1. The Bases of Energy: forms, units and efficiency

2. EGEE 102 - Energy Conservation and Environmental Protection
Energy Efficiency
Energy
Conversion
Device
Useful Energy
Output
Energy Input
Energy Dissipated
to the Surroundings
Energy is put into a device in one form or the other and that energy exits in two streams
5. Energy Efficiency

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 ?

4. Efficiency of Some Common Devices
Electric Motor
Home Oil Furnace
Home Coal Furnace
Steam Boiler (power
plant)
Power Plant (thermal)
Automobile Engine
Light Bulb-Fluorescent
Light Bulb -Incandescent
Efficiency 90 65 55 89 36 25 20 5

5. Vehicle Efficiency – Gasoline Engine
EGEE Energy Conservation and Environmental Protection
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
5. Energy Efficiency

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

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

8. 540 ° C = ° K = 813 °K
20 °C = = 293 °K

9. EGEE 102 - Energy Conservation and Environmental Protection
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.
5. Energy Efficiency

10. Schematic Diagram of a Power Plant
Stop and explain the efficiency of a typical US power plant

11. Boiler Components

12. 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

13. 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%

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

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