Trane IntelliPak SCRF 25, Installation, Operation And Maintenance Manual

Page: 59 / 120

SCXF-SVX01Q-EN 59
Units With Economizer
If the entering condenser water temperature (units with
a WSE) or the outside air enthalpy (units with an ASE)
is appropriate to use “free cooling,” the economizer
will attempt to satisfy the cooling zone temperature
setpoint.
N No otte e:: When using an ASE with economizer enabled, O/
A temperature enable can be used instead of
comparative enthalpy if the O/A temperature
falls below the economizer setpoint.
Then compressors will stage on as necessary to
maintain supply air temperature setpoint, which is
user-defined at the HI. Minimum on/off timing of
compressors prevents rapid cycling.
When both airside and waterside economizers are on a
single unit, priority must be set at the HI. The
economizer with the highest priority attempts cooling
first. Once it is operating at its maximum, and if
additional cooling is necessary, the other economizer
enables before mechanical cooling begins.
Cooling/Waterside Economizer
Waterside economizing enables when the unit’s
entering water temperature is below the unit’s entering
mixed air temperature by 4°F plus the user adjustable
economizer approach temperature. The approach
temperature default is 4°F.
Waterside economizing disables when the unit’s
entering water temperature is not below the unit’s
entering mixed air temperature by at least the water
economizer approach temperature (default value of 4°
F).The economizer acts as the first stage of cooling. If
the economizer is unable to maintain the zone (CV
units) or supply air (VAV units) temperature setpoint,
the compressor module will bring on compressors as
required to meet the setpoint.
Cooling/Airside Economizer
On units with an airside economizer, a call for cooling
will modulate the fresh air dampers open. The rate of
economizer modulation is based on deviation of the
zone temperature from setpoint; i.e., the further away
from setpoint, the faster the fresh air damper will open.
The first stage of cooling will start after the economizer
reaches full open.
N No otte e:: The airside economizer will only function freely if
ambient conditions are below the enthalpy
control settings or below the return air enthalpy
if unit has comparative enthalpy installed. If
outside air is not suitable for “economizing,” the
fresh air dampers drive to the minimum open
position. A field adjustable, factory default
setting at the HI panel or Tracer Summit can
provide the input to establish the minimum
damper position.
When outdoor air conditions are above the setpoint or
comparative enthalpy control setting, only mechanical
cooling will function and outside air dampers will
remain at their minimum position.
Mechanical Cooling
If the zone temperature cannot be maintained within
the setpoint deadband using the economizer option or
if there is no economizer, the RTM sends a cooling
request to the MCM. The compressor module checks
the compressor protection circuit before closing stage
one. After the first functional stage starts, the
compressor module monitors the saturated refrigerant
temperature and closes the condenser fan output
contact when the saturated refrigerant temperature
rises above the lower limit setpoint.
Air-Cooled Units Only
The compressor module closes the condenser fan
output contact when the saturated refrigerant
temperature rises above the lower limit setpoint.
Water-Cooled Units Only
The WSM modulates the condenser coil water valves
to maintain condenser temperature, if applicable.
Otherwise, it will check the entering condenser water
temperature to ensure it is greater than 54°F or if not, it
will lock out cooling.
Auto Changeover (Units with Heat Only)
When the system mode is in auto, the mode will
change to cooling or heating as necessary to satisfy the
zone cooling and heating setpoints. The zone cooling
and heating setpoints can be as close as 2°F (1.1°C).
Occupied Zone Temperature—Heating
Relies on input from a sensor directly in the space,
while a system is in occupied heating mode or an
unoccupied period, to stage electric heat on and off or
modulate the hydronic heating valve as required to
maintain the zone temperature within the heating
setpoint deadband. The supply fan will operate when
there is a request for heat.
Electric Heat
On units with electric heat, the zone temperature can
be controlled to a heating setpoint during the occupied
mode by cycling a single stage electric heater. An
interface can be provided for field supplied electric heat
(up to three stages).The zone temperature heating
setpoint and deadband are user defined at the HI panel.
Hydronic Heat: Hot Water or Steam
On units with hot water or steam heating, the zone
temperature can be controlled to a heating setpoint
during the occupied mode. The zone temperature
heating setpoint and deadband are user defined at the
HI panel or zone sensor. VAV occupied heating initiates
by closing a field-supplied switch or relay contacts
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