32
RT-SVX51H-EN
by energizing the appropriate outputs. The two-speed
indoor fan unit will only utilize two speeds during the
cooling operation modes described below.
Cooling Operation
For cooling operation, the unit will operate at Low Fan
Speed during Fan Only, Economizer Only, and the first
stage of compressor unit modes by Default. When the
unit receives a call for cooling, if the economizer is
enabled, the unit will energize the associated Low
Speed output and begin to modulate the OA Damper
open above minimum position up to 100% as
necessary. By default, the supply fan will remain at low
speed for the duration of Economizer-Only cooling. If
the supply fan is on when the first stage compressor is
energized, it will remain energized or energize at low
speed for the duration of Cool 1.
When there is a call for Cool 2, the second compressor
is energized and the Supply Fan will switch to High
Speed.
The unit will stage down compressors for cooling in
reverse order that they were staged and the supply fan
will follow the unit mode transitions. Once it is
determined through normal cooling control that the
second compressor is no longer necessary to meet
cooling demand, the second compressor will be staged
back and the supply fan will switch to Low Speed until
the unit stages all cooling off or receives a call for Cool
2 again. Once the Supply Fan is no longer requested
ON after a Cooling call is cleared, the Supply Fan will
remain energized at Low Speed for 60 seconds as on
traditional units.
If the economizer is enabled and is being utilized as the
first stage of cooling (Y1 active), if the unit receives a
Y2 request, the unit will energize the first compressor
and will switch the supply fan to high speed until the
Y2 request is cleared.
Economizer Minimum Position Handling
for 2–Speed Fan
Due to the low and high speeds of the indoor fan, when
the unit is in Fan Only, Cool 1, or Economizer Only and
the indoor fan is at low speed, the unit will not be
bringing in as much fresh air as normal. By setting a
higher minimum damper position this problem could
be solved, but that would mean more fresh air than
may be desired when the supply fan is at high speed.
To overcome these situations, the control will require
the setting of two economizer minimum positions to be
used when the fan is at low and high speed to
compensate for the lower amount of fresh air at lower
fan speeds and the potential for more fresh air than
desired at higher fan speeds. These minimum positions
will be obtained from the Bldg Design Min Position and
DCV Min Position pots on the RTEM-EM. The
economizer minimum position that will be utilized
while the supply fan is at low speed will be set with the
DCV Min Position pot with a range of 0-100% and the
minimum position that will be utilized while the supply
fan is at high speed will be set with the Building Design
Min Position pot with a range of 0-50%. If the Building
Design Min Position is set to be higher than the DCV
Min Position, the setpoints will be capped at the DCV
Min Position and the setpoint for the min position at
low and high fan speed will be the DCV Min Position.
Phase Monitor
The phase monitor is a 3 phase line monitor module
that protects against phase loss, phase reversal and
phase unbalance. It is intended to protect compressors
from reverse rotation. It has an operating input voltage
range of 190-600 Vac, and LED indicators for ON and
FAULT. There are no field adjustments and the module
will automatically reset from a fault condition.
Low Pressure Cutout
The low pressure cutouts are wired in series with the
high pressure cutouts and the temperature discharge
limits. If this circuit is open before a compressor is
started, the compressor in that circuit will not be
allowed to operate.
Anytime this circuit is opened, the compressor in that
circuit is turned off immediately.
High Pressure Cutout and Temperature
Discharge Limit
The high pressure controls and temperature discharge
limit are wired in series between the compressor
outputs on the LTB and the compressor contactors. If
the high pressure safety or temperature discharge limit
opens, the compressor on the affected circuit is turned
off.
Locking Safety Device with Compressor
Anti Short Cycle Timer
This device monitors compressor safety switch trips to
prevent short cycling, protecting the compressor. A
manual reset is required after a fourth safety switch
trip.
Coil Frost Protection
The Frostat
™
control monitors the evaporator coil
temperature to prevent the evaporator from freezing
due to low operating temperatures whenever there is a
demand for cooling. When a open circuit has occurred,
the Frostat opens the 24 Vac ground and opens all of
the cooling contactors.
Heating Operation
Standard unit operation for heating will continue on
units equipped with a two-speed indoor fan. During
heat mode, all units configured with staged electric or
gas heat will heat the supply air and space as normal
utilizing full speed indoor fan.
Содержание Foundation GBC180
Страница 50: ...50 RT SVX51H EN N No ot te es s...
Страница 51: ...RT SVX51H EN 51 N No ot te es s...
