Which type of control systems is NOT commonly used in HVAC applications?

In HVAC applications, the types of control systems most often employed include electronic, pneumatic, and fluidic controls, each serving specific purposes and offering various advantages in system management.

Electronic control systems are prevalent in modern HVAC setups, allowing for precise temperature regulation, programmable schedules, and integration with building management systems. They utilize sensors and microcontrollers to manage heating and cooling processes efficiently.

Pneumatic control systems, while older technology, have often been used in larger buildings to manage air distribution through pressure changes in air tubes. They operate based on the principles of air pressure and are known for their reliability in controlling actuators and valves.

Fluidic control systems, although less common than electronic and pneumatic systems, can be found in certain niche applications where flow control is required using fluid dynamics principles.

Thermal control systems, while they do exist, tend to be less common in direct HVAC applications compared to the other three. They might be referenced in broader contexts but lack the same level of implementation and sophistication required for the precise climate control demanded in modern HVAC systems. Therefore, when considering the options available, thermal systems do not feature as prominently as electronic, pneumatic, or fluidic systems in practical HVAC applications.