Introduction of FCU AHU PAU RCU MAU FFU HRV in Air Conditioning System

FCU, AHU, PAU, RCU, MAU, FU, HRV, FAU, OAC, and EAF are often heard in the HVAC industry and air conditioning water system – a series of strange terms. So, what do the concepts that these letters represent? What is the difference between them?
1. FCU (full name: Fan Coil Unit) The fan coil unit is the terminal device of the air conditioning system. Its working principle is that the air in the room where the unit is continuously recirculated so that the air is cooled (heated) after passing through the cold water (hot water) coil to keep the room temperature constant. Mainly relying on the forced action of the fan, the air is heated when passing through the heater surface, thus strengthening the convection heat exchanger between the radiator and the air, which can quickly heat the air in the room.
2. AHU (full name: Air Handling Units) Air Handling Units, also known as air conditioning boxes, and wind cabinets. It mainly relies on the rotation of the fan to drive the indoor air to exchange heat with the internal coil of the unit, and filter the impurities in the air to maintain the indoor temperature, humidity, and air cleanliness by controlling the air temperature and air volume. The air handling unit with fresh air function also performs heat and humidity treatment and filtration treatment on the air including fresh air or return air. At present, there are several types of air handling units, such as ceiling type, vertical type, horizontal type, and combined type. Among them, the ceiling-mounted air handling unit is also called a hanging cabinet; the combined air handling unit is also called a combined air cabinet or group cabinet.
3. HRV total heat exchanger HRV(full name: Heat Reclaim Ventilation) Invented in 1992 for Daikin Air Conditioning, it is now called “Total Heat Exchanger”. This type of air conditioner recovers the 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,s and other air conditioning systems, and can automatically switch ventilation modes to further improve the energy-saving effect.
4. FAU (full name: Fresh Air Unit) FAU fresh air unit provides air conditioning equipment for fresh air, which is divided into household and commercial use. Working principle: The fresh air is extracted from the outdoors and sent to the room through the fan after dust removal, dehumidification (or humidification), cooling (or heating), etc., and replaces the original indoor air when entering the indoor space. The difference between AHU air handling units and FAU fresh air units: AHU includes not only fresh air conditions but also return air conditions; FAU fresh air units mainly refer to air handling units with fresh air conditions. From a certain point of view, it is the relationship between the former and the latter
5. PAU (full name: Pre-Cooling Air Unit) The pre-cooling air-conditioning box is generally used in conjunction with the fan coil unit FCU. Its function is to pretreat the outdoor fresh air and send it to the fan coil unit (FCU).
6. RCU (full name: Recycled air-handling Uni) The circulating air conditioning box is also called an indoor air circulation unit, which mainly inhales and discharges indoor air to ensure indoor air circulation
7. MAU (full name: Make-up Air Unit) The new fan unit is an air conditioning device that provides fresh air. In terms of function, it can achieve constant temperature and humidity or simply provide fresh air according to the requirements of the user environment. The working principle is to extract fresh air outdoors, and then send it indoors through the fan after dust removal, dehumidification (or humidification), cooling (or heating), and other treatments, and replace the original indoor air when entering the indoor space. Of course, the functions mentioned above must be determined according to the needs of the user environment. The more complete the functions, the higher the cost.
8. DCC (full name: Dry Cooling Coil) (referred to as dry coil or dry cooling coil) is used to eliminate indoor sensible heat.
9. HEPA high-efficiency filter. High-efficiency filter refers to a filter screen that meets the HEPA standard, and the effective efficiency for 0.1 microns and 0.3 micron reaches 99.998%. The characteristic of HEPA nets is that air can pass through, but fine particles cannot. It has a removal efficiency of more than 99.7% for particles with a diameter of 0.3 microns (1/200 of the diameter of a hair) and is the most effective filter medium for pollutants such as smoke, dust, and bacteria. It is an internationally recognized high-efficiency filter material. It has been widely used in highly clean places such as operating rooms, animal laboratories, crystal experiments, and aviation.
10. FFU (full name: Fan Filter Units)Fan filter unit is a terminal purification device that combines fans and filters (high-efficiency filter (HEPA) or ultra-high-efficiency filter (ULPA)) to form its own power. To be precise, it is a self-powered, modular end air supply device with a filtering effect. The fan inhales the air from the top of the FFU and filters it through HEPA, and the filtered clean air is evenly sent out at a wind speed of 0.45m/s ± 20% over the entire air outlet surface.
11. OAC external air processing unit OAC external air processing unit is a Japanese name, which is used for feeding into a closed workshop, which is equivalent to the domestic fresh air processing unit MAU or FAU.
12. EAF (full name: Exhaust Air Fan) EAF air conditioner exhaust fan is mainly used in the public areas of the floor, such as corridors, stair front rooms, etc.

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