Go with the flow

By Edward Cortright on 03/06/2012

It seems that not enough is said about water quality in relation to energy efficiency or performance. Heating domestic hot water is estimated to be 13 percent of household energy consumption, making water heaters the second highest energy consumers in the home, after heating and cooling equipment. And if water is used to heat the home, then the boiler or water-heating equipment contributes to a larger portion of the household energy demand.

Chemically speaking, water is a compound with many unique and amazing attributes. Industries and commercial buildings tap into water’s energy-efficient promise every day when utilizing water cooling towers. The industrial sector recognizes that impurities in water waste energy and prove costly when present in water that is used in cooling towers for air conditioning, manufacturing and electric-power generation. Mineral-free water is efficient, cost-effective and essential to use in order to operate the equipment at the efficiency rating. Plus, mineral-free water prolongs the life of the equipment.

Water is never just water, and it is not the same, even among neighbors. Invisible hard-water minerals precipitate out of the water when heated and deposit in pipes and on heating elements proportional to their concentration in the water.

The problem of high mineral content in water 
Water that contains calcium, magnesium and silicate minerals make up what is referred to as hard water. These are some of the same minerals that get promoted as “good minerals” to have in our drinking water by various disciplines. However, minerals create operational problems for water-heating equipment. The warranties for an on-demand water heater or tankless hot-water heater can be voided when the water hardness is above 3.5 grains per gallon. Hard water is mostly measured by grains per gallon and is commonly expressed this way in water analysis reports. It is also expressed as parts per million with one grain equal to 17.1 ppm.

Recognizing the problem 
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, 45,000-watt 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.

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 energy-efficienct 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.

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 require 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 heating elements are completely submerged in water, all heat is transferred from the elements to the water in the tank. The maintenance schedule was estimated to require the field equivalent of service every 1.25 years in operation on 26 gpg of water hardness in order to maintain the water flow. A shorter life span of the heating element was projected over a 15-year service life. Scale buildup still occurs; it just does not impede the energy efficiency of heating the water, only the flow.

Solutions 
To solve the problems caused by hard water, consider the following: 

• If you are on a well, get a water analysis to understand what, if any, problems your water might present in consuming and using.
• Weigh the advantages of water conditioning if a water analysis indicate 3 gpg of water hardness or greater present in your water and you are operating or planning to use an on-demand hot-water heater. 
• Consider an electric hot-water storage heater for use when hard-water minerals are present in your water to retain the energy efficiency. 
• Explore alternative means for dealing with hard-water minerals to see if their operational parameters are appropriate for the impurities and quantities present in your water.

For a view of the executive summary of the Battelle study or for more information about water quality, visit Filtersfortap.com or email ed@filtersfortap.com.

Edward Cortright is a certified water specialist, a member of the Water Quality Association and WNCGBC, and owner of Filters for Tap, a company specializing in water filtration. He has 30 years of experience in the residential building industry.