Direct Gas Make-Up Air
42
OPTIONAL VARIABLE VOLUME
Two Speed VFD Control
• When the supply fan relay (RF) is energized, the
normally open supply fan relay (RF) contacts are
closed. This creates a run command for the VFD.
• The run command allows the VFD to pass power
to the supply fan (M1). The supply fan (M1) will
operate at maximum speed.
• When the two speed supply fan contact (S2) is
switched to the low position, power is passed to
the low speed relay (RL) which is energized.
• The normally open low speed relay (RL) contacts
are closed commanding the VFD to low speed.
• The VFD controls supply fan M1 to operate at
minimum speed.
Potentiometer VFD Control
• When the supply fan relay (RF) is energized, the
normally open supply fan relay (RF) contacts are
closed. This creates a run command for the VFD.
• The run command allows the VFD to pass power
to the supply fan (M1). The supply fan (M1)
will operate at the speed commanded by the
potentiometer.
• The potentiometer will output a 2-10 VDC signal to
the VFD analog input terminal. A 2 VDC signal will
command the VFD to minimum speed. A 10 VDC
signal will command the VFD to maximum speed.
• The VFD controls the supply fan motor (M1) to the
speed commanded by the potentiometer.
External Signal VFD Control
• When the supply fan relay (RF) is energized, the
normally open supply fan relay (RF) contacts are
closed. This creates a run command for the VFD.
• The run command allows the VFD to pass power
to the supply fan (M1). The supply fan (M1) will
operate at the speed commanded by the external
signal provided by others.
• The external signal provided by others will send
a 2-10 VDC or a 4-20 mA signal to the VFD
analog input terminal. A 2 VDC or 4mA signal
will command the VFD to minimum speed. A
10 VDC or 20 mA signal will command the VFD to
maximum speed.
• The VFD controls the supply fan motor (M1) to the
speed commanded by the external signal.
Building Pressure VFD Control
• When the supply fan relay (RF) is energized, the
normally open supply fan relay (RF) contacts are
closed. This creates a run command for the VFD.
• The run command allows the VFD to pass power
to the supply fan (M1). The supply fan (M1) will
operate at minimum speed.
• The photohelic building pressure controller will
monitor the pressure differential between the
pressure in the controlled space and the pressure
outside the controlled space.
• If the pressure differential is below the set point
range established on the photohelic controller, the
VFD will increase the supply fan speed.
• If the pressure differential is above the set point
range established on the photohelic controller, the
VFD will decrease the supply fan speed.
• If the pressure differential is within the set point
range established on the photohelic controller,
the VFD will maintain the supply fan at its current
speed.
Sequence of Operation
