[Stoves] Envirofit Stoves

Wed Dec 7 21:31:39 CST 2011

Francois,

I got an Envirofit stove (G-3300) in the mail  - the Western way to buy a stove - recently and have just started to benchmark it against other mass manufactured stoves I have on hand.  It is well constructed (though the fuel support and grate are on the flimsy side - but the support can be easily replaced with a brick), with a cast iron top, heat resistant alloy combustion chamber, and what appears to be mineral wool tightly packed into the ~8 cm space between the combustion chamber and the outer shell. It is easy to light and generally a pleasure to use (an important fuzzy metric?), but it sure seems to burn aggressively - despite the appearance of lots of excess air coming through the large front opening, the sticks immediately get so hot that the fire can quickly propagate out the front of the stove.  The outside can also get a little hot - up to 75 C after 40 minutes at full power - I can't say if this constitutes a problem, and it cools off
 very quickly.  The rest of this is commentary on my testing, in case that is of interest too (and we haven't had a list discussion of stove testing recently) - you didn't mention what details about this stove might be helpful.  Your other questions - if I can find enough wood ash I'll insulate it with that and test, since I often use it in plancha stoves, and the EcoZoom Dura Lite I am also testing has very similar construction, dimensions, insulation, operation, and performance characteristics.  Early results when using sand as a filler are looking interesting!

It takes a little time to learn a new stove so these are just preliminary observations, and anyway all cooks develop their own method - each balancing things like time to boil (via firepower), fuel conservation, smoke reduction, and ease of fire tending details according to what they consider important - so you might well experience this stove differently.  My own method is to operate the stove so that the firepower is relatively high (flames regularly spreading across the whole pot bottom, but none wrapping up the sides), my desires for both a fast time to boil and good fuel efficiency are balanced, and smoke is minimized.  I follow common rocket stove fire tending practices - using only 3-4 sticks at a time, maintaining a few millimeters between them, and regularly breaking off the charred tips.  Same as is shown in the Envirofit instruction video.  I definitely pay too much attention to the stove while testing, since I am not doing anything else
 like cooking or rearing children at the same time, so that my results could represent something like the stove's best possible performance and not what you might see in the field.

I used 10% moisture content coniferous wood (old shipping pallets - urban fuel), split into pieces of about  2 cm x 2 cm x 40 cm.  I conducted 5 outdoor partial water boiling tests (cold start segment only) with a different brand of pot skirt, using an average firepower of 3.8 kW (12 g/min, dry wood equivalent).  An average of 33 minutes was needed to bring 5 liters of water to a boil, requiring a specific fuel consumption of 83 g/liter and resulting in an average thermal efficiency of 30%.  So far I am getting more test-to-test variation than I like, so average values are only somewhat useful - what is causing my distribution, and what does it mean?

These are all corrected values - using the WBT 4.1.2 spreadsheet to take into account test-to-test differences in starting water temperature, water loss by evaporation, and wood moisture content.  As most know there is regular debate over drawing conclusions from lab WBTs, so I just use the method at home for a cursory comparison of similar stoves, and for quickly evaluating the potential impact of design changes to a specific stove.  The WBT 4.1.2 spreadsheet usually produces results which are quite similar to those from version 3.0, and I'll be trying Crispin's heterogeneous protocol, since I already periodically record the change in water temperature during tests, to see if my target firepower is consistently maintained.  It is definitely tempting to use a pot lid, after being laughed at too many times by cooks in the field when I insist that they do without one for my clumsy tests in their homes. 

The Envirofit spec sheet and performance report say that this stove should have a thermal efficiency of 33% at its rated max firepower of ~3.7 kW - note that we can't make a direct comparison because they don't use the familiar WBT (either did I since I just brought the water to a boil - the rest is coming soon), and while I can't find out all of the details of their internal protocol (called EPTP - also 3 stages but using only 4 liters, and for the cold start it only brings the water to 90 C) I do try to run my tests close to their recommended firepower.  Not having to reach boiling temperature would be fantastic, since that last degree or so takes considerable extra effort.

After too many tests on other stoves I have almost run out my softwood supply so I'll have to switch to other urban alternatives such as manufactured sticks (from dried dimension lumber), hardwoods I get from cabinet shops, or I'll start splitting our expensive local almond firewood.  I'll be adjusting other variables as well, and would like to hear if other people are doing likewise - and what performance metrics you find most useful when making comparisons. 

Charlie

________________________________
From: François Sorba <fx.sorba at id-ong.org>
To: stoves at lists.bioenergylists.org
Sent: Wednesday, November 16, 2011 1:21 AM
Subject: [Stoves] Envirofit Stoves

Hello everyone,

First I would like to thank all of you for your help regarding my question about wood ash as an insulator.
I have now another question regarding Envirofit Stoves.

Do you any of you have any previous experience with those stoves and this firm ?
What do you think of them ?

Do you know any other firm like this one (Prakti design ?)

Thanks!

François
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