Honeywell AUTOMATIC CONTROL SI Edition, Engineering Manual

Page: 103 / 512

PNEUMATIC CONTROL FUNDAMENTALS
ENGINEERING MANUAL OF AUTOMATIC CONTROL
93
Fig. 78. Heating Coil Control.
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
3 /s.
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.
Fig. 79. Mixing Damper and Discharge Air Temperature Control.
M
M
Y
2
EP
2
EP
M
Z
X
P
C X
O
P
C X
O
M
P
C X
O
P
C X
O
SR-1
SR-3
SR-2
RA
20˚C
B S M
TC-1
2
EP
DA
32˚C
B S M
TC-2
SA-1
C-X < 21˚C
C-O > 22˚C
SNAP
ACTING
RELAY
RETURN
AIR
RETURN FAN
OUTSIDE
AIR
TO COOLING
CONTROLS
TS-1
FROM
COOLING
CONTROLS
20-55 kPa N.O.
SIGNAL TO OPEN
ALL INTERIOR VAV
BOX DAMPERS AND
START HOT WATER PUMP
M15145
TO
COOLING
CONTROLS
SUPPLY FAN
AIR DURING COLD RETURN AIR (WARM-UP)
M
Y
Z
M
X
P
C X
O
SR-4
P
C X
O
SR-5
2
EP
DA
13
°
C
B S M
TC-3
L
B M
H
P-F
RA
OUTSIDE
AIR
2
EP
1
EP
TO WARM-UP
CONTROLS
TS-1
40-75 kPa
N.O.
25-75 kPa
N.O.
M
M
P E
B
RR
FROM WARM-UP
CONTROL
(AIR DURING
COLD RETURN)
M15146
SUPPLY FAN
P = 0 140 kPa
B = 140 0 kPa
40-75 kPa CHW
OPEN TO CLOSED
AIR WHEN
FAN ON
TO HEATING COIL
CONTROL AND TO
CHILLER PLANT
CONTROL
20-55 kPa HW GOES OPEN TO CLOSED
60-95 kPa CHW GOES CLOSED TO OPEN
30-75 kPa
N.C.
PI