Mixing Damper Control Sequence - Honeywell AUTOMATIC CONTROL SI Edition 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 1.9 m
25-75 kPa
N.O.
OUTSIDE
AIR
P-F L H
RA
B M
1
EP
ENGINEERING MANUAL OF AUTOMATIC CONTROL
SA-1
P O
SNAP
ACTING
RELAY
C X
C-X < 21˚C
C-O > 22˚C
20-55 kPa N.O.
M
SR-3
2
M
P O
EP
C X
SR-2
P O
C X
Fig. 78. Heating Coil Control.
3
/s.
30-75 kPa
N.C.
N.O.
40-75 kPa
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
20˚C
TC-1
M
AIR DURING COLD RETURN AIR (WARM-UP)
SUPPLY FAN
FROM
TS-1
COOLING
CONTROLS
SR-1
P X
O
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
O M
X
93
TO COOLING
CONTROLS
Y
2
EP
B S M
DA
32˚C
TC-2
TO
COOLING Z
CONTROLS
M15145
TS-1
TO WARM-UP
Y
CONTROLS
2
EP
B S M
DA
13 C
TC-3
PI
20-55 kPa HW GOES OPEN TO CLOSED
60-95 kPa CHW GOES CLOSED TO OPEN
P = 0 140 kPa
B = 140 0 kPa
RR
M B
40-75 kPa CHW
P E OPEN TO CLOSED
M15146