EGEE 102 – Energy Conservation And Environmental Protection Energy Efficiency

Definition and Scope of Energy Efficiency Energy efficiency improvements refer to a reduction in the energy used for a given service (heating, lighting, etc.) or level of activity. The reduction in the energy consumption is usually associated with technological changes, but not always since it can also result from better organization and management or improved economic conditions in the sector ("non-technical factors"). 2

3 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.

4 Energy Efficiency Energy Conversion Device Energy Input Useful Energy Output Energy Dissipated to the Surroundings

5 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

6 Device Electric Motor Home Oil Furnace Home Coal Furnace Steam Boiler (power plant) Power Plant (thermal) Automobile Engine Light Bulb-Fluorescent Efficiency Efficiency of Some Common Devices

7 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

8 Heat Engine A heat engine is any device which converts heat energy into mechanical energy. Accounts for 50% of our energy conversion devices

9 Temperature is in ° Kelvin !!!!!!! Carnot Efficiency Maximum efficiency that can be obtained for a heat engine

10 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 ?

° C = ° K = 813 °K 20 °C = = 293 °K

12 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.

13 Schematic Diagram of a Power Plant

14 Boiler Components

15 Overall Efficiency Overall Eff = Electric Energy Output (BTU) x 100 Chemical Energy Input (BTU) = 35 BTU x BTU = 35% Overall Efficiency of a series of devices = ( Thermal Energy ) x ( Mechanical Energy ) x ( Electrical Energy ) Chemical Energy Thermal Energy Mechanical Energy

16 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%

17 System Efficiency The efficiency of a system is equal to the product of efficiencies of the individual devices (sub-systems)

18 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

19 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

20 Efficiency of a Space Heater Electricity = 24% Fuel Oil = 53% Natural Gas= 70%

21 Heat Mover Any device that moves heat "uphill", from a lower temperature to a higher temperature reservoir. Examples. Heat pump. Refrigerator.

22 Heat Pump Heating Cycle Source:

23 Heat Pump Cooling Cycle Source:

24 Coefficient of Performance (C.O.P) Effectiveness of a heat pump is expressed as coefficient of performance (C.O.P)

25 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.

26 Solution Cont. T hot = 70 °F = 21°C = =294K T cold = 30 °F = -1°C = =272K C.O.P = = = 13.3

27 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 is typical.

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