David Schmidt: Yes, you are missing something
Published: 02-04-2025 5:01 PM |
In David Murphy’s Jan. 31 guest column ”All-electric rule: Costlier homes, worse efficiency” he erroneously calculates the overall efficiency of heating a home with electricity from the grid and compares it to the efficiency of the natural gas furnace in his basement. He concludes that Ordinance 24.170 would force homeowners to rely on electric heating that is 60% efficient rather than a home furnace that is roughly 90% efficient. He asks, “Am I missing something?” The answer is a definitive “Yes.”
Electric-powered heat pumps don’t just convert the electric power into heat as an electric resistance heater would. They pump heat from the outside cold air, against a temperature gradient, into the relatively warm home interior. The ratio of the heating you get in your home divided by the energy that you paid for is called the Coefficient of Performance (COP).
Mitsubishi Electric advertises a COP of “up to 4.68.” We don’t normally use the term efficiency in this context because efficiency is supposed to be limited to 100%, but this performance is analogous to an efficiency of 468%. You get more than four times the heat energy that you paid for. This performance is the compelling reason that drives us toward using electric heat pumps.
David Schmidt
Professor of mechanical and industrial engineering at UMass Amherst; teaches thermodynamics and heat transfer, Amherst
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