Economic, Emissions, and Energy Benefits From Combined Heat and Power Systems by Location in the United States Based on System Component Efficiencies

Abstract

A graphical evaluation is performed for combined heat and power (CHP) systems using screening parameters for optimized performance with respect to operating costs, emissions, and energy consumption. CHP systems have the potential to reduce operating costs, emissions, and primary energy consumption when compared with electricity purchased from the grid and thermal energy produced from a boiler, and these benefits have been shown to depend on the location where the system is to be installed as well as the characteristics of the system itself. A CHP system is analyzed in 9 U.S. cities in different climate zones which differ in both the local electricity generation fuel mix and local electricity prices. Its potential to produce economic, emissions, and energy savings is quantified based on the concepts of required spark spread, emissions spark spread, and primary energy spark spread. The corresponding parameters for cost ratio, carbon dioxide emissions ratio, and primary energy ratio are plotted on a 3-dimensional graph which illustrates these potential benefits simultaneously. The location of each point on the 3-D graph indicates for a given geographical location whether the system falls within a region of multiple potential benefits from CHP technology. The results are unique to the efficiencies of the CHP system components and the alternate heating system. A simple sensitivity analysis is then conducted to examine the influence of electrical generation efficiency, the percentage of heat recovered, and the heating system on the cost, emissions, and energy savings potential of CHP systems. Of the 9 cities analyzed, Duluth, MN, is shown to have the greatest potential to provide these three types of benefits by using a CHP system. The results are most sensitive to the values of two input parameters: CHP electrical efficiency and CHP thermal efficiency. Changes in the input efficiency values are most influential when the electrical efficiency is low, and as the amount of recovered heat goes to 0, the electrical efficiency becomes the most important factor in whether a CHP shows the potential for cost, emissions, and energy benefits.