Enertech ZS., Руководство по установке и эксплуатации, Страница: 34 / 89

34 Enertech Global IOM, ZS/ZT 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 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 3 and 4 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.
Notes:
• Consult with your representative or distributor
if you have any questions regarding
antifreeze selection or use.
• All antifreeze suppliers and manufacturers
recommend the use of either de-ionized or
distilled water with their products.
SECTION 5: UNIT PIPING INSTALLATION