34
Enertech Global
IOM, BS/BT Models
Antifreeze Overview
In areas where minimum entering loop temperatures
drop below 40°F, or where piping will be routed
through areas subject to freezing, antifreeze is
required. Alcohols and glycols are commonly used
as antifreeze. However, local and state/provincial
codes supersede any instructions in this document.
The system needs antifreeze to protect the coaxial
heat exchanger from freezing and rupturing.
Freeze protection should be maintained to 15°F
below the lowest expected entering source loop
temperature. For example, if 30°F is the minimum
expected entering source loop temperature, the
leaving source loop temperature could be 22 to
25°F. Freeze protection should be set at 15°F (30-
15 = 15°F). To determine antifreeze requirements,
calculate how much volume the system holds. Then,
calculate how much antifreeze will be needed by
determining the percentage of antifreeze required
for proper freeze protection. See Tables 4 and 5 for
volumes and percentages. The freeze protection
should be checked during installation using the
proper hydrometer to measure the specific gravity
and freeze protection level of the solution.
Antifreeze Characteristics
Selection of the antifreeze solution for closed
loop systems require the consideration of many
important factors, which have long-term implications
on the performance and life of the equipment. Each
area of concern leads to a different “best choice” of
antifreeze. There is no “perfect” antifreeze. Some
of the factors to consider are as follows (Brine =
antifreeze solution including water):
Safety:
The toxicity and flammability of the brine
(especially in a pure form).
Cost:
Prices vary widely.
Thermal Performance: The heat transfer and
viscosity effect of the brine.
Corrosiveness:
The brine must be compatible with
the system materials.
Stability:
Will the brine require periodic change out
or maintenance?
Convenience:
Is the antifreeze available and easy
to transport and install?
Codes:
Will the brine meet local and state/
provincial codes?
The following are some general observations about
the types of brines presently being used and types
not recommended:
Methanol:
Wood grain alcohol that is considered
toxic in pure form. It has good heat transfer, low
viscosity, is non-corrosive, and is mid to low price.
The biggest down side is that it is flammable in
concentrations greater than 25%.
Ethanol:
Grain alcohol, which by the ATF
(Alcohol, Tobacco, Firearms) department of the
U.S. government, is required to be denatured and
rendered unfit to drink. It has good heat transfer,
mid to high price, is non-corrosive, non-toxic
even in its pure form, and has medium viscosity.
It also is flammable with concentrations greater
than 25%. Note that the brand of ethanol is very
important. Make sure it has been formulated for
the geothermal industry. Some of the denaturants
are not compatible with HDPE pipe (for example,
solutions denatured with gasoline).
Propylene Glycol:
Non-toxic, non-corrosive, mid
to high price, poor heat transfer, high viscosity when
cold, and can introduce micro air bubbles when
adding to the system. It has also been known to
form a “slime-type” coating inside the pipe. Food
grade glycol is recommended because some of the
other types have certain inhibitors that react poorly
with geothermal systems. A 25% brine solution is a
minimum required by glycol manufacturers, so that
bacteria does not start to form.
Ethylene Glycol:
Considered toxic and is not
recommended for use in earth loop applications.
GS4 (POTASSIUM ACETATE):
Considered
highly corrosive (especially if air is present in the
system) and has a very low surface tension, which
causes leaks through most mechanical fittings. This
brine is not recommended for use in earth loop
applications.
Section 6: Unit Piping Installation