Variable speed fan, air volume flow control (FanVarSpd12)

This application function operates a variable speed fan, using internal air volume flow controller to drive the measured air volume flow to an air volume flow setpoint.

To calculate air volume flow, this AF uses an OEM box flow coefficient (K-factor) and input from a differential pressure sensor.

The air volume flow setpoint is calculated based on request signals (from the room controllers) received for heating, cooling and ventilation.

Manual input via room operating unit is also possible.

There is an optional binary input for the fan state.

Another optional binary output can be used to enable the fan operation.

This application function is NOT available for:
DXR2x09T and DXR2x10

Required elements and how to configure them:

Element

I/O

Signal type

FanVarSpd "Variable speed fan"

On-board output, Fan speed

Variable speed 0…10V

FanDiffP "Fan differential pressure"

On-board input, Fan differential pressure

0…10V or P1

Function

The figure below shows BACnet objects associated with this application function. Primary signal flow is summarized as follows:

The fan request signal(s) are received (FanVntReq / FanCReq / FanHReq) and processed into the analog output signal for fan speed (FanVarSpd).

Basic function: Accept request signal from associated room controller and pass it through a device mode logic switch; Output the result as a command to the BACnet object that controls the device.

 

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)

Interlocks

Room automation interlocks are internal signals that coordinate interaction between HVAC devices. They are not visible in ABT Site or web interface, but parameters associated with them are. See comment column for hints on parameters that affect interlock functionality.

Signal

Type

Direction

Description

Comment

AirFlCReq

Boolean

In

Air flow cooling request
▶ Initiates air flow (fan turns on) to satisfy air flow support request for cooling.

 

AirFlHReq

Boolean

In

Air flow heating request
▶ Initiates air flow (fan turns on) to satisfy air flow support request for heating.

 

AirFlDhuReq

Boolean

In

Air flow dehumidification request
▶ Initiates air flow (fan turns on) to satisfy dehumidification request from cooling coil.

 

AirFlVntReq

Boolean

In

Air flow ventilation request
▶ Initiates air flow (fan turns on) to satisfy ventilation request from OA damper.

 

AirFlHldC

Boolean

In

Air flow hold for cooling
▶ Interlock signal from DX cooling coil indicating the coil needs equipment protection air flow support. The fan is prevented from turning off for a period of time.

 

AirFlHldH

Boolean

In

Air flow hold for heating
▶ Interlock signal from electric heating coil indicating the coil needs equipment protection air flow support. The fan is prevented from turning off for a period of time.

 

AirFlSta

Boolean

Out

Air flow status
▶ Interlock signal that keeps the coil locked (or OA damper closed) at equipment protection priority (PrPrio = 5) unless the fan is running.

See Configuration section for parameters named "...AirFlSta".

AirFlVavReq

%

In

Air flow vav request
▶ In a fan-powered box (FPB) application, the VAV damper sends a proportional analog request signal (AirFlVavReq) requesting air flow, so that the box can meet an air flow / ventilation demand.

Fan-powered box application.

FanManOff

Boolean

Out

Fan manual off
▶ Interlock signal to turn off (at equipment protection priority) DX cooling coils and electric heating coils when the fan has been manually turned off (FanManOff = True). If fan device mode is set to 4:Manual speed, AND there is no demand for the fan to be on, then FanManOff will equal True.

 

Ventilation request - When FanDevMod is "Control mode" the fan is available for ventilation request (FanAvlVnt = Yes). When a ventilation request (FanVntReq) is greater than 4%, FanVarSpd is equal to or greater than FanSpdMinVnt. (switch-off hysteresis to turn fan off is 2%)

If device mode is not Control mode, FanVntReq has no effect.

Note
This feature ensures that the fan can provide a minimum ventilation air flow when there is little or no heating or cooling demand, for example the Neutral zone during temperature sequencing.

Fan heating available status - FanAvlH will equal "Yes" if FanDevMod is "Control mode" and the internal signal for air flow heating request is active (True).

Fan cooling available status - FanAvlC will equal "Yes" if FanDevMod is "Control mode" and the internal signal for air flow cooling request is active (True).

Configuration

Objects

Description

Object

Type

Default value

Fan box coefficient
▶ A number that includes an engineering units conversion factor, a constant for calibration of the sensor span, and the duct area.

FanBoxCoef

ACnfVal

150 [m3/h/SqrtPa]
4022.01 [ft3/min/inWC]
41.67 [l/s/SqrtPa]

Fan maximum air volume flow for cooling
▶ Fan maximum air volume flow to satisfy air flow support request for cooling.

FanAirFlMaxC

ACnfVal

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

Fan minimum air volume flow for cooling
▶ Fan minimum air volume flow to satisfy air flow support request for cooling.

FanAirFlMinC

ACnfVal

50 [m3/h]
29.4 [ft3/min]
13.89 [l/s]

Fan maximum air volume flow for heating
▶ Fan maximum air volume flow to satisfy air flow support request for heating.

FanAirFlMaxH

ACnfVal

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

Fan minimum air volume flow for heating
▶ Fan minimum air volume flow to satisfy air flow support request for heating.

FanAirFlMinH

ACnfVal

50 [m3/h]
29.4 [ft3/min]
13.89 [l/s]

Fan maximum air volume flow for ventilation
▶ Fan maximum air volume flow to satisfy air flow support request for ventilation.

FanAirFlMaxVnt

ACnfVal

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

Fan minimum air volume flow for ventilation
▶ Fan minimum air volume flow to satisfy air flow support request for ventilation.

FanAirFlMinVnt

ACnfVal

50 [m3/h]
29.4 [ft3/min]
13.89 [l/s]

Fan air volume flow for dehumidification
▶ Configurable for the speed of the fan upon a request for dehumidification. If AirFlDhuReq is True, fan speed will = FanAirFlDhu unless other input(s) work at a higher priority.

FanAirFlDhu

ACnfVal

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

VAV end air volume flow
▶ See FanSttAirFlFpb

VavAirFlEnd

ACnfVal

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

Fan start air volume flow by fan-powered box
▶ In a fan powered box application, the Air flow request for Vav interlock signal (AirFlVavReq) initiates fan speed operation at a value somewhere between FanSttAirFlFpb and FanEndAirFlFpb. AirFlVavReq is scaled from 0 to the end air configuration value (VavAirFlEnd). Other inputs may drive the fan speed higher.

FanSttAirFlFpb

ACnfVal

50 [m3/h]
29.4 [ft3/min]
13.89 [l/s]

Fan end air volume flow by fan-powered box
▶ See FanSttAirFlFpb

FanEndAirFlFpb

ACnfVal

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

Parameters

Description

Parameter

Default value

Nominal air volume flow
▶ Maximum air flow capacity of the VAV box. Must be no larger than 1.2 times the greater of the values of maximum air flow for ventilation or heating or cooling.

AirFlNom

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

Enable state input
▶ Must be set to 1:Yes when a binary fan status input is used.

EnStaIn

0:No

Differential pressure

Switch-on point for differential pressure
▶ Differential pressure (velocity) sensor signal value must be above this value or else the value is forced to zero.

SwiOnPtDiffP

0.2 [Pa]
0.001 [inWC]

Hysteresis for differential pressure
▶ Amount (in pressure units) below the SwiOnPtDiffP value at which the sensor velocity pressure value will be forced to zero.

HysDiffP

0.1 [Pa]
0.000 [inWC]

Interlocks

Switch-on point for air volume flow state
▶ Amount in percent of nominal flow that the value must be in order for AirFlSta to be True.

SwiOnAirFlSta

4 [%]

Hysteresis for air volume flow state
▶ Amount in percent of nominal flow that must be below SwiOnAirFlSta in order for AirFlSta to be False.

HysAirFlSta

2 [%]

Switch-on delay for air volume flow state
▶ The amount of time after the fan is commanded on before the air flow state interlock signal becomes True. Until this time elapses, the interlock signal keeps the coil or OA damper locked / closed.

DlyOnAirFlSta

30 [s]

Enable fan operation before heating coil
▶ When this parameter is set to its default (No), the fan and coil activation is "parallel" (fan and coil operate together). Setting this parameter to Yes will enable the Fan to operate through its full speed range while the coil is either off or at minimum setting.

0:No
1:Yes

EnFanOpBfHcl

0:No

Internal settings – do not change

Pressure unit
▶ Defined by selected engineering unit – do not change.

PUnit

[Pa]
[inWC]

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

FanVarSpd

Variable speed fan

AO

◉

Room segment / Device

EnFanSpd

Enable fan speed

BO

◉

Room segment / Device

FanDiffP

Fan differential pressure

AI

◉

Room segment / Device

FanSta

Fan state
▶ When FanSta is enabled (parameter EnStaIn = Yes) and FanSta is True, AirFlSta (air volume flow state) turns on after the time delay in DlyOnAirFlSta.
0:Off
1:On

Note
For FanVarSpd12, if no FanSta present, AirFlSta is still set to "on" by the output of DlyOnAirFlSta once time elapses (fan speed must be greater than SwiOnAirFlSta).

BI

◉

Room segment / Device

FanSpAirFl

Fan setpoint for air volume flow

APrcVal

●

-

FanSpAirFlRel

Fan setpoint for relative air volume flow

ACalcVal

●

-

FanAirFl

Fan air volume flow

ACalcVal

●

-

FanAirFlRel

Fan relative air volume flow

ACalcVal

●

-

FanAirFlMan

Manual fan air volume flow

APrcVal

●

-

FanVarSpdMan

Manual variable speed fan

APrcVal

●

-

FanDevMod

Fan device mode

1:Off
2:Control mode
3:Maximum speed
4:Manual speed

MPrcVal

●

-

FanAirFlCtr

Fan air flow controller

Controller

●

-

FanCReq

Fan cooling request

ACalcVal

●

-

FanHReq

Fan heating request

ACalcVal

●

-

FanVntReq

Fan ventilation request
▶ see Ventilation request above

ACalcVal

●

-

FanAvlC

Fan available for cooling
▶ see Fan cooling available status above

0:No
1:Yes

BCalcVal

●

-

FanAvlH

Fan available for heating
▶ see Fan heating available status above

0:No
1:Yes

BCalcVal

●

-

FanAvlVnt

Fan available for ventilation
▶ see Ventilation request above

0:No
1:Yes

BCalcVal

●

-

FanBoxCoef

Fan box coefficient

ACnfVal

●

-

FanAirFlMaxC

Fan maximum air volume flow for cooling

ACnfVal

●

-

FanAirFlMinC

Fan minimum air volume flow for cooling

ACnfVal

●

-

FanAirFlMaxH

Fan maximum air volume flow for heating

ACnfVal

●

-

FanAirFlMinH

Fan minimum air volume flow for heating

ACnfVal

●

-

FanAirFlMaxVnt

Fan maximum air volume flow for ventilation

ACnfVal

●

-

FanAirFlMinVnt

Fan minimum air volume flow for ventilation

ACnfVal

●

-

FanAirFlDhu

Fan air volume flow for dehumidification
▶ see Configuration

ACnfVal

●

-

VavAirFlEnd

VAV end air volume flow
▶ see FanSttAirFlFpb

ACnfVal

●

-

FanSttAirFlFpb

Fan start air volume flow by fan-powered box
▶ The Air Flow Request for Vav interlock signal (AirFlVavReq) initiates fan speed operation between FanSttAirFlFpb and FanEndAirFlFpb. AirFlVavReq is scaled from 0 to end air configuration value VavAirFlEnd. Other inputs may drive the Fan speed higher.

ACnfVal

●

-

FanEndAirFlFpb

Fan end air volume flow by fan-powered box
▶ see FanSttAirFlFpb

ACnfVal

●

-

Engineering and commissioning

Parameter EnStaIn must be set to 1:Yes if a binary fan status input is used.