Discharge Air Control Cooling (Dacc) Outdoor Air Temperature Reset - Lennox PRODIGY2.0 Application Manual

C1 = Cooling Stage 1
C2 = Cooling Stage 2
C3 = Cooling Stage 3
C4 = Cooling Stage 4
55°F Default Occupied
Discharge Air Control
Cooling Set point
Parameter
180
Figure 13. Discharge Air Control Cooling Stages - Default Values Shown
14.1.1.

Discharge Air Control Cooling (DACC) Outdoor Air Temperature Reset

Outdoor air reset can also be used to adjust parameter 159 (FREE COOL SUPPLY SP) when Discharge Air Cooling
Control is not used. All references to the Discharge Air Cooling Control set point apply to the free cooling set point.
NOTE: Parameter 287 cannot be modify directly from the M3 unit controller interface.
The DACC OAT Reset and free cooling set point can be automatically reset when outdoor air temperature becomes
cooler.
•
For DACC OAT Reset, use the Lennox UC software to access parameter 287 and enable DACC Outdoor Air
Temperature Reset.
•
For DACC OAT Reset, the discharge air cooling set point starts to increase when the outdoor air temperature drops
to the parameter 202 (DACC OAT RS ADJ SP) with a default of 80°F. The reset set point will continue to increase
at the rate equal to the parameter 201 (DACC OAT RS ADJ BND) divided by the parameter 203 (DACC OAT RS
PRP BND). See the following example:
EXAMPLE: The application calls for the discharge air cooling occupied set point parameter 180 to be 55°F when Outdoor
Air Temperature is 80°F or higher. When the Outdoor Air Temperature drops below 80°F, the set point needs to increase
proportionately with the Outdoor Air Temperature decrease (maximum set point increase of 10°F). The 10°F Outdoor Air
Temperature decrease is called the parameter 203 and the set point increase of 10°F is called the parameter 201. See
figure 14.
61
60
59
58
° °
55 F + 2 F Diff
Parameter 180 +
57
Parameter 185
ON
C2
56
55
ON
54 C1
53
55
OFF
52
Parameter 180 + Parameter
185 - Parameter 182
51
OFF
50
55°F - 5°F
Parameter 180 -
Parameter 182
Parameter 181 Unoccupied DACC_SP
Parameter 183 DAC Cooling Stage-Up Delay 3 minutes
Parameter 184 DAC Cooling Stage-Down Delay 2 minutes
Compressor Minimum Off or Run Times Apply
IMPORTANT
60
°
55 F + 6
Parameter 180 + (Para­
meter 185 X 3)
ON
C4
° °
55 F + 4 F Diff.
Parameter 180 + (Para­
meter 185 X 2)
ON
C3
OFF
Parameter 180 + (Parameter 185
X 3) - Parameter 182
° °
55 F + (2 F X 2) -5
OFF
Parameter 180 + ( Parameter
185 X 2) - Parameter 182
° ° °
F + 2 F - 5 F
5°F Discharge Air Cooling Control
Dead-band (All Stages Same Setting)
Parameter 182
°
F Diff.
° ° °
55 F + (2 F X 3) - 5 F
°
F