[Stoves] 答复: Two problems regarding WHO Guidelines ....was Re: A "Cut and Paste" Summary of the 2014 WHO Guidelines

[DONG RJ]

Colleagues,

This is an interesting discussion. My points from Chinese rural experiences are, although I have not studied the WHO guidelines,

1.    It is not common in China to use a stove without chimney. Chimney is a natural part of the stove.

2.    Even the chimney protected the indoor air quality, it can not help the out door air if the stove burn appropriately.

3.    The chimney helps the stove burning.

4.    It is not popular in China rural area to use woodchips or pellets. However, pressed biomass fuels would have bigger market in rural area when farmers are moving into central small towns, which happens quite fast in some rural areas in China. So the biomass stove study in China has two directions: (1) find appropriate pellets (2) find appropriate stoves for raw biomass (3) develop criteria for stoves testing concerning fuel/stove combustion and indoor/outdoor impacts.

Randdy

发件人: Crispin Pemberton-Pigott [mailto:crispinpigott at outlook.com] 
发送时间: 2014年12月7日 13:37
收件人: 'Discussion of biomass cooking stoves'
主题: RE: [Stoves] Two problems regarding WHO Guidelines ....was Re: A "Cut and Paste" Summary of the 2014 WHO Guidelines

 

Dear Paul

 

I think people may not have notice, may have been in shock that something so odd was accepted by an institution like the WHO, or they may feel that the problem was somehow misrepresented in the discussion.

 

There are a couple of things to clear up:


1.  EVEN WITH CLEAN STOVES, the CO and PM levels are higher than expected, with probable causes being the uses of multiple stoves, lamps, etc.   

That only means they have not tested rooms using modern appliances. For some reason we keep seeing in printed materials originating from Berkeley that ‘fan stoves are 90% cleaner than baseline open fires’ and that no other stoves are that clean. Only fan stoves. Fan stoves are not magical. Some fan stoves are a lot cleaner. Not all.

 

Some natural draft stick burning stoves are extremely clean too. And a number of TLUDs whether charcoal making or not are as clean or cleaner that ‘fan stoves’ in general, even very good ones burning wood. Pellet burning fan stoves are, so in my experience, the cleanest burning biomass stoves, however the ‘fan stoves’ of yesteryear are not as good as the newest ones.

 

In my view we should be able to report that the best wood and pellet stoves (fan or not) are 95% cleaner than the open fire baselines for PM and mush lower for CO> In fact CO is not that difficult to deal with – it can be low but it does not have to disappear – the exposure limit is actually much higher than for PM2.5.


Therefore, regarding health, we could be finding that the efforts to have ULTRA-CLEAN stoves (LPG, Solar, Electricity, biogas, alcohol) could be sufficiently undermined by household/ambient conditions that the improvements of the health of individuals are not being attained, regardless of the cost of those stoves and their fuels.  

 

Hang on a minute, who said alcohol burning stoves are clean? As you know many people report that ethanol is a ‘clean fuel’ as if that description applied to any stove+fuel combination. There is no such thing as a ‘clean fuel’. Any fuel can be burned improperly if the stove is not designed to deal with it. End of short story. I have seen some terrible ethanol burning stoves. They put out a lot of VOCs and CO, particularly at high power.


When a really good ethanol stove is in use, there is virtually nothing to detect at all. The idea that they are ‘still higher’ than is ‘safe’ is, in my view, unreasonable and unproven. 


This is NOT a reason to stop efforts for clean stoves, but it could be a reason to focus more on getting better "stove stacking" with several reasonably improved stoves instead of putting too much emphasis/financial resources on having an ultra-clean stove placed in an setting without other improvements.   

 

Well, it is pretty easy to put a chimney on any stove. Combined with a draft regulator (the tilting disk kind) they can be really good and all he PM and CO goes outdoors. In a great many communities, the homes are so dispersed that there is zero influence on other people outdoors. If this is not intuitive, it is certainly obvious. China correctly treats domestic stoves as a ‘distributed source’ for regulatory purposes. Thus concentration of emissions does not arise as an issue (in cases someone thought that was a regulatory metric).


In other words, the recent increased recommended strict reduction of emissions for health purposes might be sooooo tight that broader changes in societal issues (life-styles such as stove stacking, windows open, different light sources, etc) become more important than having the ultra clean stoves.

This is going to be a hard sell. If a stove is tested in a real kitchen that is culturally representative of the cooking conducted, the fuels used and the architecture, and the exposure of the cook or other people in the room is ‘safe’ that that is the end of the story. All we have to do is build combinations that are safe. Running around banning ‘fuels’ is not going to impress anyone, especially of the alternatives are 10 times the cost.


2.  Chimneys are insufficiently understood and/or insufficiently consistent in operation  concerning emissions.   And there is an expectation of (or allowance of, or the modelling for) 25% of emissions coming into to room.

 

Even a $15 stove (retail) sold at the Ulaanbaatar Black Market emits a tiny percentage of total emissions in to the room – and that only when someone pots a pot on or off. Even refuelling is handled through the fuel door. This 25% is simply not realistic. My question was, as a chimney is so obviously the best way to get stove emissions out of the face of the cook, why would such an assumption as 25% be considered at all! 

 

That this value (25%) is arrived at as the average value between 1% and 50% seems very crude.   IMO, a stove with a chimney that lets more than 40% of emissions enter the room is hardly deserving to be even called a chimney stove.  Not even 20% should be entering the room!!!!! 

 

Is there a stove with a chimney leading outdoors that emits 50% into the room? And as you say, why would one average a useless stove with a good one to arrive at 25%? That alone doesn’t make sense. Shall we do the same for other good and useless stoves? Why not average their emissions too? We could then claim stoves can’t ever be clean because some of them are useless. This is ridiculous.


Such an expectation or assumption in a model clearly works against a stove with a good chimney arrangement and can favor a stove with a bad chimney arrangement.   

Such an expectation is only convenient for banning the burning of all solid fuels no matter how clean and efficient. Why do that? Whose side are they on, here? Electricity is difficult to generate, expensive to distribute and unreliable on most countries. LPG is very expensive to distribute – even if it were free and limitless in supply.


There could be more to this chimney story than is currently evident.   But until it is clarified, questions will continue to be raised.

Well I think we should all have a look at the WHO process and documentation to find out who such a decision was supported in the absence of up to date information on what is burning clean.

 

The emissions from pellet burning stoves in Austria are reaching the undetectable level. Cross draft gasifiers of coal and wood are both capable of negative emissions of PM and very low values of CO. (Negative emissions means the PM is lower in the chimney than in the air going into the stove.)

 

Further, the modelling of stove emissions in a room and assuming constant emissions from an ‘overall’ measurement (say, from a filter) is a poor representation of the risk to a cook from a stove. High dose emissions during a short period provoke a very different response in the lungs than an ‘average’ dose over the whole period, assuming the total emitted is the same. As the model described does exactly what is not going to give the correct health impact assessment, we will have to rethink this entirely.

 

It is notable that on a few occasions in recent years, attempts have been made to incorporate into stove standards a clause accepting WHO emissions standards (with implied methods as well of course) without question. That is a sort of ‘appeal to authority’. Well, if the methods are as strange as has been outline, there is no way they can be accepted without review by technical experts from other quarters. The 25% assumption would be just such a trigger for such a review. It is so far from reality that it raises questions about the process that led to such a result.

 

What one must watch for is the co-opting of one ‘authority’ and the extension of its conclusions, without examination, into other realms. It is clear that the WHO team was not aware that there are far cleaner stoves than ‘fan stoves’ from 2009. The story about 90% reduction has been ‘in press’ since 2009 and has not changed, even though there have been 5 years of rapid development. That is the reason I pick 2009. By the time the GACC Roadmap was being written it was already old news. 

 

By 2011 we had coal stoves burning lignite (very low sulphur, young coal) in Ulaanbaatar that were more than 99% below the baseline. The local ambient air was so dirty from unimproved stoves that in order to find dilution gas to operate a PM diluter, it was seriously suggested to LBNL (which was trying to measure emissions in the field) that they use a GTZ-7 series stove as a source of dilution gas because it was operating cleaner than a HEPA filter. The HEPA filter was only able to get the ambient air down to 20 micrograms per m3 while the stove, after the combustion settled into a continuous mode, could strip out all PM completely – literally undetectable with a 1 µg instrument –  even though the ambient air going into the stove was 200-600 µg/m3 (which is typical for UB in winter).

 

If wood is prepared (pellets or other) it can burn that cleanly in a well-designed chimney stove and nothing like 25% of the gases come into the home. In fact if they did, it would still meet the IAQ requirements.

 

It looks to me like a plan to ban wood as a fuel by claiming it cannot be burned ‘cleanly’. The kerosene story I have told before. There are several extremely clean burning kerosene stoves and lanterns – for example all those that meet the SANS 1906 and 1243 compulsory national standards for CO in South Africa. It is the same standard as natural the gas stoves in the EU.

 

Here is a clean  burning $15 kerosene stove:



 

Show me an LPG stove that burns that cleanly.

The numbers are CO2 1.8%, CO 0ppm and CO/CO2 0.0000. Theoretically the CO level could be as high as 4 ppm given the instrument precision and the level of dilution air in the sample. I have seen two, maybe three not-that-well-designed coal stoves burn at that CO level as well. 

 

This condition was sustained from more than an hour after which I got bored.  But I never get bored of chasing technical curiosities out of stove standards.

 

Regards

Crispin

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