14 June 2002
WATER QUALITY ANALYSIS
C-1. The following analysis must be performed to determine if the quality of the
potable water is sufficient to allow the use of a direct circulation solar energy system.
a. Obtain a standard water chemistry report for the water to be used in the
system. In most cases, this report can be obtained from local water treatment centers
or most any local laboratory (a similar report is often required for determining
appropriate boiler feedwater treatment). Results of this report must include, as a
Total dissolved solids (TDS) [mg/l]
M alkalinity [mg/l]
b. Calculate the pH of saturation (pHs) of calcium carbonate (CaCO3) for the
water using Equation C-1:
pHs = 9.3 + A + B - (C+D)
where, from Table C-1:
A = value for range of TDS.
B = value for application temperature range.
(normal system operating temperature).
D = factor for M alkalinity.
c. From the results of the water chemistry report and Equation C-1, calculate
the Ryznar Index (RI) using Equation C-2:
RI = 2(pHs) pH
C-2. Using Table C-2 and the calculated RI from above, determine the tendency of
the water in question for scaling and/or corrosion. For direct use of the water in a solar
system, the RI must be between 5 and 7. For water with a calculated RI outside of this
range, the designer may either choose another system type or require water treatment
resulting in an RI within the acceptable range.