Honeywell W7750A User Manual
EXCEL 10 W7750A,B,C CONSTANT VOLUME AHU CONTROLLER
74-2958—1
24
Allowable Heating and Cooling Equipment
Configurations
Configurations
Each W7750 device can control a variety of different types of
mechanical cooling and heating equipment within roof top air
handlers. See Fig. 13 through 17 for a conceptual overview of
some typical configurations. For specific wiring details, see
the Prepare Wiring Diagrams section.
mechanical cooling and heating equipment within roof top air
handlers. See Fig. 13 through 17 for a conceptual overview of
some typical configurations. For specific wiring details, see
the Prepare Wiring Diagrams section.
STAGED HEATING/COOLING CONTROL
Staged equipment control is available for up to four stages of
heating or four stages of cooling. On the W7750, the stages
are activated through digital outputs (Triacs on the W7750B,C
and dry-contact relays on the W7750A) one for each stage
wired to 24 Vac contactors (see Fig. 27 and 30 in Step 4.
Prepare Wiring Diagrams section for wiring details). Note that
the number of physical Digital Outputs (DOs) on the controller
limits the total number of stages that can be controlled. For
example, the W7750A Model has six digital outputs, and
because one is used for the supply fan, there are five DOs
available for any combination of heating and cooling stages
(with a maximum of four stages of heating and four stages for
cooling). The W7750B Model offers two additional DOs, for a
total of eight. The W7750C offers five DOs and three Analog
Outputs (AOs). Fig. 13 shows a typical application of two
stages of heat and two stages of cooling.
heating or four stages of cooling. On the W7750, the stages
are activated through digital outputs (Triacs on the W7750B,C
and dry-contact relays on the W7750A) one for each stage
wired to 24 Vac contactors (see Fig. 27 and 30 in Step 4.
Prepare Wiring Diagrams section for wiring details). Note that
the number of physical Digital Outputs (DOs) on the controller
limits the total number of stages that can be controlled. For
example, the W7750A Model has six digital outputs, and
because one is used for the supply fan, there are five DOs
available for any combination of heating and cooling stages
(with a maximum of four stages of heating and four stages for
cooling). The W7750B Model offers two additional DOs, for a
total of eight. The W7750C offers five DOs and three Analog
Outputs (AOs). Fig. 13 shows a typical application of two
stages of heat and two stages of cooling.
Fig. 13. Fan with two stages of heating and two stages
of cooling.
MODULATING HEATING/COOLING CONTROL
The W7750 Controller provides modulating equipment control
for heating and cooling equipment (and economizer dampers,
see Fig. 16) using either Series 60 Floating Control or Pulse
Width Modulated (PWM) control, (PWM control is available on
the W7750B,C only). The Series 60 Modulating Control is
provided through two Relay digital outputs on the W7750A or
two Triac digital outputs on the W7750B,C (one to pulse the
valve actuator open and one to pulse it closed). PWM control
for heating and cooling equipment (and economizer dampers,
see Fig. 16) using either Series 60 Floating Control or Pulse
Width Modulated (PWM) control, (PWM control is available on
the W7750B,C only). The Series 60 Modulating Control is
provided through two Relay digital outputs on the W7750A or
two Triac digital outputs on the W7750B,C (one to pulse the
valve actuator open and one to pulse it closed). PWM control
positions the actuator based on the length, in seconds, of the
pulse from the digital output. For PWM, the controller outputs
a pulse whose length consists of two parts, a minimum and a
maximum. The minimum pulse time represents the analog
value of 0 percent and the maximum pulse length that
represents an analog value of 100 percent. If the analog value
is greater than 0 percent, an additional time is added to the
minimum pulse time. The length of time added is directly
proportional to the magnitude of the analog value. The PWM
actuator will begin to use the analog value at the end of the
pulse and will continue to use this value until a new pulse is
received. Refer to Appendix B under PWM Control for an
example. Series 60 actuators are generally less expensive
than those for PWM, but the trade-off is that PWM requires
only a single controller digital output while floating control
uses two DOs. Refer to Appendix B under Series 60
Modulating Control for an example. Fig. 14 illustrates a
system with modulating heating and cooling (see Fig. 29 and
31 in Step 4. Prepare Wiring Diagrams section.
pulse from the digital output. For PWM, the controller outputs
a pulse whose length consists of two parts, a minimum and a
maximum. The minimum pulse time represents the analog
value of 0 percent and the maximum pulse length that
represents an analog value of 100 percent. If the analog value
is greater than 0 percent, an additional time is added to the
minimum pulse time. The length of time added is directly
proportional to the magnitude of the analog value. The PWM
actuator will begin to use the analog value at the end of the
pulse and will continue to use this value until a new pulse is
received. Refer to Appendix B under PWM Control for an
example. Series 60 actuators are generally less expensive
than those for PWM, but the trade-off is that PWM requires
only a single controller digital output while floating control
uses two DOs. Refer to Appendix B under Series 60
Modulating Control for an example. Fig. 14 illustrates a
system with modulating heating and cooling (see Fig. 29 and
31 in Step 4. Prepare Wiring Diagrams section.
Fig. 14. Fan, modulating heating and modulating cooling.
NOTE:
Pneumatically actuated valves can be controlled
using a pneumatic transducer device. See Fig. 17.
Also, transducer devices are available from third
party vendors to convert PWM outputs to a voltage
or current signal if desired.
using a pneumatic transducer device. See Fig. 17.
Also, transducer devices are available from third
party vendors to convert PWM outputs to a voltage
or current signal if desired.
HEAT PUMP CONTROL
The W7750 Controller handles heat pump applications
similarly to staged heating/cooling control. Heat pump
applications are supported by providing outputs for up to four
compressor stages, a change-over relay for the refrigerant
reversing valve, and up to four stages of auxiliary heat. Note
that the W7750A Model has six digital outputs, and therefore,
with one DO used for the supply fan and one for the change-
over relay, there are four outputs available for any
combination of compressors and auxiliary heat stages. The
W7750B Model offers two additional DOs for a total of eight,
while the W7750C Model offers five DOs and 3 AOs. Fig. 15
illustrates a typical heat pump system with auxiliary heat.
similarly to staged heating/cooling control. Heat pump
applications are supported by providing outputs for up to four
compressor stages, a change-over relay for the refrigerant
reversing valve, and up to four stages of auxiliary heat. Note
that the W7750A Model has six digital outputs, and therefore,
with one DO used for the supply fan and one for the change-
over relay, there are four outputs available for any
combination of compressors and auxiliary heat stages. The
W7750B Model offers two additional DOs for a total of eight,
while the W7750C Model offers five DOs and 3 AOs. Fig. 15
illustrates a typical heat pump system with auxiliary heat.
M17491
MIXED
AIR
AIR
HEAT
COIL
COIL
COOL
COIL
COIL
DISCHARGE
AIR
AIR
W1 W2
Y1
Y2
-
+
FAN
FAN
STARTER
STARTER
COMPRESSORS
GAS COMBUSTION
CONTROLS
EXCEL 10
CVAHU
W7750A,B,C
T7560A,B OR T7770
MIXED
AIR
AIR
HEAT
COIL
COIL
COOL
COIL
COIL
DISCHARGE
AIR
AIR
-
+
FAN
FAN
STARTER
STARTER
CHILLED
WATER
VALVE
WATER
VALVE
HOT
WATER
VALVE
WATER
VALVE
M17492
EXCEL 10
CVAHU
W7750A,B,C
T7560A,B OR T7770