setpoint selection 1:Off 2:Auto 3:Setpoint 1 4:Setpoint 2 5:Setpoint 3	MPrcVal	●	-
FhVFaceEff		Fume hood effective face velocity	ACalcVal	●	-
FhAirFlReqEh		Fume hood exhaust air volume flow request from room	ACalcVal	●	-
FhAflMinEffEh		Fume hood exhaust effective minimum air volume flow	ACalcVal	●	-
FhAflMaxPvdEh		Fume hood maximum provided air volume flow for exhaust	ACalcVal	●	-
FhAflMinPvdEh		Fume hood minimum provided air volume flow for exhaust	ACalcVal	●	-
FhVFaceCtr		Fume hood face velocity controller	Controller	●	-
EeiRstInCol		Collection of reset energy efficiency indicator input value	ColView	●	-
	EeiRstInRs	Result of reset energy efficiency indicator input value 0:Off 1:On	BCalcVal	●	-
	EeiRstIn	Reset energy efficiency indicator input value 0:Off 1:On	BCalcVal	◉	Room segment / Field device
SpSelEhInCol		Collection of exhaust air setpoint selection input value	ColView	●	-
	SpSelEhInRs	Result of exhaust air setpoint selection input value Enumeration see FhSpSelEh	MCalcVal	●	-
	SpSelEhIn	Exhaust air setpoint selection input value Enumeration see FhSpSelEh	MI	◉	Room segment / Field device
SpSelEhOdpCol		Collection of exhaust air setpoint selection to ODP	ColView	●	-
	SpSelEhOdp	Exhaust air setpoint selection to ODP Enumeration see FhSpSelEh	MO	◉	Room segment / Field device
PrSpSelEhCol		Collection of present exhaust air setpoint selection	ColView	●	-
	PrSpSelEh	Present exhaust air setpoint selection Enumeration see FhSpSelEh	MPrcVal	◉	Room segment / Field device
FhEei		Fume hood energy efficiency indication 1:Undefined 2:Poor 3:Satisfactory 4:Good 5:Excellent	MCalcVal	◉	Hvac16
FhUcdSpVFace		Fume hood unoccupied face velocity setpoint	ACnfVal	●	-
FhOcdSpVFace		Fume hood occupied face velocity setpoint	ACnfVal	●	-
FhUcdAflEhMin		Fume hood unoccupied minimum exhaust air volume flow	ACnfVal	●	-
FhSpAirFlManEh		Fume hood exhaust manual air volume flow setpoint	ACnfVal	●	-

Engineering and commissioning

Optional.