Fume hood exhaust air setpoint, face velocity and sash sensor (FhSpEh13)

Overview

The application function "Fume hood exhaust setpoint 13, face velocity and sash area" (FhSpEh13) is used to determine the exhaust volume setpoint based on a combination of sash sensor 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. The exhaust flow setpoint is also effected by input from an operator adjustment through the ODP, room exhaust demand and fume hood operating mode (FhOpMod).

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

Main features:

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:

  1. Off
  2. Auto
  3. Setpoint 1
  4. Setpoint 2
  5. 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

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.

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 request from room: The fume hood setpoint may need to be increased due to laboratory temperature or laboratory airflow requirements. A fume hood demand request will be sent from the laboratory room to maintain proper pressurization.

The exhaust airflow request from the room (FhAirFlReqEh) will only change the exhaust airflow setpoint (FhSpAirFlEh) when the exhaust setpoint selection (FhSpSelEh) is set to auto.

The fume hood minimum (FhAflMinPvdEh) and maximum airflow provided signals (FhAflMaxPvdEh) are collected by the room. If the fume hood is not configured to allow the room to adjust the fume hood setpoint the air flow provided signals will be set to zero.

The exhaust request can change the fume hood minimum setpoint.

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.

Face velocity control: The exhaust flow setpoint is calculated separately using a velocity sensor and sash sensor(s). The two calculations use the same face velocity setpoint. The higher value is the effective exhaust flow setpoint.

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 filter constant and a correction factor are involved to convert the raw measured face velocity to the measured 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 volumetric setpoint from fume hood airflow minimum to maximum, and then converts the percentage value to airflow volumetric value, this value is further compared with the exhaust flow SP calculated from face area to choose whichever is greater for exhaust damper modulating (inner loop of cascade control).

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

Exhaust airflow setpoint: When the FhOpMod is set to Control, the exhaust setpoint selection is Auto, and the balancing state is not balancing, the exhaust airflow setpoint (FhSpAirFlEh) is calculated using the face velocity setpoint. The calculated setpoint is limited by the effective minimum and maximum exhaust airflow setpoints.

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

Emergency alarm exhaust volume setpoint: The emergency purge exhaust setpoint (SpEmgPrg) is a configuration extension, entered as a percentage of setpoint. When the fume hood device mode is set to Emergency and the balancing state is not balancing, FhSpAirFlEh is calculated using the 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 face area, and exhaust airflow minimum are used for the exhaust volume 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

0...20 [m/s], 0...3937 [ft/min]

FhUcdSpVFace

ACnfVal

0.41 [m/s]
80.0 [ft/min]

Fume hood occupied face velocity setpoint

0...20 [m/s], 0...3937 [ft/min]

FhOcdSpVFace

ACnfVal

0.41 [m/s]
80.0 [ft/min)

Fume hood exhaust manual air volume flow setpoint

FhSpAirFlManEh

ACnfVal

100 [m3/h]
58.9 [ft3/min]
27.78 [l/s]

Parameters

Description

Parameter

Default value

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. 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.

SpEhFire

50 [%]

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

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

FhSashSwiCol

Collection of fume hood sash switch

ColView

●

-

 

FhSashSwiRs

Result of fume hood sash switch

0:Closed
1:Opened

BCalcVal

●

-

FhSashSwi

Fume hood sash switch

0:Closed
1:Opened

BI

◉

Room segment / Field device

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

1:Off
2:Auto
3:Setpoint 1
4:Setpoint 2
5:Setpoint 3

MCalcVal

●

-

SpSelEhIn

Exhaust air setpoint selection input value

1:Off
2:Auto
3:Setpoint 1
4:Setpoint 2
5:Setpoint 3

MI

◉

Room segment / Field device

SpSelEhOdpCol

Collection of exhaust air setpoint selection to ODP

ColView

●

-

 

SpSelEhOdp

Exhaust air setpoint selection to ODP

1:Off
2:Auto
3:Setpoint 1
4:Setpoint 2
5:Setpoint 3

MO

◉

Room segment / Field device

PrSpSelEhCol

Collection of present exhaust air setpoint selection

ColView

●

-

 

PrSpSelEh

Present exhaust air setpoint selection

1:Off
2:Auto
3:Setpoint 1
4:Setpoint 2
5:Setpoint 3

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

●

-

FhSpAirFlManEh

Fume hood exhaust manual air volume flow setpoint

ACnfVal

●

-

Engineering and commissioning

Optional.