
217
FORM 160.54-M1
ISSUE DATE: 10/25/2019
JOHNSON CONTROLS
JCI COMPANY CONFIDENTIAL
24
SECTION 24 - SMART FREEZE PROTECTION
The smart freeze feature prevents nuisance chiller
shutdowns due to brief periods of chilled liquid flow
fluctuations or other brief operating conditions that
would normally cause LOW EVAPORATOR PRES-
SURE safety shutdowns. With this feature enabled
and activated, the chiller is permitted to ride through
these temporary conditions. Also, this feature allows
the Leaving Chilled Liquid Temperature setpoint to be
set as low as 36.0°F. Smart Freeze protection can be
enabled or disabled at the keypad, by a Service techni-
cian, using a procedure detailed in
TEM CALIBRATION, SERVICE SETPOINTS, AND
of this manual. It cannot be
used in brine cooling mode.
The basis of this feature is that the chilled liquid con-
tains an amount of heat, which cannot be eliminated
immediately. Therefore, it requires a certain amount
of time for the liquid to change to a solid. During this
period of time, those parameters that determine when
solidification will occur, are evaluated and the appro-
priate Low Evaporator Temperature shutdown thresh-
old is applied. This threshold could be lower, but not
higher than the normal safety threshold.
Smart Freeze protection uses the Evaporator Refriger-
ant Temperature as one of the variables to determine
when freezing is imminent. If the chiller is equipped
with the Evaporator Refrigerant Temperature Sensor
(RT7), and the sensor is enabled using
- SYSTEM CALIBRATION, SERVICE SETPOINTS,
is used as the refrigerant temperature. Otherwise, the
Evaporator Saturation Temperature (as derived from
the output of the Evaporator Pressure Transducer. The
pressure is converted to a temperature via the appropri-
ate refrigerant “pressure/temperature lookup table”) is
used as the refrigerant temperature.
When Smart Freeze protection is enabled, the Leaving
Chilled Liquid Temperature setpoint can be set as low
as 36.0°F. If set to less than 38.0°F, the Leaving Chilled
Liquid – Low Temperature cycling shutdown threshold
becomes a minimum of 34.0°F.
Unless Smart Freeze protection is activated, the fixed
Low Evaporator Pressure Safety thresholds (R22 – 54.3
psig, 29.6°F) (R-134a – 25.0 psig, 28.7°F) are used.
Smart Freeze protection is activated only when the fea-
ture is enabled AND the Leaving Chilled Liquid Tem-
perature setpoint is less than 38°F. Once activated, the
total number of seconds that the Evaporator Refrigerant
Temperature is below the freeze threshold is counted.
The freeze threshold is 32.8°F (refrigerant temperature
sensor RT7) or 34.0° (evaporator saturation tempera-
ture See Note 1 below.). The count is incremented
once for every second the Evaporator Refrigerant
Temperature is below the freeze threshold and decre-
mented once for every second it is above the freeze
threshold (but is never decremented below zero). Thus
if the Evaporator Refrigerant Temperature goes below
the freeze threshold for 30 seconds, then goes above
it for 10 seconds, then goes below the threshold for 5
seconds, the total number of seconds the Evaporator
Refrigerant Temperature was below the freeze thresh-
old was 25 seconds. If Smart Freeze is no longer acti-
vated due to the Leaving Chilled Liquid Temperature
setpoint being raised to greater than or equal to 38.0°F,
the total number of seconds being tracked is set to zero.
The number of seconds it will take the chilled liquid to
freeze is based on how far the Evaporator Refrigerant
Temperature is below the freeze threshold as follows:
A=
B
4053.7
Where: A = Number of seconds to freezing
B = (freeze threshold – evaporator refrigerant
temperature)
Thus, if the Evaporator Saturation Temperature is be-
ing used as the Evaporator Refrigerant Temperature
and that temperature is 26.0°F, it would take 8 minutes
and 26 seconds for the chilled liquid to freeze.
When the total number of seconds the Evaporator Re-
frigerant Temperature is below the freeze threshold ex-
ceeds the “Number of seconds to freezing”, a safety
shutdown is performed and EVAPORATOR – LOW
PRESSURE – SMART FREEZE is displayed on the
System Details line of the display.
Even though Smart Freeze protection is enabled and
activated, the Pre-Rotation Vanes Load Inhibit still oc-
curs at the same thresholds as with normal operation;
inhibit at 56.2 psig (R22) and 27.0 psig (R-134a). As