Discharge Air Control Heating (Dach) Outdoor Air Temperature Reset; Discharge Air Control Heating (Dach) Return Air Temperature Reset - Lennox PRODIGY2.0 Application Manual

14.2.1.

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 209 (DACH OAT RS ADJ SP)
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).
14.2.2.

Discharge Air Control Heating (DACH) Return 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 Return Air Temperature Reset.
•
The Discharge Air Control Heating set point can be automatically reset when return air temperature becomes
warmer.
•
For return air based Discharge Air Control Heating set point reset, the discharge air control heating set point starts
to decrease when the return air temperature rises to the parameter 212 that has a default setting of 70.0°F. The reset
set point will continue to decrease at the rate equal to the parameter 211 divided by the parameter 213. See the
following example:
EXAMPLE: The application calls for the discharge air control heating occupied set point parameter 174 to be
110.0°F when Return Air Temperature is 70.0°F or lower. When the Return Air Temperature increases above 70.0°F,
the set point needs to decrease proportionately with the Return Air Temperature increase (maximum set point
increase of 10.0°F). The 10.0°F Return Air Temperature difference is called the parameter 213 and the set point
increase of 10.0°F is called parameter 204. See figure 18.
Parameter 210 (DACH OAT RS PRP BND)
Example
°
10.0
°
110.0 F
°
100.0 F
°
40.0 F
Outdoor Air Temp.
Figure 17. Outdoor Air Reset Example
F
Parameter 208 (DACH OAT RS ADJ BND)
°
Example 10.0 F
Reset Set point (Approx. 105.0
°
50.0 F
63
Discharge Air Control
Heating Set point
° °
F at 45.0 F OAT)