Standard Chiller/HP modulare per compressore a vite con driver CAREL
Cod.: +030221241 Rel. 1.0 dated 25 September 03
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19.3 Free Cooling Thermostat
Free Cooling control exploits the calculated control set point values (taking into account any compensation) and the set Free Cooling control
differential.
The control is based on the water temperature measured by the probe located at the evaporator outlet, considering the effective supply of cold of
the Free Cooling exchanger according to the different external temperature conditions.
Two different control modes can be selected: proportional, proportional + integral - the integration constant must be set in the latter case.
The set point for thermostatic control of Free Cooling will be determined according to the nominal value of the temperature of the water you
wish the unit to produce.
According to the type of control adopted for compressor control (input - output), and as the temperature references are different, two distinct
control graphs must be identified.
In machines controlled output with a neutral zone, the Free Cooling control set point will correspond to the control set point of the compressors.
Free Cooling Set point = Compressors set Point
Free Cooling set point = Compressor set point
T Out
Compressor Neutral zone
Free Cooling Control Band
The proportional control band will be equally distributed at the sides of the set point.
In machines controlled at output with a lateral proportional band, the Free Cooling control set point takes into account an offset with respect to
the control set point of the compressors to compensate for the presence of the evaporating battery.
Free Cooling Set point = Compressors Set-point - Offset
Free Cooling set point T Out
Free Cooling Contro Band
T In
Compressor Control Band
Compressor set point
Free Cooling set point Offset
The proportional control band will be equally distributed at the sides of the set point.
In the Free Cooling control band, the activation thresholds for dedicated devices (e.g. valves and fans or speed variators) will be calculated in
different ways according to the type of selection.
As the fans and/or speed variators are shared by Free Cooling control and condensation control, if one or more compressors in a given refrigerating
circuit is/are enabled, priority will be given to condensation control to protect the circuit itself.
The Free Cooling valve will, in any event, be maintained fully open to provide as high as possible a thermal yield even at minimum ventilating
capacity.
To optimise Free Cooling performance during the machine start transients and in steady state operating situations, a by-pass time is applied for
thermostatic control of the compressors.
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