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TRG-TRC014-EN 3
period one
What Is Variable Air Volume?
notes
Rearranging the equation and using the constant supply airflow of 1,840 cfm
[0.87 m
3
/s], the supply air temperature required to balance a lesser 20,000
Btu/hr [5,862 W] space sensible load is:
Therefore, as the space sensible load drops from 40,000 Btu/hr to 20,000 Btu/hr
[11,724 W to 5,862 W], this system modulates the temperature of the constant
1,840 cfm [0.87 m
3
/s] supply air from 55°F to 65°F [12.8°C to 18.3°C].
Removing less energy from the air takes less energy from the central system.
Therefore, with this particular system, refrigeration energy savings are realized
at part load conditions, although control of space humidity levels suffers due to
the warmer supply air condition.
75°F –
20,000 Btu/hr
1.085 × 1,840 cfm
Supply
DB
=
65°F=
Constant Volume–Part Load
Space
DB
Sensible Heat Gain
Constant × Supply Airflow
–
=
Supply
DB
23.9°C –
5,862 W
1,210 × 0.87 m
3
/s
Supply
DB
=
18.3°C
=
Figure 5
Supply DB Space DB
Sensible Heat Gain
Constant Supply Airflow×
---------------------------------------------------------------------------–=
Supply DB 75°F
20,000 Btu/hr
1.085 1,840 cfm×
------------------------------------------------
65°F=–=
Supply DB 23.9°C
5,862W
1
,
210 0.87m
3
/
S
×
-------------------------------------------------–=