21
IOM, VS/VT Models, Rev A Enertech Global
Water Quality
The quality of the water used in geothermal systems
is very important. In closed loop systems the dilution
water (water mixed with antifreeze) must be of high
quality to ensure adequate corrosion protection.
Water of poor quality contains ions that make the
uid “hard” and corrosive. Calcium and magnesium
hardness ions build up as scale on the walls of the
system and reduce heat transfer. These ions may also
react with the corrosion inhibitors in glycol based
heat transfer uids, causing them to precipitate out
of solution and rendering the inhibitors ineffective
in protecting against corrosion. In addition, high
concentrations of corrosive ions, such as chloride and
sulfate, will eat through any protective layer that the
corrosion inhibitors form on the walls of the system.
Ideally, de-ionized water should be used for dilution
with antifreeze solutions since de-ionizing removes
both corrosive and hardness ions. Distilled water
and zeolite softened water are also acceptable.
Softened water, although free of hardness ions, may
actually have increased concentrations of corrosive
ions and, therefore, its quality must be monitored.
It is recommended that dilution water contain less
than 100 PPM calcium carbonate or less than 25
PPM calcium plus magnesium ions; and less than 25
PPM chloride or sulfate ions.
In an open loop system the water quality is of no
less importance. Due to the inherent variation of the
supply water, it should be tested prior to making the
decision to use an open loop system. Scaling of the
heat exchanger and corrosion of the internal parts
are two of the potential problems. The Department
of Natural Resources or your local municipality can
direct you to the proper testing agency. Please see
Table 2 for guidelines.
Table 2: Water Quality
Section 5: Unit Piping Installation
Problem Chemical(s) or
Condition
Range for Copper
Heat Exchangers
Range for Cupro-Nickel
Heat Exchangers
Range for Stainless Steel BPHE
Calcium & Magnesium Less than 350 ppm Less than 350 ppm Less than 0.1 ppm
pH Range 7 - 9 5 - 9 7 - 9
Total Dissolved Solids
Less than 1000 ppm Less than 1500 ppm No rigid setpoint
Ammonia, Ammonium Hydroxide Less than 0.5 ppm Less than 0.5 ppm No Limit
Ammonium Chloride, Ammonium Less than 0.5 ppm Less than 0.5 ppm Less than 2-20 ppm
Calcium Chloride / Sodium Less than 125 ppm Less than 125 ppm Not Allowed
Chlorine Less than 0.5 ppm Less than 0.5 ppm Not Allowed
Hydrogen Sulfide None Allowed None Allowed Less than 0.05 ppm
Iron Bacteria None Allowed None Allowed Not Allowed
Iron Oxide Less than 1 ppm Less than 1 ppm Less than 0.2 ppm
Suspended Solids Less than 10 ppm Less than 10 ppm 16-20 mesh strainer recommended
Water Velocity
Lessthan8*/s
Less than 12 ft/s Less than 5.5 m/s in the port
1. Hardness in ppm is equivalent to hardness in mg/l.Notes
2. Grains/gallon = ppm divided by 17.1.
4. Saltwater applications (approx. 25,000 ppm) require secondary heat exchangers due to copper piping between the heat exchanger.
5. Filter for maximum of 600 micron size.
3. Unit internal heat exchangers are not recommended for pool applications or water outside the range of the table. Secondary heat
exchangers are required for pool or other applications not meeting the requirements shown above.
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