Variable speed fan (FanVarSpd11)

This application function operates a variable speed fan.

The variable fan speed is calculated based on request signal for heating, cooling or ventilation.

Manual input via room operating unit is also possible.

This application function is typically configured for fan coil unit. Can also support a series or parallel fan-powered VAV box, or a heat pump.

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:
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

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 FanAirFlMinVnt as expressed in units of measured air flow. (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

Maximum fan speed for cooling
▶ Maximum fan speed for cooling (in percent) scaled through a CHAR_LIN to provide maximum cooling from the fan cooling request signal (FanCReq).

FanSpdMaxC

ACnfVal

100 [%]

Minimum fan speed for cooling
▶ Minimum fan speed for cooling (in percent) scaled through a CHAR_LIN to provide minimum cooling from the fan cooling request signal (FanCReq).

FanSpdMinC

ACnfVal

50 [%]

Maximum fan speed for heating
▶ Maximum fan speed for heating (in percent) scaled through a CHAR_LIN to provide maximum heating from the fan heating request signal (FanHReq).

FanSpdMaxH

ACnfVal

100 [%]

Minimum fan speed for heating▶ Minimum fan speed for heating (in percent) scaled through a CHAR_LIN to provide minimum heating from the fan heating request signal (FanHReq).

FanSpdMinH

ACnfVal

50 [%]

Maximum fan speed for ventilation
▶ Maximum fan speed for ventilation (in percent) scaled through a CHAR_LIN to provide maximum ventilation from the fan ventilation request signal (FanVntReq).

FanSpdMaxVnt

ACnfVal

100 [%]

Minimum fan speed for ventilation
▶ Minimum fan speed for ventilation (in percent) scaled through a CHAR_LIN to provide minimum ventilation from the fan ventilation request signal (FanVntReq).

FanSpdMinVnt

ACnfVal

50 [%]

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

FanSpdDhu

ACnfVal

50 [%]

Fan start speed 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 FanSttSpdFpb and FanEndSpdFpb. AirFlVavReq is scaled from 0 to the end air configuration value (VavAirFlEnd). Other inputs may drive the fan speed higher.

FanSttSpdFpb

ACnfVal

50 [%]

Fan end speed by fan-powered box
▶ See FanSttSpdFpb

FanEndSpdFpb

ACnfVal

100 [%]

VAV end air volume flow
▶ See FanSttSpdFpb

VavAirFlEnd

ACnfVal

100 [] 1), 2)

1) Value is taken as [m3/h] for pressure independent VAV control
2) Value is taken as [%] for pressure dependent VAV control

Parameters

Description

Parameter

Default value

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

EnStaIn

0:No

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

Interface

Interface

Description

Type

Ref.

Owned by

FanVarSpd

Variable speed fan

AO

◉

Room segment / Device

EnFanSpd

Enable fan speed

BO

◉

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 FanVarSpd11, 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

FanVarSpdMan

Manual variable speed fan

APrcVal

●

-

FanDevMod

Fan device mode

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

MPrcVal

●

-

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

●

-

FanSpdMaxC

Maximum fan speed for cooling

ACnfVal

●

-

FanSpdMinC

Minimum fan speed for cooling

ACnfVal

●

-

FanSpdMaxH

Maximum fan speed for heating

ACnfVal

●

-

FanSpdMinH

Minimum fan speed for heating

ACnfVal

●

-

FanSpdMaxVnt

Maximum fan speed for ventilation

ACnfVal

●

-

FanSpdMinVnt

Minimum fan speed for ventilation

ACnfVal

●

-

FanSpdDhu

Fan speed for dehumidification
▶ see Configuration

ACnfVal

●

-

VavAirFlEnd

VAV end air volume flow
▶ see FanSttSpdFpb

ACnfVal

●

-

FanSttSpdFpb

Fan start speed by fan-powered box
▶ In a fan powered box application, the Air Flow Request for Vav interlock signal (AirFlVavReq) initiates fan speed operation between FanSttSpdFpb and FanEndSpdFpb. AirFlVavReq is scaled from 0 to end air configuration value VavAirFlEnd. Other inputs may drive the Fan speed higher.

ACnfVal

●

-

FanEndSpdFpb

Fan end speed by fan-powered box
▶ see FanSttSpdFpb

ACnfVal

●

-

Engineering and commissioning

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