5. Energy Efficiency.ppt

7/29/2019 5. Energy Efficiency.ppt

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EGEE 102Energy Conservation

And Environmental Protection

Energy Efficiency


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EGEE 102 - S. Pisupati 2

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 andincreased domestic security.


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Energy Efficiency

Energy

Conversion

Device

Energy InputUseful Energy

Output

Energy Dissipated

to the Surroundings

InputEnergyTotal

OutputEnergyUsefulEfficiency


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InputEnergyTotal

OutputEnergyUsefulEfficiency

Illustration

An electric motor consumes 100 watts (a joule persecond (J/s)) of power to obtain 90 watts ofmechanical power. Determine its efficiency ?

= 90 W x 100 = 90 %

100 W


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Device

Electric Motor

Home Oil FurnaceHome 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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25% Of the gasoline is used to propel a car, the rest is

lost as heat. i.e an efficiency of 0.25Source: Energy Sources/Applications/Alternatives

Vehicle Efficiency

Gasoline Engine


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Heat Engine

A heat engine is any

device which

converts heatenergy into

mechanical energy.

Accounts for 50% of

our energy

conversion devices



Temperature is in Kelvin !!!!!!!

Carnot Efficiency

Maximum efficiency that can be

obtained for a heat engine



Illustration

For a coal-fired utility boiler, The temperature of highpressure steam would be about 540C and T cold, the

cooling tower water temperature would be about 20C.

Calculate the Carnot efficiency of the power plant ?



540 C = 540 +273 K = 813 K

20 C = 20 + 273 = 293 K

CarnotEfficiency() 1 293813

x100 64%



Inference

A maximum of 64% of the fuel energy can go

to generation. To make the Carnot

efficiency as high as possible, either T hotshould be increased or T cold should be

decreased.


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Schematic Diagram of a

Power Plant


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Boiler Components

Boiler

TurbineGenerator

Chemical Energy Input (100 BTU )

Thermal Energy (88 BTU )

Mech. Energy (36 BTU )

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 Mechanical Energy


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Overall Efficiency Cont..

(Thermal Energy)x(Mechanical Energy) x(Electrical Energy)Chemical Energy Thermal Energy Mechanical Energy

=E boilerx E turbine x E generator= 0.88 x 0.41 x 0.97= 0.35 or 35%


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System Efficiency

The efficiency of a system is equal to the

product of efficiencies of the individual

devices (sub-systems)


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Extraction of Coal 96% 96%Transportation 98% 94% (0.96x0.98)

Electricity Generation 38% 36 % (0.96x0.98x0.38)

Transportation Elec 91% 33%Lighting

Incandescent 5% 1.7%

Fluorescent 20% 6.6%

Step Efficiency Cumulative

Efficiency

Efficiency of a Light

BulbStep


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System Efficiency of an

Automobile

Production of Crude 96% 96%Refining 87% 84%

Transportation 97% 81%

Thermal to Mech E 25% 20%

Mechanical Efficiency-

Transmission 50% 10%

Rolling Efficiency 20% 6.6%

Step Step EfficiencyCumulative

Efficiency


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Efficiency of a Space

Heater

Electricity = 24%

Fuel Oil = 53%

Natural Gas = 70%


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Heat Mover

Any device that

moves heat "uphill",

from a lowertemperature to a

higher temperature

reservoir.

Examples.

Heat pump.

Refrigerator.


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Heat Pump Heating

Cycle

Source: http://energyoutlet.com/res/heatpump/pumping.html
http://energyoutlet.com/res/heatpump/pumping.htmlhttp://energyoutlet.com/res/heatpump/pumping.html


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Heat Pump Cooling

Cycle

Source: http://energyoutlet.com/res/heatpump/pumping.html


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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 tomaintain the temperature of a house at 70 F

when the outside temperature is 30 F.


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Solution Cont.

Thot

= 70 F = 21C =21 + 273 =294K

Tcold = 30 F = -1C =-1 + 273 =272K

C.O.P = 294

294 - 272= 294

22

= 13.3


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Consequences

For every watt of power used to drive

this ideal heat pump, 13.3 W is

delivered from the interior of the houseand 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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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 = 70F, Tcold = 40F

Buffalo: Thot = 70F, Tcold = 15F

Miami: Thot = 294K, Tcold = 277KBufalo: Thot = 294K, Tcold = 263K


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