Johnson Controls SABROE Unisab III Control, Engineering Manual

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Engineering manual - UniSAB III 1.10.8
001930 en 2021.06
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Compressor control and surveillance
Max. sep. cap load is the calculated value for the maximum true capacity load in percent, allowed at
current running conditions. When this value is between 100 and 102% the capacity inhibit function is ac-
tivated. When the value is below 100% the capacity force unload is activated.
Max. cap. slide pos. is the calculated value for the maximum mechanical capacity load in percent, al-
lowed at current running conditions. This value, which will be between 0% and 100%, is the limiting val-
ue used when the capacity force unload function is active.
Pressure Ratio is the calculated pressure ratio = P
disch
/P
suct
K. Factor is the refrigerant constant, K (Kappa).
System Compr. Ratio is the calculated system compression ratio.
Syst. Sep.Vel. Ratio is the calculated system separator velocity ratio.
Utilisation Number is the calculated utilisation ratio for the separator at current running conditions. Eg
a value of 1.00 means that the separator is fully loaded and that the capacity inhibit function is activated.
Insufficient main oil pressure (screw compressors)
Note in particular that this limiter only applies to SGC/GSV/RWF compressors (SAB 120 → 151, 193 → 355
and SAB 193 H → 355 H and SAB 273 S).
If the main oil pressure is too low , capacity will be reduced.
For compressors without VSD drive, capacity is reduced to 50%, and when capacity is between 40-50%
it cannot be increased.
For compressors with VSD drive, capacity is reduced to 20%, and when capacity is between 15-20%, it
cannot be increased.
For more information about main oil pressure calculation, see subsection 2.2.30 and 2.2.32.
See also Fig. 8 in section 2.2 Other alarms and shutdowns .
High internal pressure (SAB 193 H → → 355 H, SAB 273 S)
To secure the internal threat pressure at start-up and during operation, the capacity slide will unload if
the internal pressure is high.
If P
suct, abs
* Vic kappa > high alarm limit, then unload capacity
If P
suct, abs
* Vic kappa < high alarm limit – limit zone, then allow loading capacity.
When the capacity is unloaded, a High internal pressure alarm is given.
High suction pressure gradient (SAB 193 H → → 355 H, SAB 159 HR, SAB 273 S) and (HPC, HPO,
HPX with R717)
This limiter function is relevant for heat pump compressors to protect against condensation on the suc-
tion side caused by quickly rising suction pressure. In case of quickly rising suction pressure, the ca-
pacity slide will be prevented from unloading.
If the calculated suction pressure gradient P
suct_grad
= dP
suct, abs
/dt is higher than the high alarm limit,
then it is not allowed to decrease Yield in Auto, Remote and Manual mode. See Table 9 and Table 15.
If the calculated suction pressure gradient P
suct_grad
= dP
suct, abs
/dt – a limiting zone is lower than the high
alarm limit, then it is allowed to decrease Yield in Auto, Remote and Manual mode. See Table 9 and
Table 15
Yield decrease rate limiter (SAB 193 H → → 355 H, SAB 159 HR, SAB 273 S) and (HPC, HPO, HPX
with R717)
This Yield decrease rate limiter function is relevant for heat pump compressors to protect against con-
densation at the suction side, caused by quickly rising suction pressure. The limiter function is a slew