Central hydronic air conditioning systems, also known as central air conditioning systems, utilise chilled or hot water-filled coils to cool or heat the air. These systems are commonly used in large buildings with multiple zones or separate structures. Water has a significantly higher heat capacity than air, making it more efficient for transporting heating and cooling energy in large-scale projects. However, implementing a water system in smaller projects can complicate and increase costs due to its impact on the refrigeration system.

A typical central hydronic air conditioning system consists of an air system, water system, central heating/cooling plant, and control system. The air system, also known as the air-handling system, conditions and transports the air, distributing it to various spaces while maintaining the desired indoor environment. It includes components such as air-handling units, supply/return ductwork, fan-powered boxes, space diffusion devices, and exhaust systems.

The water system facilitates the transport of chilled and hot water from the central plant to the air-handling units, fan-coil units, and fan-powered boxes. It also handles the circulation of condenser water for cooling purposes. The central plant comprises the refrigeration system, typically in the form of chiller packages, and the boiler plant for heating.

A control system, often employing direct digital control (DDC), monitors and regulates the air and water systems, as well as the central plant. It utilizes electronic sensors and microprocessor-operated modules to analyze and calculate inputs, enabling precise control of the HVAC&R system.

Air, water, refrigeration, heating, and control systems collectively form the subsystems of an air conditioning system. Each type of system has its own components and functions, and their interaction determines the overall performance and characteristics of the air conditioning system.