Mixing Damper Control Sequence - Honeywell AUTOMATIC CONTROL Engineering Manual

OUTSIDE
AIR
SIGNAL TO OPEN
ALL INTERIOR VAV
BOX DAMPERS AND
START HOT WATER PUMP

MIXING DAMPER CONTROL SEQUENCE

Any time the AHU (Fig. 79) runs in the occupied mode
with Electric-Pneumatic Relay 1EP energized, Outside Air
airflow Controller P-F modulates the outside air damper toward
open and the return air damper toward closed (or vice versa)
in unison to maintain design outside air at 4000 cfm.
4-11 PSI
N.O.
OUTSIDE
AIR
P-F L
H
RA
B M
1
EP
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.
4-11 PSI
N.C.
N.O.
6-11 PSI
M
FROM WARM-UP
CONTROL
(AIR DURING
COLD RETURN)
SR-5
AIR WHEN
2
P
FAN ON EP
C
Fig. 79. Mixing Damper and Discharge Air Temperature Control.
PNEUMATIC CONTROL FUNDAMENTALS
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
NOTE: These dampers can control in sequence also, but
unison control positions the damper blades better for
mixing which is helpful during freezing periods. If
the outside air is provided from an outside air shaft
with an outside air fan, an outside air filter is helpful
to keep the flow sensing element/pick-up clean and
effective. Electric-Pneumatic Relay 1EP starts the
outside air system.
SUPPLY FAN
TO HEATING COIL
CONTROL AND TO
CHILLER PLANT
CONTROL
X
SR-4
P
O
Z
C X
M
M
O
X
93
ENGINEERING MANUAL OF AUTOMATIC CONTROL
TO COOLING
CONTROLS
Y
2
EP
B S M
DA
90
TC-2
TO
COOLING
Z
CONTROLS
M10301
TS-1
TO WARM-UP
Y
CONTROLS
2
EP
B S M
DA
55°F
TC-3
PI
3-8 PSI HW GOES OPEN TO CLOSED
9-14 PSI CHW GOES CLOSED TO OPEN
P=O TO 20
B=20 TO 0
RR
B
M
6-11 PSI CHW
P E OPEN TO CLOSED
M10302