1. Energy Efficiency Unit D – Electrical Principles and Technologies - Concept 3

2. Concept 3 – Energy Efficiency Energy Direct current Alternating current Power Watt (W) Kilowatt hour Law of Conservation of Energy Efficiency Joule (J)

3. Concept 3 – Energy Efficiency Learning Concept Identify the forms of energy inputs & outputs in a device or system

4. Concept 3 – Energy Efficiency Recall that energy is the ability to do work Four common forms of energy are Chemical The energy stored in chemical bonds Electrical The energy of charged particles Mechanical The energy of an object because of its motion or potential to move Thermal The total kinetic energy of all the particles in a substance

5. Concept 3 – Energy Efficiency Electrical Energy Some motors run on direct current (DC) Electricity flows in only one direction Other motors run on alternating current (AC) Electricity flows back and forth 60 times per second This is the electricity in household circuits AC / DC current

6. Concept 3 – Energy Efficiency Review: DeviceInput EnergyOutput Energy Electric Kettle Battery-Operated Toy Car Electric Blanket Cordless Telephone

7. Concept 3 – Energy Efficiency Learning Concept Apply appropriate units, measures and devices in energy transformations Measure amperage and voltage Calculate watts consumed using the formula P=I×V Calculate quantity of energy in joules using the formula E=P×t

8. Concept 3 – Energy Efficiency Power is the rate at which a device converts energy The faster a device can convert energy, the greater its power rating www.eastmarinedrive.com Power Video

9. Concept 3 – Energy Efficiency Mathematical relationship between power (P), current (I) and voltage (V) is P=I×V or watts = amperage × volts Unit of power is the watt (W) Named for James Watt Equal to one joule per second http://static.howstuffworks.com

10. Concept 3 – Energy Efficiency Example A hair dryer has a power rating of 1000 W. It is plugged into a 120-V outlet. What is the current flowing through the hair dryer? www.electronics-tutorials.ws/ I = 8.33

11. Concept 3 – Energy Efficiency Practice: A coffee maker that is plugged into a 120V outlet has 6A of current flowing through it. What is the power rating of the coffee maker.

12. Concept 3 – Energy Efficiency Power ratings on devices can be used to determine the amount of energy the device uses Energy consumption of a device is the input power multiplied by the time the device is used Energy is calculated with the formula E=P×t

13. Concept 3 – Energy Efficiency James Joule showed that both mechanical work and electricity can produce heat, and vice versa Therefore, the unit of energy is named the joule (J) www.magnet.fsu.edu www.physics.ie

15. Concept 3 – Energy Efficiency A kilowatt hour is also a unit of energy that is used instead of the joule(J). Energy calculation is the same but hours are substituted for seconds Kilowatts (kW) are substituted for watts http://blog.mapawatt.com

16. Concept 3 – Energy Efficiency Example A microwave oven has a power rating of 800 W. If you cook a roast in the oven for 30 minutes at high, how many joules of electrical energy are converted into heat? Important Reminder – joules are measured as (watt × second) E= 1440000 J or 1.4MJ

17. Concept 3 – Energy Efficiency Practice: A hand dryer is converts 129000J of electrical energy into heat energy in 60 seconds. What is the power rating of the hand dryer.

18. Concept 3 – Energy Efficiency Learning Concept Apply the concepts of conservation of energy and efficiency to the analysis of energy devices

19. Concept 3 – Energy Efficiency The Law of Conservation of Energy is a fundamental principle Energy cannot be created nor destroyed It can only be transformed from one form to another http://hrsbstaff.ednet.ns.ca www.tutorvista.com

20. Concept 3 – Energy Efficiency However, usually it is found the output energy is smaller than the input energy. Most often the missing energy is lost as heat All mechanical systems dissipate some energy, so their usable output energy is always less than the input energy http://indianapublicmedia.org/

21. Concept 3 – Energy Efficiency Learning Concept Compare energy inputs and outputs of a device Calculate efficiency using the formula

22. Concept 3 – Energy Efficiency The efficiency of a device is the ratio of useful energy that comes out of a device compared to the amount that went in The more input energy that is converted to useable output energy, the more efficient the device www.toronto.ca

23. Concept 3 – Energy Efficiency Example A quad is 20% efficient at producing useful output energy from input fuel. How many joules of input fuel energy will this quad need to produce 1000 J of useful output?

24. Concept 3 – Energy Efficiency Example Calculate the efficiency of each of the following devices DeviceInput EnergyOutput Energy Efficiency Gas-power SUV675 kJ81 kJ Gas-electric hybrid vehicle675 kJ195 kJ Natural gas furnace110 MJ85 MJ Electric baseboard heater9.5 kJ Alkaline dry cell84.52 kJ74.38 kJ Fluorescent light12.5 kJ2.75 kJ Incandescent light780 J31 J

25. Concept 3 – Energy Efficiency It is possible for an electric heater to be 100% efficient in converting electricity to heat Devices that convert electricity to other forms of energy can never be 100% efficient Any sort of movement generates a certain amount of thermal energy www.hielscher.com

26. Concept 3 – Energy Efficiency Learning Concept Investigate and describe techniques for reducing waste energy in common household devices

27. Concept 3 – Energy Efficiency Increasing efficiency depends on the purpose of the device Worst waste ‘offender’ is heat from friction Decrease friction as much as possible by using improved bearings and lubricants www.prolubricants.com

28. Concept 3 – Energy Efficiency Increasing efficiency depends on the purpose of the device Can add layers of insulation to either Reduce the amount of heat lost to the surroundings (oven) Reduce the amount of heat being transferred in (refrigerator)