Integrated stove for heating, cooking, electricity
Watch a video of the downdraft rocket stove that ASAT Inc. will show in Washington D.C. at the Alliance for Green Heat/DOE sponsored Wood Stove Design Challenge from Nov 9 to 13. ASAT gratefully acknowledges support from the US Environmental Protection Agency under EPA SBIR contract number EPD18009.
Long sticks are placed vertically in the combustion chamber where only the tips burn. A weight pushes the wood down as the ends turn into soft charcoal. Cooling fins on the top half of the feed tube help keep only the tips of the sticks burning. The room air is heated by the tall heat exchanger and cooking is possible on top of the cylinder.
The stove features a thermoelectric generator near the coals to create 18 W of electricity when the stove is running at its 10 kW high power setting. The electricity is distributed to two USB ports for high speed cell phone charging and LED lighting. Aluminum fins protrude into the combustion chamber to bring heat to the hot side of the generator, and a radiator on the bottom of the stove draws the heat away from the cold side and into the room.
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)
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!
Aprovecho Research Center
PO Box 1175
Cottage Grove, OR 97424, USA