Sequence of operation
VAV Zone II Controllers
CARRIER CORPORATION ©2019
Installation and Start-up Guide
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57
Linkage modes and determination
Linked air source modes
– In a linked system, the air source determines its operating mode and qualifies that
mode based on its own SAT. The following modes can be sent by the air source depending on its capability and
configuration:
OFF
Air source fan is off. Terminal damper is positioned approximately 70%
open to allow for system restart.
WARMUP
Air source fan is on and providing first cycle of heat when changing from
unoccupied to occupied. It may also be used as an equipment safety to
increase system airflow. The terminal’s heating setpoint temporarily
increases to the midpoint between the configured occupied heating and
occupied cooling setpoints.
HEAT
Air source fan is on and providing heat. The terminal modulates its primary
air damper to maintain the current heating setpoint.
FREECOOL
Air source fan is on and providing cooling using only the economizer and
usually during an unoccupied period. The terminal modulates its primary air
damper to maintain the midpoint between the configured occupied heating
and occupied cooling setpoints.
COOL
Air source fan is on and providing cooling. The terminal modulates its
primary air damper to maintain the current cooling setpoint.
PRESSURIZATION
Air source supply fan is on usually as a result of a fire-life safety input being
active. It may also be used as an equipment safety to increase system
airflow. The terminal modulates its primary air damper to provide the
configured maximum cooling airflow.
EVACUATION
Evacuation is usually the result of a fire-life safety input at the air source
being active. The terminal fully closes its primary air damper and disables
its terminal fan, if equipped.
VENT
All terminals treat VENT mode the same as the COOL mode. For VVT
terminals, VENT modes allows for an increase in airflow. VVT terminals use
the greater of the configured Vent Damper Position or the Minimum Cooling
Damper Position as the minimum during the VENT mode.
See the air source’s installation manual for more specific operation.
Local air source modes
– If the zone controller is stand-alone or if linkage communication fails, the zone controller
monitors the cfm (liters/second) for fan status and its SAT sensor to determine if the primary air source is
providing heating, cooling, or recirculating air in a fan-only or ventilation mode.
HEAT
For Series or Parallel Fan controllers when the zone terminal fan is off or for single
duct controllers: The zone’s local heat has not operated for at least 5 minutes, and
the SAT is more than 5 °F (2.8 °C) warmer than the space temperature. If the
terminal fan is on, the SAT must be more than 8 °F (4.4 °C) (warmer than the
space temperature.
In all cases, Heat mode is maintained until the SAT drops 2 °F (1.1 °C) below the
space temperature.
VENT
The zone’s local heat has not operated for at least 5 minutes and the SAT is between
65°F (18.3°C) and 80°F (26.6°C).
Summary of Contents for VAV Zone II
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