When you are doing research about HVAC you will hear a lot of terms such as FCU, AHU, PAU, RCU, MAU, FU, HRV, FAU, OAC, EAF, etc. To be honest it can be really confusing for someone who is not aware of the HVAC industry. In this article we are going to learn about the most common HVAC terms that are often used for HVAC systems and subsystems.
A Fan Coil Unit, or FCU in the HVAC industry, uses a fan and a coil to heat or cool the room. This system doesn’t require a Ductwork connection. FCUs are often used in work in residential, industrial, or commercial buildings. It is the most common system in the HVAC industry. The fan moves the air into the coil where the air gets cool or hot before the fan pushes air back into the room. FCU is cheaper in installation than a duct HVAC system. The FCUs are available in different types of mountings such as Ceiling, Floor, and free-standing.
An Air Handling unit or AHU is a device that is used for HVAC systems. AHU is a huge metal box indoor air conditioning device that is usually installed on the rooftop. It uses both outside and inside air for air-conditioning. The AHU collects the air by fans and removes the impurities such as dust and other particles then provides the refreshing air to rooms through the ducts. The AHU system also uses a coil filled with water or refrigerant, for cooling the air. The collected air goes through a series of air filters before it reaches the coil then sent back to ducts with the help of fans.
Recycled air handling unit or RCU is an indoor air circulation unit that controls the air circulation in HVAC. The purpose of RCU is to maintain the indoor pressure, temperature, and humidity level.
The Dry cooling coil or DCC is used in an indoor cooling system, where the coils are cooled by chilled water. The main job of the Dry cooling coil is to eliminate the sensible heat from the room. This sensible heat is either produced by people, machines, or lightning.
Makeup-air unit or MAU is also a type of HVAC system. The makeup air is designed for buildings and spaces that need high indoor air quality (IAQ). In some buildings, the air can not be recirculated. Such spaces can be dangerous for health, that’s why the MAU is designed to provide such spaces with fresh outside air. The MAU pulls fresh air from the outside to replace it with the existing air inside the building. MAU is a large handler that provides spaces with fresh conditioned air and it also produces both hot and cool air. A makeup air unit is a solution where air ventilation is highly required due to less exhaust flow.
HEPA or (High-Efficiency Particulate Filter) is a mechanical pleated air filter that is used in the HVAC industry. The HEPA filters have an air filtering efficiency of 99.97%. It can remove the air particles such as dust, bacteria, pollen, mold, and any other particle with a size of 0.3 microns (µm).
The main purpose of HEPA Filters is to provide high-quality pure air without contaminants. The air can pass through these filters but the air particle with a size of 0.3 microns or greater can not be passed. In air filters, 0.3 microns filtration is considered highly efficient since most air particles are larger in size, 0.3 microns filtration is a peace of mind. The HEPA Filters are used in operating rooms, labs, and highly cleaned places where air quality is highly concerned.
PAU stands for pre-cooling air unit in HVAC. The PAU device is a big box unit that collects high-humidity outdoor air and sends it to the AHU (Air handling unit). PAU (Pre-cooling Air Unit) also works as a dehumidifier and controls the desired humidity level in the building air.
Exhaust Air Fans or EAFs are used for removing the air from space. EAF removes the odor and humidity from the space and makes room for new fresh conditioned air. EFA (exhaust air fans) are mainly used in congested areas where air ventilation is required.
The OAC unit is a subsystem of the HVAC system. The OAC unit is used in closed spaces to feed fresh air. The OAC can control humidity, airflow, temperature, and pressure of the ventilation air.
FFU ( Fan Filter Unit)
FFU or Fan filter unit is a device that provides pure high-quality air. It is mainly used to supply purified air to laboratories, medical facilities, classrooms, and spaces where air quality is highly concerned. FFU ( fan filter unit) has its own motorized fan and a HEPA filter which purifies the air. The FFU collects the air from the top and filters it through the HEPA filter then supplies at the speed rate of 0.45m/s ± 20%.
HRV ( heat reclaim ventilation) is also known as a heat recovery ventilator or total heat exchanger. As the name states, HRV is an air ventilation system which exchanges the indoor air with fresh outside air. HRV is suitable for cold environments where the humidity level is higher. During the heating season, the HRV collects the heat from the outside air and uses the heat energy to preheat. This function is very suitable in the heating season because of the outside energy that it collects, making it very energy efficient. In the cooling season, HRV takes the heat from incoming air and takes off the load from the air conditioner. HRV can be used in conjunction with the VRV system.