High Mixed Air Temperature Alarm; Low Mixed Air Temperature Alarm; Economizer Operation; Figure 53 Mixed Air Temperature Sensors - Bard MEGA-TEC W180B Service Instructions Manual

7. To apply an offset, press ENTER key to scroll to
Offset.
8. Press UP or DOWN keys to change to the desired
value.
9. Press ENTER key to save the value.
FIGURE 53
Mixed Air Temperature Sensors

High Mixed Air Temperature Alarm

To keep the economizer from bringing in air that is too
warm, an alarm will be generated when the mixed air is
2° above the return air temperature for 300 seconds.
This alarm will not be generated if the mixed air
temperature sensor has failed. The alarm can only be
activated during a free cooling call. The alarm is a user
reset and must be cleared by the end user.

Low Mixed Air Temperature Alarm

To keep the economizer from bringing in air that is too
cold, an alarm will be generated when the mixed air
temperature is 5°F below the mixed air temperature
control setpoint for 300 seconds. If this alarm is active,
the economizer will be disabled for the current cooling
call. This alarm will reference the mixed air temperature
control setpoint to ensure that when the mixed air setpoint
changes, the alarm dynamically changes with it. This
alarm will not be generated if the mixed air temperature
sensor has failed. The alarm can only be activated during
a free cooling call and requires a user reset.

Economizer Operation

See Figure 89 on page 66 for ventilation airflow paths.
The vent option in the model number determines if the
equipment has an economizer. If the value is set to
"B", the controller will not use the economizer and the
Manual 2100-749
Page 34 of 68
type on Economizer Setup A2 will automatically change
to None. The only exception to this is emergency
ventilation will always attempt to open the dampers.
This would only apply if a unit has an economizer but
the controller is configured for no vent (B).
The economizer has four types of operation. The
first mode is "None" where the economizer is never
utilized, except for emergency purposes. The second
mode is "Dry Bulb" where the outdoor temperature is
the only consideration for economizer use on a free
cooling call. The third mode is "TempHum" where the
outdoor temperature and humidity are considered
for economizer use on a free cooling call. The fourth
mode is "Enthalpy" where the outdoor temperature,
humidity and calculated dew point are considered for
economizer operation on a free cooling call.
To change the economizer type:
1. Press MENU key to go to the Main Menu screen.
2. Press UP or DOWN keys and ENTER key to enter
USER password 2000.
3. Press UP or DOWN keys to scroll to System Config;
press ENTER key.
4. Press UP or DOWN keys to scroll to Economizer
Setup A2; press ENTER key.
5. Press ENTER key to scroll to Type (see Figure 54).
6. Press UP or DOWN keys to change the Type desired
value to None, Dry Bulb, TempHum or Enthalpy.
7. Press ENTER key to save the value and scroll to
the next parameter.
FIGURE 54
Economizer Setup
NOTE: The following parameters are for the
temperature consideration for economizer use.
Applies to Dry Bulb, TempHum and Enthalpy
type.
8. The cursor should now be on the Mixed Air Tamp
parameter.
9. Press UP or DOWN keys to change the parameter
to the desired value.
10. Press ENTER key to save the value and scroll to
the next parameter.