24
• Heating is required (Space temperature is < occupied heat
-
ing setpoint – 1
Δ
°F (.5
Δ
°C). The unit has a valid Supply
Air Temperature input
• The unit has a valid Space Temperature input
• Neither Cool nor Economizer modes have been active pre
-
viously.
The heating relays are controlled by the Heating Control PID
Loop and Heating Stages Capacity algorithm, which calculate the
required Supply Air Temperature to satisfy the space by compar
-
ing the Space Temperature to the:
• Effective Occupied Heating Setpoint when occupied
When the heating algorithm preconditions have been met, the
Heating Stages Capacity algorithm calculates the Heating Control
Setpoint during any heating mode. Anti-recycle timers are em
-
ployed to protect the equipment from short-cycling. There are
fixed application specific minimum on and off times for each heat
-
ing output (gas = 120 seconds on and 60 seconds off / electric = 15
seconds on and 10 seconds off).
During heating operation, the VAV-RTU Open may reduce the
number of active stages as the rooftop’s Supply Air Temperature
approaches the Maximum Heating SAT setpoint. A heat stage
turned off in this fashion may be started again after the normal
time-guard period has expired, if the Supply Air Temperature has
decreased below the Maximum Heating SAT setpoint.
Heating Service Alarm Timer functions are available (1 for each
stage of heat). This function tracks the number of heat run hours
and generates an alarm when the accumulated runtime exceeds the
threshold set by the adjustable heat service alarm timers.
OCCUPIED HEATING
Occupied Heating operates exactly the same as Morning Warm-up
except that heating can occur any time during the occupied period.
All the same conditions that apply to Morning warm-up apply to
occupied heating except: the restriction - Neither Cool nor Econo
-
mizer modes have been active. In its place is:
• Neither Cool or Economizer modes are currently active
and the 5 minute time guard between modes has expired.
UNOCCUPIED HEATING
The following conditions must be true for the unoccupied heating
algorithm to operate:
• The Outdoor Air Temperature is less than the Heating
Lockout Temperature setpoint
• Heating is required (Space temperature is < unoccupied
heating setpoint – 1
Δ
°F (.5
Δ
°C).
• The unit has a valid Supply Air Temperature input
• The unit has a valid Space Temperature input
• Neither Cool nor Economizer modes are active and the 5
minute time guard between modes has expired.
When the heating algorithm preconditions have been met, the
Heating Stages Capacity algorithm calculates the Heating Control
Setpoint during the heating mode and the heat operate the same as
Morning Warm-up.
Supply Air Tempering
The VAV-RTU Open provides the option to operate the heat, if so
equipped, to maintain a minimum supply air temperature during
conditions where very cold outdoor air causes the supply air tem
-
perature to fall below the configured SA Tempering Setpoint. This
occurs during periods where DCV is active and increasing the
amount of outdoor air or in cases where the system is operating at
very low airflow and the calculated economizer position has in
-
creased to maintain a constant ventilation rate. The following con
-
ditions must be true for the supply air tempering algorithm to op
-
erate:
• The SA Tempering is set to Enable
• The indoor fan is on
• The System Mode is Fan Only or IAQ Override
• The Outdoor Air Temperature < Minimum Cooling SAT
• Heat type is gas or electric and Number Of Heat Stages > 0
If the above are true, the VAV-RTU Open will monitor the SAT
sensor value and operate the first stage of heat to temper the sup
-
ply air as required in order to maintain the configured SA Temper
-
ing Setpoint. Heat operation is subject to anti-recycle timers to
protect the equipment from short-cycling. There are fixed applica
-
tion specific minimum on and off times for each heating output
(gas = 120 seconds on and 60 seconds off / electric = 15 seconds
on and 10 seconds off).
Demand Controlled Ventilation
The VAV-RTU Open provides the option to control the economiz
-
er’s minimum ventilation position based on a Demand Controlled
Ventilation (DCV) algorithm. The algorithm monitors the CO
2
sensor value and compares that value to the user defined setpoint.
A PID control calculates the required minimum economizer posi
-
tion required to satisfy the ventilation requirements of the space. A
user adjustable DCV Max Vent Damper Pos is provided to limit
the maximum amount of outdoor air that can be brought into the
unit due to the DCV algorithm.
The following conditions must be true for DCV operation:
• The DCV Control is set to Enable
• The unit has a valid IAQ sensor input
• The unit is in an occupied mode
• If the above are true, the VAV-RTU Open will monitor the
IAQ sensor value and the OAQ sensor value if the option
is provided. It will compare those values to the IAQ set
-
point and then calculate the required minimum economizer
position as required. If that calculated value is greater than
the configured DCV Max Vent Damper Pos, the value is
clamped to that maximum limit. If the DCV damper posi
-
tion is less than the calculated economizer minimum posi
-
tion for ventilation, the economizer will maintain that cal
-
culated economizer minimum position.
Demand Limit
The VAV-RTU Open may employ a demand limit strategy. De
-
mand limiting in the VAV-RTU Open works by resetting the Sup
-
ply Air Static Pressure Setpoint. The demand level at which static
pressure reset begins is defined by the parameter SP Reset De
-
mand Level which is selected by the user. The selected SP Reset
Demand Level determines at which demand level the SP Reset be
-
comes active. The amount of reset is determined by Maximum
Reset.
Unoccupied Free Cooling
The control can run a night time free cooling (NTFC) mode called
Unocc Free Cooling. In this mode the damper is utilized to bring
in outdoor air for free cooling during unoccupied periods. The fol
-
lowing conditions must be true for unoccupied free cooling to op
-
erate:
• Unocc Free Cool Enable set to Enable
• The system is unoccupied
• The outside air temperature is below the Economizer High
OAT Lockout Temp
• The outside air temperature is less than the space tempera
-
ture
• Enthalpy (if enabled) is Low
When the VAV-RTU Open schedule is unoccupied and the space
temperature rises at least 1 degree above the Occupied Cooling
Setpoint, the supply fan starts. The economizer damper opens as
necessary to cool the space. The VAV-RTU Open continues to op
-
erate in this mode until the space is satisfied or the outside air con
-
ditions are no longer suitable for free cooling.
Содержание 48LCB07
Страница 4: ...4 Fig 2 VAV RTU Open Control Module ...
Страница 8: ...8 Fig 5 VAV RTU Open Control Wiring Diagram 48LC B07 ...
Страница 9: ...9 Fig 6 VAV RTU Open Control Wiring Diagram 48LC B08 12 ...
Страница 10: ...10 Fig 7 VAV RTU Open Control Wiring Diagram 48LC B14 26 ...
Страница 11: ...11 Fig 8 VAV RTU Open Control Wiring Diagram 50LC B07 ...
Страница 12: ...12 Fig 9 VAV RTU Open Control Wiring Diagram 50LC B08 12 ...
Страница 13: ...13 Fig 10 VAV RTU Open Control Wiring Diagram 50LC B14 26 ...
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