Recognizing the problem
eLeCTrIC waTer HeaTer
The Battelle Memorial Institute tested the effect of softened water and hard water as it relates to the energy efficiency of hot-water heaters and appliances in the household, and formulated a differential for estimating the carbon footprint of homes using softened water versus hard water. The study introduces controllable amounts of hard water and soft water to the following units: • 10 gas water heaters, 40-gallon, 38,000 BTU/h burners • 10 electric water heaters, 40-gallon, 45,000watt heating elements • 10 tankless gas water heaters, 199,000 BTU/h burners. In general, the study found the electric and gas storage water heaters and the on-demand gas water heaters using softened water performed well throughout the entire testing period. Each unit maintained the factory-estimated efficiency throughout the testing period and did not require any de-liming of heating elements or pipes throughout the testing period.
electric storage Water Heater after 90 days using softened Water
electric storage Water Heater after 90 days using unsoftened Water
GaS waTer HeaTer
Quite the reverse for the electric and gas storage water heaters and on-demand gas water heaters using hard water: None lasted through the entire testing period. At some point in the testing period, all of the water heaters using un-softened water were removed from the test due to inadequate flow caused by mineral deposit buildup in the pipes. The on-demand gas water heaters operating on hard water had an 80 percent factory energyefficienct rating. These units were allowed to operate down to a 72 percent energy efficiency before they were shut down for maintenance. Maintenance required de-scaling of piping before being put back in use. Once de-limed, the units only recovered a 77 percent efficiency rating. The equivalent of 26 gpg of water hardness would require the on-demand water heater to be de-scaled every 1.6 years to maintain operation. On-demand gas hot water heaters will lose their energy efficiency rating within the first year of operation proportional to the amount of hard water minerals present in the water. A conservative estimate would be 10 percent efficiency lost in the first two years of operation with hard water, according to a 2010 article by David H. Martin in the Water Conditioning and Purification Journal.
Gas storage Water Heater after 90 days using softened Water The gas storage water heaters operating on the hard water had a 70.4 percent factory energy-efficient rating. These units were allowed to operate down to a 67.4 percent energy-efficiency performance level before they were shut down for maintenance. The units required descaling of piping before being put back in use. The maintenance schedule was estimated to re-
WNC GreeN BuildiNG CouNCil & MouNtaiN Xpress
Gas storage Water Heater after 90 days using unsoftened Water quire the field equivalent of service every two years of operating on 26 gpg of water hardness. The electric storage water heaters operating on hard water had a 93 percent factory energy-efficient rating. These units did not lose energy efficiency in heating the water during the course of the test. Since the 2012 | wncgreenbuilding.com
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