Aqua-Hot 375D, Installation Manual

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© 2008 Aqua-Hot® 375-D Hydronic Heating System Installation Manual Rev. A
E-1
The following information addresses the process of
selecting an antifreeze and water mixture ratio that pro-
vides adequate freeze, boiling, and rust/anti-corrosive
protection. A 50/50 mixture ratio is recommended,
which will result in a freeze point of approximately
-28ºF and a boil point of approximately 222ºF.
The following information should be utilized for the
purpose of clarifying some terms commonly associated
with antifreeze.
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 at-
tempt 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 begun to freeze,
producing a “slushy” consistency, the antifreeze in the
solution will continue to combat the normal expansion
of the solution as it freezes. The point in which the so-
lution 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 exist. The burst point of the antifreeze and
water heating solution is dependent upon the brand of
propylene glycol employed.
Boiling Point:
The Aqua-Hot utilizes the antifreeze and water heat-
ing solution 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 produced
is expelled rather than utilized 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 process throughout the motorhome where
it can be utilized productively 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 activate in a water solution.
Summary:
Antifreeze has three basic functions: freeze protec-
tion, boil-over protection, and anti-corrosion and rust
protection.
Antifreeze is also primarily responsible for heat trans-
fer; however, antifreeze itself does not possess accept-
able heat transfer characteristics. Therefore, as water is
an excellent heat conductor, it is added to the mixture.
A 50/50 solution of propylene glycol antifreeze and
water is recommended to provide the best perfor-
mance combination of the aforementioned functions.
If excess propylene glycol exists within an antifreeze
and water heating solution, the water’s heat absorption
properties are compromised, which could ultimately in-
hibit the Aqua-Hot from providing adequate domestic
hot water and interior heating.
Additionally, if the antifreeze and water heating solu-
tion contains over 70 percent antifreeze, the freezing
point is actually raised, resulting in less freeze protec-
tion. Please reference the attached graphical represen-
tation regarding the percentage of antifreeze to water
and how it directly affects the solution’s freezing point.
appendix E: antifreeze terms and Mixture Ratio