[Stoves] WorldStove replies to BioFuelWatyche's latestimprecisereporting of facts.

Sun Jul 31 00:58:29 CDT 2011

Dear Crispin,
I have experienced how the standard test procedure followed by the
certifying authorities discriminate against innovators. In the 1970s I
 had developed a sorghum hybrid, which required a plant population
density of 100,000 plants per acre. At this population demsity it
outperformed all other varieties. But in the Government's testing
programme, sorghum was tested at a standard plant population density
of 60,000 plants per acre. So my variety got rejected. Sorghum is also
grown in India after the rainy season. The crop makes use of the water
stored in the soil during the rainy season. Since this water is
generally inadequate to support a crop grown at the normal plant
population density, I conducted experiments in which the row to row
spacing was 150 cm instead of the normal recommended spacing of 50 cm.
I thus had a plant poulation density of only 20,000 plants per acre,
and I got a bumber harvest of 1000 kg sorghum grain per acre, which
was unheard of in this season. But my recommendation of testing the
post-rainy season sorghum at a lower population density was also not
accepted.
Yours
A.D.Karve

On Fri, Jul 29, 2011 at 8:00 PM, Crispin Pemberton-Pigott
<crispinpigott at gmail.com> wrote:
> Dear Roger
>
>
>
> As you are planning to get EPA certification for your stove I suggest that
> you look carefully at the way they are going to run the test. They are very
> particular about loading, lighting and operating the stove in ‘a certain
> way’ that they wrote down. It may well be that the way you fuel and or
> operate the stove is different from how they are going to operate it when it
> is tested. It is blindingly obvious that their method may not suit your
> stove, or anyone’s stove. It is just how they are doing things and that is
> that.
>
>
>
> The problem is of course that if you have a novel technology and a good way
> of operating that technology, and it is quite different from the EPA test
> procedure, there are going to be long faces when the results come back,
> maybe. So be prepared by looking at the test procedure and follow it to see
> how your stove performs when loaded with that wood type and size and
> operated in their manner. You might ask in advance if they will operate it
> according to your instructions (or not). The answer might make you happy,
> might not.
>
>
>
>>The average stove at the time was reportedly dumping 60 to 70 grams pm10
>> particulate emissions per hour, per stove, into our airshed.
>
> There is an assumption by the EPA that the stoves for domestic use are
> pretty much the same power, meaning the total heat delivered in MJ into the
> home is about the same for all of them. If you build a stove with a higher
> combustion efficiency, then there will be PM10 savings at the same power
> level which will translate into reduced fuel use, as you noted.
>
> If you build a stove with a lower power level and the same combustion
> efficiency, there will be a reduction in emissions not because of better
> burning, but because of reduced fuel, as you noted. It would of course be
> better to have both efficiencies: better combustion efficiency and better
> thermal efficiency. One will produce less PM10 per kg burned and the other
> will reduce the number of kg that need to be burned. Double plus!
>
> As you mentioned it, I have attached a graph of the thermal efficiency of a
> Mongolian ‘ger stove’ (they call it a ger, pronounced ‘gare’ like ‘tare’).
> As you can see it varies a great deal from 100% when the stove body is cold
> to a negative number at minute 140. The stove was fuelled at minute 12 and
> refuelled at minute 60. The steep drops in efficiency are the top of the
> stove being opened to add coal. When the top is opened huge amounts of air
> pass into the stove, cooling the stack gases with sheer volume and carrying
> away all the heat (up the chimney) at a lot temperature.
>
> There are three lines on the graph. The Green one is the instantaneous
> thermal efficiency which displays the efficiency as it changes in real
> time.  It is titled the ‘interval efficiency’ and is calculated every 10
> seconds. The Orange line is the power output in kilowatts and that number is
> the ‘cumulative’ or ‘average so far’ power during the test. The Blue one is
> the thermal efficiency, also calculated cumulatively. The reason for doing
> this is that we want to see the average heat output. We know in advance what
> the heat demand is for a building, say a very small two room house. So we
> test the stoves to see what the average power level is assuming that on
> average, the house will be warm. The stoves are produced in three power
> ranges (for the most part). This is a small one at 5 kW avg.
>
> As you will see on the chart, the efficiency after ignition of this
> traditional Mongolian stove is about 65% (the cumulative average) until
> minute 100 and is still above 60% after 2 hours, which included a
> refuelling. By minute 210 (3 hours) the average efficiency had dropped to
> 50% because of the very low efficiency during the third hour. The stove can
> be made to operate at a higher efficiency with a small fire by watching the
> stack temperature and oxygen level in the chimney then closing the damper,
> but an operator would not have the equipment to do that, so they usually
> guess at a damper setting and see what they get. In the USA and Europe
> commercially produced domestic burners have a device that measures the
> oxygen (a Lambda controller) that operates the damper automatically to
> maintain the thermal efficiency. Nothing like that in Mongolia.
>
> If the stack temperature is low, it could be because the heat exchanger (all
> the parts of the stove that warm the room) is really efficient, or it could
> also be because there is a lot of room air entering and passing through the
> stove and cooling the chimney (or some combination). Obviously there is no
> gain from such a waste which is why people put on a damper (to prevent a lot
> of excess air going through). If you know how much air is going through
> without helping the fire, you can determine the amount of dilution taking
> place (with room air). The Mongolian traditional stove at high power is
> quite efficient but it makes a lot of smoke when it is ignited and
> refuelled. At other times it is pretty good.
>
> Note that the thermal efficiency is above 70% when the power level is above
> 7.5 kW at minute 40. But later it lets way too much air in at low power,
> partly because the chimney is oversized and because they are generally
> leaky, letting in air all over the place which dilutes the stack gases,
> cools them, and carries the heat up the chimney. The note under the chart
> says that the thermal efficiency (at low power) drops to -250%. The power
> level at which this happens is on a different chart so you can’t trace it on
> this one. The point is in that condition, the stove is cooling the room
> because it is pulling in air from the room which has to be replaced by cold
> air from outside coming under the door (etc). The heat lost up the chimney
> is not enough to warm the cold air entering so the efficiency goes negative.
> Almost all stoves reach this condition but usually very late in the burn
> when the CO is high (chemical loss) and the excess air level is high (heat
> transfer efficiency loss).
>
> If the EPA is going to test your stove in a way that does not include
> operating the damper in the way you recommend, it is likely to have negative
> consequences.
>
> The producers for the American market do not necessarily make stoves that
> are optimized for clean burning and thermal efficiency. They build stoves
> that will pass the EPA test as the EPA chooses to test them. If your stove
> is highly innovative and uses shall we say, non-standard control methods, it
> may not give good results when operated the way they are going to. You may
> have to make some changes to get in as much fuel as they are planning to
> load, for example. When you explain that your stove doesn’t need as much
> fuel they will tell you the regulation says ‘load X-amount of split oak’.
> And then they will do it.
>
> Forewarned is forearmed. Do you know which EPA test (the number) will be
> used in your area?
>
> Regards
>
> Crispin
>
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-- 
***
Dr. A.D. Karve
President, Appropriate Rural Technology Institute (ARTI)

*Please change my email address in your records to: adkarve at gmail.com *