Electrical Power Section 12.2
Important Definitions Electrical Power • the rate at which an appliance uses electrical energy • measured in watts (W) or kilowatts (kW) Electrical Energy • the amount of energy used by an appliance • measured in kilowatt-hours (kW·h) or watt-seconds (W·s) • sometimes expressed in joules (J). 1 Joule = 1 W·s.
Consumer Energy Needs 1. Consumers are billed based on how much electrical energy (in kW·h) they consume. The amount of energy a customer uses depends on three factors: • the power rating of appliances used • the setting of the appliances • the amount (duration) of use
Power Rating • Appliances that consume more energy have higher power ratings. • Examples: LCD Television 0.12 kW Stove 3.2 kW 2. Why do you think the stove consumes so much more energy?
3. Power can be measured in watts, but it is usually more suitable to use kilowatts(kW). • What is the conversion between watts and kilowatts? Conversion: __________ W = 1 kW
Device Settings Actual Power vs. Power Rating • The actual power used differ from the power rating. • This is because the actual power will depend on the setting of the device. 4. Examples: • Clothes washer • Wash cycle requires more power than spin cycle • Hair dryer • High setting requires more power than low setting
Amount of Use • The longer an appliance/device is used, the moreenergy it consumes! • Energy use: • measured in kilowatt-hours (kW·h) • calculated by multiplying the power rating of a device (in kW) by the number of hours it is used (in hours, h) Energy (kW·h) Power (kW) Hours used (h)
Annual energy consumption of the model Scale compares the appliance to the most- and least-efficient models in the same class EnerGuide labels • All Canadian appliances have an EnerGuide label. • allows consumers to make informed decisions when purchasing appliances
Annual energy consumption of the model Scale compares the appliance to the most- and least-efficient models in the same class 5. Interpret the graphic: • How much energy does this appliance consume, per year? • Approximately how much energy does it use, per day? (Round to two decimals) • In terms of energy consumption, how does this appliance compare to other, similar appliances? 300 kW·h 0.82 kW·h Pretty good – on low end of scale
Sample Problem: Determining energy consumption & Cost 6. A hair dryer is rated at 1200 W. On average, it used for 5 min each school day in the morning, when the cost of electrical energy is 10.9¢/kW·h. • How much energy, in kW·h, is consumed each school day, by the hair dryer? • How much energy is consumed over all five school days in a week? • Calculate the weekly cost of using the hair dryer all five days.
Time-Of-Use Pricing • Time-of-use pricing - A system of pricing, where the price that is charged per kW·h of energy is different depending on the time of the day or week. • three different time of use prices: off-peak, mid-peak, on-peak • intervals are adjusted twice a year (summer and winter) • Energy consumption is monitored by a smart metre, which records hourly energy usage.
7. Interpret the graphic. Use correct units, where appropriate.
Energy demands change with the seasons Discuss with a partner... 8. a. In general, why do you think the peak hours change depending on the season? b. What needs make up the major electrical demands in the summer? c. What needs make up the major electrical demands in the winter? Cooling/Air conditioning Heating and lighting
d. Describe one way you could use your knowledge of time-of-use pricing, to save money.
Phantom Loads 9a. Phantomload - The electricity that is consumed by an appliance or device when it is turned off. b. Example: TV– Always in standby mode, “waiting” to receive a signal to turn on c. Features of typical devices with phantom loads: • remote controls (TV’s, stereo systems) • continuous display (like the clock on a stove) • feature rechargeable batteries (cordless phones) • external power supplies (like phone chargers)
Homework • Pg. 496 #1-4 • Pg. 495 #1-5