PowerStove: Cooking for a Third of the World M U L T I D I S C I P L I N A R Y S E N I O R D E S I G N P R O J E C T S P 1 3 4 4 1 2 0 1 2-2 0 1 3
Motivation Two and half billion people depend on biomass (wood, dung, or agriculture residues) primarily for cooking The practice of cooking with biomass has decimated many ecosystems Biomass use requires an enormous amount of human effort to gather and process Cooking with biomass creates considerable health problems that continue to plague the world s poorest populations Cookstove emissions is the second-largest global source of greenhouse gases after fossil-fuel combustion
2011-2012 Stove Project Scope To minimize the harmful effects associated with cooking, two Rochester Institute of Technology (RIT) multidisciplinary student engineering teams in partnership with a NGO will design, build, and test a more efficient, cleaner, and socially acceptable cook stove using thermoelectrics and a simple blower. The project will result in a minimum of two working stoves that will be field tested during the summer of 2012.
Project Initial Target Customer Borgne, Haiti Poorest country in Western hemisphere ($420/person-year) 75% of all energy consumed is biomass Only 4% forested land left, huge deforestation problems. H.O.P.E (Haiti Outreach - Pwoje Espwa) partner NGO
RIT Advanced Cookstove Project Goals This project will build on recent stove advancements to develop an improved stove for Haiti and other developing nations with the goals of: reducing fuel use by a factor of two or greater in order to turn the tide on deforestation and diminish the time and limited financial resources spent on cooking; creating microenterprises for assembling the advanced stoves to generate wealth and develop local expertise for maintaining the stoves in order to improve chances of sustained stove adoption; enhancing conventional cooking techniques of traditional foods; provide an electrical power source to operate auxiliary loads such as radio, lighting, charge cell phone batteries, and small UV water treatment technologies; and improve the air quality to reduce the alarming rate of respiratory deaths associated with cooking while combating global climate change.
Past Projects P10451 & 11451 Developed testing setup and process for quantifying stove efficiencies and emissions. Benchmarked Haitian stove. P10461, 11461, & 11462 Developed first generation of vendor and institutional cook stoves using thermoelectrics and blower. P12441 & P12442 Continued to develop previous years design for thermoelectric module and stove design
Project 12442 Next Generation Charcoal Cook Stove for Haiti Build on the work done by project P11461 &11462 to develop an improved cookstove for vendors and institutional users. The improved cook stove should substantially reduce (by more than 50%) the emissions and fuel needed for cooking compared to the traditional stoves currently used in Haiti. Combine efficient cook stove and thermoelectric thermal system. The stove developed by team P11461 was designed to use force draft to improve combustion and heat transfer to the pot. The stove design also made use of recycled material, attempted to reduce thermal losses by the use of radiant barriers, and increase heat transfer to pot by the use of a skirt. Some modeling and experimentation was done, but not comprehensive.
Project 12442 Preliminary Needs Affordable (initial cost <$10 at high production quantities of 1000+) Cheaper to operate than current stove (less fuel for same cooking tasks) Significantly cleaner than current stove (reduced CO and PM emissions) Easy to operate (require little user interaction and simple and intuitive processes, require the same or less effort than current practices for starting and cooking with stove.) Same or improved cooking controls (control cooking conditions for traditional Haitian cooking practices). Obtain rapid boil quickly and then bring to simmer. Be able to be fabricated and assembled using Haitian artisan practices Transportable so that a single adult can move the stove 500 meters unassisted. Rugged, can handle being dropped by user multiple times, withstand harsh conditions such as rain and high temperatures. Durable, should operate for five or more years with a use rate of at least twice a day or have simple, cheap, and easily replaceable parts. Thermoelectric module will not fail due to high temperature and gradients. Safe to operate, operator should not be injured during normal use and transport of the cook stove. Internal needs: Maintain appropriate temperature gradient across thermoelectric module Achieve desired temperature gradient quickly
Project 12442 Preliminary Specifications Production cost: <$10 for materials at 1-10K quantities, less than 3 hours of a Haitian s craftsman labor per stove. Fuel use: 50% of traditional Haitian rebar fuel use for both Full Water Boil Test (WBT) and established Controlled Cooking Test (CCT). CO emissions: 25% of tradition Haitian rebar stove emissions for both WBT and CCT PM emissions: 25% of tradition Haitian rebar stove emissions for both WBT and CCT Time to boil during WBT using traditional starting practice is ¾ the time currently achieved with the Haitian rebar stove. Surfaces of the stove that will be contacted by stove operator should not exceed 50 C. Less than 15 minutes to start and bring 2.5 liters of water to boil using traditional starting techniques. Range of heat output 1-6 kw (heat transferred to pot). Capable of using with pot diameters from 20-60 cm. Withstand pot mass up to 25 kg. Five or less tasks to maintain fire throughout a CCT after initial stove start. Any part that will need to be replaced within a three year stove life should: Be less than $3. Require less than 60 minutes to replace. Be able to be replaced with no or simple hand tools.
Project 12442 Preliminary Specifications Stove weight should be less than 8 kg. Stove volume should not exceed 0.2 m 3. Stove construction should be possible using basic Haitian fabrication capabilities Survive 20x 2-meter drop tests. Egonomics metrics? Internal Specifications: Keep a minimum temperature gradient of 200 C across a Thermonanic TE (TEP1-1264-3.4) thermoelectric module under peak power conditions (i.e. electrically loading module with the internal resistance of the module.) Reach desired temperature gradient within 20 minutes of starting the fire. Consume less than 0.6 W (i.e. ideal case, 1 W absolute max) to operate all stove internal electrical loads (i.e. fan and controls). Thermoelectric module never exceeds max operating temperature (380 C continuously and 400 C intermittently on hot side and 200 C on cold side). Thermoelectric module is mechanically loaded evenly and loading does not exceed module failure limit.
Project 12442 Project Deliverables An improved RIT stove design that has been tested and validated using a working prototype and shown to reduce fuel use and emissions by more than 50% from traditional Haitian stoves and is affordable and user friendly. Stove must be tightly coupled to thermoelectric power unit prototype being developed by P12441 Two prototype stoves to be sent to Haiti for field testing. Full and easy to follow documentation on how to fabricate and assemble the stove. Intuitive end-user operation manual with instruction of how to start, maintain, and operate the stove at optimal performance.
Project 12441 Thermoelectric Power Pack for Next Generation Cook Stove Build on the work done by project P10462 & P11462 to develop power pack for that is electrically coupled to P12442 stove and will supply sufficient power for fan and auxiliary charging. Needs: Affordable (<$10 at high production quantities) Easy to operate: require little user interaction and simple and intuitive processes. Compact, should be small so it does not extend too much from stove body. Rugged, can handle being dropped by user multiple times, withstand harsh conditions such as rain and high temperatures. Heat resistant, can be mounted on stove framing with minimal loss in lifetime. Durable, should operate for five or more years with a use rate of at least twice a day. Able to charge multiple cell phones and other typical 5V USB loads over the course of a typical institutional or vendor single stove use. Minimize stove use for sole purpose of electric power generation: unit should be able to charge one typical cell phone when no power is provided by thermoelectric to the fan. Power fan used for a force air stove during entire stove operation. Able to start fan multiple times in cases where there are multiple stove restarts. Safe to operate: operator should not be injured during normal use and transport of the thermoelectric power pack.
Project 12441 Preliminary Specifications Production cost: <$10 for materials and fabrication plus thermoelectric module at 1-10K Operate 1.2W fan continuously during stove operation with a draw of 4-12VDC. Power load using a Thermonanic TE Module (TEP1-1264-3.4) with a 20 minute warm-up period with cold side of TE going from 30 to 100 C and the hot side from 30 to 300 C. This is followed by steady state temperatures of 100 C and 300 C for 2.5 hours. Package size for entire power pack except thermoelectric module is restricted to 3 x3 x1.5 Unit should be less than 3 lbs. Package should prevent damage or significant reduction in product life to electrical components during a downpour. A minimum of 7.0 Wh of charging capacity to auxiliary loads such as cell phones through a standard USB connection over the course of a 3 hour cooking cycle Sustain surface mounting temperatures up to 350 C. Handle some sort of dynamic crush test Survive 20 2-meter drop test. Safety metrics?
Project 12441 Project Deliverables Two working thermoelectric power packs that are to be sent to Haiti for field testing. The power pack must be nicely packaged and rugged. These power packs must be fully coupled with the stove being developed by P12442. Full set and intuitive set of documentation on how to fabricate and assemble power pack units including necessary engineering pcb layouts files. Intuitive operation manual should be provided for the end-user. Instructions on how to adjust fan voltage so future teams can adjust design for different fans.
Classification of Cook Stoves Open Fire Rocket Stove http://picasaweb.google.com/lh/photo/_d6z6uis0hupx2pf1lip5a http://wings.interfree.it/html/elbow.html
Classification of Cook Stoves Gasifier Stove Forced Draft Fan Stove http://www.vrac.iastate.edu/ethos/files/ethos2009/stove%20developments/tlud%20gasifier.pdf http://www.treehugger.com/files/2006/03/philips_smokele.php
Classification of Cook Stoves Charcoal Stove Liquid or Gas Fuel Stove http://www.bioenergylists.org/stovesdoc/ezzati/new%20folder/metal.jpg http://picasaweb.google.com/lh/photo/vharzq11piftnuljr09z6g?feat=embedwebsite
Stove Innovation Adjustable skirt to improve heat transfer Outer pressurized make-up cavity Air flow Inlet air perforations for improved combustion Inner combustion chamber Thermoelectric module Heat Sink Small fan Power storage and conditioning/control Potential auxiliary power supply
Why Forced Air?
Why Forced Air?
Why Forced Air?
Stove Testing Water Boiling Test Bring 5 L of water to a boil for a Cold Start Bring a fresh 5 L of water to a boil from a Hot Start From the Hot Start, allow the water to continue to boil for 45 minutes Provides feedback on fuel consumption and thermal efficiency
Stove Testing RIT Modified Water Boiling Test Bring 2.5 L of water to boil from a Cold Start Hold the boil for one minute Simmer Stage: Allow the water to continue boiling for 20 minutes Allows to quickly verify repeatability
Results 600 500 400 Water Temperature, Carbon Monoxide and Total Weight During Modified Water Boiling Test 13.6 13.4 13.2 13 300 200 100 0 0 5 10 15 20 25 30 35 40 45 Time (min) 12.8 12.6 12.4 12.2 12 11.8 Temperature ( C) CO (ppm) Total Weight (kg)
Results
Thermoelectric Benefits Modular, scalable Solid-state, no moving parts Operate over a range of temperatures Transient thermal sources Minimal maintenance No noise, vibration
Resources Category Source Description Resource Available (mark with X) Faculty Rob Stevens ME Expertise in thermoelectrics and heat transfer X John Wellin ME Expertise in DAQ, fluids, and fan characterization X Brian Thorn ISE Product Sustainability X George Slack EE Power electronics X Jim Myers Center for Multidisciplinary Studies Haiti expert X Environment Sustainable Energy Lab ME-Stevens Lab for testing thermoelectric modules and subsystems. Lab does have ventilation and some DAQ resources X Equipment DAQ system ME-Stevens A USB based DAQ system, laptop, thermocouples, etc. are available through the Sustainable Energy Lab X Cook stove test stand SEL X Several stoves SEL X
Advise Identify the key hurdles and address them earlier rather than later. Identify and focus on the critical parts and do not get caught up with the trivial things. Test early and test often. Test components and subsystems before the entire system. Learn from the past. Pick the brains of those with experience. Define your boundaries before you design, but be flexible.