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10.2.1. Discharge Air Control Heating (DACH) Outdoor Air Temperature Reset
Note: Parameter 287 cannot be modify directly from the M3 Unit Controller interface.
Using the Lennox UC software, access Parameter 287 and enable DACH Outdoor Air Reset. If using the Lennox UC
software.
The Discharge Air Control Heating set point can be automatically reset when outdoor air temperature becomes warmer.
For outdoor air based Discharge Air Control Heating set point reset, the discharge air control heating set point starts
to decrease when the outdoor air temperature rises to Parameter 209 set point which has a default of 40°F). The reset
set point will continue to decrease at the rate equal to Parameter 208 divided by Parameter 210. See the following
example:
EXAMPLE: The application calls for the discharge air control heating occupied set point - Parameter 174 to be 110°F when
Outdoor Air Temperature is 40°F or lower. When the Outdoor Air Temperature rises above 40°F, the set point needs to
decrease proportionately with the Outdoor Air Temperature increase (maximum set point increase of 10°F). The 10°F
Outdoor Air Temperature decrease is called Parameter 213 and the set point decrease of 10°F is called Parameter 211. See
figure 17.
Parameter 210 (DACH OAT RS PRP BND)
Reset Set point (Approx. 105.0°F at 45.0°F OAT)
110.0°F
100.0°F
Discharge Air Control
Heating Set point
40.0°F 50.0°F
Outdoor Air Temp.
Example
10.0°F
Example 10.0°F
Parameter 208 (DACH OAT RS ADJ BND)
Parameter 209 (DACH OAT RS ADJ SP)
Figure 17. Outdoor Air Reset Example
To use example values, set the following parameters:
Parameter 208 – Set to 10.0°F (this setting enables Discharge Air Control Heating Outdoor Air Temperature Reset
Adjustment Band).
Parameter 209 – Set to 40.0°F (this setting enables Discharge Air Control Heating Outdoor Air Temperature Reset
Adjustment Set Point).
Parameter 210 – Set to 10.0°F (this setting enables Discharge Air Control Heating Outdoor Air Temperature Reset
Proportional Band).
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