Ornate chimneys at Hampton Court Palace, London
Ornate chimneys at Hampton Court Palace, London
Multiple ornate chimneys grace Hampton Court Palace.

An Important Health Intervention

When cooking stoves are tested in the field the emissions of PM2.5 and CO are often higher than lab results (Roden et al., 2009). The wood can be wetter, the fire is made with less attention, and many real life variables create higher levels of pollution. It’s hard to imagine that unvented cookstoves for indoor use can be invented that will protect health when too much wet fuel is pushed quickly into the combustion chamber. Even modern cars make a lot of smoke when trying to combust bad quality gasoline.

Clean burning stoves require clean fuel just like automobiles. The sticks of wood need to be relatively dry and the metering of the sticks into the combustion chamber cannot happen too quickly. Perhaps batch fed pellet stoves will have more similar lab and field results if the pellets are well made, dry, and clean?

It’s illegal to install most types of unvented combustion devices in the United States and Europe. Even natural gas room heaters and gas cooking stoves are vented. For realistic protection of health, ARC consultants try to attach chimneys to biomass cookstoves whenever possible. When the stove smokes at least the pollution goes outside above the roof line where it becomes diluted.

Health Supportive Alternatives

Adding a chimney is not always a possibility. In these cases, it is helpful to move cooking out of the closed kitchen, for example under a veranda in the open air. Increasing air exchange rates by cooking under a veranda has been shown to dramatically lower concentrations of harmful PM and CO. Even opening the door and window in a test kitchen lowered the particulate matter 1-hour concentrations between 93% to 98% compared to the closed kitchen, and the CO 1-hour concentrations were 83% to 95% lower (Grabow et al., 2013).

Hundreds of years ago in Europe chimneys were developed as a first step to take smoke and gases outside of the kitchen. In the United States millions of wood burning heating stoves are used indoors every winter. Chimneys transport the pollution outdoors where it is mixed with the outside air.

References

Roden, C. A., Bond, T. C., Conway, S., Osorto Pinel, A. B., MacCarty, N., & Still, D. (2009). Laboratory and field investigations of particulate and carbon monoxide emissions from traditional and improved cookstoves. Atmospheric Environment, 43(6), 1170–1181. https://doi.org/10.1016/j.atmosenv.2008.05.041

Grabow, K., Still, D., & Bentson, S. (2013). Test Kitchen studies of indoor air pollution from biomass cookstoves. Energy for Sustainable Development, 17(5), 458–462. https://doi.org/10.1016/j.esd.2013.05.003

Box fan with filter reduces PM2.5

ARC has built and used two Test Kitchens and now, has by far the best one, built by Andy McClean and the three summer interns. We are looking at the distribution of smoke and the effect of opening doors and windows. Past tests with the early test kitchens showed that smoke stratified by height with the highest concentrations near the ceiling. Makes sense to cook near the floor! Opening the door dramatically lowered both PM and CO. (See:  Test Results of Cook Stove Performance, page 68)

Test kitchen
Andy McClean, Chuang Li, Katie Cushman, and Jon Au built the test kitchen.

The new Test Kitchen is a bit of an improvement. It has a volume of 30 cubic meters and the air exchange rate is controlled by 48 electric fans that are evenly spaced around the top perimeter of the building. Openings (48) along the bottom perimeter let dilution air in the test kitchen.

For the first experiment in the test kitchen the air exchange rate was determined using the tracer gas decay method (CO from a charcoal stove). The speed of the fans was adjusted until 15 ACH was measured. The smoke distribution while conducting water boiling tests was measured using 30 light scattering based PM detectors (HAPEx) that were hung from the ceiling and evenly spaced throughout the volume. The emissions rate of the rocket stove was measured using an ARC PEMS that was fitted with a partial capture probe and a gravimetric system for measuring PM2.5 (new development!). The gravimetric measurement of PM2.5 was used to calibrate the HAPEx. The tester fed the fire from an opening in the side of the test kitchen so as not to be exposed to the smoke from the fire. The test kitchen was built inside a large barn that had a fan-controlled cross ventilation. The background smoke concentration was recorded during the tests.

Results from the preliminary analysis show that there was vertical stratification, that the smoke in the room was evenly mixed from side to side, and that the average room concentration was similar to that predicted by a single zone box model. Stay tuned for more results!