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6 TRG-TRC014-EN
notes
period one
What Is Variable Air Volume?
In contrast, a variable-air-volume (VAV) system delivers the primary air at a
constant temperature and varies the airflow to maintain the required space
temperature at all load conditions.
Similar to the constant-volume system, at design conditions the VAV system
will balance the same 40,000 Btu/hr [11,724 W] space sensible load with the
same 1,840 cfm [0.87 m
3
/s] of 55°F [12.8°C] supply air.
Variable-Air-Volume (VAV) System
EA
OA
RA
variable
variable
-
-
speed drive
speed drive
supply
supply
fan
fan
cooling
cooling
coil
coil
thermostat
thermostat
VAV
VAV
box
box
PA
SA
Figure 9
VAV–Full Load
40,000 Btu/hr
1.085 × (75°F – 55°F)
Supply
Airflow
=
1,840 cfm
=
11,724 W
1,210 × (23.9°C – 12.8°C)
Supply
Airflow
=
0.87 m
3
/s
=
Figure 10