The fan-powered box application has two control strategies for fan operation:

  • Serial fan operation: The air volume is only increased if the valve's or reheater's positioning signal is fully open and the room temperature exceeds or breaches an additional offset.
  • Parallel fan operation: The fan speed is increased in parallel to the valve's or reheater's positioning signal.

The two strategies are illustrated in the following examples using a modulating fan and one heating and cooling valve. Both strategies can be used in the same manner for staged fans.

Serial

Y

Output signal

 

TR

Room temperature

SpH

Effective heating setpoint

 

SpC

Effective cooling setpoint

YH

Heating valve

 

YC

Cooling valve

FanSpMaxH

Max. fan speed heating

 

FanSpMaxC

Max. fan speed cooling

FanSpMinH

Min. fan speed heating

 

FanSpMinC

Min. fan speed cooling

OfsFanSttH

Offset for fan start heating

 

OfsFanSttC

Offset for fan start cooling

Q

Fan signal

 

 

 

Figure: Example of a serial control strategy using a modulating fan

Parallel

Y

Output signal

 

TR

Room temperature

SpH

Effective heating setpoint

 

SpC

Effective cooling setpoint

YH

Heating valve

 

YC

Cooling valve

FanEndSpdPrlH

Fan end speed for parallel heating

 

FanEndSpdPrlC

Fan end speed for parallel cooling

FanSpMinH

Min. fan speed heating

 

FanSpMinC

Min. fan speed cooling

CoilVlVEndPrlH

Valve end position for parallel heating

 

CoilVlVEndPrlC

Valve end position for parallel cooling

CoilVlVSttPrlH

Valve position start fan heating

 

CoilVlVSttPrlC

Valve position start fan cooling

Q

Fan signal

 

 

 

Figure: Example of a parallel control strategy using a modulating fan

The control strategy can be configured on the fan-powered box application for the fan with the following parameters for the heating sequence.

Description

Name

Default value

Fan operation for cooling

0:Serial
1:Parallel

FanOp

1:Parallel

Fan operation for heating

0:Serial
1:Parallel

FanOp

1:Parallel