DEFROSTING
LOW TEMP
GENERAL
Periodic defrosting to keep the coil free of frost is accomplished
automatically by a time clock used in conjunction with an electric
or hot gas defrost.
For best results, temperature termination of defrost is strongly
recommended on Zero Zone cases.
DEFROST SETTINGS AND CONTROLS
Electric Defrost
Frequency: One electric defrost per day is recommended.
Time of day: Nighttime defrosting is preferred to avoid periods of
shopping or stocking.
Drip Time: Electric defrost does not require any drip time because
Zero Zone provides a built-in fan delay thermostat.
Electric Defrost Fail-safe Times:
ICE CREAM
FROZEN
FOOD
VZ 30" Door 1/day at 45 mins 1/day at 45 mins
VZT2 30" Door 1/day at 55 mins 1/day at 55 mins
MZ 24" Door & WA 1/day at 54 mins 1/day at 54 mins
At ASHRAE test conditions and 208 volt defrost heater operation,
the typical observed VZ 30" door defrost durations are 28 minutes
for ice cream and 19 minutes for frozen food. At the same
conditions, the typical observed VZT2 30" door defrost durations
are 39 minutes for ice cream and 26 minutes for frozen food. MZ
24" and WA defrost durations are 43 minutes.
Preferred Termination: For optimal performance, Zero Zone
recommends a temperature-terminated defrost, using a defrost
termination thermostat or probe sensing the coil temperature.
The VZ and VZT2 30" door case has the probe located at the
right-hand side of the coil in the center of the bottom row of tubes.
The MZ 24" door and WA case has the probe located at the right-
hand side of the coil in the top row of tubes.
If the case is so equipped, the defrost termination temperature is
50°F. Zero Zone provides a defrost termination thermostat unless
a control system defrost probe is requested.
Temperature termination based on coil temperature allows the
length of defrost to vary depending on how much frost is on
the coil and the defrost heater voltage. Coil frost is a function of
shopping patterns, stocking habits, general door maintenance and
ambient temperature and humidity. More frost requires a longer
defrost. A lower defrost heater voltage extends the defrost period.
Alternate Termination: If it is not possible to terminate the defrost
cycle based on a defrost termination thermostat or probe sensing
the temperature at the coil, and the only available temperature
probe is sensing the discharge air temperature, then the
termination temperature should be set to 65°F, zero minutes drip
time.
Zero Zone electric defrost freezers are delivered with the defrost
thermostat open-on-rise contacts wired in series with the defrost
heaters. Unless the installer rewires the defrost thermostat, the
defrost heater is de-energized when defrosting is complete.
Zero Zone VZ and VZT2 30" door electric defrost freezers are also
equipped with a high-limit, snap-disc thermostat that de-energizes
the defrost heater if the coil temperature exceeds 85°F to provide
a secondary safety termination.
Hot Gas Defrost
Frequency: One hot gas defrost per day is recommended.
Time of day: Nighttime defrosting is preferred to avoid periods of
shopping or stocking.
Drip time: Hot gas defrost requires a 5 minute drip time.
Hot Gas Defrost Fail-safe Times:
ICE CREAM
FROZEN
FOOD
Hot Gas
1/day at 30 mins
5 min drip
1/day at 30 mins
5 min drip
Reduced
Temperature Gas
1/day at 40 mins
5 min drip
1/day at 40 mins
5 min drip
MZ 24" Door & WA 1/day at 54 mins 1/day at 54 mins
Preferred Termination: For optimal performance, Zero Zone
recommends a temperature-terminated defrost, using a defrost
termination thermostat or probe attached to the dump line.
At ASHRAE test conditions, termination ranges from 12-22
minutes.
If the cases are so equipped, the defrost termination is 65°F at the
dump line. Zero Zone provides a defrost termination thermostat
unless a control system defrost probe is requested.
Defrosting - Low Temp • 39
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