Unit installation

54
Discharge pressure control
This procedure is repeated for each circuit controlling locally the discharge pressure.
• Fans are switched ON & OFF with a discrete Proportional Integral (PI) like algorithm, which also takes care
to equalize the running time of each fan (Equalizing or not is determined by setup parameter M38).
• Option is Proportional Speed Control achieved using an analog output 0÷10 V dc that can be enabled
through a set up parameter (M34). The max voltage for 100% fan speed is setting by setup parameter M39
(i.e. if fan 100% output will be equal to M39).
• Set point is determined by set up parameter M35.
• Fan always starts 20 seconds before compressor (refer to compressor starting procedure).
• If the compressor is switched off the fans control algorithm will be switched OFF (forcing therefore all fans
off): when the output of controller reaches zero or after the minimum OFF CP time.
• If Adaptive Control is selected (M71 <> 0) the HU solenoid will be energized when DP > M71. The solenoid
will be no more energized when DP < ( (M71) - (M72) ) if the 'minimum time on for unloader in adaptive
control' (M73) is elapsed from the moment of energizing.
Without Proportional Speed
With Proportional Speed
Electronic Expansion valve Control
This procedure is repeated for each circuit controlling locally the superheating value; it is enabled by M78:
• M78 = 0 then EEV is disabled;
• M78 = 1 then EEV is enabled enabled through analog output;
• M78 = 2 then EEV is enabled through serial.
The superheating value is the difference between Suction Temperature ST and Evaporating Temperature
(calculated from Suction Pressure).
The parameters of the PID control are stored in EEPROM:
• M79: Set Point for superheating control
• M80: Proportional Band for EEV control
• M81: Integral time for EEV control
• M82: MOP Maximum Operating Pressure (Maximum value of Suction Pressure allowed)
• M85: STARTING value for EEV when the compressor starts without parzialization
• M86: STARTING value for EEV when the compressor starts with parzialization
Output of PI controller
Fans ON
4
100
%
50
%
75
%
25
%
Step1
Step2
Step3
Step4
3
2
1
OUT at the start
of the PI control
% Fans ON
Output of PI controller
100
100% 50% 75% 25%
75
50
25
OUT at the start
of the PD control