Siemens BACNET 125-699 - Manual (Page 15)

Siemens Building Technologies, Inc. 7
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Applications
Basic Operation
The Siemens BACnet Heat Pump Controller—Multi-Stage provides Direct Digital Control
(DDC) technology for multiple compressor heat pump applications. Temperature control
varies with the application. If present, mixed air temperature control and up to three stages of
electric heat or staged heating and cooling can be provided.
Control Temperature Setpoints
The controller maintains a specified temperature setpoint based on Day/Night mode, the
heating/cooling mode, and the setpoint dial (if used).
Day/Night Mode
The controller maintains the specified day setpoint temperature during daytime hours and the
specified night setpoint at night.
Night Mode Override Switch
If the RTS has an override switch, it can be used to command the controller into day mode
for an adjustable period of time. This only affects a controller in night mode.
Control Loops
Heating Loop – maintains room temperature setpoint by turning compressors and electric
heat stages on and off.
Cooling Loop – maintains room temperature setpoint by turning compressors on and off and
using free cooling (mixed air control) when available.
Mixed Air Control Loop
The heat pump is controlled by three Proportional, Integral, and Derivative (PID) control
loops; a cooling loop and a heating loop. This section describes the mixed air control loop.