Honeywell VP525C, Инструкция по эксплуатации, Страница: 165 / 228

Pneumatic Control System Example
70-6925 157
H
u
m
idi
st
at
s
an
d
Th
er
m
o
st
at
s
Controller
s
Sensors
Relay
s
Switch
es
Actuators
Va
lv
e
s
Ac
ces
sor
ie
s
En
gi
ne
eri
ng
Gu
ide
Cr
o
s
s
Refere
nc
e
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.
NOTE: These dampers can control in sequence also, but uni-
son control positions the damper blades better for mix-
ing 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.
Discharge Air Temperature Control Sequence
Any time the AHU (Fig. 79) operates in the non-warm-up mode,
Switching Relay SR-4 operates to allow the normal Discharge
Air Temperature Controller TC-3 to modulate the hot water
valve closed (through Switching Relay SR-1, Fig. 77) and the
chilled water valve open in sequence, on a rising cooling load,
to maintain the Temperature Controller TC-3 setpoint. Controller
TC-3 is a PI (proportional plus integral) controller.
NOTE: In this constant 4000 cfm outside air system, if the
return air is 72F and the outside air is -5F, the mixed
air temperature will drop below 55F if the AHU airflow
drops below 52 percent of the design airflow.
Off/Failure Mode Control Sequence
If compressed air fails, both control valves open, the outside air
damper closes, and the return air damper opens.
When the fan is off, Switching Relay SR-3 (Fig. 78) positions to
close the hot water valve, Switching Relay SR-5 (Fig. 79)
positions to close the chilled water valve, the outside air damper
closes, and the return air damper opens.
M
Y
Z
M
X
P
C X
O
SR-4
P
C X
O
SR-5
2
EP
DA
55F
B S M
TC-3
L
B M
H P-F
RA
OUTSIDE
AIR
2
EP
1
EP
TO WARM-UP
CONTROLS
TS-1
6-11 PSI
N.O.
4-11 PSI
N.O.
M
M
P E
B
RR
FROM WARM-UP
CONTROL
(AIR DURING
COLD RETURN)
M10302
SUPPLY FAN
P=O TO 20
B=20 TO 0
6-11 PSI CHW
OPEN TO CLOSED
AIR WHEN
FAN ON
TO HEATING COIL
CONTROL AND TO
CHILLER PLANT
CONTROL
3-8 PSI HW GOES OPEN TO CLOSED
9-14 PSI CHW GOES CLOSED TO OPEN
4-11 PSI
N.C.
PI