The Alcohol Stove “Efficiency Percentage” Test Thread

rather than talking about "boil", measure temperature of water before and after. Assume that when you say "boil" you mean raise temperature 90 C (or whatever).

As long as there's a lid, and you don't get too close to boiling, it's fairly linear.

Best thing is to, like in Roger's tests, have a hole in lid, stick thermometer through it, make sure thermometer doesn't touch bottom, maybe in center of water in height, halfway between center and edge in the sideways direction.

You can just get a digital cooking thermometer, like for measuring temperature of fluid or meat.

Jerry, what you describe here is almost identical to my test stuff.
My starting temp was different only because my water stays between 40F and 50F (4-10C) year round. Berhaps a better test would be to start with 32F/0C water by taking a pitcher of ice water. Simply add a bunch of ice and wait till it stabilizes (about 10 minutes to reach 31F-34F or about plus/minus 1/2 degree C.) Note that there is always a difference between water supplies. Minerals/salts make more difference than a 1/2 degree C.

I avoid the altitude issue by simply heating to 200F or about 93C. Unless you are exceptionally high in a bad storm, this should cover most situations.

Condensation is probably not too important. At first, it will add heat to the system. Later it will take that same heat away as it evaporates. I doubt that himidity has much of an effect either way unless you condense enough for actual drops off the bottom. Even then it would be minor compared with the overall heat to boil two cups. This could be as high as 2-3%.

I used two cups as a measurement. This is 16oz or a pint, or, ~473ml. A more standard measurement would be 500ml.

Being as close as possible, I ran the same boil test 10 times with the exact same setup. I got a devation of about 6-7%. So, I would say that a 10% error in any measuments would be expected. Beyond that would be significant.

David: First off, I really appreciate your dedication to experiment.

I agree with your points for making the efficiency calculations more accurate: measuring weight of fuel and water in ml; measuring end-of-test heat with thermometer instead of “boil,” (which can be done with Ben’s spreadsheet); factoring in barometric pressure, which is more accurate than elevation; and accounting for the potential effect of humidity. I think adding these parameters are the natural evolution of what’s been started here. I’m all for building more complex, accurate formulas that account for more variables, if we can do it. I don’t have the background to do that, but we do have thermo engineers who frequent BPL.

On the other hand, simpler formulas allow more people to participate. For example, I don’t have an accurate enough scale for ml; my resolution is .02 oz. I don’t have a barometer. And I don’t have a hygrometer. Chances are low I’ll obtain these to do testing. And I don't need them to do comparative testing among my own experiments. This seems to always be the decision that must be made: more accurate but less data with more effort and expense, or less accurate but more data with less effort and expense. In my experience, raising the bar too high means that only a few experts participate, and you get the “academic journal” effect, ie, most people tune out. But lowering the bar too far yields junk data.

Maybe we can cover both ends of the spectrum if testers simply report which of the various spreadsheets they’re using. So far we've got:

– Ben's original sea-level spreadsheet that allows for multiple tests (mostly metric)
– Glenn's single-test sea-level spreadsheet (many measurements modified for English standard)
– Glenn & Delmar's single-test altitude spreadsheet (mostly English standard)

Well I'm still not convinced that altitude has any real bearing, since the lower boil points and the less fuel used to reach them seem to offset each other proportionately. Of course unless I go climb a mountain, I'd never be able to prove it. Barometric pressure might play a larger role, and if I had a barometer, I'd use it, maybe someday, but not today, sorry.

I won't be weighing my alcohol, since I feel a 1% variation is acceptable, and easily attainable with a simple 5 ml oral medicine dropper. I do weigh my water, and I don't think that's expecting too much from anyone on this forum, since owning a scale is practically a prerequisite to being here ;)

I like simple, keeps more people interested. Eyes tend to glaze over if things get too technical and it's just no fun anymore. Which is why I simplified Bens original spreadsheet in the first place, and to eliminate conversion errors like David mentioned. I did the same thing initially, now, no more.

I'm certainly not against more data, but I think the point of diminishing returns has been reached. Piling more data on at this point would change outcomes by what? a couple percent max? Probably not much more than boil to boil variations from crude fuel mixtures anyway.

Delmar originally suggested posting all pertinent data, not just efficiency reading outputs. I agree'd then and I still do. Anyone can then use either the "basic" calculation, or the "advanced" model to reach their desired conclusions. Meanwhile, the individual user can get good relative comparisons using whichever model they feel comfortable with to better improve his/her designs.

To this end, I feel there should be only 2 worksheets, the basic, and the advanced. We have the basic, and it should be left alone. The advanced can always be improved upon for those so inclined to push the envelope further, factoring in barometric pressure, elevation, humidy, etc. Whatever our engineering friends would happen to bestow upon us by way of formulation. The advanced worksheet can continue to grow, while the basic remains the foundation of the project. That's my 2 cents anyway.

I would also like to add that I'm under no delusion that any of us are breaking any new ground here. This has all been done before, ad nauseam. But proper understanding comes from a bit of self discovery, so there's only so many shoulders of giants we can stand on if we want a deeper learning for ourselves. I guess I think of it as a chemistry kit as a kid growing up. Nothing new, just fun to learn. :)

In a former life I was a spreadsheet geek so I'm a bit bothered by the Fuel-to-Boil formula. It's a bit more complicated than need be. As coded up, the two .789 constants cancel each other out so they are not needed

Original – C8 = The Fuel-to-Boil Formula (ml) =C4*.789*C2/C3/.789

Simplified – C8 = The Fuel-to-Boil Formula (ml) =C4*C2/C3

As I understand it, it's just a simple ratio of Boil Time to Burn Time used to estimate the amount of fuel burned to get the water boiling.

It's an interesting hypothesis that stove + setup *efficiency* may not actually vary by altitude (or that if it does, it's decimal dust). Boil time will certainly vary, but that's not the same as efficiency. At high altitude, a boil represents less fuel used to reach a lower temperature, compared to low altitude where your reach a higher temperature with more fuel. If that hypothesis holds, then the next questions to follow are: would barometric pressure or humidity affect a stove + setup's *efficiency*? Tempting as it is, let's not conflate time-to-boil with efficiency.

It's testable. As Glenn says, measure efficiency of the same stove+setup at low elevation and high. Easiest to test would be the humidity hypothesis. Do a boil in your (dry) bathroom, and another in your (moist) bathroom with the shower running. I'd guess that high humidity would lower the efficiency, but…who knows? Maybe the flame would shrug off the moisture in the air.

At any rate, each variable (humidity, altitude, pressure, wind) would need to be treated as orthogonal…just because one does or doesn't have an effect, tells us nothing about the other variables (with the exception of altitude/pressure which should be highly correlated).

PS: I like the two-formula solution, basic and advanced, for the time being. But we should test to see if advanced is actually necessary, if it gets a better bead on efficiency or not. Occam's razor, you know.

PPS: Richard: the beauty of peer review. Thanks.

Ah, there's the redundancy. I knew it was lurking in there somewhere. Delmar eluded to it earlier, but we were still trying to convert the original formula from grams to mm for fuel consumption and comparing spreadsheet readouts from the original.
Thanks Richard.

Heading over to my Fosters thread to make the appropriate changes :)

Regarding the altitude calculations within the advanced spreadsheet..

Earlier in this thread, I had mentioned "providing a chart with the corresponding boil temperatures that the end user could then enter" instead of using a formula. After thinking on this some more, I think it's the only viable option because just entering elevation into a spreadsheet does not tell the user at what temp to take a reading for boil time.

I'm at 900 feet elevation, so I plug 900 feet into the spreadsheet, but how am I to know that I should mark my boil time when the water reaches 210 degrees? I can still get my water to 212, and have been doing so, but it's 5-7 seconds after a visible boil and the water is really roiling. If there was a chart that I looked at to gather my boil temp goal for my appropriate elevation, and entered the upper temp limit accordingly, instead of the actual elevation, then I would know where to take my timer reading at and the formula would just calculate off the lower entry.

On an aside, my ratings appear to be taking about a 3/4% penalty by not factoring in my elevation. Not that my efficiency actually got any better, just that the calculations were factored at sea level from the start.

Which makes me rethink the elecation vs efficiency theory I had earlier. I still maintain that it quite possibly is a negating factor, as I mentioned, however… That would only apply when comparing the same system to itself at different elevations. The efficiency of THAT system wouldn't change much. But now if we're to compare say, Davids system at sea level, to my system at 900 feet, then I guess we probably should be factoring elevation to get an apples to apples between the different systems at their operating elevations. Am I making sense? I think my head is starting to hurt lol

Glenn, Just a quick comment on your final paragraph (still thinking about the rest of it):

The name given for the type of research where you compare David's results to Glenn's results is called "Between Subjects" data. The name given to research where David is boiling with a small lid or a big lid is called "Within Subjects" data–in that case, one subject (David) is providing multiple data points to compare with each other. Analyses with WS data are more sensitive (less random error, easier to find effects) and often have built-in controls (David did all his lid boils within an hour of each other, at the same location, so no need to collect altitude, humidity, pressure…). It's when we start comparing our gear to someone else's gear that we have to start worrying about all those other variables that might affect the results. So, yeah, if you are doing your own testing where you compare one variable to another, say, does a black pot beat a brushed pot, then a simple efficiency formula will tell you what you want to know, which is: which one wins.

What we're chasing now is a way that people can compare results with each other. That puts us into "BS" data (no pun intended) and is of greater complexity, since you try to control or account for variables that impact the results. This underscores your previous musing that we can get by with one simple formula (which we already have) and one complex formula (which we're working on). The existing formula is sufficient for WS "which setup is better" analyses; the complex formula will be best for BS "is my setup better than yours" analyses.

It would be easy to say that the WS data is what we really want and the BS data is just a pissing contest of sorts. But comparing results really does motivate us to try harder. If David and Glenn are getting 70% efficiency scores, you think Delmar can sleep on his NeoAir at night, knowing he's only getting 40%? Think of the BS data as driving innovation.

Regards knowing exact temp of boil at a particular elevation, anything wrong with using the chart we've already found?:

http://www.engineeringtoolbox.com/boiling-points-water-altitude-d_1344.html

The exactitude worries me a bit; not sure our thermometers update quickly enough (or accurately enough) to take advantage of the additional accuracy afforded by the chart.

I think that chart is great, a little too great actually. I agree that it's too much info for our purposes. I think some rounding of values would be in order. A quick overview seems to suggest that steps of 500 feet, with occasional steps (every 3500 feet or so) of 750 feet, would make for whole number temp readings that were only rounded from a 2/10 of a degree. Again, this was just a quick readthru.

Of course we could keep your calculation in the formula, and just have another cell that displayed the target temp data based on the user elevation entered, which might be more precise, and only be more complicated behind the scenes. Since we've been able to display our formulas within the forums here, a simple copy/paste method by the user should afford some leeway for spreadsheet elaborations.

Here's what I getso far with that idea:

Thoughts?

I like the display of the target temperature, that would take a lot of "slop" out of the system determining what, exactly, is an adequate boil.

Went back and reviewed my excel functions, and the vlookup command would work well here. The columns are just pasted in from the chart we found online, and I made the formula visible below. (Note I did not take the time to weed out small increments, just pasted the chart in wholesale.) As I understand the vlookup function, if you enter in a unique number not in the table, it'll default to the next lowest number that is in the table.

So, for clarity, you enter your altitude at "Enter Alt Ft" and the "Targ Temp F" is supplied by Excel's lookup function. The range E2:F86 defines the table (I only went to 20K feet), the "2" says return the matching figure from the 2nd column of the range, and TRUE gives permission to round to the next lowest number in the table.

I think at some point it'll be easier for folks to get a copy of your spreadsheet, than to build their own. You know how easy it is to misplace a parenthesis or etc. Particularly, if you put the whole lookup table into your spreadsheet. But, that's your call.

(And I can't help but get the impression that your spreadsheet really wants to be a smartphone app someday.)

Honestly, I think you are on the right track making a simple (but accurate) calculator. The easier you can make it for people to calculate their own testing, the more tests we'll have…a renaissance of stove testing, perhaps.

A final boil time is helpful, but is that what you're after? Aren't efficiency and time to boil very related but slightly different measurements?

If the temperature rise is linear enough (that's an IF, it has been said it is, but I don't know) would a "time to raise 50celsius" be a simple efficiency test?

You could plot the time per 10c rise, and blow out and weigh the fuel at 50.0c rise. Or plot temp rise every 30 seconds.

It removes starting fuel amount, stove "bloom", start temp, elevation and possibly other variables.

Would recommend 500.0g water as the baseline for any test. Cooking grade grad cyl are several percent variable once you include person-person variation. We all have a scale. Measure, weigh then repeat in a couple of days if you don't believe me.

Also, someone needs to make and share a google docs spreadsheet. And decide on a test protocol. Only then will I spend an afternoon boiling water for no good reason (5 cups of tea?). I have a brasslight to toss it's hat in the ring when the parameters are settled. Curious to see how it stacks up (it is a very heavy alc stove tho, but feels efficient).

> A final boil time is helpful, but is that what you're after?

It's specified as a target, to help you mark an accurate time to enter into the formula. Efficiency (not boil time) is the goal for this exercise.

> Aren't efficiency and time to boil very related but slightly different measurements?

Distant relations at best. Take my SuperCat, for example. Fast boil time, very poor efficiency. Sucks fuel like a '70s muscle car.

> "time to raise 50 celsius" be a simple efficiency test?

That would be a speed test. Granted, that's what some folks are after, and there are times (eg, you're hypothermic) that speed is more important than efficiency. The unstated goal of this exercise, however, is to see how little fuel we can carry and still get our oatmeal cooked each morning. We're trying to eek out every last joule of energy and turn it into heat. Too fast and it's wasteful of fuel. Too slow and the heat is carried off into the environment without completing its assignment.

If you read David's thread where he's testing "aluminum hats," you'll see that, based on boil time, we thought the hats were a bust. But then Ben calculated efficiency, not speed, and it turns out some of the hats increased efficiency. Since efficiency was what David was after, the benefit of his invention was hidden until Ben gave us a way to test. Speed as a proxy led us astray on that one.

Would love to see your brasslight tests, when you get the time.

Boil time is just one of the many variables we're trying to factor in. Boil time alone does not equate efficiency, which is how this project came into existance.

Heatup only becomes linear about 30-45 seconds after the stove warms up, after the bloom. At least that's been my observations when I monitor the process. So measuring fuel mid-burn seems haphazard at best.

A google doc sounds interesting. I don't even have a google wallet though, but I'll look into it when I get home. It would be nice to see some more parameters addressed before an actual "release" though. Barometric pressure seems an important one. I'd think if we could nail that one down, I'd be comfortable with a Version 1.0 :)

I'll be bummed if your final SS requires barometric pressure, as I own no barometer. But, if it's an important variable, it has to go in. Science Uber Alles!

http://www.scsenergy.com/scsdatawaterboil.htm

Looks like 1000 feet changes Hg. by about 1 In. and vice versa?

Well with elevation, one can neglect entering any information at all and the formula would default to sea level. Hopefully the formula can be crafted to utilize a "standard" pressure reading, for those that elect not to include barometer readings in their formula. It would just need to be stated in their posting where all the variables were listed for peer review, as discussed.

Now not being very traveled man, owning no barometer, and lacking any formal education, somebody enlighten me…

If this formula utilized ONLY barometric pressure, instead of elevation, would that not already have the elevation factored in already? Isn't this a bit of and either/or situation? I mean that's all elevation is, is a drop in air pressure… (oxygen levels for btu output is a bit beyond my scope I think)

Like this? http://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html

but nothing relating it to boil temps… yet

Seems to be something about a "Vapor Pressure Curve"…

I really should have got one of them fancy college educations. I'm not the guy to be doing this lol

Just came back to post that in my previous post I was being stupid. No need to manipulate the altitude formula, or enter altitude at all, if you are factoring in barometric pressure. Altitude is just acting as a rough proxy for barometric pressure anyway. So your "gold" formula will factor barometric pressure and your "silver" formula will substitute altitude instead.

And I see in the time it took me to think that, Glenn already figured it out.

Don't forget, Glenn, your same argument that "if you reduce the numerator, you reduce the denominator at the same time" might apply to barometric pressure too.

Seems to be what I need to enter to get the vapor pressure curve, which would allow us to enter a pressure and get a boiling point in return.

This is way over my head. Any thermal engineers out there that can put it into a simple formula that can be entered into a spreadsheet?

Is this the right thing to be chasing down at least?

I keep finding the following formula and the online calculators;
http://www.ajdesigner.com/phpvaporpressure/water_vapor_pressure_equation_temperature.php
display the correct answer, but it doesn't work properly for me if I enter the formula manually:

=1730.63/(8.07131-log(10)*P)-233.426

Where P = pressure in mmHg(760 for sea level) and the cell should output the temp in Celcius.

Where's my error? Or am I even close?

Ok, both of those responses make total sense.

What I failed to write was the most important part: still weigh before/after fuel. Just don't fret over finding an exact boil time, but focus on energy/time. joules/second wouldn't be a bad comparison.

The starting fuel doesn't matter if you just use a standard fill for your stove. The net fuel burned is what you want, so I think any test needs start/finish fuel weight.

I guess what I'm getting at is that boil isn't necessary to arrive at efficiency (though it would be nice to know). Picking a protocol that didn't concern finding boil would simplify some variables.

I also say plot the time/temp because the slope of the line becomes the data point, not a single reading. It gives internal average within a test to remove sloppy readings. I have 3 thermos for my darkroom and i can tell you each differs a few degrees once you consider reading the tiny scale.

Hope my suggestion is less sparsely explained with that.

Edit to add: you could run the stove ON the scale and get some fuel burned data at each reading. Obviously somehow protect your scale from fire.

Put all apparatus on scale (including pot and water) tare the scale. Add fuel, note weight. Light the stove, let it bloom, note weight and place the pot aboil. Note the weight every 10c (keep time for a boil if you wish ).

Does that not arrive at Celsius/gram fuel? To compare to others you need to standardize water amt.

Glenn – You've got a parenthesis or two out of place.

If you put pressure in cell B2, the following equation works (at least it gets 100 degC when I plug in 760 mmHg).

=1730.63/(8.07131-LOG10(B2))-233.426

Hi Glenn, sorry to leave you in a lurch, but I gotta get to an appointment. I did a quick and dirty linear regression (of what appears to be slightly curvilinear data, just as was the case with altitude) and this formula for predicting boil temp from In. Hg. will get you close.*** Maybe you can use it for a rough check — obviously using a formula that precisely fits the data would be best, and it looks like the one you found is curvilinear, so feel free to ignore this stop-gap measure.

C of boil = 67.2 + (1.0968 * In. Hg.)

F of boil = 153.2 + (1.9677 * In. Hg.)

Data from here: http://www.scsenergy.com/scsdatawaterboil.htm

*** By "close" I mean within 200-300 feet of actual, if we were talking altitude. I'm using feet as an analogy, because it's not as abstract as In. Hg.

Richard to the rescue again! I could have sworn I tried every possible parenthises combination. Clearly not. Thanks Richard!

Delmar, your equation would probably be close enough, but I'm working a theory for a little bit. It's straining my brain, but I like a challenge lol
By the power of google, and some great BPL crowd sourcing, I hope that by combining some data and conversion formulas together, to make a multi-scenerio do-it-all formula.
Since I've never had a barometer, I guess I wasn't aware that they're calibrated at elevation to the local weather station readings, apparently with a sea-level conversion of a .06 adjustment for every 50 feet of elevation (ok, that was off some local news channel, not accurate enough). My ignorance is quite vast, but hopefully my intelligence will win the day. Time will tell!

I agree that this would make a pretty cool app, any app developers out there? ;)

Alright, well I think I've got it down for a Version 1.0. There is an additional row for barometric pressure, but for those without barometers, it can be left with a single atmosphere standard of 29.92. Basically, just leave the default entry. By playing around with the numbers though, it does seem to make a considerable difference.

From one extreme to the other ie: Very stormy (28) to Very dry/fair (31) there is about a 5 degree boil temperature range. Quite dramatic in terms of efficiency ratings. I hope all my factors are correct.

I've used the Antoine equation with the constants for water below boiling, combined with Delmars extrapolation of the elevation variance chart, converted to Fahrenheit.

I'll look into that google docs thing when I get a chance, or I can post all the information here, as we've been doing, for copy/paste, or I can email what I have, or… All of the above. Be forewarned however, they're calling for 50-60 degree days here this week, and my cabin fever is approaching an all time high, so I might begin lagging a little in my online time :)

As far as weighing fuel before, after, or during a burn, it seems a little more complex than an average user would be willing to do. I know my scale doesn't go down to hundredths of a gram, and even weighing whole grams is finicky. They build wind boxes around this degree of scaling when done at work, I sure won't be doing that. I do agree however, that for peer to peer comparisons, a standard of 500 ml/g should be used. It's easily weighable for most any person with even a modest scale. I'm not going to make it a constant in the spreadsheet though, because some systems just aren't designed to boil that much water, and I'd still like to see them tested. That information would be presented by the user in their post though.

BTW,

The easiest way to measure "efficiency" is to measure and add enough water to keep the water from boiling. For example, use 15 ml and heat up 3 cups of water. Measure the final temperature and use that in your calculations (BTW, you have to mix the water before taking the temperature).

First, it is hard to get a consistent time as to when water boils, everyone has a slightly different interpretation. Second, when water boils, the heat transfer is somewhat inefficient. The energy superheats water creating a bubble. the bubble rises and pops at the surface, release hot vapors that are not transferred to the fluid around it. You can see this when to apply a pinpoint source of heat and the bubble rise from that particular point. Water away from that spot can be much lower than the boiling point.

My 2 cents,

Jon

Now I am going to throw you a curve ball.

The air pressure at 20,000 feet is not necessarily equal to the air pressure at 20,000 feet. Anybody who climbs Mount McKinley finds this out.

The air pressure on a 20,000 foot peak at the Equator is higher than the air pressure on a 20,000 foot peak at a higher latitude nearer to the poles. In other words, the air density at Mount McKinley is thinner than the air density at Chimborazo.

So, you are more accurate to use Barometric Air Pressure as your factor, and not Elevation.

–B.G.–

Ok, so here's my dig on efficiency.

Boiling point is actually kind of useless as a determiner for, well, for anything really. Real water temperature would be more determinate. But for our friends in the upper elevations, reaching a temperature of say, 200 degrees, is unobtainable. So we'd need a different system, like has been mentioned, we could use extreme parameters and extrapolate efficiency from the linear read out. Using too much water, too little fuel, a temperature of only 150 degrees, or other limiting factors solely for the function of extracting an efficiency rating.

All that is great for the cast of BPL, who has a fairly high scholarly membership and a critical eye. But let me pose this question: When was the last time you saw an average Joe Dirt guy like me, on a You Tube video, or a forum, say something like "Dude, I got 6 cups of water to 150 degrees with only 15ml of fuel!"? Never. It's just not fun. Not even the guys that sell stoves use that as an advertising hook. It's always about boil times. Boiling water is a universal test parameter that ordinary people can relate to. So for me at least, it's not just about finding an accurate efficiency quotient, it's about forming a set of parameters in a realm populated by average people that just want to boil water for experimental fun and comparison.

Using odd parameters like excessive water or minimal fuel doesn't test the system in question. Like guys who want to test an almond can for example. Or test variations of windscreen effectiveness on a certain pot design. Or compare my Ti pot to your Imusa mug, to Davids beer can. A linear read could be used I suppose, but there would still need to be a formula and spreadsheet used anyway, for degree rise, time elapsed, fuel used, energy consumed, etc. Some numbers could be thrown around making comparisons, but to get an efficiency rating still requires calculations. Calling this "stove" efficiency might be a bit of a misnomer, but it's not just a burner that's being tested, it's the whole stove system, and to what degree of efficiency the fuel is being utilized. At least that's my take on it.

So anyway, I'm rambling a bit, but for me, I'd like to see a simple formula that anyone can simply weigh up some water, measure out some fuel, get the local barometric pressure off a news site, put in their elevation constant, and stick a thermometer in a pot. Stop timing when the spreadsheet tells you, and get a reading. To tap into a different thread discussion, I'd say my mom could do this.

This isn't a perfect answer, and most everyone on here will find flaws and faults with it, that's the very nature of BPL lol. I understand that there are better ways to test efficiency. I realize the formulas for this simple task are more complex than need be. But I'm pretty happy with what we've achieved so far, and I'm hopeful that others will find it fun to play with. I know it's been a learning experience, and as I've repeatedly stated, that's kinda the whole fun part for me. :)

Edit: Getting a barometric reading AT elevation is problematic, since it's not posted as an absolute pressure, but an adjusted for elevation one. So to use adjusted barometric pressure AND elevation, it can be brought back to an absolute pressure reading. I've yet to find a formula for combining the two effectively. Hence my own morphed mixture. Maybe there will be a V.2.0 in the future :)