27
temper the supply air as required in order to maintain the con-
figured SA Tempering Setpoint
Once the SA Tempering Setpoint has been satisfied, the Sys-
temVu controller will begin the heat shutdown process. The
time of the heat shutdown process can be varied based on the
parameters: HEAT MIN ON and HEAT MIN OFF.
If the OAT goes above the Minimum Cooling SAT, the unit
will not provide Supply Air Tempering for 5 minutes.
The SAT DURING HEAT variable needs to be set to EN-
ABLED. This is to change the SystemVu settings to note the
supply air thermistor is located on the fan deck.
Economizer Operation
The Economizer is used for ventilation, and cooling. If the in-
door fan is not on, the economizer will not operate. If an econ-
omizer is installed, then Economizer Installed (ECON IN-
STALLED = YES) should be set to YES. The unit produces a
4 to 20mA signal which is then changed to a 2 to 10V signal
with a 500 ohm resistor, which can control the economizer ac-
tuator. The economizer output signal is displayed by the Econ-
omizer Commanded Position (ECON CMD POSITION). The
actuator’s built-in 2 to 10 VDC feedback signal is read in as an
analog input to know the actual position which is displayed as
Economizer Actual Position (ECON ACT POSITION).
MINIMUM VENTILATION
The economizer will open to allow ventilation when the indoor
fan is turned on and the unit is in the occupied state. The econ-
omizer damper position at any given time for ventilation is dis-
played as the Min Position in Effect (EFFECTIVE MIN
POS). This minimum position can be effected by the indoor
fan speed (F.SPD) and indoor air quality. To maintain a con-
stant airflow through the economizer, as the indoor fan speed
decreases or increases, the damper minimum position will in-
crease or decrease, respectively. This relationship curve is
shown in Fig. 19.
NOTE: The software point names are used in Fig. 19 as to not
clutter the graph. These points are not individually set and there-
fore only visible from a network for troubleshooting.
These units can also be equipped with optional CO
2
sensors for
additional indoor air quality control. When unit is equipped
with a return duct CO
2
sensor or return duct CO
2
sensor and
outside air CO
2
sensor, the Economizer minimum position vs.
fan speed curve will be recalculated based on the CO
2
level of
the return and/or outside air as shown in Fig. 19. When per-
forming Demand Controlled Ventilation, the damper’s Min Po-
sition in Effect (EFFECTIVE MIN POS) will operate in the
shaded area of Fig. 19 based on the IAQ Level (IAQ) and the
Commanded Fan Speed (IDF SPEED OUTPUT). See “Indoor
Air Quality (IAQ)” on page 30 for more details on Demand
Controlled Ventilation (DCV).
The damper position curve can be field adjusted per applica-
tion if needed.
1. Activate test mode to control the fan and dampers to
achieve the correct numbers.
2. Set the fan speed for the maximum amount needed for
design CFM requirements. This should also be the IDF
maximum Fan speed (MAXIMUM IDF SPEED).
3. Open the damper to the position which satisfies the highest
ventilation requirement running maximum fan speed, and
then set the Economizer minimum at maximum fan speed
(MIN POS @ MAX FAN) to this damper position.
4. Set the fan speed to a realistic operating speed in the upper
range, and then set the User Minimum Position Speed 1
(MIN POS SPEED 1) equal to that speed. This should be
somewhere in the 80% range.
5. Open the damper to the position which satisfies the highest
ventilation requirement running speed 1 fan speed, and
then set the User Minimum Position Damper Position 1
(MIN POS DAMP 1) to this damper position.
6. Set the fan speed to a realistic operating speed in the mid-
range, and then set the User Minimum Position Speed 2
(MIN POS SPEED 2) equal to that speed. This should be
somewhere in the 60% range.
7. Open the damper to the position which satisfies the highest
ventilation requirement running speed 2 fan speed, and
then set the User Minimum Position Damper Position 2
(MIN POS DAMP 2) to this damper position.
8. Set the fan speed to a realistic operating speed in the low-
range, and then set the User Minimum Position Speed 3
(MIN POS SPEED 3) equal to that speed. This should be
lowest fan speed in planned operating range.
9. Open the damper to the position which satisfies the highest
ventilation requirement running speed 3 fan speed, and
then set the User Minimum Position Damper Position 3
(MIN POS DAMP 3) to this damper position.
The shape of the curves in Fig. 19 are determined by the configu-
ration parameters: User Minimum Position Speed 1 (MIN POS
SPEED 1), User Minimum Position Damper Position 1 (MIN
POS DAMP 1), User Minimum Position Speed 2 (MIN POS
SPEED 2), User Minimum Position Damper Position 2 (MIN
POS DAMP 2), User Minimum Position Speed 3 (MIN POS
SPEED 3), User Minimum Position Damper Position 3 (MIN
POS DAMP 3), and Economizer minimum at maximum fan
speed (MIN POS @ MAX FAN). These configurations are preset
at the factory of default purposes. The Economizer minimum at
maximum fan speed (MIN POS @ MAX FAN) should be
changed based on the air balance of the unit for proper ventilation.
The user adjustable points discussed above are defaulted to
zero from the factory which forces the control to use a set of
default points. The default points should not be left for perma-
nent operation, as it may cause inadequate ventilation. Econo-
mizer minimum at maximum fan speed (
MIN POS @ MAX
FAN) and at least one set of user points User Minimum Posi-
tion Speed 1 (MIN POS SPEED 1) and User Minimum Posi-
tion Damper Position 1 (MIN POS DAMP 1) should be used to
create a linear curve to cover the broad scope of fan operation.
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