Warm-Up/Heating Coil Control Sequence - Honeywell Pneumatic Controls Engineering Manual

Pneumatic Control System Example

Warm-Up/Heating Coil Control Sequence

Any time the Supply Fan (Fig. 78) runs and the return air
temperature is below 69F, Temperature Controller TC-1 trips
Snap-Acting Relay SA-1 to position Switching Relays SR-1 and
SR-2 to initialize warm-up control. Relay SA-1 also positions
Switching Relay SR-4 to disable cooling controls. Switching
Relay SR-2 opens all interior VAV box dampers and starts the
hot water pump. Relay SR-1 switches the hot water valve from
OUTSIDE
AIR
SIGNAL TO OPEN
ALL INTERIOR VAV
BOX DAMPERS AND
START HOT WATER PUMP
156 customer.honeywell.com
SA-1
P
O
SNAP
ACTING
RELAY C X
C-X < 69
C-O >71
3-8 PSI N.O.
M
SR-3
2
M
P O
EP
C X
SR-2
P
O
C X
Fig. 78. Heating Coil Control.
normal control to warm-up control via Controller TC-2 and
modulates the hot water valve to maintain a discharge air
temperature setpoint of 90F.
NOTE: Fan powered perimeter VAV boxes are cool in this
mode and operate with the fans on and at the mini-
mum airflow (warm air) setpoints. Reheat valves at
each box operate as needed. This allows the warm-up
cycle to operate the air handling unit (AHU) fans at a
reduced and low cost power range.
RETURN FAN
RETURN
AIR
2
EP
B S M
RA
70
TC-1
M
AIR DURING COLD RETURN AIR (WARM-UP)
SUPPLY FAN
FROM
TS-1
COOLING
CONTROLS
SR-1
P
O X
C X
M
70-6925
TO COOLING
CONTROLS
Y
2
EP
B S M
DA
90
TC-2
TO
COOLING Z
CONTROLS
M10301