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TRG-TRC014-EN 15
period two
Components of a VAV System
notes
determined by the design cooling load of the space and the minimum setting is
normally determined by the space ventilation requirement or minimum airflow
for proper diffuser selection.
Most cooling-only units are applied to spaces that have no need for heat. These
units would operate in the region on the right-hand portion of this chart,
modulating between design and minimum primary airflow. When cooling-only
units are applied to spaces that do have heating requirements, the heat is
provided by a remote source such as finned radiation along the wall. In these
spaces, when the cooling load drops below the minimum airflow setting for the
unit, overcooling the space, the remote heat source activates. When space
heating is required, the remote heat source satisfies the space heating load.
Most terminal unit controllers provide an output signal to control this remote
source of heat.
In addition to controlling this remote source of heat (perimeter baseboard
radiation, in this example), single-duct VAV terminal units can directly provide
heat to a space. This can be accomplished by adding a heating coil to each
cooling-only unit or by mixing the primary air with warm plenum air before it is
delivered to the space.
Space Heating with a VAV System
remote
remote
heat source
heat source
heating
heating
coil
coil
plenum air
plenum air
terminal
terminal
mixing fan
mixing fan
Figure 24