RLC-SVX19J_SHORT-GB
22
Freeze Protection
Depending on the ambient temperature the unit may be
exposed to freeze, there are multiple options for freeze
protection. They are listed in order of highest ambient
(least freeze protection) to the lowest ambient (most
freeze protection).
For all chiller running with water under cold ambient
temperature (below 0°C), it is extremely important to
keep full water fl ow in the evaporator for an extended
time after last compressor stops. This will protect
evaporator tube from freezing by refrigerant migration.
This is why evaporator water pump output relay must
be used to control the chilled water pump. This is not
mandatory if glycol is used with protection down to
lowest ambient expected.
1. Water pump and heaters
a. Heaters are factory installed on water boxes and
evaporator shell. They will protect it from freezing
in ambient temperatures down to -20°C.Heaters are
installed on the water piping and on the pumps of
units equipped with hydraulic module.
b. Install heat tape on all water piping, pumps, and other
components that may be damaged if exposed to
freezing temperatures. Heat tape must be designed
for low ambient temperature applications. Heat tape
selection should be based on the lowest expected
ambient temperature.
c. Tracer™ UC800 controller can start the pump(s) when
freezing conditions are detected. For this option the
pumps must be controlled by the RTAF unit and this
function validated on the chiller controller.
d. Water circuit valves need to stay open at all times.
Note:
Water pump control and heater combination will
protect the evaporator down to any ambient temperature
provided power is available to the pump and the UC800
controller. This option will NOT protect the evaporator
in the event of power failure to the chiller unless backup
power is supplied to the necessary components.
Note:
When no chiller operation is possible and the pump
is already off, UC800 pump control function for freeze
protection will command the pump to turn on:
• ON if the average of the evaporator entering water
temperature, evaporator leaving temperature, and the
evaporator refrigerant pool temperature is less than
Low Evaporator Refrigerant Temperature Cutout (LERTC)
+ 2.2°C for a period of time
• OFF again if the evaporator refrigerant pool temperature
rise above LERTC + 3.3°C for a period of time
Note:
The period of time referenced for ON and OFF
conditions above described is dependent on past running
conditions and present temperature measured.
• ON if entering OR leaving water temperature < LWTC
for 16.2°C-sec
• OFF again if water temperature > LWTC for 30 min
OR
2. Freeze inhibitor
a. Freeze protection can be accomplished by adding
suffi cient glycol to protect against freezing down to the
lowest ambient expected.
b. See “evaporator glycol requirement” section for
guidance on determining the glycol concentration.
Note:
Use of glycol type antifreeze reduces the cooling
capacity of the unit and must be considered in the design
of the system specifi cations.
OR
3. Drain water circuit
For ambient temperatures below -20°C and for those
installation not including either option 1 or 2 above
described
a. Shut off power supply to unit and to all heaters.
b. Purge the water circuit
c. Blow out the evaporator to ensure that no liquid is left
inside the evaporator and the water lines. Drain the
pump.
CAUTION! Evaporator damage!
If insuffi cient concentration or no glycol is used, the
evaporator water pumps must be controlled by the
UC800 to avoid severe damage to the evaporator due
to freezing. A power loss of 15 minutes during freezing
can damage the evaporator. It is the responsibility of the
installing contractor and/or the customer to ensure that a
pump will start when called upon by the chiller controls.
Please consult the table named “Recommended Low
Evaporator Refrigerant Cutout (LRTC) and % Glycol for
RTAF chillers”.
With factory-fi tted disconnect switch option, evaporator
trace heating is taken from the live side of the isolator.
As a consequence, the heaters are energized as long as
the main switch is closed. Supply voltage to the heating
tapes is 400V.
Avoid the use of very low or near minimum chilled fl uid
fl ow rates through the chiller. Higher velocity chilled fl uid
fl ow reduces freeze risk in all situations.
Flow rates belowpublished limits have increased
freeze potential and have not been considered by freeze
protection algorithms.
• Avoid applications and situations that result in a
requirement for rapid cycling or repeated starting and
stopping of the chiller. Keep in mind that chiller control
algorithms may prevent a rapid compressor restart
after shutting down when the evaporator has been
operating near or below the LERTC limit.
•
Maintain refrigerant charge at appropriate levels. If
charge is in question, contactTrane service. A reduced
or low level of charge can increase the likelihood of
freezing conditions in the evaporator and/or LERTC
diagnostic shutdowns.
The warranty will be void, in case of freezing due to the
lack of use of either of these protections.
Evaporator Waterside
