VAV-SVN03A-EN
5
VariTrac Changeover-Bypass
System
Overview
VariTrac Changeover-bypass VAV is a comfort system solution designed for
light commercial applications. As the name implies, these systems deliver a
varying volume of air to multiple zones, each with its own thermostat, while
still utilizing a unitary machine with a constant volume fan. Changeover-
bypass VAV combines the comfort benefits of VAV with the cost effective-
ness and simplicity of packaged unitary equipment.
Central Control Panel
The VariTrac Central Control Panel is the central source of communications
and decision making between the individual zones and the air conditioning
unit. Connections to the central control panel are:
• 24 Vac power
• binary inputs for an occupied/unoccupied signal and external priority
shutdown signal (optional)
• ICS communication bus to the Trane building automation system (op-
tional)
• UCM communication bus to the zone dampers and communicating
sensor/bypass damper control and Trane Voyager
™
/Reliatel
™
rooftop unit
• binary outputs to heating, cooling, and fan of non-Voyager or Reliatel
rooftop units
Unit Control Module (UCM)
A unit control module is mounted to each individual zone damper. Inputs
and outputs consist of the twisted shielded pair communication link, zone
temperature sensor, optional CO
2
and occupancy sensors, 24 Vac power,
damper motor control, and local heat outputs. Local heat may be duct or
space mounted, and can be staged electric, pulse-width modulating electric,
and modulating or staged two-position hot water.
VariTrac Damper
Each VariTrac damper consists of an integrated 24 Vac actuator and control
box that encloses the UCM circuit board. The damper is designed to operate
in static pressures up to 1.75 inches wg.
VariTrac dampers are referred to by their dimensions:
• round damper sizes are 6, 8, 10, 12, 14, and 16 inches. The dampers con-
sists of an 18 gage galvanized steel frame with a round damper blade
assembly.
