EGEE 102 Energy Conservation And Environmental Protection

EGEE 102 – Energy Conservation And Environmental Protection Energy Efficiency EGEE 102 - S. Pisupati

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 2

Energy Efficiency Energy Input Energy Conversion Device EGEE 102 - S. Pisupati Useful Energy Output Energy Dissipated to the Surroundings 3

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 W = 90 % EGEE 102 - S. Pisupati 4

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 EGEE 102 - S. Pisupati 90 65 55 89 36 25 20 5 5

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 EGEE 102 - S. Pisupati Source: Energy Sources/Applications/Alternatives 6

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 7

Carnot Efficiency • Maximum efficiency that can be obtained for a heat engine Temperature is in ° Kelvin !!!!!!! EGEE 102 - S. Pisupati 8

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 9

540 ° C = 540 +273 ° K = 813 °K 20 °C = 20 + 273 = 293 °K EGEE 102 - S. Pisupati 10

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. EGEE 102 - S. Pisupati 11

Schematic Diagram of a Power Plant EGEE 102 - S. Pisupati 12

Boiler Components EGEE 102 - S. Pisupati 13

Overall Efficiency Overall Eff = Electric Energy Output (BTU) x 100 Chemical Energy Input (BTU) = 35 BTU x 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 15

System Efficiency The efficiency of a system is equal to the product of efficiencies of the individual devices (sub-systems) EGEE 102 - S. Pisupati 16

Efficiency of a Light Bulb Step Efficiency Cumulative Efficiency Extraction of Coal 96% Transportation 98% Electricity Generation 38% Transportation Elec 91% Lighting Incandescent 5% Fluorescent 20% EGEE 102 - S. Pisupati 96% 94% (0. 96 x 0. 98) 36 % (0. 96 x 0. 98 x 0. 38) 33% 1. 7% 6. 6% 17

System Efficiency of an Automobile Step Efficiency Production of Crude 96% Refining 87% Transportation 97% Thermal to Mech E 25% Mechanical Efficiency. Transmission 50% Rolling Efficiency 20% EGEE 102 - S. Pisupati Cumulative Efficiency 96% 84% 81% 20% 10% 6. 6% 18

Efficiency of a Space Heater Electricity = 24% Fuel Oil = 53% Natural Gas = 70% EGEE 102 - S. Pisupati 19

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 21 EGEE 102 - S. Pisupati

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) EGEE 102 - S. Pisupati 23

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. EGEE 102 - S. Pisupati 24

Solution Cont. Thot = 70 °F = 21°C =21 + 273 =294 K Tcold = 30 °F = -1°C =-1 + 273 =272 K C. O. P = 294 - 272 = 294 22 = 13. 3 EGEE 102 - S. Pisupati 25

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 26

More C. O. P. ’s Compare the ideal coefficients of performance 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 27

Miami = = 294 (294 -277) 17. 3 Buffalo = = EGEE 102 - S. Pisupati 294 (294 -263) 9. 5 28