Improved Stove Efficiency Calculator/Spreadsheet

Thank you Ben! What a great looking spreadsheet. Looking forward to trying this.

WOW, my efficiencies go WAY UP using your new SS. For example, my current "altitude" SS for a recent burn calculates 65.7%, but your new SS calculates it at 74.1%

…so, to make the biggest efficiency gains, I just need to use a different spreadsheet! LOL

Initial Impressions:

– Love the "end temperature" addition. Several times I've had to scotch an experiment because I almost but didn't quite get a boil.

– Difficult to scroll and select the options on my Mac. Any way to see more of the scrolled list than two options at a time?

– What are we to enter for Fuel Energy? For example, I'm using either Klean-Strip SLX or Klean-Strip Green. Perhaps add a list of common options here? In the ASEPT thread, Richard Cullip gives kJoule/g values and estimates, saying "…SLX which is about 50/50 [ethanol/methanol] and the last one is Kleen Strip Green denatured which is ~90% ethanol…"

– Fuel Density: "Fuel density is only used if volume is specified elsewhere." Don't understand? This stays at .7 by default?

– Boil temp goal is now "Boiling Pnt"? One mod I'll need to make is to convert that to F, which is what my thermometer displays.

Love the spreadsheet, excellent job Ben, thanks from me and from all of us.

Do we (or will we) have a central place where people can share and compare their results? I don't really have anything to contribute, but I'm planning to shamelessly leach off the scientific efforts of you fine people and just get/make whatever stove comes out on top.

> Do we (or will we) have a central place where people can share and compare their results?

I had started the "Alcohol Stove Efficiency Percentage Test Thread" for the purpose of recording tests and collecting results. Of course you can also post links in the ASEPT thread to your own thread, if you prefer.

http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=89347

Ben: This is what I mean by "hard to scroll" on the Mac. Your SS looks easy with the up/down arrows, but I don't get that, I get a partial scroll bar:

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Quite different results from the SS I'm using now:

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Why such a big difference in results?

I'm at work, so don't have access to the actual spreadsheet, but looking at this thread, something confuses me.

It looks like elevation or barometric pressure is an either/or type of entry, when both need to be factored in. Barometric pressure only affects the boil temp in extreme cases typically, but still wondering how to factor it in.

Barometers are calibrated at altitude, so that a reading of say, 29.92 is relative. The absolute pressure would be different, because of elevation, but calibration factors the elevation into the reading from a run of the mill barometer.

I thought we decided that if you put in a well-calibrated barometric (such as an internet look-up for your area), then altitude was superfluous. And if you didn't have barometric, then you should use altitude as the next best adjuster. If that's the logic, then it would make sense to have a choice between barometric (the more accurate measure for adjustment) and altitude (the next best measure for adjustment).

My concern is the disparity between the SS we have been using, and Ben's new SS. On my best boil to date, the efficiency improves by 8% using Ben's new SS. Does that mean there's an error in one or the other SS?

Well, when you look up the boiling temp in that altitude chart, that's at one (compensated) atmosphere, or 29.92 on a standard barometer. Barometric readings are local. If you brought that same barometer down to sea level, it would be off the scale, and need to be re-calibrated to that different elevation. From what I've seen, barometers have a very small pressure window, and must be calibrated at the elevation they're to be used. Google up "barometer calibration" for a better explanation than I can give.

So if you're at 5,250 feet, and you have normal weather, and your local barometer reads 29.92, you still won't boil water at 212 degrees, it will be 202 degrees. If the local barometer reads, say, 28.5 at that same elevation, because of a storm, then boiling temp is only ~200 degrees.

For example, David and Galen can BOTH have barometric pressure readings of around 30 inches, but their boil temps differ by 10 degrees due to elevation. But if either one of them have a storm front move in, they'd still need to compensate for the pressure change with a barometric reading, and their boil temps would vary accordingly.

If someone can find the ABSOLUTE barometric pressure, then that can be used instead of the combination of local barometric pressure AND elevation. I'm not sure where the assumption that local pressure was a substitute for elevation came from, and I don't know where an absolute pressure reading would come from.

Basically, elevation is "roughing in" the boiling temp, while barometric pressure is the "fine tuning". Hope I'm making sense…

Guys, I have a chart for you. This may not be quite as accurate as what you seek, but it might point you in the right direction. This shows the pressure at altitude as percentage of sea level air pressure.

–B.G.–

Glenn, I understand now, thanks. I don't own a barometer, and had been looking at these charts that equated elevation to certain barometric changes, so I was laboring under the idea of "absolute" barometric pressure. Which, as you point out, is not used.

So what you are saying is: you want a way of inputting elevation as rough adjustment, and then inputting local barometric deviation on top of that as a fine adjustment. It seems possible to convert barometric deviation from normal, to a certain number of feet of elevation gain or loss. So that would give you a "corrected" altitude, if you will. All I'm saying is, it seems possible to do.

Exactly. That's how I come up with the boil temps over on my SS. I didn't post my final version 1.0 until I had that figured out. But in discussing this, I believe I've uncovered an error in my Efficiency calculation. The barometer compensated temp is used to factor the boil temp, but it isn't carried down into the Efficiency formula, which still uses 100c with only elevation adjustments as the baseline.

In cell C10, replacing (100-.00104*C9) with (C2-32)/1.8 would replace the elevation-only adjusted number, with the barometric+elevation adjust number from cell C2. I'm kinda surprised nobody caught that yet.

EDIT: I've now made the changes over on my sheet accordingly.

Another minor hangup, is that this calculates the barometric deviation (using the Antoine equation) before the elevation factor, when I believe the elevation should be factored first, then barometric accounted for. The Antoine equation (which calculates the Vapor Pressure Curve to boil liquid based on sea level) uses constants (based on the liquid used, in this case water) and a logarithm (1730.63/(8.07131-LOG10(BaroPressure))-233.426) that I have no clue how to turn into dynamics. The differences would be quite minimal I suspect, so as always, a work in progress.

I've made mine a V.2.0 now, but it's all rather moot, since Ben has this fine, outstanding sheet with so many user variables. Well done Ben! I'm still unclear on the barometric vs elevation option in it though.

Glenn, when you use any of your past spreadsheets, how do they compare to the results of Ben's Improved Spreadsheet?

Regards your barometer-corrected SS, I confess I didn't use it…I didn't understand what you were doing at the time and ran out of time to follow it. So I failed you, peer-review wise. My plan was to develop a similar barometer-corrected SS through a different process, for the purposes of cross-checking yours. It would have been using a VLOOKUP instead of a formula, then converting the barometric pressure difference to the equivalent feet of elevation difference, and then modifying the feet of elevation used in the formula based on that. But, I never got around to it, and now have no motivation to try it, given Ben's Improved is here. I think my lack of motivation is justifiable; Ben is a thermodynamic engineer, and I am most decidedly not.

Still curious though, why my past test results (based on Ben's initial SS) improve so dramatically using Ben's Improved. What changed? Am I really getting 74% efficiency with my relatively crude setup? Have I made an input error on Ben's Improved?

I'm using open office and am having trouble scrolling through the choices too. An I also am getting way higher eff % than before ie same numbers on the prior sheet produce 64.9% and on the new ss it produces 78.2%. Might be the different program used from the original office program especially if vba was used. Also there is a significant discrepancy in amount of fuel to boil between the spreadsheets which is what I'm most interested in.
I updated the prior sheet with Glenn's update which increased the eff by a few tenths of a percent.
Here's what I get on Glenn's ss when entering the numbers from your ss Ben. I had to modify the altitude and the barometric pressure to get 200 degree boil temp. But it appears that you may have been using feet of elevation of 200 and when I do that to Glenn's sheet I get 61.0% eff. ?????

Still not sure on how Bens SS works, since it's just a picture on my iPad, and too complex of a sheet for my phone, which is where I do the majority of my SS work. I've never used google drive, so I'm sure I'm doing something wrong. I had my netbook on this morning to get a new SS snapshot, but it struggles with excel just opening it. Google drive is forbidden on work computers, and my desktop froze up, so I might be a while getting to Bens sheet. So as far as efficiency discrepencies, I have no idea. Ben has created both the original efficiency calculations, as well as this new one. Delmar and I have only introduced elevation and barometric pressure variances to the actual boil point, which of course, does effect efficiency. But the actual efficiency formula is essentially unchanged from Bens initial inception.

Galen, if you look at the chart at:
http://www.engineeringtoolbox.com/boiling-points-water-altitude-d_1344.html
You'll see that at 5,250' elevation, the boiling temp is 202 degrees. My sheet shows your 5,297' to be 202.1 degrees, which is off by about a tenth and a half. (I'm a little confused as to why you'd adjust your elevation to get a 200 degree boil temp.) It's not a linear chart, so these minor discrepancies are expected. It's the reason Delmar is using the vlookup function in his sheet and cross referencing it all to that chart (Delmar could just plug the elevation in directly, since it's really an individual constant). I went with the formula instead (which incidentally was also discovered by Delmar), to make it much easier for others to just copy and paste off the web. Ease of use and availability in exchange for some very minor discrepencies I thought was a good compromise.

After reducing pressure with elevation, adding back a little pressure with a minimal barometer rise of 30.17, brings the boil temp back up to 202.5 degrees. The barometric calculation was the only part I brought to the equation. That, and a little condensing of the info to make it easier to distribute.

It takes a pretty large barometric change to have any meaningful effect on the boil temps, or efficiency outcome, which is why the changes from my little error were only in the tenths. If there had been a storm and your barometer dropped significantly, you might have seen a 2 degree change or so, but so far everyone has had relatively calm weather, so no real foul.

As I mentioned above, elevation is the main player, with the barometer just being a minor fine tuning. We wanted to geek out on how far we could take the accuracy of this efficiency thing, and the barometer fit the bill.

Okay guys, my head is officially spinning but, no worries, I've wrapped it duct tape to make sure it doesn't explode. I now know way much more then I ever cared to about barometric pressure but have been enjoying the discussions and learning opportunities.

After looking thru Ben's new spreadsheet, as stored on Google Docs, and comparing results with older versions I understand the reason behind the differences in calculated efficiencies. It has to do with Ben's conversion factor of 0.7 used to convert btwn ml and grams of alcohol. Previous versions of the equations and spreadsheets have been using 0.786 rather than .7.

Doesn't sound like much of a difference but it has a big effect on the efficiency results. Using Ben's new input values with the .7 conversion factor yields his new efficiency of 68.6%. Change that .7 to 0.786 and the efficiency drops back to 61.1%.

.789 is what I've read… Not that .003 is very relevant lol

Glenn – We are both right. Density of alcohol is temperature dependent. Density of ethanol is .785 @25C and .789 @20C. Methanol comes in at .7865 @ 25C and .791 @20C

Ha. It's never easy is it? Nice catch on the matter btw.

Richard, kudos on the brain acrobatics it took to discover that .7 vs. .785/.786/.789 explains the difference.

So, are you recommending a change in cell C8 from .7 to .78X? And what would you set B8 to, spec grav? g/ml? lbs/gal? They all give the same result.

Results are more in line if I change C8 and set B8 to spec grav or g/ml or lbs/gal. On the test I posted above:

65.7% with the "classic" Ben/Glenn spreadsheet
74.1% with the Ben's Improved under discussion
66.1% when I change .7 to .785 in cell C8 of Ben's Improved
65.8% when I change .7 to .789 in cell C8 of Ben's Improved (.789 was the number the "classic" was using)…and now we're back to .01% of the original calculations.

For my neck of the desert, the 77F/25C (=.785) is the factor I'll be using from here out, it's more realistic.

Found an easy fix for those of us having problems with the scrolling boxes inside the SS.

First, give more vertical space to the rows that have scroll boxes by dragging the row header borders until more space appears for the rows that have scroll boxes in them.
Second, right-click or control-click (Mac) on the scroll bar portion of the scroll box. (Not inside the scroll box; on the tiny scroll bar or up/down buttons if that's all you see). Now, adjustment handles will appear.
Third, grab an adjustment handle and drag the scroll box larger, see more options, get a normal looking scroll bar on the side.

Delmar – the .78x is the density of alcohol expressed in g/ml. Set B8 to g/ml if you are entering the fuel amount in ml.

(edited to correct my original which errantly said grams)

I'm entering fuel amount in ml…still the g/ml setting for B8, I assume.

Well, we thought that a "basic" and an "advanced" set of worksheets would be a good idea.

So perhaps I'll leave mine as is (barring any future error corrections) and it could be a good basic model for relative at-home, personal comparisons. I suppose it would make for good archival reading if nothing else, as the formulas are right there in the post.

Ben's sheet clearly has the capability to move forward with a plethora of options for the ultimate enthusiast, so it seems like a great advanced edition.

Delmar – you're right. I mis-wrote grams when I should have said ml. I went back and edited my other post to clarify the oops I made.

It's hard not to get sloppy with units since there's a lot of conversions going on and, at times, it's hard to keep track of them all.

You know, when you guys get your worksheets finished, you will need to get them blessed by some thermodynamicist, and a metaphysician, and a part-time hanger-on.

–B.G.–

and don't forget to post it for ALL to enjoy and use.