Final Report on Wood Stove Decathlon from Brookhaven Lab

Reproduced below are the absract and introduction of a 17-page paper that gives an excellent overview of the technical aspects of testing stoves on the National Mall for the Wood Stove Decathlon, held in November 2013.  To read the entire report, click here.

Innovative fine particulate measurement systems for the Wood Stove Design Challenge 

R. Trojanowski1, T. Butcher1, C. Brown1, G. Wei1, Y. Ahn2 , and J. Wong2 

1. Energy Conversion Group, Brookhaven National Laboratory, Upton, New York, USA 

2. Chemical and Molecular Engineering Department, Stony Brook University, Stony Brook, New York, USA 

ABSTRACT 

The rising price of fossil resources has contributed to the increase in the amount of wood-fired residential heating appliances. Wood stoves are often overlooked by the public as a clean and renewable source due to concerns about particulate (PM) emissions. In order to gain acceptance in the market the Alliance for Green Heat and

Popular Mechanics magazine initiated a Wood Stove Design Challenge (WSDC). The selected teams designed stoves that incorporated the best practices in design and operation to maximize efficiency and minimize PM and carbon monoxide (CO) emissions since most often high emissions are seen as a result of incomplete combustion. Further, a testing protocol for the challenge was developed specifically to measure the emissions in a non-laboratory setting. Standard testing procedures may not be representative of in-use fuel and operational practices and, due to the competition venue and schedule contstraints, could not be used for the WSDC. New portable PM sampling technology released in the European market recently was adopted for the competition and evaluated to current U.S. PM measurement methods to build a correlation. 

INTRODUCTION

Tom Butcher uses the Wohler portable
particulate sampler to test a stove.

 As the price of heating oil has increased, more residents in the northeastern region of the United States have returned to heating with wood. Most existing wood stoves date from before the Environmental Protection Agency (EPA) implemented emission certification requirements for these devices. These less efficient wood stoves often cause high amounts of smoke, yielding particulates known to trigger coughs, throat and mucosal irritation, acute respiratory infections, occurrence of asthma and other diseases over prolonged exposure. A review from Bølling et al. reported residential wood combustion has also been reported to contribute significantly to raised levels of air pollution locally, both with respect to increased levels of fine particles (particulate matter with an equivalent aerodynamic diameter < 2.5 μm; PM2.5), the organic particle fraction, particle bound polycyclic aromatic hydrocarbons (PAH) and volatile organic compounds. Even those wood stoves that do meet EPA’s Phase II requirements may have unacceptably high emissions once in use. This is due to several factors including the design of the appliance, weather patterns and location, combustion activity, wood species and quality, and operator habits. While the EPA is developing new regulations, the test method used for certification is not representative of in-use fueling and operational practices. 

Designs that improve combustion and emission performance, thermal efficiency, and operational  

The Decathlon tent on the National
Mall, in between the Capitol and
the Washington monument

variability are needed in the U.S. heating market. Modern wood stoves have shown reduced reported emission factors compared to conventional wood stoves, 34-330 mg/MJ from 50-2100 mg/MJ, respectively. However, if the modern stoves are not operated correctly the combustion performance can be compromised yielding higher emissions.

This event showcased advanced technologies that could help address the problem of increased particulate emissions and enable the continued use of wood as a renewable fuel. The teams selected came from various backgrounds, ranging from established wood stove companies to independent inventors and engineering student teams. Some of the stoves selected for the WSDC were controlled by microprocessors and connected to smartphones while others were ultra-efficient stoves based on 17th century Scandinavian designs. Several state-of-the-art hybrid stoves that are already on the market were also included4. Six of the 12 finalists were from Europe. 

Teams were judged on their innovation, emission and efficiency performance, affordability and consumer ease. In November 2013 on the National Mall in Washington D.C., ten judges (made up of leading experts from Popular Mechanics, the New York State Energy and Research Development Authority (NYSERDA), the U.S. Forest Service, Washington State Department of Ecology, DOE’s Brookhaven National Laboratory (BNL), The Biomass Thermal Energy Council (BTEC), the Osprey Foundation, the Masonry Heater Association and UC Berkeley) tested and assessed the 12 stove finalists and announced an overall winner as well as winners in specific categories. 

A key challenge in this competition was measuring the particulate emissions accurately in a field environment. This project sought to develop an energy efficiency and emissions testing protocol for the WSDC which reduces the variability due to fuel and operations. The current standard test method (EPA Method 28) involves testing stoves using a dilution tunnel. Since the WSDC was held at the mall in Washington D.C., this test method would not suit and so there was the challenge of measuring the emissions in a repeatable real-time way, in a non-laboratory environment. Recently, new portable particulate measurement systems have been introduced in Europe for field inspection of biomass heating systems. Two specific products were selected for use in this project the Testo 380 and Wöhler SM 500. Both analyzers are a low cost option and offer the advantage of ease and portability. 

To determine the accuracy, precision, instrument range, and applicability for use in the WSDC for thermal efficiency and emissions of these portable direct measure analyzers, an evaluation was conducted while simultaneously following the standard methods for determining the emissions.  From laboratory testing, BNL developed a testing protocol implementing the analyzers for the competition.

To read the entire PDF report, click here.

For more information about the 2013 Decathlon, click here.

For information about the 2014 Collaborative Stove Design Workshop, click here.

Testing Observations at the Wood Stove Decathlon

By Norbert Senf

The Wood Stove Decathlon was a historic event. It was the first ever attempt to gather a collection of stoves in the field (literally, in this case) and test them for particulate matter (PM) emissions.

Norbert Senf, right, with Neils Wittus,
center, and John Ackerly

For something untried until now, the side-by-side field-testing can claim several firsts. 

It successfully compared stoves within a surprising range of categories including masonry heaters as well as retrofit kits. The project was a success not only as a media event but also in advancing the real world testing of wood burning stoves.

Cordwood is an extremely complicated fuel to get repeatable data with because it is so inherently variable. To add to the challenge, PM is particularly difficult to measure, even in a laboratory. While the test results from the Decathlon were not sufficient to provide PM numbers that allowed comparison with EPA numbers, they did allow a ranking of the stoves against each other. This is a substantial achievement in itself.

PM is the wood fuel pollutant of greatest interest since it causes the most public health concerns. Carbon monoxide (CO) is another pollutant.  It is created by incomplete combustion like PM, but it is much easier to measure. It is generally not considered a health hazard in low atmospheric concentrations outside of densely trafficked urban areas, and eventually oxidizes to CO2 on its own.

Due to new wood burning emissions regulations in Germany, two new portable instruments for measuring PM in the field were recently developed there. Fortunately, this happened just in time for the Decathlon to try them out. The instruments are limited to the 15-minute test cycle that is mandated in the German regulation, and therefore can only measure what happens during a portion of the burn. Measuring an entire test cycle will certainly be a goal for future Decathlons.

Common wisdom holds that low carbon monoxide (CO) emissions, which are easy to measure, will also ensure low PM, which is difficult to measure. The contest results did not bear this out. The stove with the lowest PM had the second highest CO. For the stove with the lowest CO, there were 4 stoves with lower PM. To be sure, the data set is limited. The 15-minute test window did not allow for average values to be measured over the burn of an entire fuel load.

Repeatability is one of the most important measures of data quality. Since each stove in the Decathlon received two (in theory) identical test runs, we can get a brief glimpse here, as well. Discarding obvious outliers, we see a coefficient of variation (CV) in repeat runs of 43% on PM, 40% on CO and 7% on efficiency. This compares favorably with EPA inter-laboratory repeatability studies, where the two stoves with the largest data sets both came in at 44% CV on PM. For masonry heaters, an MHA (Masonry Heater Association) laboratory study on repeatability with dimensional lumber fuel cribs yielded 10% CV on PM, 1.5% on CO, and 0.26% on efficiency.

The repeatability metric provides a useful baseline for judging data quality in future decathlons. There is an ongoing fueling protocol debate in the testing community between the repeatability achievable with fuel cribs, and the real world randomness of cordwood. EPA testing is currently done with cribs. To get a repeatable EPA cordwood number may require running a large number of (expensive) laboratory test runs and taking an average. To date, very little work has been done to provide data for either side of the debate.

All in all, the Wood Stove Decathlon was a great effort towards advancing our knowledge about how wood stove emissions compare in the real world. This was particularly valuable to see for different classes of appliances with no commonly defined EPA testing methods.

Valuable lessons and insights were had for designing a future challenge. Seeing the complex testing issues play out in real life was a unique educational opportunity for contestants, organizers, judges, regulators and the testing community itself.

Norbert Senf was one of the ten judges at the Wood Stove Decathlon. He joined early efforts to write codes and standards, and was a founding member of the Masonry Heater Association of North America (MHA). He currently chairs the MHA Technical Committee.

Innovative Fine Particulate Measurement Systems for the Wood Stove Design Challenge

This blog originally had a poster and text about the details of the PM analyzers that we will use at the Decathlon.  However, because some of the findings were preliminary and not finalized, we have taken down the poster and text, except for the abstract, below.  We will repost the poster and content when it is more finalized. - Editors

Abstract

As the price of heating oil has increased in the US, more residents are returning to wood heat. Most existing wood stoves date from before the EPA implemented emissions certification requirements for these devices. Even those wood stoves that meet EPA’s Phase II requirements often have unacceptably high emissions once in use. This is due to several factors including fuel quality, operator habits and design. While the EPA is developing new regulations, the test method used for certification is not representative of in-use performance and the performance criteria in the test fall short of high efficiency or low emissions.

Designs that improve combustion and emission performance, thermal efficiency, and operational variability are needed in the U.S. heating market. The Alliance for Green Heat and Popular Mechanics Magazine has initiated the Wood Stove Design Challenge (WSDC) to address these needs by developing a competition for manufacturers, innovators, and university teams working towards these objectives.

This project seeks to develop a WSDC energy efficiency and emissions testing protocol which reduces the variability in fuel and operator. The current test method (EPA Method 28 WHH) involves testing stoves using a dilution tunnel. Seeing that the WSDC is held at the mall in Washington DC, this test method does not suit. Recently, new particulate measurement systems have been introduced in Europe, both the Wöhler SM 500 and testo 380. Both analyzers are a low cost option and offer the advantage of ease and portability. To determine the accuracy, precision, instrument range, and applicability for use in the WSDC for thermal efficiency and emissions, these portable direct measure analyzers, an evaluation will be conducted while simultaneously using the standard methods for determining the emissions.

There is, also, interest in the potential use of instruments of this type for field evaluation of the performance of both stoves and boilers.

The technology of these systems include near real-time, sub-microgram sensitivity, and is the only filter-based mass monitoring technology which has these properties and does not depend on questionable, surrogate measurements for mass

Wöhler Brings New Particulate Analyzer to Wood Stove Design Challenge

The German precision test equipment manufacturer, Wöhler, is providing one of its new Wöhler SM 500 particulate analyzers to do accurate PM 2.5 testing in the field. The Wöhler unit is a Suspended Particulate Analyzer for online PM 2.5 mass concentration measurements of small solid fuel appliances. The brand new technology just came out last year to meet requirements under a new German law that requires wood stoves and boilers to be checked in the field for emissions every year. German chimney sweeps play the same role as vehicle emission testing stations in the US. If the emissions are too high, the problem has to be fixed or the system taken out of service.


The Wood Stove Design Challenge will be using the Wöhler equipment at its national exhibition to educate policy makers and the public about modern wood heater emissions. The 10 judges who are preparing for the Challenge are gaining experience in using the new Wöhler technology in anticipation of using on-site testing of emissions. The Wöhler SM 500 is now at the Brookhaven National Laboratory where one of the judges, Dr. Thomas Butcher, is performing trial testing. Other judges will join him in coming months as they test the fueling protocol and compare the Wöhler SM 500 to the traditional, but more cumbersome, dilution tunnel test procedure that is used in wood stoves tests to ensure they meet EPA emissions standards. Dilution tunnels are large, time-consuming and expensive to use and are not an option for testing up to 14 wood stoves on the National Mall over a 5-day period.