What are FCU, AHU, PAU, RCU, MAU, FFU, and HRV in Air Conditioning Systems?

1. FCU (Fan Coil Unit)

A fan coil unit (FCU) is a terminal device of an air conditioning system.

It operates by continuously recirculating the air in a room, passing it over a coil containing cold (or hot) water, thereby cooling (or heating) the air to maintain a constant room temperature. The primary mechanism relies on the fan’s forced action to heat the air as it passes over the heater surface, thereby enhancing the convection heat exchange between the radiator and the air, quickly heating the room’s air.

2. AHU (Air Handling Units)

Air handling units, also known as air conditioning boxes or fan cabinets, mainly rely on fan rotation to drive indoor air to exchange heat with the internal coil and filter impurities in the air to control the outlet temperature and air volume, thereby maintaining indoor temperature, humidity, and air cleanliness.

Air handling units with fresh air functionality also treat and filter the air, including fresh and return air. Currently, there are several forms of air handling units, including ceiling, vertical, horizontal, and combined types. Among them, ceiling air handling units are also called hanging cabinets; combined air handling units are also known as combined fan cabinets or combined cabinets.

3. HRV (Heat Reclaim Ventilation)

Heat Reclaim Ventilation (HRV) is an energy recovery ventilation system invented by Daikin in 1992 and is now known as a “total heat exchanger.”

This type of air conditioner recovers lost heat energy through ventilation equipment, reducing the load on the air conditioner while maintaining a comfortable and fresh environment. In addition, HRV can be used in conjunction with VRV systems, commercial split systems, and other air conditioning systems and can automatically switch ventilation modes to improve energy efficiency further.

4. FAU (Fresh Air Unit)

A Fresh Air Unit (FAU) is an air conditioning device that provides fresh air for residential and commercial use.

Working Principle: Fresh outdoor air is drawn in, then dusted, dehumidified (or humidified), cooled (or heated), and finally delivered indoors through a fan, replacing the original indoor air. The difference between AHU and FAU is that AHU includes both fresh air and return air conditions, while FAU mainly refers to air handling units with fresh air conditions. From a certain perspective, the former includes the latter.

5. PAU (Pre-Cooling Air Unit)

The Pre-Cooling Air Unit (PAU) generally works in conjunction with the fan coil unit (FCU) to pre-treat outdoor fresh air before sending it to the FCU.

6. RCU (Recycled Air-handling Unit)

The Recycled Air Handling Unit (RCU), also known as the indoor air circulation unit, primarily intakes and exhausts indoor air to ensure indoor air circulation.

7. MAU (Make-up Air Unit)

The Make-up Air Unit (MAU) is an air conditioning device that provides fresh air.

Depending on the environment, it can achieve constant temperature and humidity or simply provide fresh air. The working principle is to draw in fresh outdoor air, then dust, dehumidify (or humidify), cool (or heat), and finally deliver it indoors through a fan, replacing the original indoor air. Of course, the functionalities mentioned above depend on the needs of the environment, and the more comprehensive the features, the higher the cost.

8. DCC (Dry Cooling Coil)

The Dry Cooling Coil (DCC) is used to eliminate indoor sensible heat.

9. HEPA (High-Efficiency Particulate Air Filter)

A high-efficiency filter refers to a filter that meets HEPA standards, with an efficiency of 99.998% for 0.1-micron and 0.3-micron particles.

HEPA filters allow air to pass through while blocking tiny particles. Its removal efficiency for particles with a diameter of 0.3 microns (1/200th the diameter of a hair) or above can reach more than 99.7%, making it an effective filtering medium for smoke, dust, bacteria, and other pollutants. It is internationally recognized as a high-efficiency filter material and is widely used in operating rooms, animal laboratories, crystal experiments, and aviation, among other highly clean places.

10. FFU (Fan Filter Units)

Fan Filter Units (FFU) are terminal purification equipment that combines fans and filters (high-efficiency filters (HEPA) or ultra-high-efficiency filters (ULPA)) to create a self-powered unit.

Specifically, it is a modular end air supply device with integrated power and filtering capabilities. The fan draws air from the top of the FFU and passes it through the HEPA filter. The filtered clean air is then uniformly delivered across the entire outlet surface at a speed of 0.45 m/s or 20%.

11. OAC (Outside Air Conditioning Unit)

The OAC is a Japanese term for an outside air conditioning unit used to supply air to sealed factories, equivalent to the MAU or FAU in America.

12. EAF (Exhaust Air Fan)

The EAF is an exhaust fan used in public areas of a building, such as corridors and stairwells.