Custom Programming
Custom logic (control strategy/switching tables) can be used to calculate the number of requested chillers. Via parameter SYS-05, the input signal type of the input “Req_Loads“ can be defined.
Table 7. Input Req_Load
SYS-05
|
Input Req_Load
|
0
|
absolute value 0…N
|
1
|
floating value –1;0,+1
|
2
|
modulating control signal 0…100
|
- SYS-05 = 0: The input is configured for absolute values [0...n]. The calculated number is equal to the input “Req_Load”. Staging up and staging down delays protect against to off switching.
- SYS-05 = 1: The input is configured for floating control [+1/ 0/ -1]. A value of “+1” will increment the number of chiller by 1. A value of “-1” will decrement the number of chillers by 1. A value of “0” will not change the number of chillers. The input signal must be set back to “0” after an increment/decrement command.
- SYS-05 = 2: The input is configured for a [0...100] percentage value. This mode allows connecting directly a PI controller. The output signal of the PI controller is divided by the number of available loads and so the number of chillers is calculated. The next figure shows an example for 4 chillers:

Fig. 3. Calculated number of chillers