there is no particular cooling requirement. However, if deviation is large the timer will count
down fast and start the compressor.
Example 1: Suction pressure regulation has been selected. The measured suction pressure
equals the set point. The compressor is stopped and ready to start.
Set point Sp = -10°C/R
Nz = 2°C/R
Pb = 5°C/R
Start delay = 60 sec
P band factor start delay = 5.
When the measured suction pressure exceeds -9°C/R, the Start delay timer will start counting
with an interval of 5 seconds (P band factor) each time the value in the display counts one
down. If the pressure steadies, the timer will run for 5 x 60 = 300 seconds.
Should the measuring value reach -6.5°C/R, the counting interval will be 3 seconds. If the
pressure is still moving upwards and exceeds -4°C/R (the Pb limit) the timer will count in sec-
onds. The resulting total delay will range between 60 and 300 seconds and after this the com-
pressor will start.
Example 2: Discharge pressure regulation has been selected on a reciprocating compressor.
The measured discharge pressure equals the set point. The compressor is running at 100%
capacity.
Set point Sp = 30°C/R
Nz = 2°C/R Pb = 5°C/R
Delay down = 30 sec
P band factor delay down = 3.
When the measured discharge pressure exceeds 31°C/R, the timer Delay down will start
counting with an interval of 3 seconds (P band factor) each time the value in the display
counts one down. If the pressure steadies the timer will run for 3 x 30 = 90 seconds.
Should the measuring value reach 33.5°C/R, the counting interval will be 2 seconds. If the
pressure is still moving upwards and exceeds 36°C/R (the Pb limit) the timer will count in sec-
onds.
The resulting total delay will range between 30 and 90 seconds and after this the compressor
will disengage one capacity stage.
Set-up
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Engineering manual - Unisab III 1.10
001930 en 2014.09
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