EXCEL 10 W7750A,B,C CONSTANT VOLUME AHU CONTROLLER
25 74-2958—1
Fig. 15. Heat pump with two compressors and auxiliary
heat stage(s).
ECONOMIZER CONTROL
Economizer control is available concurrentl
with an
confi
uration in the W7750 when DOs are not all used b
the
heatin
and coolin
e
uipment. Two t
pes of economizer
controls are supported b
the W7750 Controller, modulatin
control and enable/disable control. Modulatin
control can be
either Series 60 Floatin
Control or PWM control
PWM
control is available on the W7750B,C
only
. A dischar
e air
temperature sensor is re
uired for modulatin
economizer
damper control. Enable/disable control is provided to emulate
the Hone
well T7300 thermostat economizer operation,
where a DO tracks the occupanc
status of the controller. An
external packa
ed economizer control then modulates the
dampers. For modulatin
control, the economizer is enabled
or disabled based on one of ten available strate
ies
see
Appendix B—Se
uences of Operation—Economizer Enable/
Disable Control section, for further details
. Fi
. 16 illustrates
a s
stem with modulatin
economizer dampers
see Fi
. 29,
31, 32 and 35 in Step 4. Prepare Wirin
Dia
rams section, for
wirin
details
.
Fig. 16. Economizer control.
PNEUMATIC ACTUATOR CONTROL
The W7750B,C Controller can control pneumatic actuators for
an
or all of the three modulatin
outputs provided b
the
control al
orithm
heat, cool and economizer
. Control of
pneumatic water/steam valves and damper actuators is
provided throu
h a transducer device usin
either Series 60
Floatin
Control or PWM DOs. A floatin
-to-pneumatic, or a
PWM-to-pneumatic transducer is re
uired for each output
si
nal. The W7750A Controller can drive Series 60 Floatin
Control to modulate coolin
valves, heatin
valves and
economizers. There are no PWM outputs confi
urable on the
W7750A model.
For pro
ects with existin
pneumaticall
actuated reheat
valves, the Excel 10 W7750 Controller output must be
converted to a pneumatic si
nal usin
a transducer device
developed for use with Excel 10 Controllers. The transducer is
MIXED
AIR
AUXILIARY
HEAT
STAGE(S)
SHARED
HEAT AND
COOL COIL
DISCHARGE
AIR
+
FAN
FAN
STARTER
COMPRESSOR AND
CHANGEOVER VALVE
COMP 1
COMP 2
CHANGEOVER
RELAY
M17493
EXCEL 10
CVAHU
W7750A,B,C
T7560A,B OR T7770
OUTDOOR
AIR
RETURN
AIR
HEAT
COIL
COOL
COIL
DISCHARGE
AIR
-
+
FAN
FAN
STARTER
DISCHARGE
TEMPERATURE
SENSOR REQUIRED
FOR ECONOMIZER
CONTROL
M
PWM OR
SERIES 60
FLOATING
MOTOR
M17494
EXCEL 10
CVAHU
W7750A,B,C
T7560A,B OR T7770
