Thermodynamics

86 | Thermodynamicswhere h st is the efficiency of the standard motor, and h eff is the efficiency ofthe comparable high-efficiency motor. Then the annual energy and cost savingsassociated with the installation of the high-efficiency motor becomeEnergy savings 1Power savings21Operating hours2Also, 1Rated power2 1Operating hours21Load factor211>h st 1>h eff 2 160 hp2 10.7457 kW>hp213500 h>year2 11211>0.89 1>0.93.22 7929 kWh>yearCost savings 1Energy savings2 1Unit cost of energy2 17929 kWh>year2 1$0.08> kWh2 $634>yearExcess initial cost Purchase price differential $5160 $4520 $640This gives a simple payback period ofSimple payback period Excess initial costAnnual cost savings $640 1.01 year$634>yearDiscussion Note that the high-efficiency motor pays for its price differentialwithin about one year from the electrical energy it saves. Considering thatthe service life of electric motors is several years, the purchase of the higherefficiency motor is definitely indicated in this case.FIGURE 2–62Energy conversion processes are oftenaccompanied by environmentalpollution.© Corbis Royalty FreeINTERACTIVETUTORIALSEE TUTORIAL CH. 2, SEC. 8 ON THE DVD.2–8 ■ ENERGY AND ENVIRONMENTThe conversion of energy from one form to another often affects the environmentand the air we breathe in many ways, and thus the study of energyis not complete without considering its impact on the environment (Fig.2–62). Fossil fuels such as coal, oil, and natural gas have been powering theindustrial development and the amenities of modern life that we enjoy sincethe 1700s, but this has not been without any undesirable side effects. Fromthe soil we farm and the water we drink to the air we breathe, the environmenthas been paying a heavy toll for it. Pollutants emitted during the combustionof fossil fuels are responsible for smog, acid rain, and globalwarming and climate change. The environmental pollution has reached suchhigh levels that it became a serious threat to vegetation, wild life, andhuman health. Air pollution has been the cause of numerous health problemsincluding asthma and cancer. It is estimated that over 60,000 people inthe United States alone die each year due to heart and lung diseases relatedto air pollution.Hundreds of elements and compounds such as benzene and formaldehydeare known to be emitted during the combustion of coal, oil, natural gas, andwood in electric power plants, engines of vehicles, furnaces, and even fireplaces.Some compounds are added to liquid fuels for various reasons (suchas MTBE to raise the octane number of the fuel and also to oxygenate thefuel in winter months to reduce urban smog). The largest source of air pollutionis the motor vehicles, and the pollutants released by the vehicles are