an average price for electricity is about 40 mj per dollar. so the coefficient of performance of a heat pump is k=qh/win. but with a heat pump, "what you get" is heat delivered. note: with a refrigerator, "what you get" is heat removed. suppose that the neighbor's home has a heat pump with a coefficient of performance of 4.00, a realistic value. that is, 19.0 \rm kw of electric power (generated by doing work at the rate 19.0 kj/s at the power plant) produces heat energy inside the home at a rate of 19.0 kj/s. this is a direct, 100% conversion of work to heat. electricity can be directly used to heat a home by passing an electric current through a heating coil. perhaps this seems a little silly, but consider the following. you can think of a heat pump as a refrigerator that is cooling the already cold outdoors and, with its exhaust heat qh, warming the indoors. heat pumps are widely used for home heating. the same engine running backward is called a heat pump if its purpose is to exhaust warm air into the hot reservoir. Aheat engine running backward is called a refrigerator if its purpose is to extract heat from a cold reservoir.
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