Unit Startup
RT-SVX24J-EN
97
Low Ambient Compressor Operation
Certain applications require compressor operation at
lower ambient conditions than standard units. Low
ambient compressor operation is a factory configured
option that allows units to operate down to -10°F by
extending the low ambient compressor lockout setpoint
range.
Standard configuration units are limited to a minimum
low ambient compressor lockout setpoint of 40° F. In
conditions below 40°F the low-pressure cutout (LPC)
switch can open in the first few minutes of initial
compressor operation due to refrigerant circulation
characteristics.To prevent nuisance LPC events at startup
in these conditions the unit controller will bypass LPC
processing for a varying period of time as defined below:
–
For ambient temps below 20°F LPC events will be
bypassed for the first 170 seconds of compressor
operation.
For ambient temps between 20° and 40°F the bypass time
reduces linearly from 170 seconds at 20°F to 0 seconds at
40°F. LPC events are not bypassed at initial compressor
start in ambient conditions above 40°F.
– An open LPC switch detected at compressor start
will result in a manual-reset compressor lockout
condition.
–
4 consecutive LPC trip occurrences after the bypass
time expires without a minimum of 3 minutes of
compressor operation between trips will result in a
manual-reset compressor lockout.
In addition to alternate LPC event processing, the second
compressor to start on each refrigerant circuit will be
disabled for 40 minutes each time a circuit starts in
ambient conditions less than 40°F. To properly maintain
head pressure control in low ambient conditions one
condenser fan on each refrigerant circuit will be controlled
by a Variable-frequency motor drive (VFD).
This fan will always be the first fan active. The VFD will
control fan speed at all times compressors are active to the
HI-adjustable Low Ambient Control Point. If head pressure
control requires additional condenser fan stages to
maintain proper Saturated CondenserTemperature within
limits they will be activated as necessary according to the
standard head pressure control fan-staging algorithm.
Units with Evaporative Condenser
Sequence of Operation
Upon a power up without water in the sump, the
condenser sump drain will be controlled to allow the sump
to hold water.The fill relay will be energized if there is a call
for mechanical cooling and if the outdoor air temperature
is greater than 10°F on units with a sump heater installed
or greater than 40°F on units without sump heat. Once the
fill solenoid is energized, the sump will begin to fill. The
minimum water level switch will close and the fill relay will
be de-energized. The sump water temperature sensor is
invalid unless the minimum water level switch is closed.
If the sump water temperature is less than the setpoint
(default is 38°F), the sump heater will be energized until
the water temperature reaches the setpoint plus 5 degrees
(43°F for default).The fill solenoid will remain closed for 20
minutes or until the water temperature is greater than 35°F.
Once a water temperature of 35°F or greater is achieved,
the fill solenoid is energized, the sump will continue to fill,
and a five minute timer is started.
When the timer expires, the compressor lockout will be
released and mechanical cooling will be allowed. Head
pressure control will be regulated by a variable speed fan
until the liquid line pressure from either circuit reaches the
upper limit, which is set on the Human Interface under the
setup menu 120°F default. The liquid line pressure is
converted to a temperature for display at the Human
Interface. When the temperature exceeds the upper limit,
the condenser sump pump will be energized. When the
sump pump is energized, water is pumped from the sump
and sprayed over the condenser coil. If the liquid line
pressure from either circuit falls below the lower limit the
sump pump will be de-energized.
When the sump pump is energized or de-energized a
change in state is observed from an auxiliary contactor to
ensure proper sump pump operation. A change in states
must be observed by the auxiliary contactor within 6
seconds of the command to change states or mechanical
cooling will be locked out on a sump pump failure causing
a manual reset diagnostic to be set.
The fill solenoid will remain energized and the water level
will be controlled by the mechanical float valve. If the
maximum level float ever closes, an information-only
diagnostic is set and the fill solenoid is de-energized.This
is an indication that the mechanical float is not adjusted
properly or a failure of the mechanical float valve has
occurred. If the maximum level input is open for two
continuous minutes, the diagnostic will be cleared and the
fill solenoid will be energized.
If the sump water temperature ever drops below 35°F, the
drain actuator will be controlled in order to drain the water
from the sump. If there is a call for mechanical cooling and
the outdoor air temp is greater than 10°F on units with
sump heat installed or greater than 40°F on units without
sump heat, the unit will be allowed to refill the sump.
0
0F
20F
40F
170
Outdoor Air Temp (
°
F)
LPC Bypass Time (sec)
Содержание SEHJ090-162
Страница 40: ...Dimensional Data 40 RT SVX24J EN Figure 13 Evaporative condenser water connection locations RIGHT SIDE VIEW ...
Страница 48: ...Installation 48 RT SVX24J EN Figure 18 Ductwork conversion ...
Страница 58: ...Installation 58 RT SVX24J EN Figure 36 5 Connected tubes 6 install panels Connected tubes 5 6 ...
Страница 75: ...Installation RT SVX24J EN 75 Figure 51 Hot water coil piping Figure 52 Steam coil piping ...
Страница 87: ...Installation RT SVX24J EN 87 Figure 57 Typical field wiring diagram for 90 to 162 ton CV control options ...
Страница 89: ...Installation RT SVX24J EN 89 Figure 59 Typical field wiring diagram for 90 to 162 ton VAV control options ...