As temperatures continue to rise or plummet, air conditioning systems have become indispensable equipment in modern residents and offices. Not only does it provide a comfortable indoor temperature, the air conditioning system can also regulate humidity, purify the air, increase air circulation, and improve indoor air quality. However, have you ever been confused by the many terms such as PAU, MAU, AHU, DCC, RCU, DDC and FCU? Let’s decipher the meaning of these abbreviations and understand their different roles in the air conditioning system.

AHU (Air Handling Unit): A type of combined air conditioning box that extracts indoor air (return air) and some fresh air to control the temperature and air volume output and maintain indoor temperature. It is usually installed in machine rooms or on the roof of buildings for distributing processed air to different rooms. AHU is suitable for medium-sized buildings and can adjust temperature, humidity, and air quality parameters according to demand.



PAU (Pre-Cooling Air Handling Unit): A primary air unit that pre-treats outdoor fresh air before sending it to the fan coil unit (FCU). It contains components such as fans, refrigeration units, and heating units. It is usually installed outdoors and is used to supply hot and cold air to the entire building. PAU is suitable for larger buildings, such as commercial centers and large hotels.



RCU (Recycled air handling unit): A type of indoor controller installed in guest rooms or offices. It is used to adjust indoor temperature, airspeed and direction, and other parameters. RCU can achieve personalized indoor comfort control.



MAU (Make-up Air Unit): An air conditioning device that provides fresh air. The functions can be constant temperature and humidity or simply providing fresh air according to the requirements of the environment. The working principle is to extract fresh air from outside and pass it through processes such as dust removal, dehumidification (or humidification), cooling (or heating), etc., and then send it to the room through a fan. When entering the indoor space, it replaces the original indoor air. Of course, the above-mentioned functions must be determined according to the needs of the environment, and the more complete the functions are, the higher the cost will be.



DCC (Dry Cooling Coil): A type of dry cooling coil used to eliminate sensible heat in the room. It is an intelligent control system used to monitor and control air conditioning and other environmental equipment. It can automatically adjust temperature, humidity, air quality, and other parameters according to environmental requirements, improve energy efficiency and provide a comfortable indoor environment.



.DDC (Direct Digital Control): Similar to DCC, it is used to control multiple air conditioners and environmental equipment in large buildings. It realizes centralized management and energy-saving optimization functions



HEPA (High Efficiency Particulate Air Filter) is a high-efficiency filter that meets HEPA standards. It has an effective efficiency of 99.998% for particles of 0.1μm and 0.3μm. The feature of HEPA filter is that air can pass through, but small particles cannot. Its removal efficiency for particles with a diameter of 0.3μm (1/200th of the diameter of hair) and above can reach more than 99.7%, making it the most effective medium for filtering pollutants such as smoke, dust, and bacteria. (The diameter of smoke particles generated by smoking is 0.5μm). It is an internationally recognized high-efficiency filtering material widely used in operating rooms, animal laboratories, crystal experiments, aviation, and other high-clean places.



FCU (File Control Unit): A fan coil unit is the end device of an air conditioning system. Its working principle is to continuously recycle the indoor air of the room, make the air pass through the cold water (hot water) coil for cooling (heating), and maintain the temperature of the room. It mainly depends on the forced action of the fan to heat the air through the surface of the heater, thereby strengthening the convective heat exchange between the radiator and the air, and rapidly heating the air in the room.




VAV (Variable Air Volume) Control System: The variable air volume controller and room temperature controller constitute an indoor cascade control, using indoor temperature as the main control quantity and air flow as the secondary control quantity. The variable air volume controller detects the actual temperature detected by the room temperature sensor, compares the difference between it and the set temperature, outputs an adjustment signal of the required air volume, adjusts the air valve at the end of the variable air volume, and changes the air supply volume to maintain the indoor temperature within the set range. At the same time, the air duct pressure sensor detects the pressure change in the air duct, adopts PI or PID control, and controls the speed of the variable air volume air conditioning machine's supply fan through a frequency converter to eliminate the impact of pressure fluctuations and maintain the air supply volume.




HRV（Heat Reclaim Ventilation）Chinese name: Energy Recovery Ventilation System. Invented for Daikin Air Conditioning in 1992, it is now called 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 with VRV systems, commercial split systems and other air conditioning systems, and can automatically switch ventilation modes to further improve energy saving effects.