Discharge Air Control Heating (Dach) Total Reset Limit - Lennox Prodigy 2.0 Application Manual

10.2.2. 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 212 (DACH RAT RS ADJ SP)
To use example values, set the following parameters:
•
Parameter 211 – Set to 10.0°F (this setting enables Discharge Air Control Heating Return Air Temperature Adjustment
Band).
•
Parameter 212 – Set to 70.0°F (this setting enables Discharge Air Control Heating Return Air Reset Set Point).
•
Parameter 213 – Set to 10.0°F (this setting enables Discharge Air Control Heating Return Air Temperature Proportional
Band).

10.2.3. Discharge Air Control Heating (DACH) Total Reset Limit

Parameter 214 has a default setting of 10°F and defines the total Discharge Air Control Heating set point reset limit. This total limit
is the sum of both return and outdoor Discharge Air Control Heating resets. This parameter limits total discharge air control
heating adjustment band and overrides the adjustment bands for Return Air Temperature and Outdoor Air Temperature -
Parameter 211 and Parameter 208 if necessary.
Control Parameter
No. Screen Name
112 HEAT STAGING OPTION
174 DACH OCC SETPOINT
175 DACH UNOCC SETPOINT
176 DACH STAGE DEADBAND
Parameter 213 (DACH RAT RS PRP BND)
Example 10.0
°
110 F
°
100.0 F
°
70.0 F
Return Air Temp.
Figure 18. Return Air Reset Example
Table 43. Discharge Air Heating Parameters Summary
Min.
Heating Staging
Option
Discharge Air
Control Heating
60.0
Occupied Set
Point
Discharge Air
Control Heating
60.0
Unoccupied Set
Point
Discharge Air
Control Heating
Stage Deadband
°
F
Parameter 211 (DACH RAT RS ADJ BND)
Example
°
10.0 F
Reset Set point Approx.105.0
°
80.0 F
RAT)
Control Value
Default Max.
Unit
0 2 2 Option
110.0 140.0 °F
95.0 140.0 °F
5.0 5.0 20.0 °F
Page 56
DACH Set point
° °
F (at 75.0 F
Description
Heating staging options:
0- No heating operation.
1- Discharge air control with up to four stages.
2- Thermostat operation.
Discharge Air Control Heating set point during
occupied period.
Discharge Air Control Heating set point during
unoccupied period.
Discharge Air Control Heating dead-band.