Energy Consumption: HOME

Short circuit Overload Circuit breaker Fuse Power OUTCOME QUESTION(S): S1-3-18: How is a household wired to ensure safety? S1-3-20: What is electrical power and how does it vary in appliances? Vocabulary and People Short circuit Overload Circuit breaker Fuse Power

Common household circuits are 120 volts and 15 amps House circuits are different than the circuits made with batteries: Uses alternating current (AC) instead of direct current (DC) Operates at a higher voltage - 120 V or 240 V Electricity controlled and moved through a main panel (fuse box) All branches off the main line are in parallel Common household circuits are 120 volts and 15 amps

Generators produce A/C current for the home DC: electrons travel in one direction – (-) to (+) AC: e- move back and forth many times a second DC is like rolling balls down a hill – need to keep adding more to the top (or run out) AC is like balls rolling along a teeter totter – don’t need more since they will just move back and forth Remember this? Generators produce A/C current for the home

There are 3 wires that bring electricity into a home: Neutral wire (white) Two “Hot” wires (black) – carrying 120 V each Normal use: 1 hot connected to neutral creates 120 V potential Larger appliances: Both hot wires connect to neutral creates 240 V There is also a safety “ground” wire - green or bare copper - removes stray electrons safely

Remember what parallel circuits offer… All house branch lines link from the main panel. Outlets and switches are all connected in parallel each branch delivers typical 120 volts total current of all branches equals 15 A break any branch without affecting any other Remember what parallel circuits offer…

There are two components that safeguard against an increase in current Safety issues: Short circuit: current bypasses the appliance. less resistance – increases branch current Branch heats up – risk of fire Overload: too many things plugged into one outlet. increased branching – increases total current Main heats up – risk of fire There are two components that safeguard against an increase in current A

Fuses “burn out” and need to be replaced Circuit Breaker: contain either magnet / metal / semiconductor all are altered by excess current - breaks circuit (kill switch) Fuse: uses a strip of metal that easily melts excess current heats metal – breaks circuit main Breakers can be reset Fuses “burn out” and need to be replaced A main

Power and Energy Consumption Power is a measure of energy over time: lifting heavier weight in the same time – more power heating a cold room faster – more power P = t E E is energy in joules t is the time in seconds Power – measured in watts – is the energy used or work done every second 1 Watt is the power of 1 joule of energy in 1 second

What is the power of the charger? An iPhone charger moves 72 000 joules of energy in the 4 hours to fully charge a drained battery. What is the power of the charger? P = t E Formula must be in seconds to work properly – time must be converted 4 h · 60 min · 60 sec = 1 h 1 min 14 400 sec P = 14400 seconds 72000 joules = 5 watts (W)

Formula must be rearranged here to solve for the new unknown How much energy, in joules, is consumed by a 120 W light bulb if it is left on for 15 min? P = t E E Formula must be rearranged here to solve for the new unknown t P = t t P · t = E 15 min · 60 sec = 1 min 900 sec E = 120 W · 900 sec = 108 000 J

Rarely do we know energy values, but we can find voltage and current requirements - sometimes they are written on the component. P = t E P = V · I E Q P = V · I · Q t Remember: Voltage = ENERGY per coulomb of electrons Current = coulombs of electrons per SECOND

A 10 amp car heater is plugged in to a standard house outlet A 10 amp car heater is plugged in to a standard house outlet. What is the power of the heater? P = V · I Standard home outlet is 120V P = 120 V · 10 A P = 1200 W Large power measurements are converted to kilowatts 1200 W · 1 kW = 1000 W 1.2 kW

Formula must be rearranged here to solve for the new unknown What is the current through a 1200 W hair dryer if it is connected to 120 V? Formula must be rearranged here to solve for the new unknown P = V · I P = V · I V V P V = I I = 1200 W 120 V = 10 A

CAN YOU ANSWER THESE QUESTIONS? S1-3-18: S1-3-20: How is a household wired to ensure safety? S1-3-20: What is electrical power and how does it vary in appliances? Vocabulary and People Short circuit Overload Circuit breaker Fuse Power

Energy Consumption: CO$T

kWh Efficiency EnerGuide OUTCOME QUESTION(S): S1-3-22: How can you lower electrical energy use of a household? Vocabulary and People kWh Efficiency EnerGuide

Purchasing Electrical Energy Energy companies charge a fee for total energy consumption (usually) per month – “hydro” bill Total energy is calculated by multiplying power by time used E P is the power in kilowatts (kW) t is the time in hours t t E = P · t P = t Notice the units: Time is in hours – seconds are not useful for home billing Power is in kilowatts – watts are too small to be useful

The same energy formula is used but the units must match (kWh) You make smoothies every day in September (30 days) using a 900 W blender for 5 min. How much energy did the blender use that month? E = P · t 900 W · 1 kW = 1000 W 0.9 kW 5 min · 1 h · 30 (days) = 60 min 2.5 hours The same energy formula is used but the units must match (kWh) E = 0.9 kW · 2.5 h E = 2.25 kWh

“Hydro” charges about $0.08 for every kilowatt-hour (kWh) used Reading a Hydro Meter Hydro meter uses 5 dials to measure energy usage: far right dial is “ones” - far left dial is “ten thousands” a reading is taken every 1-2 months Reading 23 930 (kWh) 20 769 (kWh) 3161 (kWh) energy used this month “Hydro” charges about $0.08 for every kilowatt-hour (kWh) used = $253 this month

Sample Hydro bill: kWh used Time rate This household uses natural gas for heat and has a second bill for the total amount of gas used.

It is more efficient if it does the same work with less input energy Efficiency measures how well a device converts energy into work: every device wastes some energy lost as heat, sound, poor insulation… It is more efficient if it does the same work with less input energy

This appliance will use 125 kWh of electricity per month of normal use EnerGuide labels give consumers an idea of the efficiency of an appliance: gives energy usage for regular use over time (month/yr) efficient devices will have a lower energy usage allows consumer to estimate cost of using the device This appliance will use 125 kWh of electricity per month of normal use Energy star: government-regulated symbol used to identify most efficient devices (based on tests).

CAN YOU ANSWER THESE QUESTIONS? S1-3-22: How can you lower electrical energy use of a household? Vocabulary and People kWh Efficiency EnerGuide