Comparative efficiency of caldera cone vs diy windscreen in wind

I'm aware of will rietveld's excellent analysis that highlights just how critical this is for alcohol stoves. He finds that in a 12 mph wind, an alcohol stove with a simple aluminium screen, still consumes 81% more fuel than the same stove in still air conditions.

http://www.backpackinglight.com/cgi-bin/backpackinglight/wind_dynamics_and_windscreen_design_part_2.html#.U9ppWmIayK1

You'd hope the CC does a lot better, but as per original post, I wonder by how much?

Hi Hugh. I have no "hard data", only personal, anecdotal experience, and yes, the Caldera Cone greatly improves the efficiency of an alcohol stove in the wind. Pre CC I experienced windy conditions such that 1 oz of fuel wouldn't even produce the formation of little bubbles on the bottom of the pot w/ windscreen; 1 oz of fuel using the CC would at least produce an incipient boil, probably because the cone concentrates the heat not only to the bottom of the pot but also to the sides. It was one of the best purchases I've made! Happy Trails!

Hugh, one thing to keep in mind when using Starlyte/CC…

The configuration of the Starlyte/CC does not call for the use of the skewers through the cone, so the lip of the pot sits directly on the upper lip of the cone. If the cone is set up on an uneven surface, there can be an issue with the engagement between the lip of the pot and the lip of the CC… to the extent that the pot falls onto the stove.

I had this happen but figured out pretty quickly what was caused it. Fortunately it didn't cost me a dinner. ;-)

As per Monty, I agree (also anecdotally) the CC offers significantly increased fuel efficiency in the wind. However, as with any stove combo, it is better to set up an additional wind break when possible.

"If the cone is set up on an uneven surface, there can be an issue with the engagement between the lip of the pot and the lip of the CC… to the extent that the pot falls onto the stove."

I have used a Caldera Cone and Vargo 1.5 liter pot for many years, and have never had a issue with the pot "falling through", and that includes setting up on many uneven surfaces.

Were you using the pot the Cone was designed for?

How many liters is the pot?

Anyone else experience this?

IMHO, the CC is one of the best alcohol systems out there in terms of performance, efficiency and simplicity.

Ok, that's interesting. The personal reports are reassuring but it seems that nobody has done the testing more formally.

There have been impressive efforts recently to optimise and measure stove performance , (notably here: http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=90329) but all of these tests are conducted in lab conditions – ie with no wind.

Given how central wind is as a variable affecting the real world performance of alcohol stoves, I think this should be high on the research agenda for what to look at next.

I would love to try myself now, but I'm away from home and testing equipment for the next couple of months.

just looking at a cone versus open windshield, it appears a no-brainer to me that a cone with appropriate stove will be more efficient. Heat is retained on side of pans more. (possibly larger/heavier non optimum stoves may be inefficient in cone due to thermal feedback accelerating fuel consumption)

But after 25 years of Trangia use and 5 years of cone use, I am convinced.

in still conditions difference is small but noticeable if measured IME

A possible alternative to the CC is Jim Wood's Fire Bucket design.

http://jwbasecamp.com/Articles/Fire-Bucket/

It is easy to make and I have made a couple with interlocking ends instead of screws. I use mine with a Starlyte style stove that has no pot support, so I need to use skewers for pot supports. I make my skewers from 1/16" dia. stainless steel welding rod. I find that my Starlyte style stove does not put out as much heat as a Max Cat style stove, so boil times are longer. I prefer the Starlyte style because the fuel is not as likely to spill if the stove is tipped over.

"Were you using the pot the Cone was designed for?"

Yes, Toaks 1350ml UL. I bought the whole bundle with the inferno insert, along with the 12-10 stove.

That's why I said "CAN be an issue", because I realize that my experience represents a data point of exactly 1.

Overall I adore the system, having used it with a few different alcohol stoves and in wood-burning configuration.

Bob –
Thanks for the clarification.

Stuff can always happen.
Frequency is the real question.

"Frequency is the real question."

Indeed, and I should have mentioned the pot in use in my first post. Could have a particularly narrow lip and therefore a unique issue with that pot.

Re: "it appears a no-brainer to me"

Maybe. Like you I'm confident the cc is indeed very efficient in the wind. But clearly lots of people use various diy (and commercial – click stand etc ) arrangements with varying degrees of success. The problem is we don't have much clear comparative data on what setups work pretty well in the wind and which are poor and, critically, to what degree. By contrast, there are pages full of comparative data in still air conditions – interesting, but hard to apply.

What struck me about the will rietveld analysis I linked to earlier was how what looked like a very good 360 degree windscreen setup actually did extremely poorly in the wind. This suggests intuitions may not be a good guide on these questions. People's anecdotes about cc have been very interesting and suggest it is the design to beat.

I guess it still leaves me wondering if other folk with other diy set ups reckon they can get close to the cc in terms of efficiency in the wind.

For about a decade I experimented with various ways to get more efficiency from ESBIT fuel tabs such as wind screens, stove designs, tablet "chimneys", etc.

Finally I got a CC Sidewinder and matching 3 cup pot and lid. THAT made all the difference. Now I've modified the Gram Cracker tab holder to retain the liquid residue with Brian Green's design and it doubled my tablet burn time.

So, as far as better efficiency with a caldera Cone, it's a definite YES!

Straight wall windscreens can be made to have the same efficiency as a cone shaped one.

The use of a StarLyte Stove with integrated pot support is an ideal candidate for use with a straight walled screen. The 12-10 stove with 1/2" hardware cloth pot support will work well also.

The straight wall needs to be 3/8" away from pot completely surrounding the pot. Incoming air holes need to be sufficient for combustion. Placement of air holes is important also.

If you momentarily step away from the stove efficiency and windscreen effects, the cone makes a much better pot support as compared to a straight-sided screen. It is more stable.

–B.G.–

LIkewise. Stability was also my motivation to get one.

It's the only stove I've used, alky or pressurized, that didn't have me worried about knocking it or my pot over.

I would also be curious to see a methodical test of its fuel efficiency.

Here is one set of data points that seems to indicate that the Caldera cone will do slightly better in a mild (<5-10mph) wind. I mounted the cone 1/2" higher (on some plywood shims, actually 15/32") on the second set of tests. Both were done with a heat exchanger grease pot. A lid was used. Water was 16oz, 40-43F(it varied slightly since I forgot to put it back in the fridge) and heated to 200 degrees F by digital thermometer. Fuel was all taken from the same gallon of SLX.

No Gap
5:47 5:38 6:14 5:53 5:51

1/2" gap
5:19 5:31 5:23 5:21 5:29

Each burn was loaded wiith 3/4floz of fuel. The stove was still burning in every case at 200F.

The times to boil were less with a gap. This indicated that the stove was running something less than optimal in still air or "choked." A light breeze would likely have been beneficial to the burn. A steady 1.5floz per liter could have been maintained to about a 10mph wind (mild wind.)

Note that flue gasses are "sucked" out of a cone faster than a wind will push air into it due to: a) location of the holes b) aerodynamics

"Incoming air holes need to be sufficient for combustion. Placement of air holes is important also."

Dan, would you be so kind as to elaborate on that? I mean, how many air holes, and where would they best be placed?

The quantity of holes depends on the size of your stove and the spacing between screen and pot. Height of screen also has to be figured in. Lots of variables for do it your self folks.

Placement depends on whether or not you cut a hole out of the screen for a handle on your mug/pot. If you use a Foster or Conquistador pot with a handy pot grabber there is no need for that cutout. Lots of variables, no easy answers to your questions Gary.

Thanks for your response, Dan. I understand what you are saying. But just how does the screen height play into this–does it affect the chimney effect? Does a taller screen require more air intake (1.e., more, or larger, holes)?

The taller the screen, the greater the draft. Yes, it wants to suck more air through the holes. The taller the screen, the more radiant heat reflected back to the pot for a faster heating of the water. That screen gets super hot quickly, my fingers know ;-) So yes, taller screens means larger or more holes or use the elongated openings at the very bottom edge of the screen like the design I used on the titanium windscreen used in one of the kits I produced 2 years ago. It's in the DIY gear forum/dept.

Thanks again, Dan.