[Stoves] stove test

Sun May 29 20:12:27 CDT 2016

Kirk,

Thanks for sharing and thanks for putting it in the public domain.

"This is possibly what lead to the tier 3 rating for low power specific consumption‎.  This is possibly what lead to the tier 3 rating for low power specific consumption‎"

Don't worry about it. The low power specific fuel consumption is not a valid metric in the first place. It is a nonsense number and you don't have to worry what it is.

If you want, you can determine the fuel mass needed to perform the simmer for 45 minutes. That has meaning and you can report it together with the fuel consumed during the high power phase. ‎That makes sense.

I am surprised that Ashok's staff is reporting specific fuel consumption (per litre simmered) because there is no dependent relationship between the ‎mass of fuel consumed and the number of litres of water in the pot. The calculation of the heat gained by the pot also contains an elementary mathematical error.

If your heat transfer efficiency is unusually high, it boils more water, as you describe below. This a higher quantum of heat transferred and ‎reduces the number of litres remaining, which increases the supposed mass of fuel needed to 'simmer' a litre.

If you reduce the heat transfer efficiency, which it sounds like you did, then you reduce the simmering temperature, which rewards the reduced efficiency with a 'better, specific fuel consumption, even though the stove has a poorer performance, as you note.

In short, the better the stove, the worse the low power fuel rating. Yes, the metric is that silly. This has been reported multiple times both on this list since 2007 and in a peer reviewed journal article (Zhang, Y, 2014) also previously cited here. It was also noted in the public comments prior to the IWA meeting, multiple reviews of the WBT and in the ISO Working Group 2.

At some point the metric will have to be dropped and replaced by something with a valid physical basis. ‎Until then, don't spoil your good designs trying to 'generate a good number' on any of the low power sections of the WBT. They mean zilch.

As there is no valid low power fuel/energy target, you should concentrate on reporting the turn down ratio and the minimum power that you can sustain.

It you report the high and low rate of heat gain by the pot on a "Watts per Sq cm" basis (of the heated surface) it is a valuable rating for the potential customers as it tells them what the cooking power is, and how controllable it is.

Regards
Crispin

All,

The TLUD-ND stove which we further developed at Aprovecho Research Center in
March was tested at the Lawrence Berkley Lab.  Results are attached.  The
photo of the computer screen showing the full power 6+kw graphs was taken by
Ashok Gadgil.  They have a good team doing the tests.

The stove is in route to Aprovecho RC where it will be photographed and
drawings will be made.  Apro will then update their free online tier 4 stove
book from the old TLUD-ND design to include this new design.  I am updating
the written stove description.

The designs are being put into the public domain.  I hope that the various
principles used in the stove, for turn-down and improved efficiency and
emissions, will benefit some new stove designs in the future.

The fuel used was Douglas fir pellets.  The highest power achieved was 6+ kw
with some cushion above that.  The low power is 1.6 kw with some cushion
below that.  The turn-down is then 4 to 1.  Five kw seems to be the highest
very clean power level.  The high power used in the tests was around 3.25
kw.  At these turn-down levels the ambient room temperature makes a big
difference in performance.  At 24C room temperature there was no problem
keeping the water in the 93C to 97C test simmering range.  At 30C room
temperature the simmering water temperature could not be held below 97C.
The pot skirt had to be raised to release some heat to maintain the test
temperature.  This is possibly what lead to the tier 3 rating for low power
specific consumption.  The catch 22 is that the more efficiently heat is
given to the pot, the lower the stove has to be turned down to maintain a
simmer.

Kirk

Santa Rosa, CA. USA

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