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