Grade by Grade
E. Earth and Space Systems · Conservation of Energy and Resources

Technology That Saves Energy (and Some That Uses More)

E1.2 A2.1 A2.2 A1.3 A3.1About 45 minutes
Learning goals
  • I can describe how some technologies increase energy use and others reduce it.
  • I can read an EnerGuide label to compare appliances.
  • I can describe ways I can use technology to reduce energy use.
  • I can read, change and debug code for an energy-saving smart light.

Words to know

energy consumption
How much energy is used.
EnerGuide label
A Canadian label on appliances that shows how much electricity the appliance is estimated to use in one year. A lower number means it uses less.
ENERGY STAR
A symbol on appliances and electronics that are among the most energy efficient of their kind.
standby power
Electricity some devices use while they are plugged in and "off" or sleeping.
kilowatt-hour (kWh)
A unit for measuring electrical energy. Electricity bills and EnerGuide labels use it.
sensor
A device that detects something, like motion, light or temperature, and sends a signal to a computer.
program
A set of instructions (code) that tells a computer what to do.

The little glowing lights

Tonight, turn off all the lights in your living room and look around. Do you see tiny glowing lights? On the TV, the game console, the microwave clock, a charger?

Those little lights mean the device is still using some electricity, even though it seems to be off. Technology can make us use more energy, or help us use less. It depends on the technology and how we use it.

A dim living room in the evening with a small red standby light glowing near a switched-off TV.
Look for the tiny glowing lights: devices that seem to be off can still use electricity on standby. Unplugging them saves energy. AI-generated image

Technology that can increase energy use

  • More devices: every new screen, speaker or gadget that plugs in uses some electricity.
  • Standby power: many devices use a little electricity all the time while they are plugged in and "off" or asleep.
  • Bigger and faster: a bigger screen or a bigger vehicle usually needs more energy to run.
  • Old, inefficient technology: old-style light bulbs and old appliances often use more energy than newer, efficient ones.

Technology that can reduce energy use

  • LED bulbs give the same light with much less electricity (Grade 4).
  • Programmable and smart thermostats turn the heat down automatically at night or when nobody is home.
  • Motion sensors and timers turn lights off when nobody is in the room.
  • Smart power bars cut power to devices that are switched off, stopping standby power.
  • Efficient appliances, marked with the ENERGY STAR symbol, use less energy to do the same job.
  • Heat pumps move heat into a home in winter (and out in summer), using electricity instead of burning fuel.
  • Video calls can sometimes replace a long car trip.

Reading an EnerGuide label

In Canada, many new appliances (fridges, freezers, washers, dryers, dishwashers, stoves) come with an EnerGuide label. Its big number shows how much electricity the appliance is estimated to use in one year, in kilowatt-hours (kWh). When you compare two similar models: a smaller number means it uses less energy. If you see the ENERGY STAR symbol too, it's one of the most efficient models of its kind.

Worked example

Let's compare two fridges

Pretend a family is choosing between two fridges of the same size. (These numbers are made up for practice.)

  • Fridge A: EnerGuide label says 550 kWh per year.
  • Fridge B: EnerGuide label says 400 kWh per year, with the ENERGY STAR symbol.

Which uses less energy? How much less in one year? In 10 years?

  1. Compare: 400 is less than 550, so Fridge B uses less energy.
  2. Difference in one year: 550 − 400 = 150 kWh.
  3. In 10 years: 150 × 10 = 1500 kWh less.
  4. Less electricity means a smaller bill, and less energy that had to be made by power stations.

Fridge B uses 150 kWh less each year, or 1500 kWh less over 10 years.

Energy used in one year (practice numbers)Fridge A550 kWhFridge B400 kWhENERGY STAR150 kWh lessSmaller number on the EnerGuide label = uses less energy
Comparing the two EnerGuide numbers: Fridge B uses 150 kWh less each year, so over 10 years it saves 1500 kWh.

Coding a smart light

A smart light uses a motion sensor and a program to save energy. Read the code below. Lines that start with # are notes for people; the computer skips them.

# Smart hallway light
when motion_sensor detects motion:
light = "on"
timer = 0
forever:
wait 1 second
timer = timer + 1
if timer >= 60:
light = "off"

When the motion sensor detects motion, the light turns on and the timer goes back to 0. Every second the timer goes up by 1. After 60 seconds with no motion, the light turns off.

How the smart light program worksMotion detectedlight ONtimer = 0wait 1 secondtimer = timer + 1timer ≥ 60?yeslight OFFno: keep countingAny new motion sends the timer back to 0.
The program as a flowchart. The light stays on while the timer counts up, and turns off only after 60 seconds with no motion.
Worked example

Let's test and debug the smart light code

(a) Mia walks into the hallway, then leaves. Nobody else comes. How long after she was last detected does the light turn off? (b) Jay changed the last part to if timer >= 60: light = "on". What is the bug?

  1. (a) When Mia is detected, the timer goes back to 0. Each second it goes up by 1.
  2. After 60 seconds with no motion, timer >= 60 is true, so the light turns off.
  3. (b) With Jay's change, when the timer reaches 60 the light is set to "on". It never turns off, so it wastes energy.
  4. Fix: change it back to light = "off".

(a) 60 seconds (1 minute) after the last motion. (b) The light never turns off; the last line should set the light to "off".

Emerging technology

Some new smart thermostats learn a family's schedule and adjust the heat by themselves. Some can be controlled from a phone. They can save energy, but they also collect information about when people are home, so families should think about privacy and set them up carefully with a grown-up (A2.2).

Just for fun

Riddle: Why did the TV close its eyes but keep one little light on?

It was on standby!

Hands-on activity

Home technology energy detective and design

You need: paper, a pencil and a flashlight.

  1. Standby hunt: at night, with the lights off, use a flashlight to walk around with a grown-up. Count the devices with a glowing standby light or clock. Make a list.
  2. Label hunt: look for EnerGuide labels or the ENERGY STAR symbol on appliances (the sticker is often removed after an appliance is installed, so you may need to look up the model number online with a grown-up).
  3. Thermostat check: is your thermostat programmable? Ask a grown-up what temperature it's set to at night.
  4. Design (A1.3): choose one energy problem you found. Plan a solution that uses technology, such as a smart power bar for the TV area, a timer, or a motion-sensor night light. Draw your plan and explain how it saves energy.
  5. Code (A2.1): change the smart light code so the light turns off after 2 minutes instead of 1. Then add a line so the light only turns on if it is dark.

What to look for (step 5): change 60 to 120. One possible way to add darkness: when motion_sensor detects motion and light_sensor says "dark":.

Safety: let a grown-up unplug or plug in devices. Never pull plugs by the cord or touch outlets, and don't move appliances.

Your turn

1

What does an EnerGuide label tell you?

2

What is standby power?

3

Name two technologies that help reduce energy use.

4

Name one way technology can increase energy use.

5

In the smart light code, what makes the timer go back to 0?

6

How does a programmable thermostat save energy in winter?

More practice: warm-up

1

Saves or uses more energy? Replacing an old bulb with an LED bulb.

2

Saves or uses more energy? Leaving a game console on all night.

3

Saves or uses more energy? A motion sensor on a garage light.

4

Saves or uses more energy? Switching off a smart power bar at bedtime.

5

Two dishwashers: one label says 270 kWh, the other 300 kWh. Which uses less energy?

More practice: on your own

1

Freezer A: 350 kWh per year. Freezer B: 280 kWh per year. How much less energy does B use in a year? In 5 years?

2

In the smart light code, what number would you change so the light stays on for 3 minutes after motion? To what?

3

Why might a family with more and more devices use more electricity, even if each device is efficient?

4

Name two ways you could use technology to reduce energy use in your bedroom.

5

Why is it important to think about privacy with smart thermostats and speakers?

Challenge

1

Find the bug: a student wrote the smart light code with timer = 0 inside the forever loop (instead of in the motion part). What would happen?

2

A family replaced their furnace with a heat pump. Explain how this could reduce carbon dioxide.

3

Design a morning routine for a school day that uses technology to save energy. Give three steps.

Check your understanding

Quiz

1.

On an EnerGuide label, a smaller kWh number means the appliance...

2.

Standby power is electricity used by devices that are...

3.

Which technology turns lights off when nobody is in the room?

4.

In the smart light code, what turns the light off?

5.

Which choice reduces energy use?

6.

Fridge A: 500 kWh per year. Fridge B: 420 kWh per year. How much less does B use in a year?

For parents and teachers

Big idea (E1.2): evaluate effects of various technologies on energy consumption, and describe ways individuals can use technology to reduce it. The smart-light code builds coding skills (A2.1), the smart-thermostat tip looks at emerging technology and its effects (A2.2), and the design task uses the engineering design process (A1.3).

How to help: do the standby hunt together in the evening. Show your child an EnerGuide label (on an appliance or a store website) and compare two models. If you have a programmable thermostat, show them its schedule.

Common difficulties:

  • Thinking "off" always means using no electricity. Explain standby power.
  • Reading EnerGuide numbers backwards. Smaller is better.
  • Code tracing: have your child pretend to be the computer, counting seconds out loud.

The fridge and freezer numbers in this lesson are made up for practice, not real statistics.

Safety: adults should handle plugs, outlets and moving appliances.