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Old 03-08-19, 11:41 PM   #16
Semipro
Andy
 
Join Date: Jun 2014
Location: SW VA
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Quote:
Originally Posted by ecomodded View Post
I had a look to see what info was out there on scales energy costs and found this pdf file https://www.cwt-international.com/cw...Efficiency.pdf

Highlights below

Reduced efficiency

Over time scale deposits act as an insulator,
causing the water heater to work harder and
harder to heat the water.

Scale reduces
energy efficiency of the water
heater by up to 50%

-
Each five grains per gallon of water hardness
will cause a 4% loss in efficiency

-
Water temperature decreases 5C with a
limescale thickness of 2mm after 480 seconds

- A water heater‘s useful life can be reduced by
as much as 50% through scale build-up
-
Scale deposits will cause a 4% increase in cost
for gas storage tank water heaters when using
50 gallons of hot water per day.
-
0.5 mm of hard scale increases fuel costs by
9.4%


I have seen well water make a kettle 1/2 inch thick in calcium deposits and they do burn out water heaters there was one in the yard last time I visited
These numbers seem to refer to gas water heaters where it would make sense that heat transfer rates would result in more waste up the flue. Not so with an electric resistance heater. Although an electric resistance water heater with mineral coated elements may take longer to heat water, I remain unconvinced that the overall energy efficiency of the water heater itself is diminished. Inefficiency in electrical heating systems manifests as "heat". Longer heating times do not result in lost efficiency (energy in/energy out), only diminished performance with respect to heating time.

I was unable to find the Battelle report reference but found this one: https://www.wqa.org/Portals/0/WQRF/R...xecSummary.pdf

With this chart showing test results for the efficiency change of water heaters over time. Gas, electrical resistance storage, and instantaneous gas resistance heaters were evaluated. Check out their results table below. Efficiencies for electric resistance storage WHs did not change during the test although efficiencies for gas both types of gas units decreased.

I just found a summary of Battelle findings here: https://www.kineticonaz.com/battelle-study/
Notice although they talk about loss of efficiency in gas water heaters they don't for electrical resistance units. They discuss instead for electrical units mineral buildup and heating element failure - a problem I've witnessed first hand for 18 years - not decreasing efficiency.
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Last edited by Semipro; 03-09-19 at 12:11 AM..
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