Enertech VS Series - Antifreeze Overview; Antifreeze Characteristics

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IOM, VS/VT Models, Rev A Enertech Global
Section 5: Unit Piping Installation
Antifreeze Overview
In areas where minimum entering source
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. In addition, the system needs
antifreeze to protect the heat exchanger from
freezing and rupturing. Freeze protection should
be maintained to 15°F below the lowest expected
entering loop temperature. For example, if 30°F is
the minimum expected entering loop temperature,
the leaving source 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 on previous
page for volumes and percentages. The freeze
protection should be checked during installation
using the proper hydrometer to measure the specic
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 ammability 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:
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 ammable 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 unt 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 ammable 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 in high concentrations,
and potential for high viscosity when cold (in high
concentrations). It has also been known to form a
“slime-type” coating inside the pipe when inhibitors
are not used. Do not use food grade glycol, since
it does not include inhibitors. A 25% to 30% brine
solution is a minimum concentration for required
inhibitors, depending upon brand of glycol. If using
a lower concentration (e.g. 20% provides 19°F freeze
protection), additional inhibitors must be added.
Note that some states/provinces have toxicity
requirements that must be veried based upon the
chemical composition of the inhibitors.