EGEE 102 - Energy Conservation and Environmental Protection
EGEE 102 – Energy Conservation And Environmental Protection
Energy Efficiency
Efficiency of Energy Conversion • If we are more efficient with the energy we already have there will be less pollution, less reliance on foreign oil and increased domestic security.
EGEE 102 - S. Pisupati
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Energy Efficiency Energy Input
Energy Conversion Device
Useful Energy Output
Energy Dissipated to the Surroundings
Efficiency ?
Useful Energy Output Total Energy Input EGEE 102 - S. Pisupati
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EGEE 102 - Energy Conservation and Environmental Protection
Illustration • An electric motor consumes 100 watts (a joule per second (J/s)) of power to obtain 90 watts of mechanical power. Determine its efficiency ?
Efficiency ?
=
90 W x 100 100 W
Useful Energy Output Total Energy Input = 90 %
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Efficiency of Some Common Devices Device
Efficiency
Electric Motor Home Oil Furnace Home Coal Furnace Steam Boiler (power plant) Power Plant (thermal) Automobile Engine Light Bulb-Fluorescent Light Bulb -Incandescent
90 65 55 89 36 25 20 5
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Vehicle Efficiency – Gasoline Engine
25% Of the gasoline is used to propel a car, the rest is “lost” as heat. i.e an efficiency of 0.25 102 - S. Pisupati Source: Energy EGEE Sources/Applications/Alternatives
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EGEE 102 - Energy Conservation and Environmental Protection
Heat Engine • A heat engine is any device which converts heat energy into mechanical energy. • Accounts for 50% of our energy conversion devices EGEE 102 - S. Pisupati
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Carnot Efficiency • Maximum efficiency that can be obtained for a heat engine
Temperature is in ° Kelvin !!!!!!! EGEE 102 - S. Pisupati
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Illustration
For a coal-fired utility boiler, The temperature of high pressure steam would be about 540°C and T cold, the cooling tower water temperature would be about 20°C. Calculate the Carnot efficiency of the power plant ?
EGEE 102 - S. Pisupati
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EGEE 102 - Energy Conservation and Environmental Protection
540 ° C = 540 +273 ° K = 813 °K 20 °C = 20 + 273 = 293 °K
Inference A maximum of 64% of the fuel energy can go to generation. To make the Carnot efficiency as high as possible, either T hot should be increased or T cold should be decreased.
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Schematic Diagram of a Power Plant
EGEE 102 - S. Pisupati
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EGEE 102 - Energy Conservation and Environmental Protection
Boiler Components Chemical Energy Input (100 BTU
)
Thermal Energy (88 BTU
Boiler
Turbine
)
Mech. Energy (36 BTU Generator
)
Elec. Energy Output (10.26 Wh
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Overall Efficiency Overall Eff = Electric Energy Output (BTU) x 100 Chemical Energy Input (BTU) = 35 BTU x 100 100 BTU = 35% Overall Efficiency of a series of devices =
(Thermal Energy)x(Mechanical Energy) x(Electrical Energy) Chemical Energy
Thermal Energy
EGEE 102 - S. Pisupati
Mechanical Energy 14
Overall Efficiency Cont.. (Thermal Energy)x(Mechanical Energy) x(Electrical Energy) Chemical Energy
=
Thermal Energy
Mechanical Energy
E boiler E turbine E generator x
x
= 0.88
x 0.41 x 0.97 = 0.35 or 35% EGEE 102 - S. Pisupati
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EGEE 102 - Energy Conservation and Environmental Protection
System Efficiency The efficiency of a system is equal to the product of efficiencies of the individual devices (sub-systems)
Production of Crude 96% Refining 87% Transportation 97% Thermal to Mech E 25% Mechanical EfficiencyTransmission 50% Rolling Efficiency 20% EGEE 102 - S. Pisupati
5. Energy Efficiency
Cumulative Efficiency
96% 84% 81% 20% 10% 6.6% 18
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EGEE 102 - Energy Conservation and Environmental Protection
Heat Mover • Any device that moves heat "uphill", from a lower temperature to a higher temperature reservoir. • Examples. EGEE 102 - S. Pisupati
• Heat pump. • Refrigerator.20
Heat Pump Heating Cycle
Source: http://energyoutlet.com/res/heatpump/pumping.html EGEE 102 - S. Pisupati 21
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EGEE 102 - Energy Conservation and Environmental Protection
Heat Pump Cooling Cycle
Source: http://energyoutlet.com/res/heatpump/pumping.html EGEE 102 - S. Pisupati 22
Coefficient of Performance (C.O.P)
Effectiveness of a heat pump is expressed as coefficient of performance (C.O.P)
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Example Calculate the ideal coefficient of performance (C.O.P.) For an air-to-air heat pump used to maintain the temperature of a house at 70 °F when the outside temperature is 30 °F.
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EGEE 102 - Energy Conservation and Environmental Protection
Consequences • For every watt of power used to drive this ideal heat pump, 13.3 W is delivered from the interior of the house and 12.3 from the outside. • Theoretical maximum is never achieved in practice This example is not realistic. In practice, a C.O.P in the range of 2 - 6 is typical. EGEE 102 - S. Pisupati
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More C.O.P.’s Compare the ideal coefficients of performance of the of the same heat pump installed in Miami and Buffalo. Miami: Thot = 70°F, Tcold = 40°F Buffalo: Thot = 70°F, Tcold = 15°F Miami: Thot = 294°K, Tcold = 277°K Bufalo: Thot = 294°K, Tcold = 263°K EGEE 102 - S. Pisupati
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EGEE 102 - Energy Conservation and Environmental Protection
