User Manual

Sequence of Operation
Staging Control
11
Siemens Industry, Inc.
Application Note, App 14901
140-1230
2020-02-11
ChgOvrDB: Change Over Deadband restricts how close CLG STPT and HTG STPT
can be set. A minimum deadband (default is 5°F) must to be maintained. To separate
the CLG STPT and the HTG STPT, one setpoint change may change the other
setpoint to maintain a gap between them.
Staging Control
The heat pump is controlled by a hysteresis loop (Step Control). Hysteresis prevents
the compressor/heater from frequently switching on and off. When the room
temperature reaches the corresponding switching on setpoint of a certain
cooling/heating stage, that stage is turned on. When the room temperature reaches the
corresponding switching off setpoint of a certain cooling/heating stage, that stage is
turned off.
For example, in Heating mode the thermostat switches the heater on when the
temperature drops below A, but will not turn it off until the temperature rises above B,
where B is greater than A.
If there is a call to turn on/off multiple stages, an Inter-stage Delay will apply between
the two stages being turned ON/OFF. For more information, see the Electric Heat
section.
Compressor Operation
When the HVAC Mode and REV VALVE are both in Cooling mode, the cooling staging
logic controls the compressor. When the HVAC Mode and REV VALVE are both in
Heating mode, the heating staging logic controls the compressors.
If a compressor has been ON, it will not shut OFF until its minimum ON timer has
expired. Likewise, if a compressor has been OFF, it will not turn ON until its minimum
OFF timer has expired.
In addition to the above rules, there is a time-based separation of cooling stages --
Cooling Inter-stage Delay which applies to the unit with multiple cooling stages. There
is also a time-based separation of heating stages -- Heating Inter-stage Delay which
applies to the unit with multiple heating stages.
The following paragraphs explain compressor staging:
In Cooling mode:
If CoolStg = 0, the application does not control COMPRESSOR 1.
If CoolStg ≥ 1, the application controls COMPRESSOR 1 as follows:
● If IndoorTmpEff is greater than the switching on point of the first cooling stage
(CoolingSp + 1/2 CoolingDB), and the first compressor has been OFF for at least
the time set in MIN OFF, COMPRESSOR 1 is turned ON.
● If IndoorTmpEff is less than the switching off point of the first cooling stage
(CoolingSp – 1/2 CoolingDB), and the first compressor has been ON for at least
the time set in MIN ON, COMPRESSOR 1 is turned OFF.
If CoolStg = 1, the application does not control COMPRESSOR 2.
If CoolStg = 2, the application controls COMPRESSOR 2 as follows:
● If IndoorTmpEff is greater than the switching on point of the second cooling stage
(CoolingSp + 1/2 CoolingDB + StgDifCl), the second compressor has been OFF
for at least the time set in MIN OFF, and the Inter-stage Delay timer has expired,
COMPRESSOR 2 is turned ON.
● If IndoorTmpEff is less than the switching off point of the second cooling stage
(CoolingSp – 1/2 CoolingDB + StgDifCl), and the second compressor has been
ON for at least the time set in MIN ON, COMPRESSOR 2 is turned OFF.