Low Mixed Air Temperature Alarm; Economizer Operation; Figure 40 Economizer Setup - Bard MEGA-TEC W120AP Service Instructions Manual

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

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 40).
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 40
Economizer Setup
Manual 2100-671
Page 28 of 44
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.
11. The cursor should now be on Delay parameter.
12. Press UP or DOWN keys to change the parameter
to the desired value.
13. Press ENTER key to save the value and move to
the next parameter.
14. The cursor is now on the Min Position parameter.
15. Press UP or DOWN keys to change the parameter
to the desired value (see Economizer Operation −
Minimum Position for more information).
16. Press ENTER key to save the value.
17. Press the DOWN key to navigate to the A3 screen.
NOTE: The A3 screen will not display if economizer
mode is set to None. Also, the contents of the
screen will change depending on which type is
chosen: Dry Bulb (Figure 41), TempHum (Figure
42) or Enthalpy (Figure 43). The following menu
shows the Enthalpy content which also contains
parameters that would be shown on Dry Bulb
(temperature only) and TempHum (temperature
and humidity only).
18. Press ENTER key to scroll to OA Temp Set (on
Drybulb Control and Temp/Hum Control A3
screens, this parameter will be titled Outdoor Set).
19. Press UP or DOWN keys to change the temperature
setpoint to desired value.
20. Press ENTER key to save the value and scroll to
Off Diff.
21. Press UP or DOWN keys to adjust the outdoor
temperature differential for which the economizer
is re-enabled.
22. Press ENTER key to save the value and scroll to OA
Hum Set.
23. Press UP or DOWN keys to adjust the humidity
setpoint to desired value.
24. Press ENTER key to save the value and scroll to On
Diff.
25. Press UP or DOWN keys to adjust the outdoor
humidity differential for which the economizer is
re-enabled.
26. Press ENTER key to save the value and scroll to
Dew Pt. Set.