Air Handling Units

Air handling units (AHU), are a HVAC item of plant that is used to regulate and circulate air as part of a heating, ventilating, and air-conditioning system. An AHU usually houses a fan, heating or cooling elements, filter chambers, heat recovery units, humidifiers, sound attenuators, and dampers. Air handlers usually connect to a ductwork ventilation system that distributes the conditioned air through the building and returns it to the air handling unit.

Smaller AHUs, used in localised applications, are called terminal units, and may only include an air filter, coil, and blower. These simple terminal units are called fan coil units. A larger air handler that conditions 100% outside air, and no recirculated air, is known as a makeup air unit (MAU). An air handler designed for outdoor use, typically on roofs, is known as a packaged unit (PU) or rooftop unit (RTU).

Controls are essential to regulate all aspects of an AHU, such as flow rate of air, flow of hot or cold liquid through control valves, supply air temperature, mixed air temperature, humidity, air quality. They may be as simple as an off/on thermostat or as complex as a building automation system using BACnet, MODBUS or LonWorks.

Common control components include temperature sensors, humidity sensors, actuators, motors, and controllers.