Johnson Controls SABROE Unisab III Control, Engineering Manual

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Engineering manual - UniSAB III 1.10.8
001930 en 2021.06
205/346
Set-up
Select Yes if the compressor is a reciprocating compressor type SMC/TSMC/HPC with a pressure trans-
mitter before the oil filter. With this function set to yes, the oil filter differential pressure is calculated as
oil pressure before filter minus oil pressure after filter.
22. Suction press. grad
No
Yes
Select
Yes if the compressor is part of a heat pump.
The suction pressure gradient supervision and limiter function is operative when the compressor is run-
ning. See subsection
3.2.3 Special limiters ; High suction pressure gradient .
The Suction pressure gradient limiter function protects against condensation at the suction side, which
may be caused by quickly rising suction pressure. The Suction pressure gradient supervision function
will release an alarm or shutdown if the calculated Suction pressure gradient is higher than the high
alarm or shutdown limit. See subsection 2.2.46 High suction pressure gradient shutdown .
When the Suction pressure gradient limiter function is enabled, the Yield decrease rate limiter will be ac-
tive too. The Yield decrease rate limiter sets a high limit for how fast the Yield [%] can be decreased in
all operation modes. See subsection 3.2.3 Special limiters ; Yield decrease rate limiter .
When the Suction pressure gradient limiter function is enabled, the UniSAB III will check, before start-
up, if the Suction superheat is lower than the Suction pressure gradient reset parameter. If this is the
case, the compressor will not start. A Low suction superheat alarm will be issued and compressor state
will be set to Pause .
Note: The Suct. press. grad parameter is enabled as default for screw compressor types SAB 193 H,
233 H, 283 H, 355 H, SAB 157 HR, SAB 273 S and for reciprocating compressor types HPC, HPO, HPX
using refrigerant R717. It may be enabled for all compressor types.
Guide on how to set up the alarm and shutdown limit for the Suction pressure gradient function
For the Suction pressure gradient function, the alarm and shutdown limits are set according to the fol-
lowing instruction. The alarm and shutdown limits depend on the design evaporation temperature and
suction superheat. The alarm limit is stated in
Table 46: UniSAB alarm values , and the shutdown limit is
2 times the alarm value.
See also section 2.1.7 Notes, Note 38.
Example 1 : A HeatPAC with evaporation temperature at 24°C and a HeatPAC flooded evaporator. The
alarm limit found in Table 46 is 0.5 bar/min., and the shutdown limit is 2 times the alarm limit = 1 bar/min.
Example 2 : A heat pump with evaporation temperature of 30° C and a suction superheater ensuring
min. 3K suction superheat. The alarm limit found in Table 46 is 3 bar/min., and the shutdown limit is 2
times the alarm limit = 6 bar/min.
Multiple running conditions
If the compressor is running multiple running conditions, the condition resulting in the lowest alarm and
shutdown limits should be used.
UniSAB alarm
Max. pressure
increase 1 min.
[bar]
Flooded
evaporator
Min. suction superheat [K]
ensured by suction superheater
Suction
pressure
[ °° C/R]
Suction
pressure
[bara]
< 1K 2K
3K 5K
–12 2.7 0.2 0.6 1.1 2.1
-11 2.8 0.2 0.7 1.1 2.2
-10 2.9 0.2 0.7 1.2 2.2