iWorx® VPU2
18
505-010-2, Effective: April 29, 2014
© 2014 Taco Electronic Solutions, Inc.
In addition, the VPU2 polls each zone controller (VAVI) to determine if extended occupancy (bypass) has been
requested. During unoccupied periods when extended occupancy has been requested, the VPU2 enters the occupied
mode of operation. At least once every 5 seconds a different zone controller is polled.
Operational Mode
The VPU2 operates in one of three operating modes: primary heating, primary cooling, and primary off. The operating
mode determines whether warm or cool air is supplied to the zone controllers. The VPU2 determines the operating
mode based on its internal schedule state, which is determined based on the occupancy state and internal configura-
tion variables. The VPU2 can be in one of the following operational states: morning warm-up, occupied, extended
occupancy, emergency heating, shutdown, and emergency.
Morning Warm-up
The purpose of morning warm-up is to heat up the unoccupied zones to a comfortable level before the zones are occu-
pied. During morning warm-up, the VPU2 is in heating mode: the fan is energized, the static pressure is controlled, the
economizer is disabled, and the heating stages are controlled. The VPU2 enters the morning warm-up state from shut-
down, bypass, or emergency heating states.
The VPU2 must be configured at the LCI to perform morning warm-up; a reference VAV zone must be selected, and
the optimum start time for heating must be configured. If the reference zone requires heating, and morning warm-up is
configured, the LCI advances the occupancy start time of the VPU2 and passes the number of minutes the occupancy
has been advanced. The VPU2 remains in morning warm-up until the reference zone temperature is within 1 °F of the
heating setpoint, or until the optimum start time has expired.
The VPU2 informs all of its associated VAVI controllers, regardless of their occupancy state, that morning warm-up is
being performed, to allow all associated VAVIs to take advantage of the heating mode. During morning warm-up, all
VAVI controllers control to their occupied setpoints, regardless of their occupancy state. After morning warm-up, the
VPU2 enters the occupied state and delays the staging of cooling for one stage time.
Morning Cool Down
Similarly to morning warm-up, the VPU2 can perform morning cool-down, cooling the soon-to-be occupied zones to a
comfortable level before occupancy. Morning cool-down is exactly like the occupied state, but the occupancy time has
been advanced.
The VPU2 must be configured at the LCI to perform morning cool-down: a reference VAV zone must be selected and
the optimum start time for cooling must be configured. If the reference zone requires cooling, the VPU2 enters the
occupied state.
Unlike morning warm-up, the VPU2 does not inform its associated zone controllers that it is in morning cool-down. Only
the VAVI controllers that are in the same group take advantage of the cooling and control to their occupied setpoints.
Occupied
A remote device on the network (such as an LCI) provides the current occupancy mode. There are two modes of occu-
pancy; occupied and unoccupied. The VPU2 is in the occupied state if the VPU2 is scheduled for occupancy.
In addition, the current occupancy mode is periodically retrieved from each of the zone controllers. If at least one zone
controller is currently in occupancy or occupancy extension mode the occupancy mode is overridden to the occupied
state (See Extended Occupancy).
During the occupied state the controller is normally in the cooling mode. If the mixed air temperature is 7 °F
colder
than
the supply temperature (as can happen during cold winter weather), the controller enters the heating mode, and heats
the air to the cooling setpoint. Also, the fan is energized, the static pressure is controlled, and the economizer is
enabled. In heating mode, the controller compensates for the colder air being brought in by setting the economizer to
its minimum position.
The VPU2 enters the occupied state from shutdown, extended occupied, morning warm-up, and emergency heating
states. It remains in the occupied state until the VPU2 goes into the unoccupied state and no associated zone control-
lers are occupied.
