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Operating Procedures
Prevent Freezing
Many liquids expand in volume upon cooling. This
expansion may cause pipes and other enclosed systems
containing a liquid to rupture or burst when exposed to low
temperature conditions. Burst protection is needed to
protect piping and other enclosed systems when they are
inactive as they could rupture due to expansion during cold
weather or low refrigerant pressure.
Freeze points and burst points of glycol-water solutions are
shown in
Table 11, p.
44.
In order to maintain a high quality glycol solution, the water
used in the glycol mixture must have very few impurities.
Impurities in the water can increase metal corrosion,
aggravate pitting of cast iron and steel, reduce the
effectiveness of the corrosion inhibitors, and increase the
depletion rate of the inhibitor package.
To assure inhibitor effectiveness, the levels of chlorides
and sulfates in the water should not exceed 25 ppm each.
The total hardness in terms of calcium carbonate should be
less than 100 ppm. For best long-term results, de-ionized
or distilled water is recommended. Trane can provide
concentrated solutions of Dowfrost, propylene glycol, or
premixed solutions for use with the heat pump.
NOTICE
Equipment Damage!
Failure to follow instructions below could result in
permanent damage to pump and internal cooling
surfaces.
Do not use automotive antifreeze.
Propylene Glycol
Glycol-based fluids provide such burst protection in water
solutions due to their low freezing points. As a glycol-based
fluid cools below the solution's freezing point, ice crystals
begin to form, and the remaining solution becomes more
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 heat pump. If the concentration of glycol is sufficient,
no damage to the heat pump from fluid expansion should
occur within the temperature range indicated in
p.
45. 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
supercooling. 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
44
temperature falls, the slush becomes more and more
viscous and finally fails to flow.
Table 11. Freeze and burst protection chart
Water/Glycol
Temperature
20°F (-7°C)
10°F (-12°C)
0°F (-17.8°C)
-10°F (-23°C)
-20°F (-29°C)
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
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.
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 BPHE, 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 22,
Freeze Protection
18% glycol mixture
29% glycol mixture
36% glycol mixture
42% glycol mixture
46% glycol mixture
Table 10, p.
43. These capacity correction
Burst Protection
12% glycol mixture
20% glycol mixture
24% glycol mixture
28% glycol mixture
30% glycol mixture
ARTC-SVX009A-EN
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