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How "Clean" Is "Lean"? Survey Assesses Emissions Models for Combined Heat and Power Systems

How "Clean" Is "Lean"? Survey Assesses Emissions Models for Combined Heat and Power Systems


January 3, 2007

Washington, D.C. — Today the American Council for an Energy-Efficient Economy (ACEEE) released a new report, Survey of Emissions Models for Distributed Combined Heat and Power Systems.  The report reviews existing models’ attempts to quantify or describe the emissions effects of combined heat and power (CHP) systems.  The models surveyed vary in design, scope, and detail, but they all commonly seek to capture the functions of an energy economy and use knowledge of economic interactions to simulate the effects of economic and policy changes.

Despite the multitude of benefits of a CHP installation, relatively few tools exist for estimating the displaced emissions, or for predicting how CHP affects constrained transmission systems or distributed emissions implications.  “CHP systems offer huge improvements in system efficiency over traditional electricity generation. However, the difficulty in analyzing the emissions displaced by both the heat and power outputs of these CHP systems has hampered the development of effective policies.  Quantification of ‘displaced emissions’ would be immensely helpful,” said Anna Shipley, co-author and ACEEE Industry Program Research Associate.

The Integrated Planning Model (IPM), Average Displaced Emissions Rate (ADER), Market Allocation (MARKAL), All Modular Industry Growth Assessment (AMIGA), Oak Ridge Competitive Electric Dispatch (ORCED), and National Energy Modeling System (NEMS) models are all reviewed in the report. The U.S. Environmental Protection Agency’s (EPA) CHP emissions calculator is also profiled. While the approximate operation of each model is discussed, this survey seeks to specifically explain how these models handle emissions and how CHP and thermal energy are considered within the models.

Although a variety of well-established energy and emissions models exist, few tools capture the collective local and remote emissions benefits of a CHP system. “The absence of a comprehensive tool to estimate displaced emissions penalizes CHP by not allowing the full appreciation of the environmental benefits,” said Neal Elliott, co-author and ACEEE Industry Program Director.

The creation of such a tool might be approached by following the framework discussed in the report, initially providing coarse guidance and subsequently allowing the determination of specific benefits attributable to a CHP system. The CHP Emissions Calculator published by EPA is a good effort toward addressing some of these goals. However, the tool is too simplistic to allow geographical resolution of the displaced emissions. It is hoped that a more comprehensive tool, or the integration of the Emissions Calculator methodology into a more sophisticated model, will be performed.  “Hopefully this study will encourage the modeling community to attempt a more robust and accurate assessment of CHP emissions,” said Shipley.

Survey of Emissions Models for Distributed Combined Heat and Power Systems is available online for free download at http://aceee.org/pubs/ie071.htm or a hard copy can be purchased for $16 plus $5 postage and handling from ACEEE Publications, 529 14th Street, N.W., Suite 600, Washington, D.C. 20045, phone: 202-507-4000, fax: 202-429-2248, e-mail: aceee_publications@aceee.org.