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O O p p e e r r a a t t i i n n g g P P r r o o c c e e d d u u r r e e s s
indicated in
Figure 19, p.
they eventually either crystallize like ice or become
increasingly viscous until they fail to flow and set up
like glass. The first type of behavior represents true
freezing. The second is known as super-cooling.
Glycols do not have sharp freezing points. Under
normal conditions, propylene glycol sets to a glass-like
solid, rather than freezing.
The addition of glycol to water yields a solution with a
freezing point below that of water. This has led to the
extensive use of glycol-water solutions as cooling
media at temperatures appreciably below the freezing
point of water. Instead of having sharp freezing points,
glycol-water solutions become slushy during freezing.
As the temperature falls, the slush becomes more and
more viscous and finally fails to flow.
Table 8. Freeze and burst protection chart
Water/Glycol
Freeze
Temperature
Protection
20 °F (-7 °C)
18% glycol mixture
10 °F (-12 °C)
29% glycol mixture
0 °F (-17.8 °C)
36% glycol mixture
-10 °F (-23 °C)
42% glycol mixture
-20 °F (-29 °C)
46% glycol mixture
The precise concentration of glycol for a particular
chiller is affected by several key factors such as
ambient temperature extremes, entering and leaving
water temperatures, and chiller size. A chiller's
optimum glycol concentration is modified by these
considerations as reflected in
capacity correction factors are the "best informed
estimates" for chillers with copper evaporators. The
percentages may vary depending on the materials and
alloys of the heat exchangers, total surface area, the
amount of present or future fouling, and the brand of
glycol used.
40
40. When liquids are cooled
Burst Protection
12% glycol mixture
20% glycol mixture
24% glycol mixture
28% glycol mixture
30% glycol mixture
Table 7, p.
39. These
The calculations in this table are most accurate for
Dowfrost (propylene glycol) and Dowtherm (ethylene
glycol) branded products. Consult your local supplier
or engineering contractor for more precise
recommendations.
Storage Provisions
The chiller controls are designed for storage in ambient
temperatures from -20 °F (-29 °C) to 145 °F (63 °C) with
relative humidity from 0% to 100%. The glycol should
be removed from the chiller if the unit is to be stored
for extended periods. Although fluids can be drained
via the plug in the bottom of the evaporator, the
inhibitors in an approved glycol solution will best
protect the surfaces of the evaporator against oxidation
if the glycol remains inside the chiller during storage.
Figure 19. Water/Glycol concentration freezing
points (in degrees fahrenheit)
ARTC-SVX001B-EN
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