Investigation of real-life operating patterns of wood-burning appliances using stack temperature data

Abstract

A study was undertaken to identify patterns of consumer use of outdoor wood boilers or outdoor wood furnaces (technically referred to as outdoor wood-fired hydronic heaters (OWHHs)) and indoor wood stoves (IWSs) to inform the development of performance testing protocols that reflect real-life operating conditions. These devices are manually fed, and their usage protocols are a function of a number of variables, including user habits, household characteristics, and environmental factors. In this study, researchers logged the stack wall temperatures of 4 OWHH and 20 IWS units in the states of New York and Washington over two heating seasons. Stack wall temperature is an indicator of changes in combustion modes. Two algorithms were developed to identify usage modes and cold and warm start refueling events from the stack wall temperature time series. A linear correlation analysis was conducted to evaluate the effect of heat demand on usage patterns. The results and methods presented here will inform the cataloging of typical operational patterns of OWHHs and IWSs as a step in the development of performance testing procedures that represent actual in-home usage patterns.Implications: Current US regulatory programs for residential wood heating use a certification program to assess emissions and efficiency performance. Testing under this program uses a test that burns 100% of a single, standardized wood fuel charge to assess performance at different steady-state load conditions. This study assessed in-field operational patterns to determine if the current certification approach accurately characterized typical homeowner use patterns.

A review of regulatory standard test methods for residential wood heaters and recommendations for their advancement

“…Similarly, procedures for EPA ALT-140 are based on temperature data collected from 20 US homes over one or two heating seasons. This study indicated that temperature profiles of the external wall of the stack were highly irregular, and they were not able to accurately capture fuel reloading events [45]. Given the diversity of user behavior, laboratory test cycles must balance between accurately representing residential operation and providing replicable experimental procedures for consistently characterizing heater performance.…”

“…The fundamental purpose of the test cycle is to provide uniform operating conditions for repeatably evaluating and comparing heater performance. While this is useful for establishing compliance to regulations, the emissions and performance results may not be representative of residential operation [11][12][13][14][15]45,46]. For example, many test methods do not account for start-up, cool-down, fuel loading, and other transient periods that occur during normal operation.…”

“…The test cycle also includes ignition, burn out, and other required phases of heater operation that are omitted from standardized test methods. The Northeast States for Coordinated Air Use Management (NESCAUM) built upon the principals of the beReal method to create EPA ALT-140, which aims to reflect the operational practices typical of homes in the US [45,46,49,50].…”