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EXCEL 10 W7750A,B,C CONSTANT VOLUME AHU CONTROLLER
27 74-2958—1
Dirty Filter Monitor
The air filter in the air handler can be monitored b
y
the W7750
and an alarm is issued when the filter media needs
replacement. The two methods of monitorin
g
the filter are:
1.
Connectin
g
a differential pressure switch to a di
g
ital
input on the W7750A or W7750B,C.
2.
Wirin
g
a 2 to 10V differential pressure sensor to a
volta
g
e input on the W7750B,C. If the analo
g
input
sensor is used, its measured value 0 to 5 inw
(
0 to 1.25
kPa
)
is compared to a user-selectable setpoint
(
FltrPressStPt—valid ran
g
e: 0 to 5 inw
(
0 to 1.25 kPa
))
,
and the Dirt
y
Filter alarm is issued when the pressure
drop across the filter exceeds the setpoint.
Indoor Air Quality (IAQ) Override
The Excel 10 W7750 Controller provides IAQ ventilation
control usin
g
one of two different methods of detectin
g
poor
air
q
ualit
y
. The first is with an IAQ switch device connected to
a di
g
ital input on the W7750 Controller, where a contact
closure indicates poor air
q
ualit
y
, and initiates the IAQ
Override mode. The device can detect poor air
q
ualit
y
usin
g
an
y
desired measure such as CO
2
, VOC, CO, etc. The
second method, which is onl
y
available on the W7750B,C, is
throu
g
h an analo
g
input that connects to a CO
2
sensor
(
2 to
10V
)
. The measured value of CO
2
from this sensor
(
0 to 2000
PPM
)
is compared to the setpoint
(
IAQSetpt
)
. When the CO
2
level is hi
g
her than the setpoint
(
800 PPM
adjustable
)
, the
IAQ Override is initiated. The IAQSetpt h
y
steresis is 50 PPM,
IAQ Override is deactivated at a CO
2
level less than 50 PPM
below setpoint.
The effect of initiatin
g
the IAQ Override mode is that the
economizer dampers are allowed to open above the standard
minimum position settin
g
to allow more fresh air to enter the
buildin
g
. See Appendix B—Se
q
uences of Operation, for
further control details.
Smoke Control
The Excel 10 W7750 Controller supports smoke-related
control strate
g
ies that are initiated either via a network
command
(
DestEmer
g
Cmd
)
or from a local
(
ph
y
sicall
y
connected
)
smoke detector di
g
ital input. The details of the
W7750 smoke-related control operation are described in
Appendix B—Se
q
uences of Operation.
Freeze Stat
A freeze stat can be monitored b
y
the W7750 and issue a
freeze stat alarm indicatin
g
the CVAHU is in dan
g
er of
freezin
g
its coil. The details of the W7750 freeze stat related
control operation are described in Appendix B—Se
q
uences of
Operation.
Modes of Operation
The possible modes of operation for the W7750 Controller are
listed in Table 5.
Table 5. Modes Of Operation For The Excel 10 W7750 Controller .
Mode Description Events causing a controller to switch to this mode
Effective Occupancy (User Address: StatusOcc)
OCCUPIED
Controller is in Occupied mode An
y
of the followin
g
: Network input
(
DestSchedOcc
)
containin
g
a
time-of-da
y
schedule fla
g
from either the Excel 10 Zone Mana
g
er or an
L
ON
W
ORKS
Bus Controller; Time Clock DI, Occupanc
y
Sensor DI; or
from Network input
(
DestManMode
)
for manual override to OCC mode.
DestManMode has the hi
g
hest priorit
y
, followed b
y
the Time Clock DI,
and then DestSchedOcc.
STANDBY
Controller is in Standb
y
mode Either:
(
A
)
Network input
(
DestSchedOcc
)
containin
g
a time-of-da
y
schedule fla
g
from the Excel 10 Zone Mana
g
er or other L
ON
W
ORKS
Bus node is STANDBY, or
(
B
)
Network input
(
DestSchedOcc
)
is
OCCUPIED and the Occupanc
y
Sensor DI is UNOCCUPIED.
UNOCCUPIED
Controller is in Unoccupied mode Network input
(
DestSchedOcc
)
containin
g
a time-of-da
y
schedule fla
g
from the Excel 10 Zone Mana
g
er or L
ON
W
ORKS
Bus, or the network
input DestManOcc has a value of UNOCCUPIED.
BYPASS
OCCUPIED
Controller is in Occupied mode throu
g
h
a B
y
pass command
This mode is derived from the schedule occupanc
y
(
DestSchedOcc
)
havin
g
a state of UNOCCUPIED and a manual re
q
uest for occupanc
y
from one of three sources. Two of these are si
g
nals ori
g
inated external
to the unit, and received b
y
DestManOcc and DestB
y
pass. The third
source for an occupanc
y
re
q
uest is from an override button located on
a wall module. These three sources are arbitrated in a scheme
determined b
y
the confi
g
uration parameter
(
Network Wins or Last-in
Wins from OvrdPriorit
y)
.
Override Modes (User Address: StatusOvrd)
OCCUPIED
Controller occupanc
y
mode was
overridden to Occupied mode
Network input
(
DestManOcc
)
containin
g
a time-of-da
y
schedule
override si
g
nal of OCCUPIED from the Excel 10 Zone Mana
g
er or
other L
ON
W
ORKS
Bus device.
STANDBY
Controller occupanc
y
mode was
overridden to Standb
y
mode
Network input
(
DestManOcc
)
containin
g
a time-of-da
y
schedule
override si
g
nal of STANDBY from the Excel 10 Zone Mana
g
er or other
L
ON
W
ORKS
Bus device.