What s a Kilowatt-hour Good For?

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Conrad Clark
9 years ago
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1 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

As with many things, getting the answers to this requires a little math so let s play a little math energy game.

2 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 / 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: kw x 0.25 h = kw-h 1 kw-h / kw-h = 8 This appliance can do its task 8 times on 1 kw-h of energy. 2 P a g e

So, given 1 kw-h of energy, a 500 W appliance will run for: 1 kw-h / 0.

3 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

4 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

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

5 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

Waffle breakfasts (assuming 20 minutes to cook one breakfast) Electric Iron 1000 W Goal: Pieces of clothing ironed (assuming 2 minutes per piece) Microwave

6 Solution Key Appliance W kw Goal Solution 42" LCD TV Hours 42" plasma TV Hours Air conditioner Hours Aquarium (10 gallon) Hours Blender Milkshakes (1 minute per) Blow drier Dry heads (3 minutes per) Ceiling fan Hours CFL lamp Hours Classroom lighting Hours Clock radio Days Coffee maker Pots (1 per 5 minutes) Desktop computer and LCD monitor Hours Dishwasher (no heating/drying) Loads (45 min) Electric blanket Nights (8 hours per night) Electric clothes drier Loads of laundry (45 min) Electric heater Hours Electric iron Pressed clothing (2 minutes per piece) Electric oven Roast turkeys (2 hours per) Incandescent lamp Hours Laptop computer Hours LED lamp Hours LED night light Days Microwave oven Meals (15 minutes per) Refrigerator Days Toaster Toast (2 per 2 minutes) Waffle iron Waffle breakfasts (20 minutes per) Xbox Hours 6 P a g e

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.

home energy consumption list A list of electric household appliances, and their operating cost yukonelectrical.com

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