A heat engine running backward is called a refrigerator if its purpose is to extract heat from a cold reservoir. The same engine running backward is called a heat pump if its purpose is to exhaust warm air into the hot reservoir. Heat pumps are widely used for home heating. 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. Perhaps this seems a little silly, but consider the following. Electricity can be directly used to heat a home by passing an electric current through a heating coil. This is a direct, 100% conversion of work to heat. That is, 20.0 kW of electric power (generated by doing work at the rate 20.0 kJ/s at the power plant) produces heat energy inside the home at a rate of 20.0 kJ/s. Suppose that the neighbor's home has a heat pump with a coefficient of performance of 4.00, a realistic value. NOTE: With a refrigerator, "what you get" is heat removed. But with a heat pump, "what you get" is heat delivered. So the coefficient of performance of a heat pump is K=QH/Win. An average price for electricity is about 40 MJ per dollar. A furnace or heat pump will run typically 300 hours per month during the winter. What does one month's heating cost in the home of a neighbor who uses a heat pump to provide the same amount of heating? Express your answer in dollars. ▸ View Available Hint(s) Cost2 = ΜΕ ΑΣΦ ? 2.70 Submit Previous Answers × Incorrect; Try Again; 26 attempts remaining 69 $
A heat engine running backward is called a refrigerator if its purpose is to extract heat from a cold reservoir. The same engine running backward is called a heat pump if its purpose is to exhaust warm air into the hot reservoir. Heat pumps are widely used for home heating. 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. Perhaps this seems a little silly, but consider the following. Electricity can be directly used to heat a home by passing an electric current through a heating coil. This is a direct, 100% conversion of work to heat. That is, 20.0 kW of electric power (generated by doing work at the rate 20.0 kJ/s at the power plant) produces heat energy inside the home at a rate of 20.0 kJ/s. Suppose that the neighbor's home has a heat pump with a coefficient of performance of 4.00, a realistic value. NOTE: With a refrigerator, "what you get" is heat removed. But with a heat pump, "what you get" is heat delivered. So the coefficient of performance of a heat pump is K=QH/Win. An average price for electricity is about 40 MJ per dollar. A furnace or heat pump will run typically 300 hours per month during the winter. What does one month's heating cost in the home of a neighbor who uses a heat pump to provide the same amount of heating? Express your answer in dollars. ▸ View Available Hint(s) Cost2 = ΜΕ ΑΣΦ ? 2.70 Submit Previous Answers × Incorrect; Try Again; 26 attempts remaining 69 $
Chapter4: The Second Law Of Thermodynamics
Section: Chapter Questions
Problem 4.2CYU: Check your Understanding Show that QhQh=QcQc for the hypothetical engine of Figure 4.10 The second...
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Transcribed Image Text:A heat engine running backward is called a refrigerator
if its purpose is to extract heat from a cold reservoir.
The same engine running backward is called a heat
pump if its purpose is to exhaust warm air into the hot
reservoir. Heat pumps are widely used for home
heating. 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. Perhaps this
seems a little silly, but consider the following. Electricity
can be directly used to heat a home by passing an
electric current through a heating coil. This is a direct,
100% conversion of work to heat. That is, 20.0 kW of
electric power (generated by doing work at the rate
20.0 kJ/s at the power plant) produces heat energy
inside the home at a rate of 20.0 kJ/s. Suppose that
the neighbor's home has a heat pump with a coefficient
of performance of 4.00, a realistic value. NOTE: With a
refrigerator, "what you get" is heat removed. But with a
heat pump, "what you get" is heat delivered. So the
coefficient of performance of a heat pump is
K=QH/Win. An average price for electricity is
about 40 MJ per dollar. A furnace or heat pump will
run typically 300 hours per month during the winter.
Transcribed Image Text:What does one month's heating cost in the home of a neighbor who uses a heat pump to provide the same amount of heating?
Express your answer in dollars.
▸ View Available Hint(s)
Cost2 =
ΜΕ ΑΣΦ
?
2.70
Submit
Previous Answers
× Incorrect; Try Again; 26 attempts remaining
69
$
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