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Water Heating Efficiency

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Jono_w

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Hey Brewers,
Thought this little bit of research this guy has done on water heating might be of some interest to the electric / gas heating debate.

LINK
 

seravitae

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nice, those numbers seem wierd, especially for the immersion element/kettle. Heating using an internal immersion element efficiency is near 100%, somehow he's losing ~80% through the kettle walls/insulation?? Even with how thin kettle plastic is.. seems not right.
 

QldKev

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I agree with sera, I think that write up is so far from the truth in a lot of the tests. I know on my HLT with elec heating I get no that far from 100% efficiency of heating.
 

Jono_w

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Some of the numbers he quotes are taking into consideration how the electricity is generated verses burning the fuel such as gas directly.

"The adjusted efficiency is the fossil fuel equivalent if electricity is derived from fossil resources (coal, natural gas) at 35% efficiency"
 

QldKev

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I understand that, but if we concentrate on the raw numbers prior to the power station calcs.

As one example for his electric kettle
"Using the middle number, I calculate 69% efficiency. I get 78% if I use the shortest time, when I thought I was at boil. But by the time I shut it off, we were down to 57%, and falling."
This is prior to the calculation for how efficient the power station is. I think the main issue is the testing is done on such a small volume the factor of how much loss is taken to heat the vessel and any inaccuracy within the test is exaggerated.

Using my HLT with I start with the initial fill of 80L of water, in a heavy gauge stainless vessel. It is insulated on the sides fairly well, and just a heavy stainless lid. I would have to do the exact calculation, but using the water heating calc from my website (and many others out there) I would claim at least 95% efficiency of the electric heating element output against the water ramping rate.


Another example from his heating 500ml using the stove element used 640kj

Most people will agree that using a LPG burner we average 1kg of LPG for a standard 23batch in a BIAB system (ie. same heat source to heat strike water and for full boil)
1kg of LPG = 1.985 litres LPG = 47.132 BTU
100,000 B.T.U. = 105.5 Mj
So for a full brew we use roughly 50Mj or energy.

But we are heating approx 60x the 500ml initially.
60 X 640kj = 38,400kj
= 38Mj just to get the water to the boil.
But somehow from the remaining 12Mj we are supposed to be able to maintain a full rolling boil for an hour.
I think 1/3 the LPG to raise the heat and 2/3 to maintain the boil would be more realistic. (guesstimate going by using 3ring, Mongolian and NASA burners over many brews, allowing at same setting to hold rolling boil it would take 30mins to get to a boil from tap temp; but realistically they would normally get the water to the boil faster) So a realistic number would be closer to 270kj to heat the 500ml water.


QldKev
 

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