Guest Blog: We are reposting a 2012 blog from Instructables by Tecwyn Twmffatt at Goat Industries. It describes an early effort to build a thermoelectric wood stove. This blog is part of a series of blogs providing information for the 2018 Wood Stove Design Challenge.
Introduction: Thermoelectric Power Generation (TEG)
Step 1: Part 2 of 3
A ten unit Thermoelectric generator system is shown being constructed and then fitted to a wood burner. The theoretical maximum output is 200 watts. The video shows how the generator was put together and how the wood burner was modified to get maximum heat through the TEGs. The TEGs themselves are able to withstand a constant 325 degrees C on the hot side and require plenty of heat to get the 20 watts that each of them are capable of producing.
Step 2: Part 3 of 3
In part 3 we successfully generate a significant amount of energy from the woodburning stove. In the first session, a circulation pump, a fan and 10 x 10 watt flood lights are powered up. In the second session, we attempt to get a more balanced load wired up to the tegs and measure a noticable increase in power output. The 10 tegs are wired up in 2 parallel strings and, from the manufacturer's specification, the optimum output voltage is 14.4v . The nearest that we manage is 13.8v, at which we generate 120 watts. The specifications suggest that 200 watts is possible when the load is matched.
Step 3: Full Playlist
31 Minutes of Thermoelectric video heaven!
Step 4: Creating the 1 TEG Generator
Here we are going to build the single TEG generator shown in the first video.
Step 5: Tools and Equipment
Parts: Thermoelectric power generator TEG module (GM250 449 )
...... buy direct from China at: www.thermonamic.com/
Aluminium block 102 x 115 x 20 mm
Steel block 102 x 115 x 10 mm
1/4" BSP blanks x 6 of
1/4" BSP male stud push fit pneumatic fittings for 10 mm pipe x 2 of (See photo above)
5 mm Hex bolts x 40 mm x 2 of
25 litre water butt
OD 10 mm ID 8 mm nylon pneumatic pipe
12V water pump
12V LEDs, 1 watt x 20 of Tools: 1/4" threading tap
5 mm metric coarse threading tap
Drill 11.5 mm
Drill 5.5 mm
Drill 4.2 mm
Plasma cutter / Grinder with cutting discs
Step 6: Drilling and Tapping the Cooling Block
Use the engineering drawing to produce internal coolant passage ways in the aluminium block. I ended up drilling all the way through to the other side and using more of the 1/4" blanks. Connect the 1/4" pipe fittings to the block and plumb in the pump. Add antifreeze to the water in the water butt if it's likely to get cold at all. To create a 'sandwich' with the hot block (steel block), the TEG and the cooling block, drill and tap holes in the steel block for the 5mm bolts. Weld the hot block into the side of the wood burner and recreate the TEG sandwich, tightening the bolts up with a torque wrench (see attached file). Connect up LEDs on the TEG, turn on the pump, light the wood burner and off you go!
Step 7: 10 TEG Layout
If you really must build the 10 TEG generator, the photo above shows what is involved. I have got CAD drawings, PCB drawings etc. If anybody is interested. Not for the faint hearted! PCB 03.pcb
CAD files 02.zip Heated Up!
|The late Paul Tiegs, one of the
greatest authorities on wood
stoves, conducted the
interviews for the EPA.
|John Crouch, HPBA’s
foremost wood stove expert.
John Crouch, HPBA: I wouldn’t use the term “close the loop-hole”. I would say, “is the proper place to cut off the definition of a wood heater?” We all know the whole discussion during the Reg-Neg ignored this emerging category of pellet stoves. So this gets back into my other broader comment, which is, instead of going back in and changing the NSPS in a piecemeal fashion, there needs to be a true revision of the whole thing that deals with the category of pellets and masonry heaters and outdoor furnaces.
Rick Curkeet, Intertek: Yes. The way to amend the regulation is to simply remove the 35:1 air/fuel ratio exemption. This has never been required by fireplaces (they meet the 5 kg/hr minimum burn rate exemption criterion anyway). Pellet units are readily able to meet emissions requirements and the exemption only encourages making these units less efficient to avoid the regulation.
Bob Ferguson, Consultant: The 35:1 cutoff was intended for fireplaces. However, pellet stoves are the only product that even take advantage of the air-fuel exemptions. Fireplaces generally use the burn rate exemption. Pellet stoves probably don’t need to be regulated at all. They are all quite clean burning. Let the marketplace decide if exempt stoves are acceptable. If pellet stove users demand products that use fewer pellets (more efficient), the manufacturers will respond.
Skip Hayden, Researcher: Yes. In Canada, we recommend that people buy only EPA-approved pellet stoves. We have developed a high ash pellet stove that’s operating around 85% and its emissions are about 0.3 g/hr or less.
|Dan Henry, a founder of Quadrafire
stoves is one of industry’s most
Dan Henry, Aladdin: There is no data that indicates that even a poorly operating stove is a dirty burning appliance. They are inherently clean, becoming more and more reliable, and don’t fix them if they aren’t broken.
Dennis Jaasma, University of VA: Pellet stoves are inherently clean burning unless there is something very bad about their design. I am not concerned about regulating the currently uncertified units unless their field emissions are bad compared to certified stoves.
Robert C. McCrillis, EPA: Yes, all pellet stoves should be affected facilities and not subjected to that 35:1.
|Ben Myren one of Amreica’s most
thoughtful and experienced stove tester.
Ben Myren, Myren Labs: I agree, no more loop-holes. The new technology stoves that are coming on the market are going to be totally new critters. I don’t think that turning down the air- to-fuel ratio, to make it whatever it is, should get you out of the loop. Some of those suckers have got to be just filthy. I mean you look at the flame. I’ve seen them burn at the trade show; you know, the glass is sooting up on the edges. You can just see it.
|Michael van Buren was a technical
expert with The Hearth Products
Association, now HPBA
Michael Van Buren, HPBA: I don’t know what that loop-hole does, whether it really affects the operation of the stove and the efficiency of the stove.
Question: According to a Department of Energy survey out of the 20.4 million households that used a wood burning appliance in 1993, less than 0.3 million used a wood burning furnace as their primary source of heat. Are there enough wood-fired central heating furnaces in use to merit their closer evaluation? How many commercially available models are there? Are there emissions data for them? Should they be certified?
John Crouch: The  EPA New Source Performance Standards killed the indoor furnace industry and created this little loop-hole which the outdoor furnace industry is beginning to exploit and kind of underscores the need for a more comprehensive wood burning regulation which sets out over a several year period to codify all forms of wood burning technology.
|Rick Curkeet tested stoves for Intertek
labs and is one of industry’s top experts.
Rick Curkeet: I don’t know how many new units are being produced but I’m sure it’s a very small number. Still, one really poor unit can be a significant problem if it’s in your neighborhood. There have never been any standards for testing this type of product for emissions and efficiency. However, we have adapted existing methods and can say that the performance range is very wide. Poor designs may be 30% or less efficient and produce nearly 100 grams/hr emissions rates. Good designs are able to approach certified wood stove performance levels.
Bob Ferguson: I don’t feel there are enough units being sold to merit any activity what-so-ever. There are only a handful of manufacturers. I don’t think there has been anything published–so if testing has been conducted, it is probably a good assumption that the numbers aren’t that good. They shouldn’t be certified, as you would have to develop test methods and standards. The country would be better off using the money to pay manufacturers to phase out of production, sort of like the agricultural method of paying farmers not to grow certain crops.
|The late Skip Hayden, one of the main
wood stove authorities during the 1980s
Skip Hayden: The number of central wood furnaces in Canada, certainly in comparison to the United States, would be higher. In our Eastern provinces, it’s a relatively common add-on to existing oil furnaces. Generally, they are as dirty as can be.
Dan Henry: I think a lot of these are used in rural areas and considering the fuels that are out there, I don’t think they should be regulated. Maybe just a spot check of some sort. I think the only thing that would benefit would be the testing laboratories. If it emits particulate into an air shed where it can have an adverse effect on the industry (my ability to make a living), then yes.
also ran a research
test lab at the
University of VA.
Dennis Jaasma: Yes, central heaters merit further evaluation. I don’t know how many models are available. I think EPA has done some work on them, but I do not know any results. Yes, they should be certified. They are in danger of becoming extinct if they don’t wind up with a certification program.
Robert C. McCrillis: In some localities I think these furnaces are a problem; I don’t know how many are commercially available. I think I can name off six or eight companies and each one makes several models, but I don’t know what the total market is, maybe 10,000 – 15,000 a year. The little bit of testing that we did here, says that they are probably on a par with a conventional wood stove. The way those things work, they have a thermostatically operated draft and when the thermostat shuts off the draft closes, so you get this real smoldering burning situation. Secondary combustion technology probably wouldn’t work. Possibly a catalytic technology would, but I just don’t think it stays hot enough in there. I guess that really depends on the impact.
Ben Myren: I don’t think they should be exempt for any reason. As to the rest of it–are there emissions data for them? I suspect there are. Should they be certified? Yes they should be certified. Nobody should be exempt from the process.
Michael van Buren: I think there should be some type of testing on them.
- 1.1 Are in-home emission reductions as compared to conventional stoves shown in Table 1 for catalytic and non-catalytic certified stoves reasonable?
- 1.2 Are efficiencies shown in Table 2 for catalytic and non-catalytic certified stoves reasonable?
- 1.3 Can catalytic technology for use in wood stoves be fundamentally improved?
- 1.4 Is the use of manufactured fuel (densified and wax logs) a credible emission
- 1.5 For non-catalytic stoves the heat retention adjustment with refractory material of various densities can reduce particulate emissions. How big an effect can this have?
- 1.6 Approximately one half of the particulate emissions occur during the kindling phase for non-catalytic wood stoves and more than half for catalytic wood stoves. Are there improvements in technology that can mitigate this problem? Can specially designed high BTU wax logs be used to achieve a fast start and reduce kindling phase emissions?
- 1.7 Should masonry heaters with tight fitting doors and draft control be classified as a wood stove and be subject to some type of certification even though most weigh more than 800 kg?
- 1.8 Are the emissions and efficiencies for masonry heaters, based on in-home tests, shown in Tables 1 and 2 reasonable?
- 1.9 The OMNI staff feels the emissions per unit of heat delivered (e.g., lb/MBTU or g/MJ) is a more appropriate way to rank the performance of wood burning appliances than emission factors (lb/ton or g/kg) or emission rates (g/hr). — Comments?
- 1.10 Default efficiency values are used for wood stoves. This coupled with the fact that emission factors or rates (not g/MJ) are used to rank wood stoves does not provide an incentive for manufacturers to increase the efficiency of their stoves. — Comments? Should an efficiency test method as described (FR v. 55, n 161, p. 33925, Aug. 20,1990) be required to be used and the results listed?
- 1.11 Have certified stove design and performance improved since the first certified stoves? If so, how?
- State-of-the-art of fireplace emission control technology.
- 2.1 Are the emission factors and efficiencies for the in-home use of fireplaces and inserts shown in Tables 3 and 4 reasonable?
- 2.2 There appear to be only a few practical design or technology options for fireplaces that will potentially mitigate particulate emissions. — What designs and technologies are available? What retrofit options are there?
- 2.3 The use of wax fire logs reduces emissions over the use of cordwood. Can the formulation of wax logs be changed to produce even less emissions?
- 2.4 What are the distinctions between a masonry fireplace and a masonry heater?
- 2.5 As with wood stoves, the OMNI staff believe that the mass of emissions per unit of heat delivered is a better way to rank the performance of fireplaces than emission factors or emission rates.
- State-of-the-art of wood-fired central heating furnace emission control technology.
- 4.1 Are the emissions and efficiencies for the in-home use of pellet stoves shown in Tables 1 and 2 reasonable?
- 4.2 The 35:1 air-to-fuel ratio cut-off for certification has produced two classes of pellet stoves — those that are certified and those that are not. The latter class may have models that are less efficient and have higher emissions than the former. Should the regulations be amended to close the loop-hole and discourage the practice of intentionally designing models with a higher air-to-fuel ratio to avoid certification?
- 4.3 Have pellet stove design and performance improved since the first models were introduced? If so, how?
- Correspondence between in-home and laboratory emission test results.
- 6.1 How accurately do certification tests predict in-home performance?
- 6.2 How would you design research testing in the laboratory to simulate in-home use?
- EPA Method 28 strengths and weaknesses.
- 7.1 Method 28 is in part an “art”. Fuel loading density, fuel moisture, fuel characteristics (old vs new growth, grain spacing, wood density) and coal bed conditioning can be adjusted within the specification range of the method to influence results. In your experience what things have the most effect on particulate emissions? How much influence can they have?
- 7.2 Burn rate weighting is based on very limited data and the cities from where the data were obtained are not very representative of wood use nationwide (see Table 6). How can the weighting scheme be improved to be more representative of the nation as a whole?
- 7.3 The equation for the calculation of the air-to-fuel ratio as in Method 28A is in error. The error produces a small but significant difference in the calculated air-to-fuel ratio. Should the method be corrected or should it be left as a “predictor” of the air-to-fuel ratio?
- Performance deterioration of EPA-certified wood stoves in the field.
- 9.1 It is the opinion of many in the wood stove industry that catalysts last only five years and that a stove designed for a catalyst operated without a functioning catalyst can produce as much emissions as a conventional stove. — Comments?
- 9.2 Field studies in Glens Falls, NY, Medford, OR, Klamath Falls, OR and Crested Butte, CO showed that emissions from some catalytic stoves became appreciably worse even after two to three years of use. Inspection of stoves in Glens Falls showed that catalyst deterioration and leaky bypass systems were responsible. Have improvements been made in the design of catalytic stoves to minimize these problems? Is it reasonable to require homeowner training on the proper use of catalytic stoves and/or to incorporate into their costs an inspection and catalyst replacement program?
- Stress test pros and cons.
- 10.1 A short-term laboratory woodstove durability testing protocol was developed to predict the long-term durability of stoves under conditions characteristic of in- home use (see EPA-600/R-94-193). It was concluded in that study that damage occurs during those occasional times when a woodstove is operated in the home at exceptionally high temperatures. The laboratory stress test was designed to operate a woodstove at very high temperatures over a one to two week period to predict long-term durability under in-home use. Is this a reasonable approach?
- 10.2 Should a stress test be made part of the certification process?
- Feasibility of developing separate emission factors for dry and wet wood and for
- 11.1 Optimum wood moisture for low particulate emissions seems to be in the 18% to 20% range. Are you aware of any data that will allow the impact of wood moisture to be isolated from other variables? Could it be different for wood from different tree species?
- 11.2 Wood from different tree species clearly burns differently. The chemical make-up and density of wood from different tree species is different. For example wood from coniferous trees has more resin than wood from deciduous trees. It is believed that particulate emission factors will be different for wood from different tree species. If this is true different parts of the country may have different emissions factors for residential wood combustion. Are you aware of any data that document different emission factors for wood from different tree species?
- 12.2 Should the home owner be provided with a maintenance manual or a training course at the time of purchase? Should a maintenance program be part of the purchase price particularly for catalytic stoves?
- 12.3 What would the key elements of routine maintenance be?
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