The cooling capacity of the machine is automatically adjusted to match the cooling load by changes in the position of the compressor inlet-guide vanes (see Fig. 8-13).
A temperature-sensing device in the circuit of the chilled water leaving the machine cooler continuously transmits signals to a solid-state module in the machine-control center. The module, in turn, transmits the amplified and modulated temperature signals to an automatic guide vane actuator.
A drop in the temperature of the chilled water leaving the circuit causes the guide vanes to move toward the closed position. This reduces the rate of refrigerant evaporation and vapor flow into the compressor. Machine capacity decreases. A rise in chilled water temperature opens the vanes. More refrigerant vapor moves through the compressor and the capacity increases.
The modulation of the temperature signals in the control center allows precise control of guide vane response, regardless of the system load.