Chilled Water System Return Temperature Control (SYS = 0)

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

-