Johnson Controls SABROE Unisab III Control User Manual

6.2. Sequencing
6.2.1 Multisab sequencing
Multisab is a distributed compressor control system which is very useful when more compres-
sors are working together (e.g. connection to the same suction line). With Multisab it is possi-
ble to start, stop and capacity regulate compressors according to the varying cooling require-
ments.
Multisab is a standard function in Unisab III. The system is described in detail in the Unisab
III sequence manual. In order for Multisab to work, all Unisab III units which should partici-
pate in the distributed control must be physically connected via the Danbuss communication
network. Fig. 40 in subsection 8.5.3. Configuration of RS485 port/Danbuss describes how to
connect the units.
To get optimal use out of Multisab it is very important that certain key parameters are selec-
ted correctly by the user as explained in subsection Multisab regulation. To explain the con-
tents of the Sequencing picture, the following key parameters are described here: Compr. no,
Start no, System no, System regulator, Multisab Master, Compr. Mode, Compr. Status, Multi-
sab Status and Control Mode.
6.2.2 Sequencing parameters
Always make sure that all Unisab III units on a network have different compressor numbers,
i.e. two units are not allowed to have the same Compr. no. See subsection 6.4.4. Plant.
System no tells Multisab which compressors are going to work together.
Fig. 20 below shows two examples.
UNISABUNISAB
UNISAB
UNISAB
UNISAB
UNISAB
UNISAB
UNISAB
Suction line, sub-plant 1
System no. = 1
System no. = 2
Suction line, sub-plant 2
Compr. 1
Compr. 2
Compr. 3
Compr. 4
Separated compressor plants
Common compressor plant
Common
Multisab
network
Multisab
network
System no.
= 1 or 2
Suction main line 1
System no. = 1
Suction main line 2
System no. = 2
System no.
= 1 or 2
System no
= 1 or 2
System no.
= 1 or 2
Compr. 1
Compr. 2
Compr. 3
Compr. 4
Fig. 20: Examples of compressor systems
In the left example two separate compressor plants are connected on a common Danbuss
network. In this system it is very important that:
• Unisab no. 1 has the same System no as Unisab no. 2
• Unisab no. 3 has the same System no as Unisab no. 4
• System no of Unisab 1 and 2 differs from System no of Unisab 3 and 4
In the right example each of the four compressors can be independently connected to any of
the two suction main lines. In this example is also important that System no is correct. How-
ever, it is particularly important that when changing the valve settings, the System no of the
relevant Unisab III units is changed accordingly as this does not happen automatically.
Set-up
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Engineering manual - Unisab III 1.10
001930 en 2014.09

Johnson Controls SABROE Unisab III Control Specifications

General

Brand	Johnson Controls
Model	SABROE Unisab III Control
Category	Control Systems
Language	English