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OPERATING SEQUENCES
Staged Air Volume (2- - Speed) Fan Motor
The Fan Speed Relay Board in the main unit determines
the operating speed (Low or High) of the indoor fan based
on space thermostat demand conditions. See Table 10 for
this logic.
Table 10 – Supply Fan Speed Logic
TSTAT
OUTPUT
G/OCC
0--- V
Y1
0--- V
Y2
0--- V
W1
0--- V
SUPPLY
FAN
OFF
MOTOR
SPEED
W7220 Economizer Control
Tables 11 and 12 provide the W7220 Input/Output Logic.
Table 11 describes economizer functions for a unit without
a CO
sensor. Table 12 describes economizer functions for
2
a unit with Demand Control Ventilation (CO
connected). The supply fan speed is included in these
tables for reference; this is neither an input or output of
the W7220 controller.
Base Unit Controls
Base unit includes standard electromechanical controls,
Staged Air Volume (2- - speed supply fan motor with VFD),
EconoMi$er X (with W7220 controller) and thermostat or
unitary controller that energizes the G terminal in cooling
and heating to control the supply fan operation.
Cooling, Unit With EconoMi$er X Without CO
For Occupied mode operation of EconoMi$er X, there
must be a 24- - v signal at terminal G at the unit's Central
Terminal Board from the thermostat; supply fan motor
will start and run in Low Speed. The signal at G is
connected to W7220 input OCC, placing the EconoMi$er
X control in Occupied mode; the economizer actuator is
commanded open to the MIN POS L ventilation position.
Removing the signal at OCC places the EconoMi$er X
control in Unoccupied mode; the economizer actuator is
driven back to full- - closed position.
When free cooling using outside air is not available, the
unit cooling sequence will be controlled directly by the
space thermostat. Thermostat call for Stage 1 Cooling
energizes CTB terminals G and Y1; supply fan motor
starts and runs in Low Speed. The Y1 demand is received
at W7220 terminal Y1- - I. Outside air damper position will
be at MIN POS L. W7220 output Y1- - O is energized; first
stage mechanical cooling starts.
If the space temperature continues to rise, the thermostat
will call for second stage cooling; CTB terminal Y2 is
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24---V
24--- V
24--- V
0--- V
24---V
24--- V
0--- V
0--- V
24---V
0--- V
0--- V
0--- V
LOW
LOW
HIGH
search engine
also energized.
Speed. The Y2 demand is received at W7220 terminal
Y2- - I. Outside air damper position will shift to MIN POS
H. W7220 output Y2- - O is energized; second stage
mechanical cooling starts.
As space temperature falls, the thermostat will remove its
call for second stage cooling; CTB terminal Y2 call is
removed. The supply fan motor shifts back to Low Speed.
The W7220 input Y2- - I is also removed; the outside air
damper is repositioned to MIN POS L and output Y2- - O is
de- - energized, stopping second stage mechanical cooling.
As space temperature continues to fall and space cooling
load is satisfied, the thermostat will remove its call for
24--- V
first stage cooling; CTB terminal Y1 call is removed. The
0--- V
W7220 input Y1- - I is removed; output Y1- - O is
0--- V
de- - energized, stopping first stage cooling.
24---V
When CTB terminal Y1 is de- - energized, terminal G may
remain energized, indicating Continuous Fan operation.
The supply fan motor will continue to run in Low Speed.
HIGH
W7220 input OCC remains energized; the outside air
damper remains in MIN POS L. If CTB terminal G is also
de- - energized with Y1, indicating AUTO Fan operation,
then the supply fan motor will stop. The W7220 input at
OCC is removed; the outside air damper closes.
When free cooling is available as determined by the
appropriate changeover command (outdoor dry bulb,
outdoor enthalpy, differential dry bulb or differential
sensor
2
enthalpy), a space thermostat call for Stage 1 Cooling
energizes CTB terminals G and Y1; supply fan motor
starts and runs in Low Speed. The G demand is received
at W7220 input OCC; outside air damper moves to MIN
POS L. The Y1 demand is received at W7220 terminal
Y1- - I. The W7220 economizer control will modulate the
outside air damper open and closed to maintain the unit
cooling supply air temperature at setpoint MAT SET
(default 53_F (12_C)). Compressor will not run.
During free cooling operation, a supply air temperature
(SAT) above MAT SET will cause the outside air damper
2
to modulate between MIN POS L setpoint and 100%
open. As SAT decreases and approaches setpoint MA LO
SET (default 45_F (7_C)), the outside air damper will
maintain at the MIN POS L setting. With SAT below MA
LO SET, the outside air damper will be closed or at
minimum (see FREEZE POS) When SAT rises to MA LO
SET plus 3_F, the outside air damper will re- - open to MIN
POS L setting.
Should 100% outside air not be capable of satisfying the
space cooling load, space temperature will rise and the
thermostat will call for second stage cooling; CTB terminal
Y2 is also energized. The supply fan motor shifts to High
Speed. The Y2 demand is received at W7220 terminal Y2- - I.
Outside air damper position will shift to MIN POS H. Time
delay parameter 2SP FAN DELAY (default 5 minutes) will
commence, blocking W7220 output Y1- - O and allowing the
free cooling with High Speed fan operation to attempt to
satisfy the space cooling load without additional mechanical
cooling. After the delay period, W7220 output Y1- - O is
energized, starting first stage mechanical cooling. Damper
will modulate to maintain SAT at MAT SET concurrent with
Compressor 1 operation.
16
The supply fan motor shifts to High
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