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LINKAGE BASED OPERATION
The VAV-RTU Open will control the compressors, economizer
and heating outputs based on the space temperature inputs and set
-
points received from the zoning master through Linkage. The
VAV-RTU Open supports Carrier Open air terminals with Airside
Linkage or (VAV-RTU Open with version 2) can operate as a
standalone VAV rooftop serving third party BACnet air terminals.
An optional CO
2
IAQ sensor mounted in the space can influence
the economizer minimum position. The following sections de
-
scribe the operation for the functions of the VAV-RTU Open
through Linkage.
Occupancy
Occupancy is the fundamental overall control of equipment. The
unit can be in one of two states: Occupied or Unoccupied. These
are usually referred to as periods because they represent periods of
any given day. Before VAV-RTU Open can operate specific func
-
tions of the equipment it is installed on, occupancy must be deter
-
mined. Occupancy only comes from the Linked zoning system.
Indoor (Supply) Fan
The indoor fan can be configured to operate in three different
manners. The configuration point Fan Mode determines how the
fan will run. The fan will always be disabled if a fire shutdown or
safety chain alarm is active. A valid space temperature and supply
air temperature must be available for the fan to operate. There is a
unit start delay in effect when the unit is transitioning from unoc
-
cupied to occupied. The following describes specific fan operation
based on the Fan Mode configuration value.
AUTO
When Fan Mode is set to Auto, VAV-RTU Open will cycle the fan
on and off based on the demand for heating, and cooling. There is
a configurable fan off delay that is upheld before shutting the fan
off after conditioning has ended.
CONTINUOUS
When Fan Mode is set to Continuous, VAV-RTU Open will cycle
the fan based on occupancy. The fan will run continuously when
-
ever the unit is occupied and operate in the auto mode during the
unoccupied period.
ALWAYS ON
When Fan Mode is set to Always On, VAV-RTU Open will run the
fan all the time regardless of occupancy or demand.
FAN OFF DELAY
A Fan Off Delay allows the supply fan to continue operating after
heating or cooling stops. If the following alarms are active, the fan
turns off immediately, regardless of the occupancy state or
demand:
• Fire Shutdown
• Safety Chain
• Supply Air Temp Sensor alarm
The VAV-RTU Open does not include smoke-control functions
such as smoke-purge, zone-pressurization, or smoke-ventilation.
INDOOR (SUPPLY) FAN STATUS
The VAV-RTU Open has an optional Supply Fan Status input to
provide proof of airflow. If this is enabled, the point will look for a
contact change whenever the Supply Fan Relay is on. If it is not
enabled then it will always be the same state as the Supply Fan
Relay. The cooling, economizer, heating, CO
2
and power exhaust
routines will use this input point for fan status.
Cooling
The VAV-RTU Open application and configuration determines the
specific cooling sequence. The VAV-RTU Open controls 3 stages
of mechanical cooling. The number of stages is not configurable.
The following conditions must be true for the cooling algorithm to
operate:
• Cooling is required. (If occupied, the space temperature is >
occupied cooling setpoint if reset is disabled or space tem
-
perature > occupied heating se 1
Δ
°F (0.5
Δ
°C)] if re
-
set is enabled. If unoccupied, space temperature is > unoccu
-
pied cooling setpoint).
• Outdoor Air Temperature, if valid, is greater than the
Cooling Lockout Temperature setpoint
• The Supply Fan is on
• The unit has a valid Supply Air Temperature input
• The unit has a valid Space Temperature input
• Heat mode is not active and the 5-minute time guard be
-
tween modes has expired
• Economizer cooling is unavailable, or if Economizer cool
-
ing is active, the economizer is open > 90% for at least
5 minutes, the OAT > [Supply Air Setpoint + 5
Δ
°F
(2.7
Δ
°C)], SAT > Supply Air Setpoint, and cooling mode
is active (SPT > CSP if reset is disabled or SPT > HSP +1
if reset is enabled).
The cooling relays are controlled by the Cooling Control PID
Loop and Cooling Capacity algorithm. They calculate the desired
number of stages needed to satisfy the supply air temperature set
-
point.
When the cooling algorithm preconditions have been met, the
compressors are energized in stages, as applicable. Anti-recycle
timers are employed to protect the equipment from short-cycling.
There are fixed 3 minute minimum on-times, and 1 minute off-
times for each compressor output.
During compressor operation, the VAV-RTU Open will reduce the
number of active stages to only one if the rooftop supply air tem
-
perature falls below the Supply Air Setpoint. During mechanical
cooling, should the SAT fall below the configured Minimum
Cooling SAT value of 45°F (7.2°C), the economizer will modulate
more open to maintain the minimum SAT. During integrated cool
-
ing, should the SAT fall below the configured Minimum Cooling
SAT value of 45°F (7.2°C), the economizer will modulate more
closed to maintain the minimum SAT. The Minimum Cooling
SAT is user configurable between 45°F (7.2°C) and 75°F (23.9°C)
Compressor Service Alarm Timer functions are available (1 for
each compressor). This function tracks the number of compressor
run hours and generates an alarm when the accumulated runtime
exceeds the threshold set by the adjustable compressor service
alarm timers.
Supply Fan
The VAV-RTU Open supply fan is configured for Variable Speed
operation:
• Fan speed is controlled to maintain the configured duct
static pressure setpoint.
The VAV-RTU Open supply fan may be configured for 1 of 3 Fan
Modes:
• Auto - The fan cycles on/off in conjunction with heating or
cooling.
• Continuous - The fan runs continuously during occupancy
and intermittently during unoccupied periods with heating
and cooling.
• Always On - The fan runs continuously regardless of occu
-
pancy or calls for heating and cooling.
Occupancy is determined by Linkage.
A Fan Off Delay allows the supply fan to continue operating after
heating or cooling stops.
If the following alarms are active, the fan turns off immediately,
regardless of the occupancy state or demand:
• Fire Shutdown
Summary of Contents for 48LCB07
Page 4: ...4 Fig 2 VAV RTU Open Control Module ...
Page 8: ...8 Fig 5 VAV RTU Open Control Wiring Diagram 48LC B07 ...
Page 9: ...9 Fig 6 VAV RTU Open Control Wiring Diagram 48LC B08 12 ...
Page 10: ...10 Fig 7 VAV RTU Open Control Wiring Diagram 48LC B14 26 ...
Page 11: ...11 Fig 8 VAV RTU Open Control Wiring Diagram 50LC B07 ...
Page 12: ...12 Fig 9 VAV RTU Open Control Wiring Diagram 50LC B08 12 ...
Page 13: ...13 Fig 10 VAV RTU Open Control Wiring Diagram 50LC B14 26 ...
Page 55: ......