D-EOMCP00104-14_01EN
Operating Manual
14/35
EWYD_BZ
5.4.3
Return setpoint override
The base setpoint is modified on the base of evaporator
T and of a max reset value, of a value of OAT to start reset and
a value of OAT to apply max reset, as shown in the picture below:
5.5 Compressors capacity control
Two types of capacity control are implemented:
•
Automatic: the compressor start/stop and its capacity are automatically managed by the software to allow the setpoint
respect
•
Manual: the compressor is started by the operator and its capacity is managed by the operator acting on the system
terminal. In this case the compressor will not be used by the software to allow the setpoint respect.
Manual control is automatically switched to Automatic control if any safety action is required on the compressor (safety
standby or unloading or safety shutdown). If this case the compressor remains in Automatic and must be re -switched to
Manual by the operator if required. Compressors in manual mode are automatically switched in automatic mode at t heir
shutdown. The compressor load by may be evaluated on the basis of:
•
Calculation of loading and unloading pulses
•
Analogic slide valve position signal (optional)
5.5.1
Automatic Control
A specialized PID algorithm is used to determinate the magnitude of corrective action on capacity control solenoid. The
compressor loading or unloading is obtained keeping the loading or unloading solenoid energized for a fixed time (pulse
duration), while the time interval between two subsequent pulses are evaluated by a PD controller. If the output of the PD
algorithm doesn’t change, the time interval among pulses is constant; this is the integral effect of the controller, at a
constant error the action is repeated with a constant time (with the additional feature of a vari able integral time). The
0
Max
Reset
Start Reset T
Reset Delta T
OAT
0
Start Reset T
Max Reset
Reset Delta T
Evap
T
Used Setpoint
Used Setpoint
