
140 VAV-PRC011M-EN
Application Considerations
VariTrane VAV Terminal Units
The function of the VariTrane™ terminal unit in a VAV control zone is to vary the volumetric airflow
rate to the zone. VariTrane units are available with either microprocessor-based DDC controls or
pneumatic or analog electronic controls. Factory-installed controls are available with all types of
terminal units.
VAV Terminal Unit Types
Single-Duct
Single-duct terminal units control the volumetric flow of supply air to the space to maintain the
zone temperature at setpoint. These units are generally applied in cooling-only VAV zones that
require no heat during occupied hours. If local zone heat is necessary it can be provided either
remotely (for example, perimeter heat) or by terminal reheat (either electric or hot water coils).
Dual-Duct
Dual-duct terminal units are used in a special type of air distribution system where the main system
has both warm air and cold air separately ducted to each terminal unit. The flow of both warm air
and cool air is modulated, delivering air to the VAV zone at variable air volumes as well as variable
temperatures. Since full capacity occupied heating is always available, control of additional local
heat is not provided.
Figure 9. Single-Duct cooling only unit (L) and single-duct unit with hot water coil (R)
Figure 10. Dual-Duct terminal unit
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