United States Environmental Protection Agency Air and Energy Engineering Research Laboratory Research Triangle Park, NC 27711 Research and Development EPA/600/SR-93/096 July 1993 Project Summary Development of Residential Wood Consumption Estimation Models Walid Ramadan and Mark G. Smith Data on the distribution and usage of firewood were obtained from a pool of household wood use surveys. Based on a series of regression models de- veloped using the STEPWISE proce- dure in the SAS statistical package, two variables appear to be most pre- dictive of wood use per household: (1) heating degree days, and (2) percent- age of households that burn wood as a main heat source. The average number of cords burned in fireplaces is esti- mated as a function of the total num- ber of cords burned per household, availability of wood, and population density. Models were also developed to estimate the distribution of wood- burning devices. Variables that appear to be most predictive of the percentage of wood stoves are percentage of households that burn wood as a main heat source, heating degree days, avail- ability of wood, and percentage of ur- ban population. Input data, predicted values, and deviations from actual val- ues are tabulated for each model. Graphs for each model show both ac- tual and predicted values for the vari- ables being estimated. This Project Summary was developed by EPA's Air and Energy Engineering Research Laboratory, Research Tri- angle Park, NC, to announce key find- ings of the research project that is fully documented in a separate report of the same title (see Project Report ordering information at back). Introduction This report presents several statistical models that have been developed to pre- dict wood fuel use in residential applica- tions based on a review of available resi- dential wood use surveys conducted for local area planning or State Implementa- tion Plan (SIP) inventory development These models could be used to improve the emissions estimates for residentia wood fuel consumption in areas that aro not required, and therefore are not likely to conduct household surveys. The mod els may also be included in the Area an; I Mobile Source Subsystem (AMS) of tru- Aerometric Information Retrieval Systen (AIRS). Database Development Data on the distribution and usage o firewood are needed in order to accu rately characterize the resulting air pollu tion impacts. Currently, the most accurate • means of estimating residential wood com bustion levels in a given area is througT direct surveys of households. Wood use surveys were obtained from several states including Colorado, Connecticut, Idaho Maine, Montana, Nevada, New Hampshire Oregon, Vermont, and Washington. Whik most surveys reviewed were oonductec specifically to evaluate wood use in ar area, some were conducted for other pur poses, but still included questions pertain ing to wood burning. Most of the survey? reviewed were from and within Montana Colorado, and Washington. The geo graphic levels at which the surveys wen conducted ranged from small towns tc entire states. Only a fraction of the sur veys clearly defined the boundaries of the survey area. Of the surveys, 58% wen conducted prior to 1985; the remaining 42% were conducted during or after 1985 State-level survey results were collectec for Colorado, Michigan, and Washington These surveys were not used in the anaiy sis because the focus of this effort was tc develop models applicable at the county level. Many other surveys collected were not usable due primarily to a lack of infer mation on the surveys' boundaries, and/or Printed on Recycled Pape< ------- the lack of questions in the Surveys that would result in estimates of fuel wood use. Finally, in areas where more than one survey had been conducted, only the most recently complete was used. Over- all, 68 surveys were obtained, of which 40 were used in the analysis. Statistical Analysis Before designing new models, several existing models were examined that quan- tify residential wood combustion. Two stud- ies in particular were reviewed which esti- mate firewood usage at the county level. One, conducted by Brookhaven National Laboratory, performed a regression analy- sis on survey data collected by the U.S. Forest Service. The other study, by Skog and Watterson, performed a regression analysis on the survey data collected as part of the New England Fuelwood Sur- vey. The models and their results are briefly described and their application to the surveys collected presented. Conclusions Based on a series of regression models developed to estimate wood use and dis- tribution of wood-burning devices, the two variables that appear to be most predic- tive are heating degree days and percent- age of households that burn wood as a main source of heat. A variety of local factors can directly impact the number of wood-burning households and the quan- tity of wood burned by each. Such factors include the historical availability and rela- tive price of other heating fuels, and the heat content of firewood in the area where the survey was conducted. The latter fac- tor is important because wood use is mea- sured by cords, a volume measurement. A cord of pine contains approximately 65% of the heat content of a cord of oak. Limitations on the estimates of wood use presented here do not necessarily lie in the methodology but with the data used as inputs for the models. The accuracy of the data collected is in doubt because there was no independent verification. It is likely that the variability in the data is due in large part to the respondents' inac- curate impression of how much wood is in a cord. Another limitation is that the geo- graphical boundaries of many of the sur- vey areas were poorly defined. Finally, the validity of the surveys themselves is questionable especially in those areas that showed large discrepancies between the reported estimates of households using wood as a main heating fuel and the cor- responding Census statistics. The residential wood consumption mod- els developed here may be improved by Walid Ramadan and Mark G. Smith are with TRC Environmental Corp., Chapel Hill, NC27514. Robert C. McCrillis is the EPA Project Officer (see below) The complete report, entitled "Development of Residential Wood Consumption Estimation Models," (Order No. PB93-199 248/AS; Cost: $19.50, subject to change) will be available only from: National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Air and Energy Engineering Research Laboratory U.S. Environmental Protection Agency Research Triangle Park, NC 27711 United States Environmental Protection Agency Center for Environmental Research Information Cincinnati, OH 45268 Official Business Penalty for Private Use $300 including a number of socioeconomic vari- ables such as cost of other energy forms in comparison to wood energy and aver- age household income. The models can also be improved by conducting more sim- plified and specialized wood use surveys. Future guidance on the development and use of surveys of residential wood use should attempt to gather more detailed information specifically on appliance char- acteristics (i.e., catalytic, EPA-certified), wood characteristics, and wood-burning practices. Simplified surveys reduce the number of nonrespondents and the num- ber of unanswered questions. Missing an- swers in surveys present problems when the data collected in a survey are subject to statistical analysis because statistical procedures cannot be immediately used if there are missing values. In addition, the models can be further improved by incor- porating cross-sectional data from areas that conduct surveys periodically. Cross- sectional data may be used to develop wood use projection models and will cap- ture the effects of changing socioeconomic factors on wood use patterns. Finally, the wood use models presented in the report can be validated, using field surveys to show how accurately the models estimate wood use in areas where no surveys are planned. 'U.S. Government Printing Office: 1993 — 750-071/80027 BULK RATE POSTAGE & FEES PAID EPA PERMIT No. G-35 EPA/600/SR-93/096 ------- |