Johnson Controls
5513350-JTG-1018
83
The economizer suitability should also be synchronized to
allow all the units to use the OA damper for free cooling
when available. This also avoids a situation where one unit
is operating in economizer mode while another unit operates
in mechanical cooling mode.
The occupancy for the twinned units must also be synchro
-
nized to allow all units to switch between occupied and unoc
-
cupied modes simultaneously. This includes the occupancy
schedule and warm-up/cool down if enabled.
The DCV is synchronized to allow the OA damper minimum
position to be reset equally between the units. This requires
the indoor CO
2
values from the units to be shared and the
maximum to be passed to the reset logic to ensure sufficient
outside air is brought in for proper ventilation. The indoor
CO
2
setpoint also synchronizes so the reset calculation is
the same across all units.
The exhaust fan system must be synchronized to allow for
proper building pressurization. This requires the building
static pressure values from each unit to be averaged be-
fore passing to the PID. The building static pressure setpoint
also synchronizes, and any change to one setpoint must be
shared with the other rooftop units.
The smoke control feature is synchronized to ensure all
units properly switch between the purge, pressurization,
or depressurization modes. This requires the three smoke
control binary inputs and their priorities on each unit to be
shared so if any binary input is ON, all twinned units respond
the same way.
The temperature control, return fan systems, and safety
shutdowns can operate individually on each unit. The tem
-
perature setpoints synchronize to allow for similar operation
between the units. The temperature loops are not required
to be as tightly coupled as the supply and exhaust fan sys-
tems.
The twinning feature also has the following additional re
-
quirements:
•
BAS interface board required for twinning application
• VAV system types only
• All units must be the same size
• Fan systems have tuning disabled
• External control not supported
• The same static pressure probe can be connected to
all discharge pressure transducers
• The same static pressure probe can be connected to
all building pressure transducers
Unit Protection
The unit utilizes several system safeties to ensure unit pro-
tection, including low voltage, compressor system status
monitoring, low and high pressure cutout monitoring, suc
-
tion temperature monitoring, freeze protection, fan over-
load, shutdown, furnace limit, and MAT low limit.
Conditions that cause the unit to be locked out require user
intervention. Refrigeration fault lockouts cannot be reset
from the BAS. All other fault lockouts can be reset from
network input or local UI.
Unit Shutdown
Any time the normally closed contact opens, all relay out-
puts immediately de-energize and the unit shuts down. An
alarm generates and displays on the unit controller.
Unit Test
Start-Up Wizard
Field service technicians use the start-up wizard function to
complete the unit configuration and start-up. It is a sequence
of automatic self-tests and manually verified tests that are
required for start-up documentation. For each test, a PASS/
FAIL, date/time stamp, and relevant system data are record-
ed. After the testing sequence completes, a report with the
recorded results is stored and downloadable via USB.
Air Balancing Wizard
The air balancing wizard is a grouping of configuration
screens used for testing and calibrating airflow measur
-
ing stations, overriding damper positions, overriding fan
speeds, and other functions to assist service technicians
and air balancers.
Commissioning Mode
Commissioning mode is a function used for manually oper-
ating the unit during a service call or commissioning dem-
onstration. It allows for the unit components to be operated
individually. The unit must not be operated in this mode for
an extended period, therefore commissioning mode termi-
nates automatically after 60 minutes unless extended at
the local UI for another 60 minutes.
Cooling and heating is disabled unless the supply fan sta-
tus is proven. Unit protection and safeties remain active
and logged during commissioning mode.
Controls (Continued)
