Thursday, June 28, 2018

Meet the teams: Backed by the EPA and DOE, top cookstove designers tackle the heatstove

This post is the sixth in a series introducing the 12 teams participating in the 2018 Wood Stove Design Challenge in November.

By John Ackerly, Ken Adler, and Shoshana Rybeck, Alliance for Green Heat

Cook stoves and international development 

Dean Still (left) with participants at an
Ethos conference near Seattle.
Dean Still leads the team at the Advanced Studies in Appropriate Technology Lab (ASAT) and has been involved with the international cook stove community for decades. He and his team have achieved many key breakthroughs in testing, stove design, instrumentation, and like most researchers and developers, they have had their share of dead ends, disappointments and flops.  

The New Yorker magazine featured Dean in a 2009 article about engineers who need to design stoves that cost no more than $10 so even the world’s poorest people can afford them. So, when we told Dean that cheap stoves by our standards were between $500 and $1,000, he laughed and said, “you would think that should be easy.”

ASAT won a $300,000 grant from the EPA to build a heat stove that makes electricity, thirty times more than the $10,000 that each team is getting from DOE through the Alliance for Green Heat. ASAT has another advantage that only a few teams have in the competition: they operate a testing lab so they can measure changes in emissions and efficiency with each iteration of the prototype.

ASAT's sister group, Aprovecho hosts
annual "stove camps" where innovators
work together to built and test designs
The challenge for ASAT is whether they translate their experience and skill making cookstoves into a successful heating stove that performs well in the lab and in the field. There is a tight timeline and ASAT is new to the way the EPA measures PM and efficiency for heat stoves—and the way that tests will be conducted at the Stove Challenge. Translating lab test protocols to real world emissions may be even tougher for cook stoves and oversight of cook stove labs is weak compared to EPA-approved heat stove labs. But the cook stove community is far more transparent, and test results and technologies are more freely shared in the common battle of a global enemy—daily exposure to wood smoke from traditional cooking practices.

ASAT’s strategy

Dean Still with Prince Charles, who
has been an advocate for the modern,
cleaner cookstoves
ASAT’s stove is unique from the start—it’s a rocket stove.  Rocket stoves are most common as a developing world cook stove where you feed small diameter fuel into an insulated chamber and let it burn the ends of the sticks. Rocket stoves designed for heating are usually called “rocket mass stoves” but the prototype coming to the competition in November 2018 will be a new, high tech, low mass hybrid of the Rocket stove.  

ASAT is using an expansive strategy and are integrating many innovative technologies, from fabric filters to laser smoke sensors that automatically adjust secondary air.  By keeping an open mind, the ASAT team is winnowing down technologies, but the danger is that they are doing this on a very short time-line and the prototype is still going through major changes with less than 6 months prior to the competition.

ASAT's lab in Cottage Grove, OR
ASAT is working to make a stove mostly for the Asian market that can benefit those who struggle to get heat and electricity independently with ultra-low emission rates. The stove will include an electrostatic filter for PM to capture escaping emissions. Dean says his stove will have “jets of pre-heated secondary air that create a zone of mixing like in the carburetor of a car where a combination of high temperatures, residence time and complete mixing result in close to complete combustion. The fan speed, the amount of smoke, CO, CO2, and temperature in stove will be shown on a LTD screen. A PM sensor in the chimney automatically adjusts the velocity of the secondary air jets.”

Thermoelectric technology 

With help from the EPA, ASAT is developing a stove that can be used to cook food, heat the home and create electricity mainly for rural households in Asia that have intermittent or no electricity. To do this, electronic designer and manufacturer Karl Walter and lab manager Sam Bentson have created a new type of TEG that fits into the evolving design. The team is currently working on the fifth iteration and are focusing on how to create reliable electricity in the most inexpensive way possible. 

Sam Bentson, ASAT Lab Manager
The team has been building their own TEG that is making electricity without the use of a water cooling system. Instead, their TEG uses a large radiator that is essentially an aluminum fin designed to move the most air at the lowest wattage possible. With the team solely using a radiator and not including a water cooled system, or even a fan, the model is far less expensive, which appeals to ASAT's dedication to making this as affordable as they can. The team hopes to develop a TEG for less than $100 that creates at least 15 watts of power, using a switch mode voltage regulator and usb connection. Karl Walter says, “Water cooling is great but there is also something to be valued in a simpler, robust approach.”

Creating an affordable cook stove with an attached TEG that does not have “moving parts” is no easy task. Thankfully, with the financial support of the DOE and EPA, ASAT has been able to fully delve into this project and work through the challenges they have faced. Karl says that for their team the largest challenges had to do with temperature differentials and power outputs. He says that finding a “realistic power output was difficult” as well as figuring out “what happens when you overheat the stove.” But, the team is on a two year contract for their EPA project and with a year remaining, they are optimistic about the future development of their product and plan to have a model prototype ready for market testing within the next 4 months.

ASAT follows the old adage to think globally and act locally. Their efforts to create stoves that benefit people around the world have had tremendous support from national and regional organizations and they hope to expose the powerful technology they’ve been working on to a larger audience at the challenge in November. 

Contact the team at:

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