Household Energy Consumption
The average single-family household in the United States consumes 98 million Btu of energy each year. How many tons of coal must be burned to produce that amount of energy?
Approach
To calculate the amount of coal necessary to produce this energy, we will use the heating value of coal listed in Table 7.3
Table 7.3
Heating Values for Certain Fuels*
| Heating Value, H | |||
| Type | Fuel | MJ/kg | Btu/lbm |
| Gas | Natural gas
Propane |
47
46 |
20.2×10^{3} 19.8×10^{3} |
| Liquid | Gasoline
Diesel Fuel oil |
45
43 42 |
19.3×10^{3} 18.5×10^{3} 18.0×10^{3} |
| Solid | Coal
Wood |
30
20 |
12.9×10^{3} 8.6×10^{3} |
| *The numerical values are representative, and values for specific fuels could vary with their chemical composition. | |||
as 12,900 Btu/lbm and apply Equation (7.6)
Q = mH (7.6)
to determine the coal’s mass. In Table 3.5,
Table 3.5 Certain Derived Units in the USCS
| Quantity | Derived Unit | Abbreviation | Definition |
| Length | mil | mil | 1 mil = 0.001 in. |
| inch | in. | 1 in. = 0.0833 ft | |
| mile | mi | 1 mi = 5280 ft | |
| Volume | gallon | gal | 1 gal = 0.1337 ft^3 |
| Mass | slug | slug | 1 slug = 1 (lb . S^2)/ft |
| pound-mass | lbm | 1 lbm = 3.1081 \times 10^{-2}(lb s^{2})/ft | |
| Force | ounce | oz | 1 oz = 0.0625 lb |
| ton | ton | 1 ton = 2000 lb | |
| Torque, or moment of a force | foot-pound | ft · lb | — |
| Pressure or stress | pound/inch^2 | psi | 1 psi = 1 lb/in^2 |
| Energy, work, or heat | foot-pound | ft · lb | — |
| British thermal unit | Btu | 1 Btu = 778.2 ft . lb | |
| Power | horsepower | hp | 1 hp = 550 (ft . lb)/s |
| Temperature | degree Fahrenheit | °F | °F = °R-459.67 |
| Although a change in temperature of 1° Rankine also equals a change of 1 °F, numerical , numerical values are converted using the formula. | |||
