An air handling unit (AHU) is a device used to regulate and circulate air as part of a heating, ventilation, and air conditioning (HVAC) system. An AHU takes in outside air, reconditions it, and distributes it to the desired locations. It typically consists of a fan, filter, and heat exchanger. An HVAC system, on the other hand, is a complete system that includes the AHU as well as other components such as ducts, vents, and controls. An HVAC system is responsible for controlling the temperature, humidity, and air quality of a building or space. It is designed to provide a comfortable environment for occupants.