Trane TRG-TRC014-EN Parallel Versus Series Fan-Powered, Components of a VAV System, period two

period two

Components of a VAV System

notes

Series, Fan-Powered

100%				maximum
				primary
				airflow
to space	heating		tempering
	plenum air
airflow				minimum
				primary
%		primary air		airflow
0%				design
design		space load
heating load			cooling load

Figure 31

In the cooling mode, the primary airflow is reduced as the cooling load in the space decreases. The total supply airflow to the space remains constant, a combination of cool primary air and warm plenum air. If the space cooling load drops below the minimum primary airflow setting for the unit, or if space heating is required, a heating coil can be used to further warm the supply air to the space.

The maximum airflow for the airflow modulation device typically equals the terminal fan airflow. This means that at the design cooling load, primary airflow equals supply airflow.

Parallel Versus Series Fan-Powered

▲Constant airflow to the space

▲Acoustics

▲Fan energy consumption

Figure 32

Series, fan-powered units are generally considered the premium VAV system because while the central system operates as a variable-volume system, the spaces receive constant supply airflow. Increased air motion in the space improves comfort at all load conditions and the constant airflow simplifies diffuser selection.

20 TRG-TRC014-EN