Standard Chiller/HP modulare per compressore a vite con driver CAREL
Cod.: +030221241 Rel. 1.0 dated 25 September 03
22
10 Control
There are two different modes for controlling the control thermostat:
• Control according to the water temperature values measured by the probe located at the evaporator inlet.
• Control according to the water temperature values measured by the probe located at the evaporator outlet.
In the first case, control is proportional based on the absolute value of the temperature measured by the probe; in the second case, neutral zone
control is used, and is based on the period when of the temperature measured by the probe is maintained, beyond certain thresholds.
However, the choice of the control type depends on the type of compressor managed.
If the controlled compressor is of the stepped capacity control type, in that case, both types of control can be used indifferently.
If the controlled compressor is of the continuous capacity control type, in that case, control based on outlet temperature only can be used.
10.1 Inlet temperature control
Inputs used:
• Water temperature at evaporator inlet
Parameters used:
• Type of unit
• Total number of compressors
• Type of compressor capacity control
• Number of Capacity Control Steps
• Control set-point
• Proportional band for control at inlet.
• Type of control (proportional or proportional + integral)
• Integration time (if the proportional + integral control is enabled)
• Time between start-up and first capacity control
• Time between first and second capacity control
• Time between second and third capacity control
• Time between third and fourth capacity control
Outputs used :
• Liquid Solenoid
• Windings for compressor Line - Delta - Star
• All compressor capacity control relays
Evaporator Inlet
Temperature
Control
set point
Control band
1 3 2 4
The thermostatic control according to the values measured by the temperature probe at evaporator inlet, is based on proportional control.
According to the total number of configured compressors and capacity control steps per compressor, the set control band will be subdivided into
a certain number of steps of equal amplitude.
When the activation thresholds of the individual steps is exceeded, a different compressor or capacity control steps will be activated.
To determine the different activation thresholds, the following relations must be applied:
Total number of control steps : Total number of compressors * Number of capacity control/compressor steps
Step proportional amplitude = Proportional control band / Total number of control steps
Step activation thresholds = Control set-point + (Step proportional amplitude * Step sequential number [1,2,3…]
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