Outdoor Air Suitability; Enthalpy Setpoint - Lennox Prodigy M2 Application Manual

7.6.

Outdoor Air Suitability

There are six options available to determine outdoor air suitability (OAS) for free cooling. See table 24. Economizer settings
are shown for each mode in figure 9.
The appropriate sensors are provided when the economizer is factory−configured. When the economizer is field−configured,
the ODE mode requires additional field−provided sensor(s). See table 24. The TEMP mode uses sensors provided with all
units.
Free cooling mode
Temperature offset
Temperature setpoint
Remote
Enthalpy differential (Potentiometer set to DIFF)
Enthalpy setpoint (Potentiometer set to A−D)
Global input
Note−All economizer modes of operation, except DSET, will modulate dampers to 55°F (13°C) discharge air.
ODE DIFFERENTIAL
(Outdoor Enthalpy)
C
B D
Set to DIF
A DIF
ENTH SET PNT
7.7.

Enthalpy Setpoint

This setting pertains to the ODE free cooling mode only. The M2 will enable free cooling when outdoor air enthalpy (A7) is
less than the enthalpy setpoint. Table 25 shows the approximate enthalpy setpoints for each potentiometer setting at 50%
relative humidity.
The recommended enthalpy setpoint is A" If the The recommended enthalpy setpoint is A". If the
economizer is allowing air which is too warm or too economizer is allowing air which is too warm or too
humid to enter the system, the enthalpy control may humid to enter the system, the enthalpy control may
be changed to a lower setting (B, C, or D).
Example: At setting A", the enthalpy control will modulate dampers open when outdoor air is at 73°F and 50% relative
humidity. If space temperatures are too warm, rotate the potentiometer to B". The enthalpy control will now modulate damp-
ers open when outdoor air is 70°F and 50% relative humidity.
506457−01 05/10
Table 24. Free Cooling Options
DIP SW
positions
1,2 to TMP
1,2 to TMP
1,2 to TMP
1,2 to ODE
1,2 to ODE
1,2 to GLO
TEMP OFFSET,
TEMP OAT STPT, and
Remote MODE.
ODE
(Outdoor Enthalpy)
B
Set to A
A
ENTH SET PNT
Figure 9. Economizer free cooling settings
Table 25. Enthalpy Control Setpoints
MODE CONTROL
Selection Selection
TEMP OFFSET
TEMP OAT STPT
TEMP ANY
ENTH N/A
ENTH N/A
GLOBAL N/A
C
D
DIF
Control Enthalpy Control Setpoint At 50% Relative Humidity
Setting
A
B
C
D
Page 26
7.
OAS setpoint calc if
CONTROL is SENSIBLE
OAT<RAT−OFFSET (0 to 40 F)
OAT<OAT STPT (41 to 70 F)
OAS sent by network.
ODE<IDE
ODE<POT
GLO input
GLO
(Global Enthalpy)
Approximate Degrees F (C)
73 (23)
70 (21)
67 (19)
63 (17)
Economizer