User Manual

Sequence of Operation
Electric Heat (Optional)
12
Siemens Industry, Inc.
Application Note, App 14901
140-1230
2020-02-11
● An Inter-stage Delay timer must be enforced between the second cooling stage
OFF and the first cooling stage OFF to ensure that the first compressor will not be
turned off until the second compressor has been turned off for the time set in the
Inter-stage Delay.
In Heating mode (and compressors are not locked out by low outdoor temperature):
If HeatStg = 0, the application does not control COMPRESSOR 1.
If HeatStg ≥ 1, the application controls COMPRESSOR 1 as follows:
● If IndoorTmpEff is less than the switching on point of the first heating stage
(HeatingSp – 1/2 HeatingDB), and the first compressor has been OFF for at least
the time set in MIN OFF, COMPRESSOR 1 is turned ON.
● If IndoorTmpEff is greater than the switching off point of the first heating stage
(HeatingSp + 1/2 HeatingDB), and the first compressor has been ON for at least
the time set in MIN ON, COMPRESSOR 1 is turned OFF.
If HeatStg = 1, the application does not control COMPRESSOR 2.
If HeatStg = 2, the application controls COMPRESSOR 2 as follows:
● If IndoorTmpEff is less than the switching on point of the second heating stage
(HeatingSp – 1/2 HeatingDB - StgDifHt), the second compressor has been OFF
for at least the time set in MIN OFF, and Inter-stage Delay timer has expired,
COMPRESSOR 2 is turned ON.
● If IndoorTmpEff is greater than the switching off point of the second heating stage
(HeatingSp + 1/2 HeatingDB - StgDifHt), and the second compressor has been
ON for at least the time set in MIN ON, COMPRESSOR 2 is turned OFF.
● An Inter-stage Delay timer must be enforced between the second heating stage
OFF and the first heating stage OFF to ensure that the first compressor will not be
turned off until the second compressor has been turned off for the time set in the
Inter-stage Delay.
Electric Heat (Optional)
If at least one stage of electric heat is being used (AUX HTG STG > 0, and FAN MODE
= ELECTRIC), the electric heat is controlled as follows:
● If HTG STG2 is an electric heater, follow the heating sequence for Compressor 2
described in the Compressor Operation section.
● If HTG STG3 is an electric heater that is not the highest heating stage:
If IndoorTmpEff is less than the switching on point of the third heating stage
(HeatSp – 1/2 HeatingDB – StgDifHt*2), HTG STG3 has been OFF for at least
the time set in MIN OFF, and the Inter-stage Delay timer has expired, HTG STG3
is turned ON.
If IndoorTmpEff is greater than the switching OFF point of the third heating stage
(HeatSp + 1/2 HeatingDB – StgDifHt*2), and HTG STG3 has been ON for at least
the time set in MIN ON, HTG STG3 is turned OFF.
● If HTG STG3 is an electric heater that is also the highest heating stage:
If IndoorTmpEff is less than the switching on point of the third heating stage
(HeatSp – 1/2 HeatingDB– StgDifHt*2), HTG STG3 has been OFF for at least the
time set in MIN OFF, and the Inter-stage Delay timer has expired, HTG STG3 is
turned ON.
If IndoorTmpEff is greater than the switching off point of the third heating stage
(HeatSp + 1/2 HeatingDB – StgDifHt*2), and HTG STG3 has been ON for at least
the time set in MIN ON, HTG STG3 is turned OFF.