Aqua-Hot 375-d Service Manual page 14

Freeze Point and Burst Point:
Antifreeze lowers the freezing point of any liquid, to which it
has been added, by preventing the formation of ice crystals;
however, as the ambient temperature continues to decline,
the water in the solution will attempt to attain a solid state.
The point in which the water begins to solidify is termed the
"Freeze Point." Although the water in the solution has be-
gun to freeze, producing a "slushy" consistency, the anti-
freeze in the solution will continue to combat the normal
expansion of the solution as it freezes. The point in which
the solution can begin to expand, due to colder temperatures,
is called the "burst point." Once the solution reaches the
burst point, the potential is present for ruptured pipes to ex-
ist. The burst point of the antifreeze and water heating solu-
tion is dependent upon the brand of propylene glycol em-
ployed.
Boiling Point:
The Aqua-Hot utilizes the antifreeze and water heating solu-
tion as a transportation means for the heat produced from the
internal processes. The antifreeze absorbs the heat created
until its boiling point is reached; it is at this point that the
liquid turns to a gas and is expelled to prevent the heating
system from overheating. Each time the boiling point is
reached, a loss of efficiency occurs because the heat pro-
duced is expelled rather than used for the function of the
heating system. Therefore, a higher boiling point is desired
in order to combat the loss of efficiency, which allows the
antifreeze to transport the heat created from the internal pro-
cess throughout the motorhome where it can be used produc-
tively rather than dissipating due to its change from a liquid
to a gas.
Rust and Anti-Corrosive Inhibitors:
Another major function of antifreeze is to provide protection
to the internal metal components of the Aqua-Hot hydronic
heating system from corrosion and rust. Antifreeze is able to
perform this function by the addition of rust- and anti-
corrosive inhibitors, which are designed specifically to acti-
vate in a water solution.
Summary:
Antifreeze has three basic functions: freeze protection, boil-
over protection, and anti-corrosion and rust protection.
© 2009 Aqua-Hot
S 1: I
ECTION NTRODUCTION TO THE
Antifreeze is also primarily responsible for heat transfer
characteristics. Therefore, as water is an excellent heat con-
ductor, it is added to the mixture. A 50/50 solution of pro-
pylene glycol antifreeze and water is recommended to pro-
vide the best performance combination of the aforemen-
tioned functions. If excess propylene glycol exists within an
antifreeze and water heating solution, the water's heat ab-
sorption properties are compromised, which could ultimately
inhibit the Aqua-Hot from providing adequate domestic hot
water and interior heating.
Additionally, if the antifreeze and water heating solution
contains over 70 percent antifreeze, the freezing point is ac-
tually raised, resulting in less freeze protection.
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375D Hydronic Heating System Service Manual—Rev. A
A -H 375D
QUA OT
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