What s a Kilowatt-hour Good For? Introduction Given 1 kw-h of energy, what can an electrical appliance do? How long will a lamp shine before it s consumed 1 kw-h? How many slices of toast can a toaster make? How many loads of wash can a washing machine get done? As with many things, getting the answers to this requires a little math so let s play a little math energy game. Setup Print out and cut up enough appliance cards (see end of this game packet) so that there are 5 cards per student in the class. Randomly divide the cards into one envelope for each student, 5 cards in each. Pass them out to your students when you are ready for them to play the game. What To Do Each appliance card represents a typical electrical appliance that might be found in a home or school. The power rating, in Watts, is shown for each appliance. Each appliance card also lists a goal. This is the work that you want to accomplish using the appliance given a certain amount of energy to run it. This goal might be hours of running time, number of pots of coffee made, or loads of laundry dried, for example. For each appliance card, you will apply 1 kilowatt-hour of energy to accomplish the listed goal. Use the worksheet on the next page to do the calculation and record your results. When the students are ready to play, tell them they have a certain amount of time to play the game and calculate all of the card goals. The amount of time will depend on the math-readiness of the class, but should be short enough to put a little bit of pressure on them. When they re ready, start the clock. Discussion 1 P a g e
Energy Worksheet For each Appliance Card, determine the total amount of work the appliance can accomplish with 1 kilowatt-hour of energy. See example calculations below. Appliance Power (W) Power (kw) Goal Solution Examples: To determine how many hours an appliance will run on 1 kw-h of energy, use the formula Time = Energy / Power, with Energy equal to 1 kw-h. So, given 1 kw-h of energy, a 500 W appliance will run for: 1 kw-h / 0.500 kw = 2 hours To figure out how many times an appliance can do its task on 1 kw-h (make toast, wash a load of laundry, make a milkshake), first use the formula Energy = Power x Time to calculate how many kw-h it consumes to do the task, then divide 1 kw-h by that amount. So for a 500 W appliance that takes 15 minutes to do its task once, the energy it consumes is: And dividing 1 kw-h by that amount: 0.500 kw x 0.25 h = 0.125 kw-h 1 kw-h / 0.125 kw-h = 8 This appliance can do its task 8 times on 1 kw-h of energy. 2 P a g e
LED Night Light 0.5 W Goal: DAYS of Clock Radio 4 W Goal: DAYS of LED Lamp 7 W Incandescent Lamp 60 W CFL Lamp 18 W Desktop Computer and LCD Monitor 290 W Laptop Computer 45 W Refrigerator 100 W Goal: DAYS of 42 LCD TV 160 W 3 P a g e
Dishwasher (no electric heating or drying) 200 W Goal: NUMBER OF LOADS (assuming 45 minutes per load) Air Conditioner (small) 500 W Toaster 750 W Goal: PIECES OF TOAST (assuming 2 minutes to toast 2 slices) Coffee Maker 900 W Goal: POTS OF COFFEE (assuming 5 minutes to make 1 pot) Electric Heater 1400 W continuous operation Electric Oven 2000 W (at 350 o F) Goal: NUMBER OF roasted turkeys (assuming 2 hours to cook a turkey) Electric Clothes Drier 4400 W Goal: NUMBER of laundry loads (assuming 45 minutes to dry one load) 42 Plasma TV 330 W continuous operation XBOX 70 W continuous excitement 4 P a g e
Classroom Lighting 600 W continuous lighting Aquarium (10 gallon) 30 W (pump, heater, and lighting included) Ceiling Fan 50 W Electric Blanket 200 W Goal: NIGHTS of use (assuming 8 hours per night) Blow Drier 1000 W Goal: Number of times drying hair (assuming 3 minutes per drying) Waffle Iron 1200 W Goal: Waffle breakfasts (assuming 20 minutes to cook one breakfast) Electric Iron 1000 W Goal: Pieces of clothing ironed (assuming 2 minutes per piece) Microwave Oven 1000 W Goal: NUMBER of meals cooked (assuming 15 minutes to heat a meal) Blender 300 W Goal: NUMBER of milkshakes (assuming 1 minute per milkshake) 5 P a g e
Solution Key Appliance W kw Goal Solution 42" LCD TV 160 0.16 6.25 Hours 42" plasma TV 330 0.33 3.03 Hours Air conditioner 500 0.5 2.00 Hours Aquarium (10 gallon) 30 0.03 33.33 Hours Blender 300 0.3 200.00 Milkshakes (1 minute per) Blow drier 1000 1 20.00 Dry heads (3 minutes per) Ceiling fan 50 0.05 20.00 Hours CFL lamp 18 0.018 55.56 Hours Classroom lighting 600 0.6 1.67 Hours Clock radio 4 0.004 10.42 Days Coffee maker 900 0.9 13.33 Pots (1 per 5 minutes) Desktop computer and LCD monitor 290 0.29 3.45 Hours Dishwasher (no heating/drying) 200 0.2 6.67 Loads (45 min) Electric blanket 200 0.2 0.63 Nights (8 hours per night) Electric clothes drier 4400 4.4 0.30 Loads of laundry (45 min) Electric heater 1400 1.4 0.71 Hours Electric iron 1000 1 30.00 Pressed clothing (2 minutes per piece) Electric oven 2000 2 0.25 Roast turkeys (2 hours per) Incandescent lamp 60 0.06 16.67 Hours Laptop computer 45 0.045 22.22 Hours LED lamp 7 0.007 142.86 Hours LED night light 0.5 0.0005 83.33 Days Microwave oven 1000 1 4.00 Meals (15 minutes per) Refrigerator 100 0.1 0.42 Days Toaster 750 0.75 80.00 Toast (2 per 2 minutes) Waffle iron 1200 1.2 2.50 Waffle breakfasts (20 minutes per) Xbox 70 0.07 14.29 Hours 6 P a g e