Flow Controller 3
R e v. : F e b u r a r y 9 , 2 0 1 6
14
G e o t h e r m a l H e a t P u m p S y s t e m s
Antifreeze Selection
Table 4: Antifreeze Percentages by Volume
NOTICE:
DO NOT use automotive windshield washer
fluid as antifreeze. Most washer fluid contains
chemicals that will cause foaming.
�
WARNING!
�
WARNING!
Always use properly marked vehicles (D.O.T.
placards), and clean/suitable/properly identified containers
for handling flammable antifreeze mixtures. Post and
advise those on the jobsite of chemical use and potential
dangers of handling and storage.
�
CAUTION!
�
CAUTION!
Always obtain MSDS safety sheets for all
chemicals used in ground loop applications including
chemicals used as antifreeze.
Methanol - Methanol or wood alcohol is considered toxic in
any form, has good heat transfer, low to mid price, flammable
in concentrations greater than 25%, non-corrosive, and low
viscosity. Methanol has delivered outstanding performance in
earth loops for over 20 years. Its only drawbacks are toxicity
and flammability. Although methanol enjoys widespread
consumer use as a windshield washer fluid in even higher
concentrations, some local codes may limit its use in earth
loops. To increase safety, a premixed form should be used on
the jobsite to increase the safety factor. Pure methanol can be
purchased from any chemical supplier.
Ethanol - Ethanol or grain alcohol exhibits good heat
transfer (slightly less than methanol), higher price, and is
flammable in concentrations greater than 10%. Ethanol
is generally non-corrosive and has medium viscosity.
Ethanol in its pure form is considered nontoxic and shows
promise as a geothermal heat transfer fluid. However the
U.S. Bureau of Alcohol, Tobacco, and Firearms (ATF) limit
its distribution. All non-beverage ethanol is required to be
denatured and rendered unfit to drink. Generally this is done
by adding a small percentage of toxic substances such
as methanol, benzene, or gasoline as a denaturant. Many
of these denaturants are difficult to identify by the casual
user and many are not compatible with polyethylene pipe.
Only denatured ethanol can be purchased for commercial
use. The use of ethanol is not recommended because of
the unknown denaturants included in the solution, and their
possible toxicity and damage resulting to polyethylene
piping systems. Denaturing agents that are petroleum based
can damage polyethylene pipe.
Ethylene glycol - Generally non-corrosive, expensive,
medium heat transfer, considered toxic. Its toxicity has
prevented its widespread use in the ground source industry
in spite of its widespread use in traditional water-source
heat pump applications. Ethylene glycol is not currently
recommended as ground-source antifreeze.
Propylene glycol - Nontoxic, non-corrosive, expensive, hard to
handle when cold, poorest heat transfer, has formed “slime-
type” coatings inside pipe. Poor heat transfer has required
its removal in some systems. Propylene glycol is acceptable
in systems anticipating loops temperatures no colder than
40°F [4.4°C]. These systems typically use antifreeze because
of low ambient conditions (outside plumbing or cooling
tower, etc.). When loop temperatures are below 40°F [4.4°C],
the fluid becomes very difficult to pump and heat transfer
characteristics suffer greatly. Only food grade propylene glycol
is recommended to prevent the corrosion inhibitors (often
present in other mixtures) from reacting with local water and
‘coming out’ of solution to form slime type coatings inside heat
exchangers and thus hinder heat transfer. If propylene glycol
must be used (e.g. code requirements), careful consideration
of loop Reynolds numbers, pump selection and pressure drop
must be considered.
Potassium acetate - Nontoxic, good heat transfer, high price,
non-corrosive with added inhibitors, low viscosity. Due to its
low surface tension, Potassium Acetate has been known to
leak through mechanical fittings and certain thread sealants.
A variant of the salt family, it can be extremely corrosive when
exposed to air. Potassium Acetate is not recommended in
ground-source applications due to the leaking and (ultimately)
corrosion problems associated with it.
Contact the Technical Services Department if you have any
questions as to antifreeze selection.
Type
Minimum Temperature
for Low Temperature Protection
10°F
[-12.2°C]
15°F
[-9.4°C]
20°F
[-6.7°C]
25°F
[-3.9°C]
Methanol
Propylene Glycol
Ethanol*
21%
29%
23%
17%
24%
20%
13%
18%
16%
8%
12%
11%
* Must not be denatured with any petroleum based product
