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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
routines will use this input point for fan status.
Cooling (standalone mode)
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 RAT is > occupied
cooling setpoint if reset is disabled or RAT > occupied
Δ
heating setpoint + 1
°F (.5
occupied, RAT or space temperature (if configured) is >
unoccupied 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 RAT input
•
Heat mode is not active and the 5-minute time guard
between modes has expired
•
Economizer is unavailable, or if Economizer cooling is ac-
tive, the economizer is open > 90% for at least 5 minutes,
the OAT > [Supply Air Setpoint + 5
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
and power exhaust
2
Δ
°C), if reset is enabled. If un-
Δ
Δ
°F (2.7
°C)], SAT >
cooling, if the SAT falls 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 cooling, if
the SAT falls 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 stage of compression). This function tracks the number of
compressor run hours and generates an alarm when the accumu-
lated runtime exceeds the threshold set by the adjustable compres-
sor service alarm timers.
Supply Fan (standalone mode)
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 occu-
pancy and intermittently during unoccupied periods with
heating and cooling.
•
Always On — The fan runs continuously regardless of oc-
cupancy or calls for heating and cooling.
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
•
SAT sensor alarm
•
SPT sensor alarms
The VAV-RTU Open does not include smoke-control functions
such as a smoke-purge, zone-pressurization, or smoke-ventilation.
Each of these modes require a field-designed circuit to operate the
following by local fine codes:
•
RTU supply fan
•
RTU economizer
•
RTU power exhaust
The VAV-RTU Open many be configured to accept a Supply Fan
Status input to provide proof the supply fan is operating. When
enabled, a loss or lack of fan status will stop heating and cooling
operation.
A supply Fan Alarm Service Timer function is available to track
the number of supply fan run hours and generate an alarm when
the accumulated runtime exceeds the set threshold.
Economizer (standalone mode)
The economizer dampers are used to provide free cooling when
the outside conditions are suitable and Indoor Air Quality, if
optional CO
sensor is installed.
2
The following conditions must be true for economizer operation:
•
The Outdoor Air Temperature is < RAT and OAT is < the
Economizer High OAT Lockout Temp setpoint
•
The indoor fan is on
•
The unit has a valid Supply Air Temperature input
•
The unit has a valid RAT sensor input
•
The unit has a valid Outdoor Air Temperature input
If the VAV-RTU Open provides variable supply airflow to the
VAV system and maintains a constant minimum ventilation. As
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