Filter
Top Products
TRG-TRC013-EN 39
notes
period three
Fan Capacity Control
The previous discussions assumed that the fan would perform at a single
operating point, located by the intersection of the system resistance and fan
performance curves, in a constant-volume system. This type of system
provides a constant volume of variable-temperature air to control the
environment of a building.
A variable-air-volume (VAV) system, however, controls the environment by
varying the volume of constant-temperature air. This places additional
demands on fan performance and brings up the subject of fan capacity control.
In a VAV system, the quantity of air being delivered to each space is controlled
by a modulating device (a blade damper or an air valve) that is contained within
a VAV terminal unit (box). This device is controlled by a thermostat to provide
only the quantity of conditioned air needed to balance the space load. As the
device modulates, the overall system resistance changes.
Air Conditioning Fans
period three
Figure 58
VAV System
supply
supply
fan
fan
thermostat
thermostat
VAV
VAV
box
box
Figure 59