Guest Column: Top-down and Bottom-up Combined Heat & Power

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CHP systems Photo by the DOEMunicipalities, businesses, and even individual homeowners are right now looking at equipment that will provide both heat and electricity from a single fuel consumed in their structure. In top-down combined heat and power systems, (CHP), fuel is consumed to make electricity and the by-product, “waste heat,” is captured and used to heat water or spaces in or around the building. In bottom-up CHP, the fuel is consumed first to provide heat, and any excess heat is used to generate electricity.

California, New York and Connecticut offer financial and other incentives for CHP installations, recognizing that they provide resiliency in storms and whenever the grid is stressed for other reasons; they also recognize that the fuel efficiency of these systems exceeds that of conventional systems by 40% according to the DOE. For an in-depth look at the many benefits of CHP, see the DOE’s March 2016 report entitled “Combined Heat and Power (CHP) – Technical Potential in the United States.”

Fuel cell CHP systems range from relatively cool (if the fuel cell is the proton exchange membrane type preferred by hydrogen electric vehicle manufacturers), to extremely hot molten carbonate and solid oxide fuel cell systems, to the most common phosphoric acid fuel cells with moderately hot temperatures. Conceptually, fuel cells all create electricity from hydrogen and other fuels electrochemically. The fuel is consumed but not burned. However, with the higher temperature fuel cells running at from 650 to well over 1000 degrees centigrade, they are also appropriate for a bottom-up heat-first CHP installation.

Rick Smith is the President of the Maine nonprofit, Hydrogen Energy Center. Look for his comments in the hydrogen blog.
Article graphic from the US Department of Energy.

For further reading, see the article on Renewable Energy Hub.