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concentrated in glycol. This ice/water/glycol mixture results
in a flowable slush, and remains fluid, even as the
temperature continues to cool.
The fluid volume increases as this slush forms and the
temperature cools, flowing into available expansion volume
in the chiller/heat pump. If the concentration of glycol is
sufficient, no damage to the chiller/heat pump from fluid
expansion should occur within the temperature range
indicated in
Figure 23, p.
51. When liquids are cooled 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 17. Freeze and burst protection chart
Water/Glycol
Freeze Protection
Temperature
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/
heat pump is affected by several key factors such as
ambient temperature extremes, entering and leaving water
temperatures, and chiller/heat pump size. A chiller/heat
pumps optimum glycol concentration is modified by these
considerations as reflected in
capacity correction factors are the best informed
ARTC-SVX010A-EN
Burst Protection
12% glycol mixture
20% glycol mixture
24% glycol mixture
28% glycol mixture
30% glycol mixture
Table 16, p.
50. These
estimates for chiller/heat pump 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/heat pump 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/heat pump 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/heat pump during storage.
Figure 23. Water/Glycol concentration freezing points
(in degrees fahrenheit)
Operating Procedures
51
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