Cooling Mode; Discharge Air Control With Modulating Re; High Discharge Air Temperature Condition; High Static Lock - Carrier Omnizone 50BVC Installation, Start-Up, Service And Controls Operation And Troubleshooting

For discharge air control applications the minimum on-
times and off-times in Table 29 are applicable:
Table 29 — Discharge Air Control
COMPR 1 COMPR 2
Min Min Min Min
ON OFF ON OFF
10 5 10 5
If for any reason the compressor alarms reset, the unit com-
pressors will start within 10 seconds of each other.
COOLING — Cooling will be enabled whenever:
• Unit is in occupied mode
• The fan output is on
• The loop valve is open
COOLING MODE — When commanded into cooling
mode, the unit will energize the condenser water valve and
wait for its valve end switch to be made prior to energizing
the compressors.
Once the valve has been proved open the unit will com-
mand the compressor to stage according to the cooling percent-
age required. This value is provided via a reverse acting PID
loop which compares the supply air temperature (SAT) value
and the SAT cooling set point (AV:66).
The unit monitors return air temperature to assure air enter-
ing the unit is greater than 60 F (adjustable) prior to running in
the cooling with modulating hot gas reheat, when the controller
is set to operate with multiple reset points. If the controller is
set to operate with single return temperature reset the factory
default value will be the free cooling value 50 F (adjustable).
If at any time the cooling set point is greater than the return
air temperature (RAT) the unit will enter into economizer assist
mode.
Compressors will be staged as follows:
Compressor 1 will run:
When the fan is running
AND the condenser valve is proved.
AND the cooling demand is greater than 25%
Compressor 2 will run:
When compressor one has run for 10 minutes
AND the cooling demand is greater than 50%
Compressor 3 will run:
When compressor two has run for 10 minutes
AND the cooling demand is greater than 75%
Compressor 4 will run:
When compressor 2 has run for 10 minutes
AND the cooling demand is greater than 90%
When the unit runs in cooling mode the hot gas re-heat valve
will be enabled and modulated to maintain supply air tempera-
ture set point, factory default is 55 F (AV:93, adjustable) ± 4° F.
DISCHARGE AIR CONTROL WITH MODULATING
RE-HEAT — When in cooling mode, if the unit is equipped
with modulating hot gas re-heat, the hot gas re-heat will be
enabled and modulated to maintain supply air temperature
set point, factory default is 55 F (adjustable) ± 4° F.
COMPR 3 COMPR 4
Min Min Min Min
ON OFF ON OFF
10 5 7 5
The cooling stages can be reset based on a single point or
multiple return air temperature (RAT) values as follows:
Single:
Free Cooling
Mechanical Cooling
Multiple:
Free Cooling
Mechanical Cooling
(Comp 1)
Mechanical Cooling
(Comp 2)
Mechanical Cooling
(Comp 3)
Mechanical Cooling
(Comp 4)
All values have a hysteresis of 2.0° F.
If discharge air set point reset is required, when the value of
the discharge air set point is greater than the value of the return
air reset for a particular compressor, the return limit will have
to be adjusted via the BACnet tool to compensate for the de-
mand changes and release. The particular compressor stage or
the unit must be set to a single reset point and the discharge set
point reset can be adjusted as needed.
Any of the following alarms will immediately shut down all
compressor stages. Refer to the sensor section or the integra-
tion points list for default values:
• Leaving water high
• Leaving water low
• Entering later low
• Fan alarms
• Low static pressure
• Water differential pressure switch (DPS)
• Smoke
DISCHARGE AIR TEMPERATURE (DAT) SENSOR — The
DAT sensor is shipped loose in the electrical controls box com-
partment and is to be field installed in the supply duct work and
terminated on UI-6 of the I/O Flex 6126 controller.
The sensor should be installed where the air flow pattern is
laminar to avoid temperature stratification. If supplemental
heating is to be installed then the DAT sensor should be mount-
ed downstream of the discharge side of the heating coil.

HIGH DISCHARGE AIR TEMPERATURE CONDITION

(COOLING) — DAT measurements are tested for a high
limit trip above 70 F. An alarm is asserted for high discharge
air temperature under the following conditions:
• DAT is above the high limit for 5 minutes
• Fan operation asserted

• Cooling mode

• Valid DAT sensor measurement
HIGH STATIC LOCK — The controller will monitor the
static pressure high limit switch (if installed) and will incre-
ment a counter every time the static pressure switch trips. A
High Static Alarm will be generated, and will reset automat-
ically. Upon receiving the alarm 3 times, the unit will lock
out to protect the ductwork and prevent cycling of major
unit components.
If the lock state is reached in addition to the high static
alarm, code 100 will be set and broadcast over the BACnet net-
work via the Systems Status point (AV: 16).
Since the controller interprets this as an issue that needs
technical assistance, the unit can only be reset from its HMI
BACview tool.
51
50 F < RAT
RAT > 50 F (enabled)
50 F <RAT < 59°F
60 F <RAT < 69 F (adj.)
70 F <RAT < 77 F (adj.)
78 F <RAT < 83 F (adj.)
RAT > 83 F (adj.)