|Rene Bindig and Niels Wittus,
designers of the Pellwood stove.
A German designed Wittus stove that is dispersed by a New York company, and a stove created by Seraph Industries, the smallest U.S. pellet stove manufacture, gained very first and next spot in the 2016 Pellet Stove Design and style Challenge.
This was the 3rd Stove Style Obstacle
marketing innovation in wood and pellet heating to assist buyers minimize fossil heating fuels with appliances that burn up considerably cleaner and far more proficiently than common stoves.
The Wittus Pellwood stove is an really modern prototype that can burn up each pellets and cordwood, bringing innovative technologies from basement furnaces up into the living room to accomplish quite reduced emissions of significantly less than fifty percent a gram for every hour.  The next place stove, Seraph’s Phoenix F25i, is practically ready for certification testing.  It also reached a quite clean burn up, persistently beneath 1 g/hr. and has modern characteristics to assist and inspire the client to maintain the stove working well.
|The Seraph group with AGH President
John Ackerly (proper).
Other stoves highlighted really modern patterns, which includes the futuristic searching, radiant warmth Torrefire stove with a glass burn up pot. In addition, the gravity fed Vibrastove, with a melt away plate instead of pot, employed only one tiny admirer and made its personal electrical power for off-grid use.
The Section of Energy’s Brookhaven Nationwide Lab hosted the function. The Lab carried out in depth tests of the opposition stoves and will offer valuable data for the EPA, business and other stakeholders about the strengths and weaknesses of tests protocols.
Each stove was examined 3 instances, to see if the stove operated persistently or regardless of whether the screening protocol could direct to variable benefits.
|The Torrefire pellet stove.
“Designing a very inexpensive, high carrying out pellet stove should not be rocket science,” stated Dr. Tom Butcher, Head of the Power Resources Division at Brookhaven National Laboratory
. “But in some techniques its tougher than rocket science due to the fact reliable gasoline combustion is extremely challenging to design for and check,” he mentioned.
“What helps make this competitors wonderful is the new concepts from the competing teams and the spirit of collaboration.”
Pellet stoves are extensively seen as a modern, cleaner, and a consumer-friendlier substitute to twine wood stoves.
A lot more states and applications are beginning to give more substantial rebates and incentives for pellet stoves than cord wooden stoves, and are starting to target on the stricter emission specifications that will consider influence in 2020.
This Style Obstacle showed that the 2020 expectations for particulate issue would not be hard for pellet stoves to achieve, but that numerous pellet stoves have mediocre efficiencies.
|Steve Spevak, designer of the
Vibrastove and Dr. Tom Butcher
(right) throughout testing.
The Pellet Stove Design Problem is a partnership in between numerous organizations and organizations that are interested in checking out the prospective of technology to satisfy a increasing need for renewable strength.
The principal funder,
the New York State Strength Investigation and Advancement Authority (
NYSERDA), operates Renewable Warmth New York
, a multi-layered incentive software for pellet heating equipment at the residential, commercial and industrial scale.  Other partners
contain the United States Forest Service, Brookhaven Nationwide Lab and point out agencies from Massachusetts and Washington, alongside with major specialists from Clarkson College, the Masonry Heater Affiliation and the Osprey Foundation.
The Design and style Problem brought virtually a hundred college students, stove builders, backyard inventors,
lecturers, regulators and authorities with each other to talk about and discussion the condition of the pellet stove engineering, indoor and outdoor air top quality problems and deployment approaches.  Of distinct notice had been a few college teams that are designing stoves from engineering departments at SUNY Buffalo, SUNY Stony Brook and the University of Maryland.  The speakers
incorporated Adam Baumgart-Getz from the EPA, Marius Wohler from the European BeReal initiative, nanoparticle skilled Dr. Barbara Panessa-Warren and scores of other people.  Presentation abstracts
are available along with most of the powerpoint displays
|Marius Wohler, a single of the European
presenters, describing the BeReal survey
and tests, foremost to new screening
protocols in Europe.
The occasion coordinator, the Alliance for Environmentally friendly Heat, is discovering a return to sophisticated twine wood stove technologies and employing the Countrywide Shopping mall in Washington DC yet again as a location in 2017.  Stakeholders are invited to get in touch with email@example.com
with enter about the following Design and style Problem.
– – –
The Alliance for Green Warmth promotes modern wood and pellet heating systems as a reduced-carbon, sustainable and inexpensive energy solution. The Alliance performs to progress stove innovation by way of engineering competitions and advises state and federal organizations on strengthening plans that require wooden and pellet heating. Founded in 2009, the Alliance is an impartial non-profit organization based in Takoma Park Maryland.
Posted by Earth Stove on April 2, 2016 with No Comments
This is an except of a much longer, and more technical paper by Prof. Gael Ulrich’s -“BioCombustion Institute Bulletin #3.” Gael calculated the efficiency of six popular pellet stoves, finding a wide difference. The highest, the Italian made Piazzetta Sabrina was 76% efficient and the lowest was the Enviro M55 Insert at 51% efficient. In between were the Ravelli RV80 (62%), Englander PDCV55 (63%), Quadrafire Mt Vernon AE (64%) and Harman Accentra 52i (71%).
He did this by using performance data produced by the Alliance for Green Heat, who tested these 6 stoves over a 30-day period. The Alliance operated the stoves, often for 24 hours a day, testing them almost every day at various heat output settings and averaging the results. All the stoves were purchased new, without the knowledge of the manufacturers and operated with the same PFI certified pellets. The Alliance produced an in-depth report about the findings, but we did not report the efficiency values because the instrument we used was a Testo 320, which produces a proprietary European (LHV) number, not the kind of efficiency values that are used and reported in North America.
Gael’s full paper can be downloaded as a PDF here, which is quite technical. We reproduced the less technical parts which are accessible to a wider audience.
One conclusion is that many pellet stoves lack a very simple solution to increasing their efficiencies – larger heat exchangers. Gael found that “All [the stoves], except the Enviro and Quadrafire, appear capable of adding another 5 to 10 percentage points by increasing heat exchange area to reduce the flue gas temperature.” This solution may only add $ 100 – $ 200 to the price of a stove but would save consumers far more in fuel costs.
One thing is clear: more expensive stoves do not necessarily provide consumers with higher efficiency. The Englander is sold by big box hardware stoves for $ 1,100, and is on par or better in efficiency than stoves that sell for $ 3,000 or $ 4,000. This is significant because the big pellet stove manufactures do not release the actual efficiency of their stoves to consumers and consumers have virtually no way to tell which models are lower or higher efficiency. The EPA contributed to a myth that pellet stoves have high efficiencies by giving them a default efficiency of 78%. Emerging data shows the average pellet stove is likely around 70% efficiency, but many big name brands make pellet stoves that have efficiencies in 50s and 60s. This analysis begins to dismantle the lack of transparency in efficiency values that manufacturers have tried to maintain for many years.
Biomass Combustor Efficiency
BioCombustion Institute Bulletin #3
(Gael Ulrich: 16 March 2016)
|Gael Ulrich was a professor of
Chemical Engineering at the
University of New Hampshire
If flue gas temperature and composition are known, one can calculate the efficiency of a biomass combustor using the so-call “stack loss” technique. This paper explains in detail why that is possible and how to do it. Fortuitously, during the preparation of this bulletin, the Alliance for Green Heat published data from their testing of six pellet stoves this past September. Test equipment used in the AGH study delivered composition, temperature, and efficiency numbers. Investigators declined to report the efficiency numbers for various reasons, although they do mention a range of 60 to 75%.
Using the AGH temperature and concentration data, I made independent calculations as described in detail herein. I find one of the six stoves operating at 51% efficiency, three in the low 60s, and the remaining two operating at 71 and 76%. I also conclude from my analysis that some of these units use “dilution as the solution to pollution.” If we consider actual emissions in grams per hour or milligrams per MegaJoule of heat delivered instead of parts per million in flue gas, the rating is rearranged with one stove deemed second dirtiest becoming the cleanest and that ranked third cleanest becoming the dirtiest. Factors that influence efficiency and cleanliness and how to improve these important performance properties are also discussed herein.
As pointed out in BCI Bulletins #1 (Units) and #2 (Emissions), biomass is intrinsically a clean fuel composed primarily of carbon, hydrogen, oxygen, and ash. If burned properly, with ash un-entrained, flue gases from biomass can be as clean as those from natural gas and perhaps even cleaner than from oil. The problem, of course, is that biomass is neither a liquid nor a gas like these fossil fuels. Burning a solid cleanly and efficiently is much more difficult. Bulletin #2 dealt with cleanliness and the standards expected. This one focuses on efficiency and how it can be measured for a biomass burner.
Instruments and software are available to deliver efficiency ratings and other data even to an ignorant user with enough money to buy them. But to use these tools intelligently, one must know how they function and should be able to calculate efficiency separately and from scratch. This bulletin describes how to do that.
Efficiency is a concept that everyone understands, but different people often define it differently. Let’s solve that problem first. For simplicity, visualize a biomass combustor as a black box with fuel and air flowing in; flue gases and ash flowing out. … As defined by logic, efficiency is the ratio of useful heat released to fuel energy provided. Fuel Energy is the Higher Heating Value, a quantity that has been carefully measured over the last couple centuries by scientists for all common fuels.
1. Burn with the least amount of excess air possible.
2. Operate with the lowest feasible flue gas temperature.
3. Use dry fuel.
Alliance for Green Heat Data
The AGH study ran for a period of 30 days. Investigators found results that showed little drift with time. Five of the six stoves operated with more than 200% excess air; beyond maxima considered in Figure 7. One could derive additional curves for these high air rates just as was done for the lower percentages of excess air, but I chose to extrapolate instead, creating the dashed lines in Figure 9.
Efficiencies for the six AGH pellet stoves as read from Figure 9b are listed in Table 6.
Table 6. Calculated efficiencies of pellet stoves studied in the September 2015 Alliance for Green Heat test series.
Stove O2 % X’s Air Flue Gas Efficiency e
Brand Conc. (Figure 8) Temp. (oC) (Figure 9b)
Enviro 18.7% 800% 150 51 %
Ravelli 16.8% 400% 195 62 %
Englander 16.0% 315% 222 63 %
Harman 15.0% 245% 205 71 %
Piazzetta 13.5% 175% 203 76 %
One of the six operated at 51% efficiency, three in the low 60s, and the remaining two operated at 71 and 76%. These numbers are consistent with the range mentioned in the AGH report.
Piazzetta achieves superiority through low excess air rate. Enviro, at the other end of the spectrum, would have an even lower efficiency if its flue gas temperature were as high as the others. All, except Enviro and Quad, appear capable of adding another 5 to 10 percentage points by increasing heat exchange area to reduce the flue gas temperature.
What about Pollution? The AGH data demonstrate an interesting application of using “dilution as a solution to pollution.” The Harman emitted flue gases containing about 820 ppm CO while the Enviro emitted 534 ppm. But the Harman operated with about 240% excess air; the Enviro with 800%. And, the Harman was 22% more efficient.
At the same pellet burning rate, the Enviro produces roughly 900/340 or 2.6 times as much flue gas as the Harmon, and its useful heat delivery rate is only 82 percent as great. Thus, in terms of mass of CO per kJ of delivered heat, a better measure of actual pollution, the Enviro is (2.6/0.82)*(534/820) = 2.1 or about twice as bad as the Harmon. Based on the data provided, I calculated mg of CO per MJ of useful heat delivered for the six pellet stoves. Results are listed in Table 7.
Table 7. Calculated CO emissions of pellet stoves studied in the September 2015 Alliance for Green Heat test series.
Brand % X’s Air Efficiency e (ppm) heat normalized**
Enviro 800% 51% 534 3000 850 (2.7)
Ravelli 400% 62% 428 1100 365 (1.2)
Englander 320% 62% 542 1200 387 (1.2)
Quad 480% 64% 318 930 318 (1.0)**
Harman 240% 71% 821 1300 487 (1.5)
Piazzetta 170% 76% 648 780 370 (1.2)
*Normalized to Quad as the reference.
**Normalized to Quad as the reference using Wikipedia formula.
In terms of mass per unit of useful heat, the Enviro emits about four times as much CO as the Piazzetta (3000 versus 780 mg/MJ or roughly 130 versus 35 milligrams per hour).
What about non-steady-state? My analysis assumes the appliance operates at steady state with feed rates and temperatures invariant with time. This is valid for automatic-feed pellet stoves but not for wood stoves that are fed batch-wise. There, the burn mode migrates from de-volatilization and combustion of light organics, gradually progressing to char or carbon burn-out. Fortunately, stage changes are slow relative to combustion kinetics. At any given time, the analysis described herein can be used to analyze the appliance at that instant. To more accurately reflect the performance of a batch-fired wood burner, one must record data over a complete firing cycle and then integrate results to obtain an average. This is further complicated by the fact that heat of combustion changes with time. That for carbon, for instance (near burn-out), is about 30,000 kJ/kg. Since the overall HHV for biomass is 20,000 kJ/kg, that for the volatiles must be lower than this.
What about moisture condensation? Mark Knaebe advocates improving efficiency by increasing heat exchange surface to the extent that water in the flue gas is condensed, adding its latent heat to the useful Q. This requires dropping flue gas temperature below the dew point. With low amounts of excess air, the dew point might be as high as 60 deg-C, but with 400% excess air, where many pellet stoves operate, the dew point is nearer 30 deg-C.
As cleaner appliances develop, the prospect of taking advantage of this extra heat becomes more intriguing because the condensate will be purer and non-fouling. The added heat transfer surface and increased capital cost, however, may not be practical.
Ray Albrecht suggests that temperatures in the range of 1000oC or greater are needed to achieve good burnout of flue gases. He stresses the importance of preserving flame temperature by insulating the combustion chamber to make sure reaction is complete before gases enter the heat exchanger.
Staging the air feed can promote gasification and partial combustion at low excess air conditions where temperatures are higher. Preheat can almost deliver a one-to-one increase of flame temperature with increased feed air temperature. Staging and preheat are common in newer biomass burners.
Catalysts are another important way to promote oxidation at lower temperatures than those needed otherwise.