Johnson Controls SABROE UniSAB III Engineering Manual page 203

Set-up
13: Economiser (screw compressor)
No
Yes
Select this function if the compressor is connected to an economiser. Thus the economiser is con-
nected/disconnected according to compressor operation. The connection is important for regulation of
the compressor volume ratio.
14: Eco low cap (screw compressors)
0 to 100%
If the actual slide capacity is higher than the set value, the economiser is connected. If the slide capacity
is the %-setting stated in the economiser Neutral zone below this value, the economiser is
disconnected.
15: Neutral zone
5-20%
This parameter shows in % how much capacity must be reduced from the setting in eco low cap to dis-
connect the economiser.
16: Eco high suct press
-100 to 100°C/R
With ECO operation a suction pressure value can be entered in ° C/R. If the suction pressure of the
economiser is above this value, the solenoid valves connected in the economiser system will be closed.
Hysteresis is 2°C/R. In a combined ECO and HLI operation, the set value must not be above -20°C/R.
17: Unloading (reciprocating compr.)
Normal
Total
Additional steps
VSD Normal
VSD Total
See subsection 3.4.6 Rota (VSD) for more information about the step unloading strategy for reciprocat-
ing compressors with a different kind of coupling; with and without frequency drive.
Select Normal - in general - if the compressor is not equipped with frequency drive and Centa soft cou-
pling and if the compressor is not equipped with total unload mechanics or with additional step mechan-
ics. Select Normal for TCMO compressors not equipped with frequency drive.
Select Total for SMC compressors equipped with total unload mechanics.
When selecting Total the compressor still activates the first capacity steps during start-up - but during
operation (Man/Auto/Remote) it can run down to 0% capacity. In order to avoid too high oil temperature
in this operating mode, there is a 300 second time limit (timer no. 12 Total unload). When this timer ex-
pires, the compressor stops.
Select Additional steps for SMC/HPC and CMO/HPO compressors equipped with additional step me-
chanics and with an extra solenoid valve for additional steps. SMC 112 and 116 have two solenoid
valves, one is mounted on digital output no. 9 (similar to other compressors with Additional steps) and
the other (valve B) is mounted on digital output no. 3.
Select VSD Normal for SMC and CMO compressors mounted with frequency drive (VSD) and Centa
soft coupling. This choice is made if the compressor should not be able to run totally unloaded. Never
select VSD Normal for compressors mounted with Rexnord coupling.
Engineering manual - UniSAB III 1.10.8
001930 en 2021.06 203/346