The most common types of cooling system can been classified as centralized or partially centralized air/water systems, or local systems.
Centralized plant
A centralized cooling system has all the plant located in single area, for example in a basement or roof-top plant room. One or more air-handling units (AHUs) condition the air which is then supplied by ductwork to the floors/spaces within the building.
The air-handling units typically contain heating and cooling coils, a humidifier, filters, and fans to move the air.
One or more chillers will typically be located nearby to provide chilled water for the cooling coil(s). Hot water for the heating coil(s) is provided by a heat-raising system (such as gas boilers or heat pumps).
Centralized air systems
Centralized air systems can be categorized as:
Constant volume (CV)
Variable air volume (VAV)
Partially centralized air/water systems
In a partially centralized air/water system the bulk of the cooling/heating is carried out within the occupied space by individual room units such as fan coils. These are supplied with hot/chilled water from a central plant area via a pipework system.
Partially centralized air/water systems consist of:
Fan coils
Chilled beams
Chilled ceilings
Room-based heat pumps
Central plant also supplies outside air throughout the building by means of ductwork for ventilation dilution of odors and prevent build up of CO2 . The size of the ductwork installation and associated air-handling plant is smaller than that required by the centralized air system. Unlike a centralized air system, air is only required for ventilation. Consequently, the high volume of air necessary to carry the building’s heating/cooling requirements is avoided.
Local systems
Local systems are not linked to any centralized plant and only provide cooling in the immediate space where they are located. They may or may not provide ventilation depending on their level of complexity. The common type of local systems are local systems
Split units
Variable refrigerant flow (VRF).
