If you are boiling off equal amounts of water with electric and gas, how can anyone claim that gas is putting more BTUs into the wort? That is impossible, otherwise the boil off would be different.
How can you claim that gas is applying more BTUs to the wort when electric is reaching a boil faster? Again, wouldn't the fact that the heating time is faster then prove that there are more BTUs being applied to the wort by electric?
Last edited by willynilly; 03-21-2010 at 05:28 PM.
Isn't boil off governed by surface area of the kettle being used? Amongst other things.
A 4,000W heating element is only delivering 13,648 BTU/hr. Even at a 50% loss to the direct fire method, a 170,000 BTU/hr burner will still get 85,000 BTUs/hr into the liquid.
We are talking about the same kettle, different heating sources, so again you can throw out the geometry variables. BUT, if you want to include them, that is fine... but surface area affects boil off very little. This is in part because of what you posted GM, 970BTUs per pound water to get the phase change... it will change phases if you have those BTUs in there, regardless of the surface area of the medium you are heating.
I know that a 4000W heating element is only 13.6K BTUs, that is what makes the efficiency of gas burners to sad. I know that 20% sounds REALLY bad, but this has been proven on more than a few gas fired rigs here. The real world number are what matter and although it sounds impossible, they are true numbers posted by brewers.
That 4000W element will reach a boil faster than a 55K BTU burner. People have been testing this for a while, and the HIGHEST eff. I have seen anyone post from their gas burner is 30%... the average is about 23%.
If you have a gas burner, then test it for us. Get a precise amount of water in your kettle, take the start temp and end temp and the time. We can then compare that BTU calculation to the rated BTUs of your gas burner.
What I know is this... boil off and heating time is related to the BTUs applied. If your kettle and volume are the SAME, then you can throw out all of the other variables.
This being said... in my gas keggle I was boiling off 1.3 gallons/hour with a vigorous boil. In my electric kettle I am boiling off 1.3 gallons/hour with 3700W (dialed down from 9000W) So, we can easily assume that the BTU application to the wort is the same, otherwise there would be a discrepancy in the boil off rate. You said it yourself GreenMonti, when you posted the BTUs required to vaporize water.
Also, the 9000W BK (30k BTUs) is reaching a boil in 13 gallons from 160F in 11 minutes... how fast is a much larger gas burner doing this? 30K BTUs isnt much, not much at all, but I can tell you that is a huge volume to heat in 11 minutes! If you had a 60K BTU gas burner, youd be waiting a very long time, I can tell you how long... about 40 minutes according to my watch.
Rated BTUs mean nothing when talking about gas burners, the ACTUAL BTUs that are doing the work, are much much less. The only way to know what you are getting into your kettle, is to do the math. Weight in pounds water, start temp, end temp and the elapsed time.
BTUs applied is easy to calculate, there is no need to speculate. Heating time and boil off are mainly products of the BTUs applied. So, what is the boil off, what is the heating time? The faster the heating time, the more BTUs you are applying, the greater the boil off, the greater the BTUs you are applying.
10F rise per minute in 5 gallons of strike water with (9000W) 30K BTU is pretty impressive, but you cant get that with a 60K BTU burner, you can get about half that (which is about 25% eff)
Last edited by willynilly; 03-21-2010 at 05:32 PM.
If you are heating faster, you are applying more BTUs.
If you are boiling off the SAME, you are applying the SAME BTUs.
If you are heating slower, you are applying fewer BTUs.
If you are boiling off LESS, you are applying LESS BTUs.
This is where the whole "gas applies more BTUs to the wort" argument doesn't make any sense to me. It isn't faster, and it isn't boiling off more, so how can it be applying more BTUs? And, if it is slower and not boiling off more, what would you use to justify the statement that it IS applying more BTUs?
Last edited by willynilly; 03-21-2010 at 05:45 PM.
Isn't boil off governed by surface area of the kettle being used? Amongst other things.
A 4,000W heating element is only delivering 13,648 BTU/hr. Even at a 50% loss to the direct fire method, a 170,000 BTU/hr burner will still get 85,000 BTUs/hr into the liquid.
Lets assume you are getting 85,000 BTUs into your kettle (50% eff)... your numbers would look like this.
In 5 gallons, you would be seeing about 50F PER MINUTE rise in temp. Wow.
You would reach a boil, from 160F in 5 gallons in about ONE minute. Wow!
You would reach a boil from 160F in 13 gallons in about 4 minutes. DANG!
As you can see, 50% eff. is HIGHLY unlikely, because people are NOT seeing these heating times. If you DOUBLE the above mentioned heating times, you are now down to 25% eff on that burner.
So if you assume 25% eff. then you can start talking gas usage.
If I use 4kW to boil for an hour (which I do), then that is 13648 BTUs, 4kW for an hour will cost me about $.68 (this takes into consideration 10 minutes to REACH the boil at a higher wattage) It takes about 5000 BTUs to reach that boil... so I am using a total of 18600 (ish) BTUs per boil.
When I boiled with gas, I would get about 5 boils from a tank of LP. That is about 17.5 pounds of propane, each pound containing about 22K BTUs. The full tank contains about 385,000 BTUs, divided by 5 brews, that is about 77,000 BTUs per boil.
Compare the BTU useage that I have between my electric kettle per session (77,000) and my propane burner per session (18,600) and you can see that my burner is 24% eff compared to my electric kettle. Typicaly the HIGHER the BTU rating of the burner, the less eff. it is. The kicker is that my electric kettle is over 2x as fast to reach the boil, and then boils off the same amount as my gas burner.
As you can see, the BTU usage is much different between electric and gas, which is directly affected by the eff. of each type of heat. Gas would cost about $3.20 per session whereas electric was about $.68 per session (for boil only) It is only a couple bucks, so who really cares, but this proves that electric is more eff. and less costly.
Last edited by willynilly; 03-21-2010 at 06:11 PM.
Help me with the math here, if you have 13 gallons at 8.4Lb/gallon and need to add 970 btu's/Lb for all the liquid to reach a boil, how long is it going to take with 9 Kw. What might seem like a boil is related to the high surface temperature of the elements flashing the surrounding water to steam but it seems that there is not enough total energy in the kettle to reach a true boil. The water heating to boil temperature is only 15% of the energy needed to boil, the other 85% is the heat added before boil happens.
Help me with the math here, if you have 13 gallons at 8.4Lb/gallon and need to add 970 btu's/Lb for all the liquid to reach a boil, how long is it going to take with 9 Kw. What might seem like a boil is related to the high surface temperature of the elements flashing the surrounding water to steam but it seems that there is not enough total energy in the kettle to reach a true boil. The water heating to boil temperature is only 15% of the energy needed to boil, the other 85% is the heat added before boil happens.
In your example, almost no one would be reaching a boil, as you would need over 100K BTUs to boil 13 gallons That doesn't even sound right, does it?
To correct this, it takes 970 BTUs to create a POUND of vapor. So if you are boiling off 1.3 gallons of water over an hour you are looking at 10.84 pounds over an hour. That is 10,500 BTUs over an hour. Or are you planning to boil off all 13 gallons in that hour? It doesn't take many BTUs to boil off water as you can see. 4000W (13648 BTUs) is PLENTY of power to accomplish this.
My water boils at 209F, and it takes 11 minutes to get there from 160F. Then I turn it down to 4000W and I get a 1.3 gallon per hour boil off, how much are you boiling off?
I see no difference at all in the boil off rate between my electric kettle and gas, which tells me that the BTUs being applied are the same, I mean, it would have to be, right? Only difference is I am not waiting to get to a boil like I am with my gas kettle.
100K BTU burner actually putting 12K BTUs into the boiler? Yes, that is common.
Gas is really not eff., it isnt applying any more BTUs, otherwise it would heat faster than electric, but it doesn't. So if a heating element isn't "boiling" the wort, then a gas burner certainly isnt either.
Last edited by willynilly; 03-21-2010 at 06:49 PM.
GreenMonti's efforts with the boiler and calendria were a way that we could measure the heat delivered to a known quantity of water by the steam generation/condensation heat transfer. With the ability to turn 4.2 Lbs/Min to steam in the boiler and then back to water in the kettle we were able to quantify the heatflow and record the times and temperatures. As the numbers were calculated, the formulas were found to match actual results for heat transfer based on water flow into boiler and its conversion to steam.
All said and done what ever method makes beer is all that matters in the long run, this should not end up a electric Vs.gas debate as they are entirely different methods.
My efforts to date have been direct injection of steam for wort heating/step mashing, and soon to follow with GreenMonti's help, steam wort boiling.
When revised boiler coils and calandria are installed in new system the data logging in the control software will help resolve the questions about amount of heat needed to boil.
I dont care what method people use to heat their systems either. But it does no good to have a plethora of false information out there, that doesn't benefit the community.
Bottom line, you need about 10,500 BTUs to boil off what most HBers boil off in an hour. According to testing completed by myself and others, gas burners under a kettle are 20-30% eff. and therefore typically heat slower than electric kettles, it is just a matter of BTUs and volume.
This thread started off as a gas boil vs electric boil thread... that is why it is where it is.
Both work well, I have used both extensively, but to say that electric kettles are slow, more costly to operate (energy), or that they do not truely "boil" the wort, are all false.
Whether you have a 4000W heating element or a 60K BTU burner, you are doing the exact same thing, same times, same boil off... one is just louder and more expensive to operate than the other during that hour.
Last edited by willynilly; 03-21-2010 at 07:06 PM.
I thought this was better up here then in the DIY where I hang out. The question is,
What constitutes a good boil?
I am wondering this due to another thread about BTUs. I am having a difficult time with the BTUs right now. I have learned that an additional 970 BTUs is needed to convert 1 lb of water into 1 lb of steam. With the electric revolution for boiling wort and my lack of knowledge on what an electric boils looks like. I decided to post this up in hopes it could be discussed and have a little clarification. I did a Google search and the first video of an electric boil that came up was this one. I know he has a thread here and also has this video up on here. My question is, is this a good enough boil?
The interesting thing to me on this is......There is no bubbles. Zero gas formation. There for not getting the extra 970 BTUs needed to convert the water/wort into steam. What is being seen is just the lost heat due to evap and not a change in state due to heat input. If this is to be considered a good enough boil, then the gas folks can turn things down a bit and save some coin.
So it takes 10,500 BTUs to boil off about 1.3 gallons of water in an hour...
That 7000 BTU kettle is over 21,000 BTUs directly applied to the water...
Why would you go assuming that it is not powerful enough to facilitate the state change? Seems to me that it is overpowered by 100%
Help me with the math here, if you have 13 gallons at 8.4Lb/gallon and need to add 970 btu's/Lb for all the liquid to reach a boil, how long is it going to take with 9 Kw. What might seem like a boil is related to the high surface temperature of the elements flashing the surrounding water to steam but it seems that there is not enough total energy in the kettle to reach a true boil. The water heating to boil temperature is only 15% of the energy needed to boil, the other 85% is the heat added before boil happens.
Assuming the contents are at 212, for each 970 BTU you will get one pound of water to convert to steam.
A 9000W element is equivelent to 30600 BTU/hr.
(30600 BTU/hr) / (970 BTU/lb.) = 31.5 pounds of water vaporized in 1 hour. That is 3.78 gallons.
BTW, "flashing the surrounding water to steam" would be boiling. Don't fool yourself that entire contents of a pot over a flame is boiling: it is only the bottom inside surface of the pot that is boiling.
That doesn't even sound right, does it? 
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