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Table 1 - Water
Quality
Requirements
for Open-Loop
Geothermal
Heat Pump
System
Parameter
HX Material
Closed
Recirculating
Open
Loop and Recirculating
Well
pH/Calcium Hardness
All
pH <7.5 and Ca Hardness <100ppm
Method
6.0 - 7.5
Ryznar Stability Index
All
--
If > 7.5 minimize steel pipe use
-0.5 to +0.5
If <-0.5 minimize steel pipe use.
Langelier Saturation Index
All
--
Based upon 150°F HWG and Direct well,
84°F Indirect Well HX
<0.2 ppm (Ferrous)
Iron Fe 2 (Ferrous)
All
--
If Fe2. (ferrous) >0.2 ppm with pH 6-8, 02<5 ppm check
(Bacterial Iron Potential)
for iron bacteria
<0.5 ppm of Oxygen
Iron Fouling
All
--
Above this level deposition will occur
6 - 8.5
6 - 8.5
pH
All
Monitor/treat as needed
Minimize steel pipe below 7 and no open tanks with pH <8
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.
Hydrogen Sulfide (H2S)
All
--
Copper alloy (bronze or brass) cast components are OK
to <0.5 ppm
Ammonia ion as hydroxide,
chloride, nitrate and sulfate
All
--
<0.5 ppm
compounds
Maximum
Allowable
at Maximum
Water Temperature
50°F
75°F
100°F
Copper
--
<20 ppm
NR
NR
Maximum Chloride Levels
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
_i
_
........
<10 ppm of particles and a
<10 ppm (<1 ppm "sandfree" for re-injection) of particles
Particulate Size and
All
maximum velocity of 1.8 m/s.
and a maximum velocity of 1.8 m/s. Filtered for maximum
Erosion
Filtered for maximum 841 mi-
841 micron [0.84 mm. 20 mesh] size. Any particulate that
cron [0.84 mm 20 mesh] size
is not removed can potentially clog components
NOTES:
Closed recirculating
system is identified by a closed pressurized
piping system.
Recirculating
open wells should observe the open recirculating
design considerations.
NR - application
not recommended
"--" No design Maximum
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