Making a Three-Stone Hearth as Efficient as an Improved Cookstove | Hacker News Reader

Making a Three-Stone Hearth as Efficient as an Improved Cookstove

thesolutionsjournal.com

84 pointsnkurz34 comments

I am unfortunately distracted by the large number of significant digits. House 1 burned 2.785kg @ 0.038150685 kg/min, which implies a precision of micrograms per minute,

Using decimal math, that works out to exactly 72.99999986894075427479218263 minutes. Realistically, it's 73 minutes. There are only 2 significant digits so the reported rate should be 0.038 kg/minutes.

Also, there's is a factor of 3 variation in wood/meal unit, compared to 25% improvement in switching stoves. Why aren't all of the houses using the efficient cooking technique of house 3? For that matter, how reproducible are the numbers for each house?

Finally, I see that house 2 had no gains, using about the same wood/meal unit with all three stoves. Does this mean that about 1/3rd of the users of the stove will see no gain to switching? Or does it mean that there isn't enough data to draw a good statistical conclusion? What are the odds of seeing these results purely from random chance?

"Unfortunately, results from House 3 were often unreliable due to operational difficulties that caused large variations in meal size, type, and preparation."

I'd love to know the human story behind these "operational difficulties".

From TFA:

"The operator and the conditions of use largely determine the effectiveness of operation."

I am unable to find that text in the article. I am even unable to find the word 'operator'.

In any case, I pointed out that there's a 3x difference between two houses, so I am in complete agreement with that statement. My post asks a different question, which is, what is the error range on the observed results? What are the odds that the stove doesn't actually have an effect on wood use, but that some other factor ('operator and the conditions of use') resulted in the observed differences?

Ah, sorry, tab mixup on my end, the quote is from another article linked in the comments below; http://www.lowtechmagazine.com/2014/06/thermal-efficiency-co...

Anyway, the question you pose is a good one.

Might be simple placebo effect, here have this super efficient stove.

I think you mean Hawthorne effect?

I dont think so? They observed three families, but most likely told one of them all about the new amazingly efficient stove.

"The Hawthorne effect (also referred to as the observer effect) is a type of reactivity in which individuals modify or improve an aspect of their behavior in response to their awareness of being observed."

So, folks are talking about efficiency, but seemingly missing the emissions impact of this. The health consequences of cooking with wood and burned waste are a major factor in why something like this is so valuable. The issue is mentioned a number of times in the article, in terms of mentioning visible soot, etc. but even it doesn't really cover how unhealthy it is to cook on a stove like this in an enclosed or semi-enclosed space for decades. Recent studies of stuff like fireplaces and the like indicate wood burning fires and stoves can be (much) worse than smoking cigarettes for your respiratory health. If a $1 upgrade to stoves (plus other innovations like cheap DIY charcoal production which other groups have worked on) can make the air quality vastly better for folks in the poorest regions, it can change outcomes dramatically over decades, and can save money in the long run. Health care, even the abysmal level of health care offered in rural villages in developing nations, costs a lot more than $1 per family to provide.

It'd be interesting to test whether fuel savings (immediate) or health benefits (long-term) drive adoption better.

Probably the former, for many, since even we in the west still cling to our fireplaces, even though most of us don't need them to stay warm. I have a friend who installed an ancient iron wood stove in her converted bus motorhome, against my recommendation. She loves the damned thing. She cooks on it, too, so she runs it regularly.

Part of the appeal for her is the perceived environmental benefits (though I've tried to explain the carbon and ecological footprint of a wood stove is much worse than propane, even though the propane had to be pumped out of the ground and transported). People are weird and stubborn and have odd beliefs about traditional ways being superior and safer than modern ways. The other part of the appeal is she gets the fuel for free just by roaming around in the woods. Propane costs $15/month, or much more during winter months, if you're needing heat.

Anyway, the point of that rambling is that immediate benefits probably trump long-term in this case for many people. Folks struggling from day-to-day don't have the privilege of thinking long-term. But, folks making decisions about how to help raise the people of developing nations out of poverty have to think of both.

Looks like increasing the efficiency by providing a better airflow path. This will also make them burn hotter but presumably the cooks can compensate for that.

Nice result from what is essentially steel scrap.

It's also a matter of preventing the burnt ash from clogging the airflow as it collapses downwards.

True, I saw it more like the typical stove "floor" which has holes in it so that ash can fall past the airflow intake into a collection area below. The effect being exactly as you describe, airflow remains constant even while burning.

Burning hotter is fine; simply use less fuel to compensate (which is the whole point of this invention).

Hey does anyone have experience in designing such stoves (or stoves in general)?

I found these were quite good overview articles:

http://www.lowtechmagazine.com/2014/06/thermal-efficiency-co...

http://www.lowtechmagazine.com/2014/07/cooking-pot-insulatio...

There's an irregular community around the 'Rocket stove' concept who seem to love playing around with different stove designs. It's briefly mentioned in the article, but it's a good starter term to search if you're interested in more information.

An experiment I've always been interested in trying, but lack the tools to carry out, is to take a nice dry unsplit log and drill/file the core out of it in a somewhat conical vent shape. It would be interesting to see what it would look like if you could get the log burning on the inside with the axis vertical and good space for airflow underneath.

This is only related insofar as the term 'rocket stove' reminded me of the plan, but I thought it was worth sharing in case anyone with a woodworking router in their garage wanted to give it a try.

Stoves can be fun. Spend much time talking to backpackers and you'll find a few who are constantly experimenting with how to cook faster, more efficiently, and with simpler lighter rigs. It's their hobby.

Are there any better pictures?

+1 A cursory look at the prototype they assembled would appear to indicate several easy DFM wins, but it would be nice to have a clearer picture.

Induction cooktop.

More efficient. Solar powered (renewable) so no need for going out for fuel which can be very dangerous and time intensive. Much, much safer than an open flame. No fumes. Small footprint and extremely portable. Robust. Cool.

Better yet, all of the people that this product is designed for should just move to Aspen. Every house there already has an induction cook top, or at least an electric or gas one.

Solar panels, wiring, energy storage, and the cooktop itself are very expensive by the standards of these communities. They also rely on rare earths and other hard-to-source materials.

This insert costs $1 and can be locally manufactured, locally maintained.

I believe the parent is referring to reflective solar stoves. There is a picture of one in the article. It's basically just a parabolic mirror and you put the food at the focal point.

The article said that the village had such stoves, but the weren't adopted for some reason. I may have missed it (I was skimming), but it would be interesting to see why they weren't adopted. My guess: having to orient your cooking around the position of the sun. Possibly the women do not have flexible enough time schedules to do it.

Parent is pretty clearly referring to using solar photovoltaic panels to generate electricity to operate an induction cooktop. Pretty sure parent grossly lacks an understanding of what global poverty is.

I knew a guy who worked in the Peace Corps in Lesotho, trying to get people to use reflective stoves. His experience is that people didn't want to use them because (a) they liked traditional cooking [who doesn't?] and (b) insofar as they had aspirations, it was to buy a propane bottle and a burner, like the middle class people in their area.

A friend of mine was in Burkina Faso for some NGO (might have been Peace Corps). Originally they tried a PV setup for some of the more rural villages. Every time they'd come back to ask how things were working the panels had been stolen and sold off. Eventually they gave up on PV altogether.

Small footprint? Any idea how many square feet of solar would be requires to maintain a cookstove? ... at night? ... during bad weather winter? A stove needs to be reliable year-round. So you would need panels and some sort of storage medium (batteries). There are no small footprints.

From an environmental angle, burning wood to cook food might sound bad, but trees can grow back. So it is still a step up from burning coal/oil/LNG (either directly or via electricity).

A colleague of mine has spent fifteen years on and off working on remote small-scale hydropower in Afghanistan. These villages (~ 100 families) can afford installations that give each house ~50 W. Enough for lighting, maybe some small electronics, but even a small heating element (300 W) is way too big. An induction oven draws 1200 W per element...

But lighting is a game changer for these people. For instance it means kids can read after sunset, improving literacy and education in general.

Another interesting thing he told me: they still use fluorescent tube lights in all new installations, and have no plans to switch to LEDs. The reason is that LED bulbs are compatible with incandescents, so whenever a bulb breaks, people will replace it with the cheapest bulb they find (i.e. incandescent), and that will not only reduce the efficiency, but overload the power "grid". So fluorescents win in the long run.

And these are available for $1USD to rural families in India?

Why not suggest they switch to cooking sous vide? That's only incrementally more out of touch.

How much do those cost?

Also I have recently changed to induction cooktop and it sucks in comparison to a gas stove.

Reply on news.ycombinator.com