This function requires a chilled water system return temperature sensor.
The input “SysRetTemp” will be used as the controlled variable. The setpoint is defined by the datapoint “SysRetTempSp”, the proportional band by the parameter SRT-01 and the integral time by the parameter SRT-02. When “Enable“ input becomes true (= 1) after start-up, the control will be enabled. The following diagram shows the control signal for system return temperature control.
Fig. 1. Chilled Water System Return Temperature Control
To determine the requested number of chillers, the “SysRetCtrlSig“ control signal (0...100 %) will be divided by the number of chillers as defined by parameter SYS-01. The following diagram shows the relation between control signal and the number of calculated stages. In the diagram, SYS-01 is set to a value of “4”.
Fig. 2. Calculated number of stages
Table 4. Parameter List
Description |
Value Range |
Default Value |
Unit |
SYS-04: calculation method; 0 = SRT only 1 = SST/ SRT 2 = chiller capacity |
0…2 |
0 |
- |
SRT-01: P-band SRT Control |
0…1000 |
4 |
K |
SRT-02: I-time SRT Control; 0 = disable |
0…3600 |
0 |
sec |
SYS-01: number of chillers |
0…12 |
3 |
- |