The Water Quality Research Foundation (WQRF) initiated the Battelle Study to test devices fed with softened and unsoftened water under controlled laboratory conditions designed to accelerate the waterside scaling in Electric Water Heaters and quantify the performance efficiency.
This portion of the study was conducted to investigate the interaction of water hardness levels on the performance of electric water heaters. They also wanted to quantify the amount of scale formation within the hot water heater due to hard water as well as forming an opinion about the life span of the hot water heater as it is affected by hard water deposits.
Battelle set up and tested ten storage-type electric water heaters with the following specifications using an accelerated scaling methodology developed at Battelle. They used 10 Electric Water Heaters of 40 gallon capacity with 4500Wheating elements.
Five were tested without any preconditioning of the water supply, and the other five were tested using a water softener to remove hardness from the water supply. Five units were chosen in order to be able to calculate 95 percent confidence intervals for the results.
At the start of the test, and at approximately one week intervals, the thermal efficiency of each water heater was measured to determine the change in efficiency as waterside scale built up in each water heater. Each water heater
was instrumented to measure the inlet and outlet water temperature at 15-second intervals, the amount of hot water generated, and the amount of electric energy used to produce the hot water. These data were used to calculate the average thermal efficiency of the water heater.
In summary, the electric water heaters on soft water, performed well throughout the entire testing period. Although the pressure regulators and needle valves were tweaked throughout the testing to maintain constant testing conditions, all of the water heaters on soft water required
minimal attention because the conditions were very stable. This is reflected in the efficiency data for these units that show the efficiency remained essentially constant over the duration of the testing with the variations being within the experimental error of the instrumentation and testing protocol.
In contrast, none of the electric water heaters on unsoftened water made it through the entire testing period because the outlet piping system consisting of one-half inch copper pipe, a needle valve, and a solenoid valve became clogged with scale buildup. Although the pressure regulators and
needle valves were tweaked throughout the testing to try to maintain constant testing conditions, all of the water heaters on unsoftened water were removed from the testing at some point due to the inability to maintain sufficient flow.
The cost implications of these findings are addressed in this report.
The electric water heaters on both softened and unsoftened water were able to maintain a constant efficiency throughout the entire test period because the heating elements were completely submerged in the water.
However, the life of the heating element in unsoftened water is expected to be shortened due to scale buildup increasing the operating temperature of the element. The average rate of scale buildup in the electric storage water heaters on unsoftened water was about 907 g/yr (2.00 lb/yr), compared to the average rate of scale buildup on soft water was about 14 g/yr (0.03 lb/yr), which is almost negligible.
So in summary, each 5 gpg of water hardness caused 0.4 pounds of scale accumulation each year in electric storage tank household water heaters. Up to 30 pounds of calcium carbonate rock like scale deposits can accumulate in electric water heaters over their service life before failing when used with unsoftened water. The Battelle Memorial Institute says “The life of the heating element can be expected to shorten due to scale buildup increasing the operating temperature of the element” in the electric storage water heaters operating on unsoftened water.