36
Unwanted Side Effects of Improper Water Quality
•
Corrosion
•
Scale
•
Fouling
•
Biological Contamination
Cooling Water Chemistry Properties
•
Electrical Conductivity
•
pH
•
Alkalinity
•
Total Hardness
•
Dissolved gases
Chillers at their simplest have two main heat
exchangers: one that absorbs the heat from the
process (evaporator) and one that removes the heat
from the chiller (condenser). All our chillers use
stainless steel brazed plate evaporators. Our air-
cooled chillers use air to remove heat from the
chiller; however, our water-cooled chillers use either
a tube-in-tube or shell-in-tube condenser which has
copper refrigerant tubes and a steel shell. These, as
are all heat exchangers, are susceptible to fouling of
heat transfer surfaces due to scale or debris. Fouling
of these surfaces reduces the heat-transfer surface
area while increasing the fluid velocities and
pressure drop through the heat exchanger. All of
these effects reduce the heat transfer and affect the
efficiency of the chiller.
The complex nature of water chemistry requires a
specialist to evaluate and implement appropriate
sensing, measurement and treatment needed for
satisfactory performance and life. The
recommendations of the specialist may include
filtration, monitoring, treatment and control devices.
With the ever-changing regulations on water usage
and treatment chemicals, the information is usually
up to date when a specialist in the industry is
involved. Table 19 shows the list of water
characteristics and quality limitations.
Table 19 – Fill Water Chemistry Requirements
Water Characteristic
Quality Limitation
Alkalinity (HCO
3-
)
70-300 ppm
Aluminum (Al)
Less than 0.2 ppm
Ammonium (NH
3
)
Less than 2 ppm
Chlorides (Cl
-
)
Less than 300 ppm
Electrical Conductivity
10-500µS/cm
Free (aggressive) Carbon Dioxide
(CO
2
)†
Less than 5 ppm
Free Chlorine(Cl
2
)
Less than 1 PPM
HCO
3-
/SO
42-
Greater than 1.0
Hydrogen Sulfide (H
2
S)*
Less than 0.05 ppm
Iron (Fe)
Less than 0.2 ppm
Manganese (Mn)
Less than 0.1 ppm
Nitrate (NO
3
)
Less than 100 ppm
pH
7.5-9.0
Sulfate (SO
42-
)
Less than 70 ppm
Total Hardness (dH)k
4.0-8.5
* Sulfides in the water quickly oxidize when exposed to air;
therefore ensure agitation does not occur when taking a water
sample. 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 the range shown. The
term pH refers to the acidity, basicity, or neutrality of the water
supply. Below 7.0, water is acidic. Neutral water contains a pH of
7.0.
† Dissolved carbon dioxide calculation is from the pH and total
alkalinity values shown below or measured on the site using a test
kit.
Dissolved Carbon Dioxide, PPM = TA x 2[(6.3-pH)/0.3] where TA =
Total Alkalinity, PPM as CaCO3
