Table of Contents
Advertisement
The Smart Freeze feature prevents nuisance chill er
shut downs due to brief periods of chilled liquid fl ow
fl uc tu a tions or other brief operating conditions that
would nor mal ly cause Low Evaporator Pressure Safe ty
shut downs. With this feature enabled and activated, the
chiller is per mit ted to ride through these temporary con-
di tions. Also, this feature allows the Leaving Chilled
Liquid tem per a ture Setpoint to be set as low as 36.0ºF.
Smart Freeze protection can be enabled or dis abled at
the Key pad, by a Service Technician, using a pro ce dure
de tailed in the "System Calibration, Service Setpoints
and Reset Procedures" section of this book. 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 im me -
di ate ly. Therefore, it requires a certain amount of time
for the liquid to change to a solid. During this pe ri od
of time, those pa ram e ters that determine when so lid i f-
i ca tion will occur, are evaluated and the ap pro pri ate Low
Evaporator Temperature shutdown threshold is applied.
This threshold could be lower, but not high er than the
normal Safety threshold.
Smart Freeze protection uses the Evaporator Re frig -
er ant Tem per a ture as one of the variables to de ter mine
when freez ing is imminent. If the chiller is equipped with
the Evap o ra tor Refrigerant Tem per a ture Sensor (RT7),
and the sensor is enabled using the "Sys tem Calibration,
Ser vice Setpoints and Reset Pro ce dures" section of this
book, this value is used as the re frig er ant temperature.
Oth er wise, the Evaporator Sat u ra tion Temperature (as
de rived from the output of the Evap o ra tor Pressure
Trans duc er. The pressure is con vert ed to a tem per a ture
via the ap pro pri ate re frig er ant "pres sure/tem per a ture
look up ta ble") is used as the re frig er ant tem per a ture.
When Smart Freeze protection is Enabled, the Leav ing
Chilled Liq uid Temperature Setpoint can be set as low
as 36.0ºF. If set to < 38.0ºF, the LEAVING CHILLED
LIQ UID – LOW TEMPERATURE cy cling shut down
thresh old becomes a minimum of 34.0ºF.
Unless Smart Freeze protection is activated, the fi xed
Low Evap o ra tor Pressure Safety thresholds (R22 – 54.3
PSIG, 29.6ºF) (R134a – 25.0 PSIG, 28.7ºF) are used.
YORK INTERNATIONAL
SECTION 21
SMART FREEZE PROTECTION
SMART FREEZE protection is activated only when
the feature is enabled AND the Leaving Chilled Liquid
Tem per a ture Setpoint is < 38ºF. Once activated, the
total num ber of seconds that the evaporator refrigerant
tem per a ture is below the freeze threshold is counted.
The freeze thresh old is 32.8ºF (refrigerant temp. sen-
sor RT7) or 34.0º (evap o ra tor saturation temp. See
Note 1 below.). The count is incremented once for every
second the evap o ra tor re frig er ant tem per a ture is below the
freeze thresh old and decremented once for ev ery second
it is above the freeze threshold (but is never decremented
below zero). Thus if the evaporator re frig er ant temperature
goes be low the freeze threshold for 30 seconds, then goes
above it for 10 sec onds, then goes be low the threshold for 5
seconds, the total number of sec onds the evaporator re frig -
er ant tem per a ture was below the freeze threshold was 25
sec onds. If Smart Freeze is no longer activated due to the
Leaving Chilled Liquid Tem per a ture Setpoint being raised
to > 38.0ºF, the total num ber 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:
Number of seconds to freezing =
(freeze thresh old–evaporator refrigerant tem per a ture)
Thus, if the Evaporator Saturation Temperature is be ing
used as the evaporator refrigerant temperature and that
temperature is 26.0ºF, it would take 8 minutes and 26
seconds for the chilled liquid to freeze.
When the total number of seconds the evaporator
re frig er ant 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
ac ti vat ed, the Pre-rotation Vanes Load inhibit still oc curs
at the same thresholds as with normal op er a tion; in hib it
at 56.2 PSIG (R22) and 27.0 (R134a). As in nor mal
op er a tion, loading will be allowed when the pres sure
in creas es to 57.5 PSIG (R22) and 28.0 PSIG (R134a).
FORM 160.54-M1(503)
4053.7
21
129
Advertisement
Table of Contents
