11
IOM, WD Models
Enertech Global
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 loop temperature. For example, if 30°F is
the minimum expected entering loop temperature, the leaving
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 3a and 3b 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:
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.
Potassium acetate (GS4): 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.
Antifreeze Charging
Calculate the total amount of pipe in the system and use Table
5 to calculate the amount of volume for each specific section
of the system. Add the entire volume together, and multiply
that volume by the proper antifreeze percentage needed
(Table 5) for the freeze protection required in your area. Then,
double check calculations during installation with the proper
hydrometer and specific gravity chart (Figure 6) to determine if
the correct amount of antifreeze was added.
Section 6: Antifreeze