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EGEE 102 – Energy Conservation And Environmental Protection Energy Efficiency
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EGEE 102 - S. Pisupati2 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.
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EGEE 102 - S. Pisupati3 Energy Efficiency Energy Conversion Device Energy Input Useful Energy Output Energy Dissipated to the Surroundings
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EGEE 102 - S. Pisupati4 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 ? = 90 W x 100 = 90 % 100 W
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EGEE 102 - S. Pisupati5 Device 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 Efficiency Efficiency of Some Common Devices
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EGEE 102 - S. Pisupati6 25% Of the gasoline is used to propel a car, the rest is “lost” as heat. i.e an efficiency of 0.25 Source: Energy Sources/Applications/Alternatives Vehicle Efficiency – Gasoline Engine
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EGEE 102 - S. Pisupati7 Heat Engine A heat engine is any device which converts heat energy into mechanical energy. Accounts for 50% of our energy conversion devices
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EGEE 102 - S. Pisupati8 Temperature is in ° Kelvin !!!!!!! Carnot Efficiency Maximum efficiency that can be obtained for a heat engine
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EGEE 102 - S. Pisupati9 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 ?
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EGEE 102 - S. Pisupati10 540 ° C = 540 +273 ° K = 813 °K 20 °C = 20 + 273 = 293 °K
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EGEE 102 - S. Pisupati11 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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EGEE 102 - S. Pisupati12 Schematic Diagram of a Power Plant
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EGEE 102 - S. Pisupati13 Boiler Components
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EGEE 102 - S. Pisupati14 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 Mechanical Energy
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EGEE 102 - S. Pisupati15 Overall Efficiency Cont.. ( Thermal Energy ) x ( Mechanical Energy ) x ( Electrical Energy ) Chemical Energy Thermal Energy Mechanical Energy = E boiler x E turbine x E generator = 0.88 x 0.41 x 0.97 = 0.35 or 35%
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EGEE 102 - S. Pisupati16 System Efficiency The efficiency of a system is equal to the product of efficiencies of the individual devices (sub-systems)
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EGEE 102 - S. Pisupati17 Extraction of Coal96%96% Transportation98%94% (0.96x0.98) Electricity Generation38%36 % (0.96x0.98x0.38) Transportation Elec91%33% Lighting Incandescent5%1.7% Fluorescent20%6.6% Step EfficiencyCumulative Efficiency Efficiency of a Light Bulb Step
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EGEE 102 - S. Pisupati18 System Efficiency of an Automobile Production of Crude96%96% Refining87%84% Transportation 97%81% Thermal to Mech E25%20% Mechanical Efficiency- Transmission50%10% Rolling Efficiency20%6.6% Step Step Efficiency Cumulative Efficiency
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EGEE 102 - S. Pisupati19 Efficiency of a Space Heater Electricity = 24% Fuel Oil = 53% Natural Gas= 70%
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EGEE 102 - S. Pisupati20 Heat Mover Any device that moves heat "uphill", from a lower temperature to a higher temperature reservoir. Examples. Heat pump. Refrigerator.
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EGEE 102 - S. Pisupati21 Heat Pump Heating Cycle Source: http://energyoutlet.com/res/heatpump/pumping.htmlhttp://energyoutlet.com/res/heatpump/pumping.html
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EGEE 102 - S. Pisupati22 Heat Pump Cooling Cycle Source: http://energyoutlet.com/res/heatpump/pumping.html
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EGEE 102 - S. Pisupati23 Coefficient of Performance (C.O.P) Effectiveness of a heat pump is expressed as coefficient of performance (C.O.P)
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EGEE 102 - S. Pisupati24 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 - S. Pisupati25 Solution Cont. T hot = 70 °F = 21°C =21 + 273 =294K T cold = 30 °F = -1°C =-1 + 273 =272K C.O.P = 294 294 - 272 = 294 22 = 13.3
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EGEE 102 - S. Pisupati26 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.
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EGEE 102 - S. Pisupati27 More C.O.P.’s Compare the ideal coefficients of performance of the of the same heat pump installed in Miami and Buffalo. Miami: T hot = 70°F, T cold = 40°F Buffalo: T hot = 70°F, T cold = 15°F Miami: T hot = 294°K, T cold = 277°K Bufalo: T hot = 294°K, T cold = 263°K
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EGEE 102 - S. Pisupati28 = 294 (294-277) =17.3 = 294 (294-263) =9.5 MiamiBuffalo
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