36
Table 20 – Enthalpy Operation No DCV (CO
2
Sensor) -- 2 Speed Fan
Demand
Controlled
Ventilation
(DCV)
Outside Air ---
Good to
economize?
Y1‐I Y2-I Fan Speed Y1-O Y2-O Occupied Unoccupied
NO CO
2
SENSOR
No
Off Off Low 0-v/Off 0-v/Off MIN POS L Closed
On Off Low 24-v/On 0-v/Off MIN POS L Closed
On On High 24-v/On 24-v/On MIN POS H Closed
Ye s
Off Off Low 0-v/Off 0-v/Off MIN POS L Closed
On Off Low 0-v/Off 0-v/Off MIN POS L to Full-Open Closed to Fu ll-Open
On On High
DELAY
[
24-v/On
0-v/Off * MIN POS H to Full-Open Closed to Full-Open
*
With stage 3 delay (STG3 DLY) in Advanced setup menu can turn on second stage of mechanical cooling Y2 –O after the delay if the call for Y1---I and Y2---I
have not been satisfied.
[
With 2SP FAN DELAY (Advanced Setup Menu) when in the economizing mode there is a delay for the high speed fan to try to satisfy the call for second
stage cooling by turning on the fa n to high and opening the OA damper 100% befor e the first stage mechanical cooling is ena bled.
Table 21 – Enthalpy Operation With DCV (CO
2
Sensor) -- 2 Speed Fan
Demand
Controlled
Ventilation
(DCV)
Outside Air ---
Good to
economize?
Y1‐I Y2-I Fan Speed Y1-O Y2-O Occupied Unoccupied
Below set
No
Off Off Low 0-v/Off 0-v/Off VENTMIN L Closed
On Off Low 24-v/On 0-v/Off VENTMIN L Closed
On On High 24-v/On 24-v/On VENTMIN H Closed
Ye s
Off Off Low 0-v/Off 0-v/Off VENTMIN L Closed
On Off Low 0-v/Off 0-v/Off VENTMIN L to Full-Open Closed to Fu ll-Open
On On High 24-v/On 0-v/Off* VENTMIN H to Full-Open Closed to Full-Open
Above set
No
Off Off Low 0-v/Off 0-v/Off VENTMIN L to VENTMAX Closed
On Off Low 24-v/On 0-v/Off VENTMIN L to VENTMAX Closed
On On High 24-v/On 24-v/On VENTMIN H to VENTMAX Closed
Ye s
Off Off Low 0-v/Off 0-v/Off VENTMIN L to VENTMAX Closed
On Off Low 0-v/Off 0-v/Off VENTMIN L to Full-Open Closed to Fu ll-Open
On On High
DELAY
[
24-v/On
0-v/Off* VENTMIN H to Full-Open Closed to Full-Open
*
With stage 3 delay (STG3 DLY) in Advanced setup menu can turn on second stage of mechanical cooling Y2 –O after the delay if the call for Y1---I and Y2---I
have not been satisfied.
[
With 2SP FAN DELAY (Advanced Setup Menu) when in the economizing mode there is a delay for the high speed fan to try to satisfy the call for second
stage cooling by turning on the fa n to high and opening the OA damper 100% befor e the first stage mechanical cooling is ena bled.
Enthalpy Settings
When the OA temperature, enthalpy and dew point are
below the respec tive setpoints, the outdoor air can be used
for econom izing. Fig. 42 shows the new single enthalpy
boundaries in the W7220. T here are 5 boundaries
(setpoints ES1 through ES5), which are defined by dry
bulb temperature, enthalpy and dew point.
Refer to Table 22 for ENTH CURVE setpoint values.
The W 7220 calculates the enthalpy and dew point using
the OA temperature and humidity input from the OA
entha lpy sensor. When the OA temperature, OA humidity
and OA dew point are all below the selected boundary, the
economizer sets the economizing mode to YES,
economizing is available.
When all of the OA conditions are above the selected
boundary, the conditions are not good to economize and
the mode is set to NO.
Fig. 42 shows t he 5 current boundaries. There is also a
high limit boundary for differential enthalpy. The high
limit boundary is ES1 when there are no stages of
mechanical cooling energized and HL (high limit) when a
compressor stage is energized.
Table 22 provides the values for each boundary limit.
Two--Speed Fan Operation
The W7220 controller has the capability to work with a
system using a 2--speed supply fan. The W7220 does not
control the supply di rectly but uses the following input
status to determine the spee d of the supply fan and
controls the OA damper to the required position.
State Fan Speed
OCC Low
Y1 Low
Y2 High
W High
The W (heating mode) is not controlled by the W7220 but
it requires the status to know where to position the OA
damper for minimum position for the fan speed.
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