Greenheck Fan VSU Make-Up Air Unit with Direct-Fired Gas Heater 470654 - Manual (Page 20)

20 Model VSU Make-Up Air
®
Operation - Recirculating Units
(optional)
NOTE
Blower Start-Up, as shown on page 14, should be
performed before the blower is run.
Recirculation Operation
The recirculation operation option is recommended
when the ventilation equipment provides the primary
source of heating for the space. A minimum of 20%
outdoor air is mixed with up to 80% filtered recirculated
air. Control strategies include 2-position and modulating
dampers.
Before the unit is left in service, the recirculation control
system should be tested.
2-Position Damper
A 2-position spring return actuator is used to control
the return air amounts. The
damper moves from open to
closed. If power is cut to the unit,
the outdoor air damper will fail to
close.
Turn the recirculating switch on
the remote control panel to each
position and confirm that the return
air damper adjusts accordingly.
The damper actuator may take a
few minutes to open or close.
Modulating
Potentiometer Control — a modulating spring return
actuator is used to control the return air amounts.
The return air damper modulates
from fully open to fully closed
based on a signal from a remote
potentiometer.
To test potentiometer operation,
turn the potentiometer to the two
extremes. With 80/20 recirculation,
confirm that the return air damper
fully opens and fully closes. When
the potentiometer is at 0, the return
air damper will open. When the
potentiometer is at 100, the return
air damper will close. The damper
actuator may take a few minutes to open or close.
70 65 75
80
85
90
60
55
GREENHECK
®
(OPTIONAL)
BLOWER
DIRTY FIL TERS
MAIN V AL VES
RECIRCULA TION
EXHAUST
SUPPL Y
HEA T
(OPTIONAL)
2-Position
Damper Control
70 65 75 80
85 90
60
55
(OPTIONAL)
BLOWER
DIRTY FILTERS
MAIN VALVES
EXHAUST
SUPPLY
HEAT
(OPTIONAL)
GREENHECK
®
Potentiometer
Control
70 65 75 80
85 90
60
55
(OPTIONAL)
BLOWER
DIRTY FILTERS
MAIN VALVES
EXHAUST
SUPPLY
HEAT
(OPTIONAL)
GREENHECK
®
PHOTOHELIC
Building
Pressure Control
Building Pressure Control — a
modulating spring return actuator
is used to control the return air
amounts. The return air damper
modulates from fully open to fully
closed based on a signal from a
remote pressure sensing device.
Turn both knobs to the upper most
pressure setting. You may have
to remove the outdoor pressure
tap tubing. The return air damper
should close.
Set both knobs at the lowest setting and the damper
should open. It may take one to two minutes for the
damper to reach the desired position.
Reset the correct pressure limits before starting the unit.
This picture shows a typical
photohelic setting. Typical
settings are 0.0 in. wg for the
lower and 0.10 in. wg for the
upper pressure setting. The
needle in this photo indicates
a negative building pressure.
During correct operation, the
indicating needle will remain
between or near the setting
needles.
External Signal — a modulating spring return actuator
is used to control the return air amounts. Return air
damper modulates from fully open to fully closed based
on an external 2-10 VDC or 4-20 mA signal (by others).
The return air damper will close with a 10 VDC or 20 mA
signal. The return air damper should open with a 2 VDC
or 4mA signal. The damper actuator may take a few
minutes to open or close.
Pressure Setting Knobs
Pressure Setting
Needles
Pressure Indicating
Needle
Photohelic Gauge
Operation - Electrical
Electrical Sequence
1. Exhaust Fan Contact (S1) Closed
(optional)
• Power passes to N.C. exhaust overload contact
(ST2 OL) (optional)
• Power passes to exhaust starter(s) ST2
• N.O. exhaust starter switches are energized and
closed
• Power passes to exhaust fans
• Exhaust fan(s) (M2) start
2. Supply Fan Contact (S2) Closed
• Power passes through N.C. field supplied fire
contact (FSC)
• Power passes through N.O. exhaust fan contact
(ST2), which is closed when the exhaust relay
(ST2) is activated (optional)