Trane Arctic Thermafit AXM, Installation, Operation And Maintenance Manual

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38 ARTC-SVX006A-EN
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
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
The precise concentration of glycol for a particular heat
pump is affected by several key factors such as ambient
temperature extremes, entering and leaving water
temperatures, and heat pump size. A heat pump’s optimum
glycol concentration is modified by these considerations as
reflected in
Table 7, p. 37 . These capacity correction
factors are the “best informed estimates” for heat pump
with copper load heat exchangers. 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.
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 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 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 brazed plate heat
exchanger, the inhibitors are an approved glycol solution
will best protect the surfaces of the load heat exchanger
against oxidation if the glycol remains inside the heat pump
during storage.
Figure 18. Water/Glycol concentration freezing points
(in degrees fahrenheit)
Operating Procedures