Operating Procedures
ARTC-SVX005A-EN 49
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.
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.
The precise concentration of glycol for a particular chiller/
heater is affected by several key factors such as ambient
temperature extremes, entering and leaving water
temperatures, and chiller/heater size. A chiller’s optimum
glycol concentration is modified by these considerations
as reflected in above Table 10, p. 48. These 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.
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.
Table 11. Freeze and burst protection chart
Water/Glycol
Temperature Freeze Protection Burst Protection
20 °F (-7 °C) 18% glycol mixture 12% glycol mixture
10 °F (-12 °C) 29% glycol mixture 20% glycol mixture
0 °F (-17.8 °C) 36% glycol mixture 24% glycol mixture
-10 °F (-23 °C) 42% glycol mixture 28% glycol mixture
-20 °F (-29 °C) 46% glycol mixture 30% glycol mixture
Figure 28. Water/Glycol concentration freezing points (in degrees fahrenheit)
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