12
RT-SVF69C-EN
Sequence of Operation
diagnostic system through the Zone Sensor or Building
Automation System will be required. Cycling unit power
will also clear the fault.
Low Ambient Operation
During low ambient operation, outside air temperature
below 40°F, the RTRM will cycle the compressors and
outdoor fan motors "Off" for approximately 3 minutes after
every 10 minutes of accumulated compressor run time.
The indoor fan motor will continue to operate during this
evaporator defrost cycle and the compressors and
outdoor fans will return to normal operation once the
defrost cycle has terminated and the compressor "Off"
time delay has been satisfied.
ReliaTel Control Cooling with
an Economizer
The economizer is utilized to control the zone temperature
providing the outside air conditions are suitable. Outside
air is drawn into the unit through modulating dampers.
When cooling is required and economizing is possible, the
RTRM sends the cooling request to the unit economizer
actuator to open the economizer damper.
The RTRM tries to cool the zone utilizing the economizer to
slightly below the zone temperature setpoint. If the mixed
air sensor (MAS) senses that the mixed air temperature is
below 53°F, the damper modulates toward the closed
position.
If the zone temperature continues to rise above the zone
temperature setpoint controlband and the economizer
damper is fully open, the RTRM energizes the modulating
eFlex compressor. If the zone temperature continues to
rise above the zone temperature setpoint controlband and
the economizer damper is fully open, the RTRM instructs
the compressor inverter drive to increase the compressor
speed to allow more compressor capacity.
If the eFlex compressor is running at its maximum
capacity and the zone temperature continues to rise above
the zone temperature setpoint controlband and the
economizer damper is fully open, the RTRM energizes the
first fixed speed compressor, while simultaneously
instructing the compressor inverter drive to decrease the
eFlex compressor capacity to allow a smooth system
capacity transition. If the zone temperature continues to
rise above the zone temperature setpoint controlband and
the economizer damper is fully open, the RTRM instructs
the compressor inverter drive to increase the eFlex
compressor speed to allow more compressor capacity.
If the eFlex compressor is running at its maximum
capacity and the zone temperature continues to rise above
the zone temperature setpoint controlband and the
economizer damper is fully open, the RTRM energizes the
second fixed speed compressor, while simultaneously
decreasing the eFlex compressor speed to allow a smooth
transition of system cooling capacity.
All compressor capacity transitions are accompanied by
corresponding IDM and ODM speed adjustments to allow
optimal unit cooling performance. The ECA continues to
modulate the economizer damper open/closed to keep the
mixed air temperature that is calculated by the RTRM.
If economizing is not possible, the ECA drives the damper
to the minimum position setpoint when the indoor fan
relay is energized and allows mechanical cooling
operation. When the unit is equipped with the optional fan
failure switch, wired to the RTOM, the RTRM will stop all
cooling functions and produce an analog output if the fan
failure switch does not open within 40 seconds after a
request for fan operation. When the system is connected
to a remote panel, the "SERVICE" LED will flash when this
failure occurs.
Economizer Set-Up
Adjusting the minimum position potentiometer located on
the unit economizer actuator (ECA) sets the required
amount of ventilation air.
Two of the three methods for determining the suitability of
the outside air can be selected utilizing the enthalpy
potentiometer on the ECA, as described below:
1.
Ambient Temperature-Controlling the economizing
cycle by sensing the outside air dry bulb temperature.
lists the selectable dry bulb values by
potentiometer setting.
2. Reference Enthalpy-Controlling the economizer cycle
by sensing the outdoor air humidity.
lists the
selectable enthalpy values by potentiometer setting. If
the outside air enthalpy value is less than the selected
value, the economizer is allowed to operate.
3. Comparative Enthalpy-By utilizing a humidity sensor
and a temperature sensor in both the return air stream
and the outdoor air stream, the unit control processor
(RTRM) will be able to establish which conditions are
best suited for maintaining the zone temperature, i.e.
indoor conditions or outdoor conditions.
The potentiometer located on the ECA is non-functional
when both the temperature and humidity sensors are
installed.
Table 11.
Potentiometer settings
Potentiometer
Setting
Enthalpy Dry
Bulb
A
27 Btu/lb (63 kJ/kg)
73°F (22.8°C)
B
25 Btu/lb (58 kJ/kg)
70°F (21.1°C)
C
(a)
(a) Factory setting
23 Btu/lb (53 kJ/kg)
67°F (19.4°C)
D
22 Btu/lb (51 kJ/kg)
63°F (17.2°C)
E
19 Btu/lb (44 kJ/kg)
55°F (12.8°C)