Freeze Avoidance - Trane IntelliPak Installation, Operation And Maintenance Manual

General Information
mounted in the filter section just above the exhaust
damper actuator and is connected to the ECEM (1U52).
Field supplied pneumatic tubing must be connected
between the space being controlled and the transducer
assembly.
Morning Warm-Up - Zone Heat (CV and VAV)
When a system changes from an unoccupied to an
occupied mode, or switches from STOPPED to AUTO, or
power is applied to a unit with the MWU option, the heater
in the unit or external heat will be brought on if the space
temperature is below the MWU setpoint.The heat will
remain on until the temperature reaches the MWU
setpoint. If the unit is VAV, then the VAV box/unocc relay
will continue to stay in the unoccupied position and the
VFD output will stay at 100% during the MWU mode.When
the MWU setpoint is reached and the heat mode is
terminated, then theVAV box/unocc relay will switch to the
occupied mode and the VFD output will be controlled by
the duct static pressure. During Full Capacity MWU the
economizer damper is held closed for as long as it takes to
reach setpoint. During Cycling Capacity MWU the
economizer damper is allowed to go to minimum position
after one hour of operation if setpoint has not been
reached.
Compressor Motor Winding Thermostats
CSHD compressors (20-70 Ton) Air-Cooled and (24-
80 Ton) Evaporative Condensers
The compressors contains an internal line break overload
which stops the compressors under a number of operating
conditions that cause excessive motor temperature.These
include rapid cycling, loss of charge, abnormally high
suction temperatures, excessive amperage, phase loss
and low voltage
CSHN Compressors (75 - 130 Ton) Air-Cooled and
(89 Ton) Evaporative Condensers
PTC sensors are embedded in the motor windings of each
Scroll compressor.These sensors are wired to the
protection module which protects the motor from over
temperature that can occur under a number of abnormal
operating conditions.These include rapid cycling, loss of
charge, abnormally high suction temperatures, low
voltage and excessive amperage.
During a request for compressor operation, if the
Compressor Module (SCM) detects a problem outside of
normal parameters, it turns any operating compressor(s)
in that circuit "Off" , locks out all compressor operation for
that circuit, and initiates a manual reset diagnostic.
VZH Variable Speed Compressors
Over current and over torque protection for VZH
compressors are provided by theTRV200 inverter. VZH
over temperature protection is not required.
18

Freeze Avoidance

Freeze Avoidance is a feature which helps prevent freezing
of hydronic heat coils and avoiding nuisance hydronic
heat freezestat trips.This is accomplished by opening
inactive hydronic heat valve(s) at low ambient
temperatures.
Typically, when the unit is in a mode where the supply fan
is off, the OA temperature is monitored. If it falls below 45
ºF (5 degrees above the freezestat), the hydronic heat
valve(s) are opened to the Standby Freeze Avoidance
Position. When the OA temperature rises above 47 ºF ,
occupied mode is requested, or the supply fan is
requested ON the hydronic heat valve(s) release to normal
control.
When the supply fan is commanded on, the OA dampers
will remain closed for one minute to remove the heat from
the hydronic heating coil.This prevents freezestat trips
and falsely loading the supply air temperature causing
premature compressor operation.This function is
disabled if the Standby Freeze Avoidance Position is set to
0%.
Supply Air Temperature Low Limit
Uses the supply air temperature sensor input to modulate
the economizer damper to minimum position in the event
the supply air temperature falls below the occupied
heating setpoint temperature.
Freezestat (4S12)
This is a binary input device used on units with Hydronic
Heat. It is mounted in the heat section and connected to the
Heat Module (1U50). If the temperature of the air entering
the heating coil falls to 40°F , the normally open contacts on
the freezestat closes signalling the Heat Module (1U50)
and the Rooftop Module (RTM) to:
• Drive the Hydronic Heat Actuator (4U15) to the full
open position.
• Turn the supply fan "Off" .
• Closes the outside air damper;
• Turns "On" the SERVICE light at the Remote Panel.
• Initiates a "Freezestat" diagnostic to the Human
Interface.
High Duct Temp Thermostats (Optional 3S16,
3S17)
These are binary input devices used with a Trane
Communication Interface Module (TCI).They provide
"high limit" shutdown of the unit and requires a manual
reset.They are factory set to open if the supply air
temperature reaches 240°F , or the return air temperature
reaches 135°F . Once tripped, the thermostat can be reset by
pressing the button located on the sensor once the air
temperature has decreased approximately 25°F below the
cutout point.
RT-SVX36K-EN