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EXCEL 10 W7750A,B,C CONSTANT VOLUME AHU CONTROLLER
7 74-2958—1
Control Application
W7750 s
y
stems in commercial buildin
g
s t
y
picall
y
incorporate
a packa
g
ed air handler s
y
stem that delivers a constant
volume of air at preconditioned temperatures to the zone
bein
g
served. Each zone is usuall
y
serviced b
y
a separate
AHU; however, sometimes two or more AHUs service the
same zone. Note that the W7750 is not desi
g
ned to control
Variable Air Volume
(
VAV
)
air handlers or Multi-Zone air
handlers, where one air handler simultaneousl
y
controls the
space temperature in man
y
zones.
The W7750 can control sta
g
ed or modulatin
g
heatin
g
and
coolin
g
coils, mixed air economizer dampers, and the s
y
stem
fan. Control of heat pump units, where the compressor
(
s
)
is
used for both coolin
g
and heatin
g
, is also provided. The zone
the W7750 services can use a T7770 or T7650 for space
temperature sensin
g
and an L
ON
W
ORKS
Bus network access
for users. Fi
g
. 2 shows a t
y
pical W7750 control application.
Fig. 2. Typical W7750 control application.
Control Provided
The W7750 Controller is desi
g
ned to control a sin
g
le air
handler to maintain the units space temperature at the current
setpoint. Heatin
g
and coolin
g
control is provided for either
sta
g
ed or modulatin
g
e
q
uipment. Up to four sta
g
es of
mechanical coolin
g
and up to four sta
g
es of heatin
g
are
allowed. Modulatin
g
outputs can be either
floating type
such
as a Series 60 control, or Pulse Width Modulated
(
PWM
W7750B,C onl
y)
control.
The economizer dampers can be controlled directl
y
with
floatin
g
or PWM outputs, or indirectl
y
usin
g
a di
g
ital output as
an enable/disable si
g
nal to a packa
g
ed economizer controller.
The economizer enable function, which decides when to allow
outdoor air to be used for free coolin
g
, can be confi
g
ured to
one of ten strate
g
ies based on the inputs. For more details,
see Appendix B—Se
q
uences of Operation. When the
economizer position is controlled from the W7750, the
minimum position settin
g
(
for ventilation re
q
uirements
)
can be
ad
j
usted based on indoor air
q
ualit
y
(
IAQ
)
needs in the space.
IAQ monitorin
g
is provided throu
g
h either a CO
2
sensor or a
di
g
ital input from a space-mounted IAQ limit switch.
For heat pump confi
g
urations, up to four compressors can be
controlled, alon
g
with up to four sta
g
es of auxiliar
y
heat, and a
heat/cool chan
g
e over valve. Includin
g
the suppl
y
fan, the
combination of these items ma
y
not exceed ei
g
ht outputs if a
W7750B,C is used, or six outputs for a W7750A.
(
The ei
g
ht
outputs on the W7750C consist of five di
g
ital and three analo
g
outputs.
)
WINDOW CONTACT
OCCUPANCY
SENSOR
M
OA TEMP
FILTER
FAN
COOL
COIL
HEAT
COIL
DA TEMP
RA TEMP
EXCEL 10
W7750
CVAHU
T7770 OR T7560A,B
RETURN
AIR
DISCHARGE
AIR
OUTDOOR
AIR
CEILING
ROOF
-
+
M17488