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Table 1 – Water Quality Requirements for Open--Loop Geothermal Heat Pump System
POTENTIAL PROBLEM WATER CHARACTERISTIC
ACCEPTABLE VALUE
COPPER CUPRO---NICKEL
pH (Acidity / Alkalinity) 7 --- 9 7 --- 9
SCALING
Hardness (CaCO3, MgCO3) < 350 ppm < 350 ppm
Ryznar Stability Index 6.0 --- 7.5 6.0 --- 7.5
Langelier Saturation Index --- 0 . 5 --- + 0 . 5 --- 0 . 5 --- + 0 . 5
CORROSION
Hydrogen Sulfide (H2S) < 0.5 ppm* 10---50 ppm
Sulfates < 125 ppm < 125 ppm
Chlorine < 0.5 ppm < 0.5 ppm
Chlorides < 20 ppm < 150 ppm
Carbon Dioxide < 50 ppm < 50 ppm
Ammonia < 2 ppm < 2 ppm
Ammonia Chloride < 0.5 ppm < 0.5 ppm
Ammonia Nitrate < 0.5 ppm < 0.5 ppm
Ammonia Hydroxide < 0.5 ppm < 0.5 ppm
Ammonia Sulfate < 0.5 ppm < 0.5 ppm
Dissolved Solids < 1,000 ppm < 1,500 ppm
IRON FOULING
Iron (Fe2+ Iron Bacteria Potential) < 0.2 ppm < 0.2 ppm
Iron Oxide < 1 ppm < 1 ppm
EROSION
Suspended Solids < 10 ppm, < 600 μmsize** < 10 ppm, < 600 μmsize**
Maximum Water Velocity 6ft./sec. 6ft./sec.
* No ”rotten egg” smell present at < 0.5 ppm H2S.
** Equivalent to 30 mesh strainer
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
S Following the above recommendation, along with adequate water flow rates, will greatly decrease the rate of fouling/scaling of the coaxial heat
exchanger.
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