Flow Condenser (Chillpac/Pac - Optional); Level Control; Dx Control - Johnson Controls SABROE Unisab III Control Engineering Manual

Compressor control and surveillance

3.6.5 Flow condenser (ChillPAC/PAC - optional)

A shutdown No condenser flow is given after a short delay when there is no flow through the
condenser, i.e. no signal from the condenser flow switch. The shutdown delay time is set in
the Flow condenser timer.
This function is enabled in Set up/Configuration/Plant/Flow cond. It is active when the com-
pressor is running, i.e. the condenser pump is started.

3.6.6 Level control

The PID regulator can be set up for HP or LP liquid level regulation of an evaporator or a con-
denser.
A liquid level 4-20 mA transmitter measures the liquid level in the evaporator or condenser.
The liquid level range is 0 to 100%.
The PID regulator will control an analogue expansion valve in order to regulate the ammonia
liquid level according to the liquid set point. The output range is 0 to 100 %. The expansion
valve is a motorised valve. In series with this valve there is a solenoid stop valve which is ac-
tive when the compressor is running.
The PID regulator settings are made in the picture Control values/Process Temp/Evaporator
level/Control. If the regulator is too fast or too slow you may adjust the Proportional band
and/or the Integral time values up or down accordingly.
LP: with this function the evaporator will be filled from the top. When the level rises above the
SP setting the valve must close.
HP: with this function the condenser will be drained from the bottom. When the level rises
above the SP setting the valve must open.
This function is enabled in Set up/Configuration/Plant/Level control. It is active when the
compressor is running.

3.6.7 DX control

The PID regulator can be set up for suction superheat regulation of the evaporator liquid fill-
ing. This function is enabled in Set up/Configuration/Plant/Level control. The DX regulation is
only active when the compressor is running.
Note: The Unisab III DX function is only released for freon refrigerants.
Superheat regulator
The PID regulator will control an analogue expansion valve in order to regulate the liquid level
according to the superheat set point. If the "Suction superheat" is lower than the set point,
the opening position will be decreased. If the "Suction superheat" is higher than the set point,
the opening position will be increased. The opening value depends on the PID calculation.
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