Direct Gas; Electrical - Greenheck DG Installation, Operation And Maintenance Manual

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)
• Power passes to N.C. supply overload contact
(ST1 OL)
• Power passes through N.C. contact on optional
freeze protection timer (RT4) which remains closed
if the temperature has remained above the set point
• Power passes to optional inlet damper which
opens
• When damper is fully opened, damper relay (D1) is
energized and optional N.O. damper limit switch
(DL1) closes
• Power passes to and energizes supply starter relay
(RF)
• Power passes to N.O. fan contact (RF), which is
energized and closed
• Supply starter (ST1) is energized
• Supply starter contact (ST1) closes and power
reaches and energizes supply fan
• Supply fan (M1) starts
3. Heat Contact (S4) Closed
• Power passes to N.O. fan relay (RF) which is
energized and closed
• Power passes to optional inlet air sensor contact
(TS4) which is energized and closed if the inlet air
temperature is below the set point
• Power passes to and energizes the heat relay (RH)
• N.O. heat relay contact (RH) closes
• Power passes to N.C. high limit control contact
(HLC1) which is closed if temperature has remained
below set point
• Power passes to optional N.O. and N.C. high and
low gas pressure contacts (PS4 and PS3), which
are both closed if gas pressure is within the set
range
• Power passes to N.O. and N.C. airflow switches
(PS2) which are closed if there is proper airflow
across the burner
24 Direct Spark Ignition Make-Up Air
• Power passes to terminal TH on the Flame
Safeguard (FSG) which begins it's sequence
(see Direct Gas Burner Sequence)
4. Optional Evaporative Cooling Contact (S4)
Closed*
• N.O. contact on fan relay (RF) is energized and
closed
• Power passes to optional inlet air sensor contact
(TS4) which is energized and closed if the inlet air
temperature is above the set point
• Power passes to and energizes cool relay (RC)
• N.O. contact on cool relay (RC) is energized and
closed
• Power passes to optional evaporative cooling
pump (P1)
*If DX or chilled water coils are used rather than an evaporative
cooler, the cooling sequence of operation will depend on the
coil controls. Cooling coil controls are supplied by others.
Direct Gas Burner Sequence
1. Supply Fan Contact Closed
• Power passes to the supply fan and heat switch
2. Heat Contact Closed
• Power passes to the heat relay then to the Flame
Safeguard
3. Flame Safeguard (FSG) Sequence
• Checks for proper airflow
• Verifies no flame present at burner
• Initiates 15 second prepurge
• Sends power to open gas valve (V2) and energizes
the spark generator
• Tries for up to 10 seconds to light and confirm
flame
• Shuts down spark generator
• Continuously monitors the flame and airflow
®