Electrical Energy Use in the Home

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Electrical Energy Use in the Home

• Lesson 14

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Electrical Energy Use in the Home

• Last week we calculated how much energy
  appliances use and how this correlates to the
  length of time that they are used.
• Energy power x time
• Now we are going to look at how much it costs to
  use the electricity.

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• Just like meat at the Northern has a price per
  pound, electricity has a cost per kilowatt hour
  (kWh).
•  
• If the cost of a kilowatt is 0.08, all we need
  to know is how much energy is used to find out
  how much it will cost.
• Cost of energy used amount energy used (kWh) x
  price per kWh

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Example 1

• If a 500 W refrigerator/ freezer uses 75 kWh of
  energy, and it costs 0.08/kWh. How much does it
  cost to operate the refrigerator for one month?
• Cost of energy used amount energy used x price
  per kWh
• Cost of energy used 75 kWh x 0.08 / kWh
• 6.00
• Therefore, it costs 6.00 dollars a month to run
  the fridge.

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Example 2

• A 200 watt TV is used 12 hours a day for 30 days.
  How much will it cost to run if each kWh costs
  0.08?
• E P x t
• E (200W 1000W) x (12 h x 30 days)
• E 0.2 kW x 360 h
• E 72 kWh
•  
• Cost of energy used amount energy used x price
  per kWh
• Cost of energy used 72 kWh x 0.08/kWh
• Cost of energy used 5.76

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Practice questions

• Try the 4 questions, if you need help just ask
• A microwave oven uses 15kWh a month. How much
  does it cost to run for one month?
• Cost of energy used amount energy used x price
  per kWh
• Cost of energy used 15 kWh x 0.08 kWh
• Cost of energy used 1.20

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• A toaster uses 5kWh hours of electricity per
  month, what would it cost to use?
• Cost of energy used amount energy used x price
  per kWh
• Cost of energy used 5kWh x 0.08 kWh
• Cost of energy used 0.40

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• A 60 W incandescent bulb uses 30 kWh a month. How
  much does it cost to run for one month?
• Cost of energy used amount energy used x price
  per kWh
• Cost of energy used 30 kWh x 0.08 kWh
• Cost of energy used 2.40

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• A 500 W clothes dryer uses 150 kWh of electricity
  a month. How much does it cost to run for one
  month?
• Cost of energy used amount energy used x price
  per kWh
• Cost of energy used 150 kWh x 0.08 kWh
• Cost of energy used 12.00

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Efficiency and Conservation
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• Although the cost of one incandescent light bulb
  is relatively inexpensive, it is important to
  remember that there are multiple light bulbs in
  every house and many are left on for multiple
  hours a day. The cost of lighting can quickly add
  up when you calculate all of the light bulbs in a
  house.

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• Fluorescent bulbs cost much more to use than
  incandescent light bulbs do but they use less
  energy for the same amount of light. Which one is
  more cost effective in the end? A few factors
  must be looked at cost of the bulb, life of the
  bulb and power usage. We will compare the bulbs
  over the life of one fluorescent.

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• Bulb 1 60 watt incandescent
• Cost 0.50
• Life 1 000 h
• Power 60 W
• Since incandescent bulbs burn out faster we will
  need to calculate the cost of all of the bulbs.
  10 000 h 1000 h 10 bulbs.
• 10 bulbs x 0.50 5.00

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• Energy used
• E P x t
• E (60W 1000kW) x (10 000 h)
• E 0.06 kW x 10000 h
• E 600 kWh

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• Cost of energy used amount energy used x price
  per kWh
• Cost of energy used 600 kWh x 0.08 kWh
• Cost of energy used 48.00
• Total cost for 10 00 hours of light
• Cost of bulbs cost of energy
• 5.00 48.00 53.00

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• Bulb 2 13W fluorescent
• Cost 10.00
• Life 10 000 h
• Power 13 W

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• One bulb provides 10 000 hours of light so we
  only need to buy one bulb.
• Total bulb cost 10.00

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• Energy used
• E P x t
• E (13W 1000kW) x (10 000h)
• E 0.013 kW x 10000 h
• E 130 kWh
• Cost of energy used amount energy used x price
  per kWh
• Cost of energy used 130 kWh x 0.08 kWh
• Cost of energy used 10.40

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• Total cost for 10 00 hours of light
• Cost of bulbs cost of energy
• 10.00 10.40 20.40

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• Now we can calculate how much the fluorescent
  bulb would save us after 10 000 hours.
• Savings total cost of low efficiency appliance
  total cost of high efficiency appliance
• 53.00 - 20.40
• 32.60 .

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Methods of conserving energy

• Thawing frozen food in the refrigerator
• Using a microwave instead of a conventional oven
• Cleaning dust from light fixtures
• Replacing light fixtures and appliances with more
  efficient ones when they wear out.
• Drying laundry on a clothes line

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Methods of conserving energy

• Blocking sunlight with shades and blinds to
  reduce air conditioning use
• Using timer switches and programmed thermostats
• Turning down the heat in the winter by 1and
  turning up the air conditioner by 1.
• Turing off lights when leaving a room or reducing
  the time lights are on.
• Sealing up drafts around the house.

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Calculating the Cost of Power Worksheet