NIWA scientists find wood burners need careful owner-drivers?


New Zealanders love their wood burners and keeping warm in winter, but wood burners and how they are being used are the major contributors to winter urban air pollution. NIWA scientists are assessing the emissions from wood burners, and learning more about how users' behaviour may affect emissions.NIWA air quality scientist project leader Jeff Bluett says that the way wood burners are operated is an important component of their performance. As wood burner engineering designs become more sophisticated, operator behaviour becomes relatively more important.

This research and its findings will be of value to all New Zealanders, because during winter in almost all urban areas in New Zealand, domestic wood burners are a major contributor to air pollution, more so than vehicles.

"We are finding that when we look at the distribution of emissions, wood burners in particular houses, are 'gross emitters'. They are producing grossly disproportionate amounts of particulates. What we want to do is identify the reasons why those gross emitting events occur. One of the main aims of the work is to provide useful information that may allow policy makers to manage emissions to an acceptable level," says Bluett.

For 21 days over the winter of 2011, NIWA scientists entered the homes and lives of six households in the Christchurch area, installing equipment to monitor the emissions from wood-burners. They monitored six burners of different ages, and designs.

The equipment, developed by the Australian Commonwealth Scientific and Industrial Research Organisation (CSIRO), gives real-time data on particulate and gaseous emissions, temperature and flow of exhaust gases in the chimney.

NIWA scientists attached sample lines to flues and monitored emissions every night. They had instruments continuously recording parameters inside the house, when fires were lit, including temperature and relative humidity, and how long the room stayed warm. The scientists analysed fuel samples, and measured the weight of wood that people were using and loading into their wood-burners. Scientists gained a good deal of information about what fuel people used and how much wood was burned each night.

"The data will be used to refine estimates of the quantity and timing of particulate pollution discharged from domestic wood burners, identify the causes of gross emission burn events, and improve our understanding of the factors which determine when people light their fires, and the duration and amount of fuel used each night," says Bluett.

An Environment Canterbury study from 2002 has already found that rate of air pollutant emissions from wood-burners is significantly higher when they are operated in the home compared to the performance that is achieved under laboratory conditions. They also observed that a large proportion of the emissions occur within the first hour of a fire being lit. The NIWA study confirms this, and shows that there are bursts of high emissions soon after the burner has been reloaded with wood.

The type of fuel being used and the conditions within the firebox appear to be strong factors that help determine the emission levels. The full set of findings from the study should be available in early 2012.

This research is part of the Atmospheric Environment Heath and Society programme that aims to address some fundamental air quality management issues that regional councils are facing. NIWA leads the programme, which is funded by the Ministry of Science and Innovation. The wood burner emissions measurements were also 60% co-funded by Environment Canterbury and Auckland Council.

How to use a woodburner efficiently: 

Instruments recording measurements (Colin Grace)
Research subject: Air Quality