How is capacity control most likely achieved in a centrifugal compressor?

Capacity control in a centrifugal compressor is most effectively achieved by adjusting the size of the vane passages. This method allows for precise modulation of the flow area within the compressor, enabling it to effectively respond to changes in demand. By changing the geometry of the passages, the compressor can optimize its performance for different operating conditions.

When the effective area of the passages is increased, more air can flow through the compressor, leading to higher capacity. Conversely, reducing the area limits the airflow, which can lower the capacity of the compressor. This mechanism is particularly beneficial in applications where variable load conditions are present, as it allows the system to operate efficiently across a range of conditions without the need for frequent speed adjustments or more complex methods.

In contrast, altering the airflow rate directly can be a consequence of adjusting the size of the vane passages rather than a primary method of control. Changing motor speed can also affect capacity, but this approach may introduce challenges in energy efficiency and system responsiveness. Varying the temperature of the refrigerant is not a method used for managing compressor capacity; it instead influences the overall system performance.