Adding forced draft and chimneys to biomass cookstoves helps to meet WHO IAQ guidelines
From section 5.4.1 Roles of clean fuels and lower emission solid fuel stoves
“As recognized in these guidelines, and specifically in Recommendation 2, which addresses policy during transition, improved solid fuel stoves will continue to make an important contribution to the needs of a substantial proportion of lower income and rural homes where primary use of clean fuels is not feasible for some time to come. Work to develop substantially improved solid fuel stoves should continue in parallel with, but not hinder or displace, efforts to encourage transition to clean fuels. The contribution of solid fuel stoves to the mix of devices and fuels promoted will depend on the completeness of combustion that can be achieved when such technologies are in everyday use (as demonstrated through emissions testing), and the consequent reductions in health risks.” (pg.62)
https://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.png00Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2024-03-01 17:28:562024-03-01 17:28:58From The WHO on Lower Emission Solid Fuel Stoves
Damon Ogle and the ARC staff have a long history, starting in Central America and Mexico, listening to folks praising their stoves with chimneys. There are now millions of beautiful Latin American kitchens in which the dangerous smoke is transported out of the house, as it is in the USA/Europe. The Rocket stove can be about 50% more fuel-efficient compared to the open fire, so about half the smoke is made. But that is not good enough to protect health inside a home.
Although health-protecting chimneys are seen in Latin America and India, it’s rare to see chimneys in Africa.
One simple African stove with chimney is seen above. A sunken pot (or pots) sits down near the fire exposing its bottom and sides to the flame. The pot seals into the hole and the smoke flows up the chimney, not into the lungs of the cook and her children.
Since 1976, ARC has continued to work with local communities worldwide to try to save fuel and protect health. Trying to protect climate requires very clean combustion and we’re working on that, too.
https://aprovecho.org/wp-content/uploads/2023/05/image.png300400Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2023-05-11 15:59:572023-05-11 16:00:38African Mud Stoves with Chimneys
When the air exchange rate is doubled, the concentration of smoke is reduced by half. The average house in low middle income countries is estimated to have around 12 air exchanges per hour (ISO 19867-3). When ARC measured the air exchange rate outdoors in a gentle breeze it was found to be about 120 per hour. Exposure to smoke could theoretically be dramatically reduced by moving outside.
Changing stoves costs money and the transition to an improved stove is often a time consuming process. ISO reports that even stoves with chimneys (that often leak) only reduce concentrations of smoke in houses by around 75%. Experimenting with increasing the air exchange rate is probably the most cost-effective intervention to protect health.
When we went to villages where women cooked outside, Dr. Winiarski would frequently ask the women if digging a well, etc. might be more important than new Rocket stoves. That is one of the things that we loved about Larry!
The air in a kitchen has to be very clean to protect women and children from multiple diseases. Unfortunately, moderate amounts of smoke seem to damage health almost as much as higher concentrations.
As exposure rises from zero, the chance that a child will get pneumonia increases sharply and then levels off so that indoor air with 200μg/m3 PM2.5 is almost as dangerous as air at 400μg/m3 (Burnett et al., 2014). The World Health Organization Intermediate Guideline for PM2.5 is 35μg/m3.
In order of effectiveness, when cooking in a kitchen, health interventions seem to be:
Venting smoke up a functional chimney.
Increasing the fresh air entering the kitchen to dilute smoke and gases. (When the outdoor air is clean and the air exchange rate is doubled, the indoor air pollution is reduced by half.)
Burning up almost all of the smoke in the stove.
Unvented Rocket stoves, and other ‘moderately clean burning’ stoves (such as a carefully tended open fire with pot skirt), emit much too much smoke and gas to protect health in houses.
Cooking outside, especially upwind of the fire in a bit of breeze, is highly effective in lowering harmful concentrations of PM2.5.
Cooking outside seems to be a first choice intervention, when applicable. Even ‘moderately clean burning biomass stoves’ can be used when the cook is upwind of the fire in a bit of a breeze, meeting the WHO Intermediate Guideline for PM2.5.
Of course, cooking with a low emission stove is preferable, when possible!
https://aprovecho.org/wp-content/uploads/2021/05/ghana-practical-stove.jpg500375Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2022-06-10 17:57:592022-06-10 17:58:01Cooking Outdoors as a Health Intervention
I didn’t realize that natural gas is mostly methane
which is about 84 times worse for climate change compared to CO2.
As reported in the recently published study “Methane and NOx Emissions from Natural Gas Stoves, Cooktops, and Ovens in Residential Homes,” methane leaks are bad news for both environmental and personal health. (Lebel, et al, Environ. Sci. Technol. 2022, 56, 4, 2529–2539)
The abstract in the Lebel
article states:
Natural gas stoves in >40 million U.S.
residences release methane (CH4) ─a potent greenhouse gas, through
post-meter leaks and incomplete combustion.
Using
a 20-year timeframe for methane, annual methane emissions from all gas stoves
in U.S. homes have a climate impact comparable to the annual carbon dioxide
emissions of 500,000 cars.
In addition to methane emissions, co-emitted
health-damaging air pollutants such as nitrogen oxides (NOx)
are released into home air and can trigger respiratory diseases.
Our data suggest that families who don’t use
their range hoods or who have poor ventilation can surpass the one hour
national standard of NO2 (100 ppb) within a few minutes of
stove usage, particularly in smaller kitchens.
https://aprovecho.org/wp-content/uploads/2022/03/3.24.22-methane.jpg408440Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2022-03-24 14:24:402022-03-24 14:31:06Natural Gas, Methane and Nitrogen Oxides
Dos por Tres Stove with Chimney, photo courtesy of Proyecto Mirador
During an ETHOS panel discussion on Cooking,
Health, and Climate, it was great to see that the Justa stove with chimney
protected health so well. Chimneys are mandated by law in the USA/Europe/China
and many other countries. When Mahatma Gandhi returned to India from England he
introduced chimneys as a logical upgrade of kitchens.
The WHO (2018) listed five prescriptions to protect health:
Use only clean household energy when available
While waiting for gas, use technologies like low-emission biomass cook stoves
Minimize the time children spend around smoky fires
Increase ventilation
Install a chimney
Functional chimneys are the historical first step to protect health. It’s so pleasant to sit and chat in the clean kitchen when a Justa, Dos por Tres, or Patsari stove is being used! Following up with improved combustion efficiency helps to protect climate and outdoor air quality.
https://aprovecho.org/wp-content/uploads/2022/02/1594px-Proyecto_Mirador_Dos_por_Tres.jpeg11991594Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2022-02-03 19:05:262022-02-03 19:05:28Justa, Dos por Tres, Patsari Stoves!
I hope that you are living in a smoke free environment! There’s a forest fire about 40 miles east of the lab that floods our valley with smoke when the wind slows down. I just looked up and noticed that it was getting hard to see Blue Mountain, a sure sign that the northwesterly wind wasn’t pushing hard enough to clear the skies. It reminded me of living on the Coromandel Coast in India where a blue sky was unlikely even at the beach.
Burning up smoke is not all that difficult to do: just thoroughly mix the smoke into the flame. But that doesn’t happen in a forest fire (or in a three stone fire). The smoke and flame go in different directions. The industrial reduction of PM2.5 often depends on both improved combustion efficiency and the post-combustion filtration/scrubbing of emissions. When I can’t see Blue Mountain anymore, I switch on a box fan that has a 20” by 20” by 1” furnace filter taped onto the inlet side of the fan. The fan pulls the dirty air in my office through the filter and the PM2.5 is removed from the air that I’m breathing.
We wrote a paper describing how the same fan and filter reduced PM2.5 when installed in a hood over the stove. We used a washable filter and hoped that the combination of a clean burning stove with post combustion filtration of smoke might help to protect inside and outside air quality. Check out the paper: Still, D. K., Bentson, S., Murray, N., Andres, J., Yue, Z., & MacCarty, N. A. (2018). Laboratory experiments regarding the use of filtration and retained heat to reduce particulate matter emissions from biomass cooking. Energy for Sustainable Development, 42, 129–135. https://doi.org/10.1016/j.esd.2017.09.011
https://aprovecho.org/wp-content/uploads/2021/09/9.1.21-UW-smoke-flyer.jpg15151160Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2021-09-01 11:30:072021-09-01 11:49:10Smoke In The Air!
Reducing/removing smoke from the kitchen improves health. Adding a chimney is one recommended solution.
In
2014, the World Health Organization (WHO) published intermediate and final
indoor air guidelines for vented and unvented biomass cooking stoves. Their
strong recommendation directed governments and implementers to advocate
technologies and fuels that are proven to protect health. The WHO advises
implementers that to protect health the cook stove intervention should not
exceed the following air pollutant emission rates in actual use:
WHO Intermediate Emission Rate Targets:
Unvented stove
Vented stove
PM 2.5:1.75 mg/min
PM 2.5: 7.15 mg/min
CO: 0.35 g/min
CO: 1.45 g/min
Many newer biomass cookstoves with chimneys meet the WHO Targets of 7mg/minute for PM2.5 and 1.45 g/minute for CO when tested in the laboratory. Adding chimneys to cook stoves makes them more costly, but ARC designers are relieved to have a “line drawn in the sand.” As seen in Sam and Shikhar’s video last week, experiments in the ARC Test Kitchen showed that a natural draft hood can also be a big help in protecting health.
Protecting outdoor air quality is equally important. Dr. Nordica MacCarty (Oregon State University) will be investigating effects on indoor and outdoor air when the combination of a natural draft earthen hood and an earthen stove with Jet-Flame is used in houses in Malawi.
Industrial technologies routinely achieve strict standards for combustion efficiency and further reduce emissions with post combustion techniques. Introducing these well-known applications into cook stoves seems a logical progression. Clean up combustion and, at the same time, clean up the indoor and outdoor air. We have been very successful doing this in the US and Europe, and China is now on the same path.
The WHO vented stove Emission Rate Targets are based
on 75% of the smoke and gases being removed up the chimney and out of the
house. In their review of field studies, an average of 25% of the smoke and gas
remained in the kitchen. Almost none of the residential biomass heating stoves
in the United States meet the WHO Targets for PM 2.5 but the chimney transports
the smoke outside where it is diluted by clean outdoor air to safe levels of
concentration.
Meeting emission targets is a necessary and ever present goal. At the same time, wood burning stoves can be improved in many other ways. Improving the smoky mud stove to use less fuel is not a complete cure but is very helpful, benefitting the user who either pays for the fuel or has to collect it. The functional chimney makes a tremendous difference by sending smoke and gas out of the kitchen, making it a more pleasant and healthy environment. Making the high mass stove safer results in fewer burns. The list of improvements goes on and on – making the stove better at cooking local foods, increasing the number of air exchanges per hour in the kitchen, moving the kitchen outdoors, etc.
In the real world, positive changes are hard to accomplish
but are always great.
https://aprovecho.org/wp-content/uploads/2021/08/8.4.21-WHO-standards.jpg677580Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2021-08-03 19:40:472024-06-24 16:46:56Meeting the World Health Organization Emission Rate Targets
The old saying, “if you can’t handle the heat, get out of the kitchen,” is not lost on us when we are working in the test kitchen. It takes us a while to get the vertical and horizontal grid of Climate Solution Consulting’s HAPEx particulate matter monitors started and positioned. Then ARC’s PEMS-PC partial-capture based emissions sampler has to collect a zero point of the gasses in the atmosphere. Don’t forget the temperature sensors (where is that data?) and the wood. This is after reviewing yesterday’s work, discussing a plan for the day, and watering the garden. So, by the time the young scientist rolls into the test kitchen in the Oregon summer, currently home of America’s largest wildfire, it’s about 100°F and rising. But science must go on.
ARC’s four year old test kitchen is currently being used to test a natural draft hood of our design. Our experiment allows us to operate the fire without being exposed to the emissions from the fire. We used to use a vacuum cleaner as a positive pressure ventilator, but now we sit outside of the room and feed the fire through a glove box. After seeing that the hood was effective enough to reduce the concentration of PM2.5 in the test kitchen to below 35 ug (averaged over 24 hr), we turned the hood around and made a video for you of us doing the water boiling test while enjoying a smoke free kitchen.
Enjoy the video (and know that those loud pumps and fans go
with the bit about it being hot in the kitchen).
Please send your photos and stories of natural draft hoods!
We don’t want to lose this beautiful technology.
-Sam Bentsen, Aprovecho Research Center General Manager
It’s fascinating to read the ISO 19867 Standards for cookstoves and I agree with a lot of it. Many of us in the ‘stove world’ were involved for years in creating those documents. One of the big improvements is testing stoves at high, medium, and low power while reporting the results with the firepower.
We forgot to do that in the International Working Agreement started in Peru at the Partnership for Clean Indoor Air meeting in 2011. Since stoves generally make fewer emissions at low power it was a temptation to reduce the firepower and achieve a higher score on the Tiers. Since firepower was not seen on the Tier scorecard, it was really not possible to compare performance. And as we know, people tend to like high power stoves. It’s so great that this problem has been fixed in ISO 19867.
How to get a Tier 5 score for emissions? Use a chimney.
Santa understands the importance of chimneys… Happy Holidays from the Aprovecho team!
The chimney transports most or all of the PM2.5 and CO out of the kitchen. Only “fugitive” emissions escape into the room. In ISO 19867 the fugitive emissions are used for the emission rate values. For unvented stoves, total emissions are used for the emission rate values. Just make sure that your chimney and stove do not leak.
It makes sense. Here in rural Oregon, unfortunately, smoke pours out of chimneys all day and night as folks stay warm with wood. Heating stoves can be very smoky! The airtight chimney and stove get essentially all of the smoke outside of the building where concentrations are and stove get essentially all of the smoke outside of the building where concentrations are diluted.
Now, of course, at ARC we try to combine high combustion efficiency with effective chimneys. We need to protect the quality of the outside air, as well. The combination is intended to protect indoor and outdoor air. If the outdoor air is polluted it is less effective in lowering harmful concentrations. Combustion efficiency is always great and to protect health it must increase when the outside air quality is degraded. In Beijing you don’t want to add one more milligram of smoke into the air!
An indoor/outdoor air quality planning tool.
Sam Bentson created an excel spreadsheet that explains how protecting indoor and outdoor air quality are related. You can download the spreadsheet here, and learn how to use it for project planning: aprovecho.org/portfolio-item/project-planning/
https://aprovecho.org/wp-content/uploads/2016/03/project-planner-2-crop-600x335.png333600Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2020-12-23 16:04:492020-12-23 16:04:51It is easy to get a Tier 5 score for PM2.5 and CO!
Lance MacCarty
