How can capacity control of a large compressor be achieved?

Capacity control of a large compressor is primarily achieved through the use of unloaders. Unloaders are mechanisms that allow the compressor to adjust its capacity by regulating the amount of refrigerant that is allowed to enter the compressor cylinders. By using unloaders, the compressor can effectively operate at various load conditions, providing a means to manage energy efficiency and system performance.

When the demand for cooling decreases, unloaders can deactivate some of the compression cylinders, reducing the compressor's capacity to match the lower cooling load. This capability is essential for ensuring that the system does not overcool a space or run inefficiently by operating at full capacity when it isn’t necessary. This not only helps in maintaining optimal temperatures but also leads to energy savings.

In contrast, the other options do not serve the same purpose as unloaders in the context of capacity control for compressors. Solenoid valves and hand valves are primarily used for controlling the flow of refrigerant, while dampers are primarily used for airflow regulation. None of these options provide the same level of operational flexibility and efficiency management as unloaders do for compressors. Thus, unloaders stand out as the most effective solution for capacity control in large compressors.