Despite a multitude of energy efficiency benefits produced by combined heat and power (CHP) installations, few tools exist for estimating the displaced emissions or predicting how CHP affects constrained transmission systems or distributed emissions implications. A new report attempts to quantify the emissions and consider the overall effect on emissions from various kinds of CHP systems.
The report - The Survey of Emissions Models for Distributed Combined Heat and Power Systems - was produced by the American Council for an Energy-Efficient Economy (ACEEE).
“CHP systems offer huge improvements in system efficiency over traditional electricity generation,” says Anna Shipley, research associate with ACEEE and co-author of the report. “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,” she said.
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. Toward that end, the report reviews several mechanisms aimed at achieving such quantification. That includes the Integrated Planning Model; the Average Displaced Emissions Rate; the All Modular Industry Growth Assessment; the Oak Ridge Competitive Electric Dispatch; and the National Energy Modeling System. The U.S. Environmental Protection Agency’s CHP emissions calculator is also profiled. The report summarizes the approximate operation of each of those analytical methods and seeks to specifically explain how these models handle emissions and how CHP and thermal energy are considered within the models.
“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, another co-author and ACEEE industry program director.
The report offers a possible framework for creating a comprehensive analytical tool by providing guidelines and allowing the determination of specific benefits attributable to a CHP system. The authors say the CHP Emissions Calculator published by the Environmental Protection Agency is a good effort toward addressing some of these goals. However, the tool is too simplistic to allow geographical resolution of the displaced emissions and hopes 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 from ACEEE Publications.
-Steve Blankinship