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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
y
with an
y
confi
g
uration in the W7750 when DOs are not all used b
y
the
heatin
g
and coolin
g
e
q
uipment. Two t
y
pes of economizer
controls are supported b
y
the W7750 Controller, modulatin
g
control and enable/disable control. Modulatin
g
control can be
either Series 60 Floatin
g
Control or PWM control
(
PWM
control is available on the W7750B,C
only
)
. A dischar
g
e air
temperature sensor is re
q
uired for modulatin
g
economizer
damper control. Enable/disable control is provided to emulate
the Hone
y
well T7300 thermostat economizer operation,
where a DO tracks the occupanc
y
status of the controller. An
external packa
g
ed economizer control then modulates the
dampers. For modulatin
g
control, the economizer is enabled
or disabled based on one of ten available strate
g
ies
(
see
Appendix B—Se
q
uences of Operation—Economizer Enable/
Disable Control section, for further details
)
. Fi
g
. 16 illustrates
a s
y
stem with modulatin
g
economizer dampers
(
see Fi
g
. 29,
31, 32 and 35 in Step 4. Prepare Wirin
g
Dia
g
rams section, for
wirin
g
details
)
.
Fig. 16. Economizer control.
PNEUMATIC ACTUATOR CONTROL
The W7750B,C Controller can control pneumatic actuators for
an
y
or all of the three modulatin
g
outputs provided b
y
the
control al
g
orithm
(
heat, cool and economizer
)
. Control of
pneumatic water/steam valves and damper actuators is
provided throu
g
h a transducer device usin
g
either Series 60
Floatin
g
Control or PWM DOs. A floatin
g
-to-pneumatic, or a
PWM-to-pneumatic transducer is re
q
uired for each output
si
g
nal. The W7750A Controller can drive Series 60 Floatin
g
Control to modulate coolin
g
valves, heatin
g
valves and
economizers. There are no PWM outputs confi
g
urable on the
W7750A model.
For pro
j
ects with existin
g
pneumaticall
y
actuated reheat
valves, the Excel 10 W7750 Controller output must be
converted to a pneumatic si
g
nal usin
g
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