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• Most ULT freezers that are designed for
environments having a maximum humidity
of 80% and 32°C maximum ambient air
temperature. ULT freezers typically make use
of air-cooled condensers, so if the ambient
temperature is too high, cooling eciency
is degraded. Avoid placing a ULT freezer in
an area exposed to direct sunlight, or in an
enclosed area without adequate ventilation.
If it is necessary to place freezers closer than
10 cm in an enclosed area, water cooled
condensers may be needed.
• Oil logging, or ice build-up in the refrigerant,
can become an issue in ULT freezers. In the
mid-1980’s, almost every ULT freezer had
this problem due to paran wax-based oils.
This type of wax was prone to solidify in
capillary tubes. Wax-free synthetic oils largely
eliminated this problem. However, ice can still
form in capillary tubes for other reasons.
• To prevent oil logging, manufacturers use
heaters inside the capillary tubes to prevent
oil from becoming too cold. Oil can also be
run through separators outside of the system
to remove ice and reduce maintenance down
time due to oil logging.
What facilities concerns are there?
• ULT freezers need chilled process water,
reliable power, and vacuum.
• High quality freezers provide a manual way for
operators to release the door when vapor lock
occurs, with a vacuum release valve
• Higher end freezers also need data ports
to communicate logged data or for remote
temperature sensing, and some need battery
backup power.
• Freezers located in areas with seismic activity
have brackets that secure the unit to the walls.
• The proper power source is important, as well
as correct receptacles in the area where the
ULT freezer is located. Most are 208V-2230V
at 60 Hz, 15Amp single-phase circuits, but
some customers need 115V with 20Amp
single-phase circuits. Very few freezers are
able to maintain even -57C° at 115V and
15Amp, the exception being small, low
interior volume freezers.
• Some ULT freezers provide voltage boosters,
for buildings that provide less than the rated
220V in the USA or 230V in Europe. There is
a greater need for voltage boosters in the
United States where it is common to have
208V available, instead of 220V. A freezer
compressor will fail much more quickly if run
at lower than correct voltage. The voltage
booster can lengthen the life of a compressor.
