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In areas with extremely hard water, the owner should be in-
formed that the heat exchanger may require additional system
maintenance and occasional acid flushing.
Water Supply and Quality
— Check water supply. Water sup-
ply should be plentiful and of good quality. See Table 3 for wa-
ter quality guidelines.
In all applications, the quality of the water circulated
through the heat exchanger must fall within the ranges listed in
the Water Quality Guidelines table. Consult a local water treat-
ment firm, independent testing facility, or local water authority
for specific recommendations to maintain water quality within
the published limits.
Table 3 — Water Quality Guidelines
LEGEND
*Heat exchanger materials considered are copper, cupronickel,
304 SS (stainless steel), 316 SS, titanium.
†Closed recirculating system is identified by a closed pressurized
piping system.
**Recirculating open wells should observe the open recirculating
design considerations.
††If the concentration of these corrosives exceeds the maximum
allowable level, then the potential for serious corrosion problems
exists.
Sulfides in the water quickly oxidize when exposed to air, requir-
ing that no agitation occur as the sample is taken. Unless tested
immediately at the site, the sample will require stabilization with a
few drops of one Molar zinc acetate solution, allowing accurate
sulfide determination up to 24 hours after sampling. A low pH and
high alkalinity cause system problems, even when both values
are within ranges shown. The term pH refers to the acidity, basic-
ity, or neutrality of the water supply. Below 7.0, the water is con-
sidered to be acidic. Above 7.0, water is considered to be basic.
Neutral water contains a pH of 7.0.
To convert ppm to grains per gallon, divide by 17. Hardness in
mg/l is equivalent to ppm.
IMPORTANT: Failure to comply with the above required
water quality and quantity limitations and the closed-
system application design requirements may cause damage
to the tube-in-tube heat exchanger. This damage is not the
responsibility of the manufacturer.
CONDITION
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 N/A pH < 7.5 and Ca Hardness, <100 ppm
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 N/A
6.0 - 7.5
If >7.5 minimize steel pipe use.
Langelier Saturation Index All N/A
–0.5 to +0.5
If <–0.5 minimize steel pipe use.
Based upon 150 F HWG and direct well, 85 F indirect well HX.
Iron Fouling
Iron Fe
2+
(Ferrous)
(Bacterial Iron Potential)
All N/A
<0.2 ppm (Ferrous)
If Fe
2+
(ferrous) >0.2 ppm with pH 6 - 8, O
2
<5 ppm check for iron
bacteria.
Iron Fouling All N/A
<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 N/A
<0.5 ppm
At H
2
S>0.2 ppm, avoid use of copper and cupronickel piping or HXs.
Rotten egg smell appears at 0.5 ppm level.
Copper alloy (bronze or brass) cast components are okay to <0.5 ppm.
Ammonia Ion as Hydrox-
ide, Chloride, Nitrate and
Sulfate Compounds
All N/A <0.5 ppm
Maximum Chloride Levels
Maximum allowable at maximum water temperature.
50 F (10 C) 75 F (24 C) 100 F (38 C)
Copper N/A
<20 ppm NR NR
CuproNickel N/A <150 ppm NR NR
304 SS N/A <400 ppm <250 ppm <150 ppm
316 SS N/A <1000 ppm <550 ppm <375 ppm
Titanium N/A >1000 ppm >550 ppm >375 ppm
Erosion and Clogging
Particulate Size and
Erosion
All
<10 ppm of particles and
a maximum velocity of
6 fps. Filtered for maxi-
mum 800 micron size.
<10 ppm (<1 ppm “sandfree” for reinjection) of particles and a maxi-
mum velocity of 6 fps. Filtered for maximum 800 micron size. Any par-
ticulate that is not removed can potentially clog components.
Brackish All N/A
Use cupronickel heat exchanger when concentrations of calcium or
sodium chloride are greater than 125 ppm are present. (Seawater is
approximately 25,000 ppm.)
HWG — Hot Water Generator
HX — Heat Exchanger
N/A — Design Limits Not Applicable Considering Recirculating
Potable Water
NR — Application Not Recommended
SS — Stainless Steel