iWorx® VPU2
505-010-2, Effective: April 29, 2014
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© 2014 Taco Electronic Solutions, Inc.
The current operational mode information is periodically transferred to the VAVI over the communications network. The
following information is transferred to the VAVI from the primary air source controller:
• Operational Mode (primary cool, primary heat, primary fan only, primary off)
• Alarm Conditions (IAQ Mode, Heat Failed On)
• Supply Air Temperature
Shutdown
When the space being controlled by the VPU2 is unoccupied, the controller operates in the shutdown state. The air
handler package unit is off, and there is no control of the static pressure or duct temperature.
The VPU2 is in the shutdown state when the occupancy status is “unoccupied,” and no associated controllers are occu-
pied or in extended occupancy. The VPU2 enters the shutdown state from Occupied, Extended Occupancy and Emer-
gency Heating Stages.
The controller can enter an unoccupied cooling state from shutdown when an associated VAVI zone controller's space
temperature is 1 °F warmer than its unoccupied cooling setpoint. During this cooling state, the controller is in cooling
mode; the fan is energized, the static pressure is controlled, the economizer is enabled provided it has been configured
to operate in the unoccupied mode, and the cooling stages are controlled. The controller remains in the cooling state
for thirty minutes or until no associated controllers are requiring cooling, after which the VPU2 reverts to the shutdown
state.
Extended Occupancy
When the VPU2 is in Shutdown state and a VAVI zone controller has indicated extended occupancy, the controller
enters the Extended Occupancy state (also known as
Bypass
). The Extended Occupancy state acts identically to the
Occupied State.
The VPU2 remains in the extended occupancy state until the VAVI's extended occupancy is over, the VPU2 enters
morning warm-up or cool-down, the VPU2 enters the occupied state, or the VPU2 enters the Shutdown state.
Emergency Heating
The VPU2 enters the emergency heating state from shutdown when an associated VAVI zone controller's space tem-
perature is 10
°F colder than its unoccupied heating setpoint. During the emergency heating state, the VPU2 is in heat-
ing mode: the fan is energized, the static pressure is controlled, the economizer is disabled, and the heating stages are
controlled. The VPU2 remains in the emergency heating state for thirty minutes, after which the VPU2 reverts to the
shutdown state.
Emergency
The VPU2 enters the emergency state (from any state) when there is an emergency condition. Emergency conditions
are:
• Mixed air low limit
• Heat stuck on
• Fan failure
• Smoke alarm
During the emergency state, the air handler package unit is off and there is no control of the static pressure or duct
temperature. The VPU2 remains in the emergency state until the controller is reset.
