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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