The Little Engines That Can
Learning Objectives - After this course, you should be able to:
- Define combined heat and power (CHP) and be familiar with the various terms and alternative names associated with it.
- Explain why CHP is more energy-efficient than conventional power generation and state how much energy it saves.
- List the prime movers and fuel types that are commonly specified for CHP systems in commercial buildings.
- Understand the regulatory and economic forces that are encouraging CHP in some regions of the United States and creating barriers in others.
The predominant method of generating electricity in the United States—by burning fossil fuels at central power plants—is extraordinarily inefficient. Only about a third of the fuel's energy makes its way to end users while the other two-thirds is lost as waste heat along the way, according to “Combined Heat and Power: Effective Energy Solutions for a Sustainable Future,” a 2008 report prepared by the U.S. Department of Energy's Oak Ridge National Laboratory (ORNL).
This fact, coupled with increasing concerns over significant power outages across regional electric utility grids, has triggered renewed interest in the decentralized approach to power generation now generally referred to as combined heat and power, or CHP. With the appropriate mix of technologies and proximity to end users, local CHP systems recover and reuse heat from electrical generation or industrial processes that would otherwise go to waste. In doing so, typical CHP systems can achieve energy efficiencies of between 60 and 80 percent.
By using fuel more efficiently than a conventional power plant, a CHP system lowers operating costs for the building owner, lessens congestion on the local utility grid, and reduces overall air pollution and greenhouse gas emissions. In addition, if permitted by regulation, on-site generation systems can be designed to remain in operation during grid failures.
Traditionally, CHP systems were large and primarily served industrial sites, medical and college campuses, and urban districts. Such systems were, and often still are, referred to as cogeneration plants. Today, cleaner, quieter, and smaller systems are available and slowly finding their way into individual buildings, at least in certain regions of the country. CHP systems developed for single structures are sometimes referred to as building combined heat and power, or BCHP.
Illustration by Ryan Boyle