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2 TRG-TRC014-EN
notes
period one
What Is Variable Air Volume?
This equation describes the performance of a constant-volume, variable-
temperature system at various load conditions.
With these design conditions:
space sensible heat gain = 40,000 Btu/hr [11,724 W]
space dry-bulb (DB) temperature = 75°F [23.9°C]
supply air dry-bulb (DB) temperature = 55°F [12.8°C]
constant = 1.085 [1,210]
the system balances the load with 1,840 cfm [0.87 m
3
/s] of 55°F [12.8°C]
supply air.
Sensible Heat Gain
Constant × (Space DB – Supply DB)
Supply
Airflow
=
40,000 Btu/hr
1.085 × (75°F – 55°F)
Supply
Airflow
=
1,840 cfm
=
Constant Volume–Full Load
11,724 W
1,210 × (23.9°C – 12.8°C)
Supply
Airflow
=
0.87 m
3
/s
=
Figure 4
Supply Airflow (cfm)
Sensible Heat Gain
Constant (Space DB Supply DB)–×
------------------------------------------------------------------------------------------------------=
Supply Airflow
40,000 Btu/hr
1.085 75°F55°F–()×
----------------------------------------------------------
1,840 cfm==
Supply Airflow
11,724 W
1,210 23.9°C12.8°C–×
----------------------------------------------------------------
0.87m
3
/S==