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Table 2 – Water Quality Requirements for Open-- Loop Geothermal Heat Pump System
Water Quality Parameter HX Material Closed Recirculating Open Loop and Recirculating Well
Scaling Potential - Primary Measurement
Above the given limits, scaling is likely to occur. Scaling indexes should be calculated using the limits below:
pH/Calcium Hardness
Method
All -- pH <7.5 and Ca Hardness <100ppm
Index Limits for Probable Scaling Situations - (Operation outside these limits is not recommended)
Scaling indexes should be calculated at 150°F for direct use and HWG applications, and at 90°F for indirect HX use.
A monitoring plan should be implemented.
Ryznar Stability Index All --
6.0 - 7.5
If > 7.5 minimize steel pipe use
Langelier Saturation Index All --
-0.5 to +0.5
If <-0.5 minimize steel pipe use.
Based upon 150°F HWG and Direct well,
84°F Indirect Well HX
Iron Fouling
Iron Fe² (Ferrous)
(Bacterial Iron Potential)
All --
<0.2 ppm (Ferrous)
If Fe²* (ferrous) >0.2 ppm with pH 6-8, O2<5 ppm check
for iron bacteria
Iron Fouling All --
<0.5 ppm of Oxygen
Above this level deposition will occur
Corrosion Prevention
pH All
6-8.5
Monitor/treat as needed
6-8.5
Minimize steel pipe below 7 and no open tanks with pH <8
Hydrogen Sulfide (H
2
S) All --
At H S>0.2 ppm, avoid use of copper and copper nickel
piping or HXs. Rotten egg smell appears at 0.5 ppm level.
Copper alloy (bronze or brass) cast components are OK
to <0.5 ppm
Ammonia ion as hydroxide,
chloride, nitrate and sulfate
compounds
All -- <0.5 ppm
Maximum Chloride Levels
Maximum Allowable at Maximum Water Temperature
50°F 75°F 100°F
Copper -- <20 ppm NR NR
cupronickel -- <150 ppm NR NR
304 SS -- <400 ppm <250 ppm <150 ppm
316 SS -- <1000 ppm <550 ppm <375 ppm
Titanium -- >1000 ppm >550 ppm >375 ppm
Erosion and Clogging
Particulate Size and
Erosion
All
<10 ppm of particles and a
maximum velocity of 1.8 m/s.
Filtered for maximum 841 mi-
cron [0.84 mm 20 mesh] size
<10 ppm (<1 ppm "sandfree" for reinjection) of particles
and a maximum velocity of 1.8 m/s. Filtered for maximum
841 micron [0.84 mm. 20 mesh] size. Any particulate that
is not removed can potentially clog components
NOTES:
S Closed recirculating system is identified by a closed pressurized piping system.
S Recirculating open wells should observe the open recirculating design considerations.
S NR - application not recommended
S "—" No design Maximum
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