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TRG-TRC014-EN 19
period two
Components of a VAV System
notes
When in cooling mode, the supply airflow to the space equals the primary
airflow. When in tempering and heating modes, the space receives a constant
supply airflow equal to the minimum primary airflow plus the plenum airflow
delivered by the terminal fan. Usually the primary airflow is not allowed to shut
off completely because of the space requirement for ventilation air.
A series, fan-powered terminal unit consists of an airflow modulation device
and a small, constant-volume fan, packaged so that their airflow paths are in
series. The terminal unit fan operates continuously whenever the space is
occupied. The fan draws air from either the primary air stream or the plenum,
based on the thermostat in the space. This results in a constant volume of
supply air delivered to the space at all times.
supply
supply
air
air
terminal
terminal
mixing fan
mixing fan
plenum
plenum
air
air
Series, Fan-Powered
primary
primary
air
air
Figure 30