In the broadcast of terms, an air system consists of a complete cycle of air movement. For this context, an air system can be defined as a mechanical assembly of components through which air moves and is cleaned and cooled, known as conditioned air.
The figure shows one of the components of a system. Air enters the system through a louver, passes through a filter and then enters the fan, which is the heart of the system. The fan adds energy to the air, causing it to flow through the coil into the main and distribution ductwork to the dampers – which control the volume flow rate – and exits the system through each diffuser. The cycle is completed when the air returns to the louver at the inlet to the system.
Each component in the system must be selected to meet certain performance requirements, and be properly installed and operating if the system is to perform as intended. The pressure loss of each component in the system must be determined and the fan must be selected to deliver the required airflow as it overcomes the sum of the pressure losses in the system.
The louver should be selected to meet system requirements at the desired airflow. The filter must be selected to meet cleanliness requirements while offering a minimum pressure drop. The fan must be installed so air can freely enter it and discharge from it. The ductwork must be sized so air velocity is low and pressure losses are minimized. Each turn or take-off in the ductwork system must be sized and contracted to minimize pressure losses and reduce noise.
Furthermore, the dampers must be selected to provide proper control of air serve other functions as specified. The diffusers must be picked for their ability to redirect airflow at a minimum of pressure loss.
Source: The Air Movement and Control Association's “Techspec.”
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