Discharge Air Control Cooling (Dacc) Outdoor Air Temperature Reset - Lennox Prodigy 2.0 Application Manual

10.1.1. 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.
°
65.0 F
°
55.0 F
To use example values, set the following parameters:
•
Parameter 201 – Set to 10.0°F (this setting is for Discharge Air Control Cooling Outdoor Air Temperature Adjustment
Band.
•
Parameter 202 – Set to 80.0°F (this setting is for Discharge Air Control Cooling Outdoor Air Temperature Cooling Reset
Set Point
•
Parameter 203 – Set to 10.0°F (this setting is for Discharge Air Control Cooling Outdoor Ambient Air Temperature
Cooling Proportional Band.
10.1.2. Discharge Air Control Cooling (DACC) Return Air Temperature Reset
Return air reset can also be used to adjust Parameter 159 when Discharge Air Control Cooling is not used. All references
to the Discharge Air Control Cooling set point apply to the free cooling set point.
The DACC RAT and free cooling set point can be automatically reset when outdoor air temperature becomes cooler.
Note: Parameter 287 cannot be modify directly from the M3 Unit Controller interface.
•
For DACC RAT Reset, use the Lennox UC software to access Parameter 287 and enable DACC RAT Reset.
•
For DACC RAT Reset, the discharge air cooling set point starts to increase when the return air temperature drops to
the Parameter 205 (DACC RAT RS ADJ SP) which has a default of 70.0°F. The reset set point will continue to increase
at the rate equal to the Parameter 204 (DACC RAT RS ADJ BND) divided by the Parameter 206 (DACC RAT RS PRP
BND). See the following example:
DACC OAT RS PRP BND
Parameter 203
°
Example 10.0 F
° °
70.0 F Out­
80
door Air Temp.
Parameter 202 (DACC OAT RS ADJ SP)
Figure 14. Outdoor Air Reset Example
IMPORTANT
°
Reset Set point (Approx. 60.0
DACC OAT RS ADJ BND
Parameter 201
°
Example 10.0 F
F
IMPORTANT
Page 50
°
F at 75.0 F OAT)
DACC or Free Cooling Set point