Friday, September 12, 2014

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.