Lesson 4.4: Efficiency Around the House

Lesson 4.4: Efficiency Around the House

How many machines do you have in your home?  You may think there are only a few, but think again.  There is the refrigerator, the stove, light bulbs, furnace, TV, stereo, hairdryer, toaster, and many more.  All these machines use energy, energy that is becoming more expensive. 

Read Efficiency around the House on page 146 to learn more about the efficiency of machines in the home. Then, answer these questions.  

Question 1. What is the most efficient, an electric motor or a gasoline motor?  Support your answer with the percent efficiency of each.

Question 2. Batteries are the most efficient technology.  Why do we not use batteries as the source of energy for all things in our homes?  

Question 3. Why are incandescent light bulbs so inefficient?  How can you improve the efficiency of light bulbs?

Question 4. What does the Energuide number indicate?

Question 5. What does kW·h represent?

Question 6. If five 60W bulbs are left on for four hours, how many kW·h of electricity are used?

Question 7. There is a problem with the Energuide label shown on page 146.  What is wrong with the label?

 

Check your answers with those that follow.

 

 

 

 

 

 

 

 

 

 

 

Answers to Questions:

Question 1. What is the most efficient, an electric motor or a gasoline motor?  Support your answer with the % efficiency of each.

According to table 7.1 in the textbook, electrical appliances are 80% to 90% efficient.  Gasoline engines are 25% to 40% efficient.  Considering the worst and best efficiencies, 80% to 40%, electric motors are more efficient.  In reality, electrical motors are about 90% efficient.

Question 2. Batteries are the most efficient technology.  Why do we not use batteries as the source of energy for all things in our homes? 

Batteries are a very expensive source of electricity.  Batteries also produce a lot of waste for the electricity they produce.  Batteries cannot produce enough electricity to heat our homes, or even cook our food.  Batteries are used to power small, portable tools such as flashlights and music players.  Large batteries are used to start our cars. New battery technology has resulted in hybrid cars using gasoline as well as batteries. 

Question 3. Why are incandescent light bulbs so inefficient?  How can you improve the efficiency of light bulbs?

Incandescent light bulbs are very inefficient because they waste a lot of energy as heat.  Light bulbs are made to produce light. Incandescent means that the wire is heated to a white hot temperature to produce light.  Fluorescent bulbs are more efficient because they produce less waste heat.  If you replace ordinary incandescent light bulbs with fluorescent bulbs, you will improve the efficiency and save energy and money.

Question 4. What does the Energuide number indicate?

The Energuide number indicates the number of kW·h of electricity the machine will use in an average year. 

Question 5. What does kW·h represent?

kW·h represents the amount of electricity used when 1000 watts is used for 1 hour.

Question 6. If five 60W bulbs are left on for four hours, how many kW·h of electricity are used?

The amount of electricity used would be 5 ? 60W ? 4 h = 1200 W·h = 1.2 kW·h.

Question 7. There is a problem with the Energuide label shown on page 146.  What is wrong with the label?

The label is misleading.  The Office of Energy Efficiency gives the following information about what the parts of the label mean.

• The shaded bar scale displays the energy-consumption range for appliance models of this type and size. The figure at the left end of the scale indicates the lowest energy-consumption rating; the figure on the right indicates the highest.
• An arrow just above the bar scale shows where the appliance ranks relative to similar models.

Now, look at the label shown in the textbook, and give attention to where this appliance ranks (look at the arrow).  It appears that this is a quite efficient model because the arrow points close to the most efficient model at 561 kWh.

                               

But look carefully.  The worst model uses 587 kWh.  The arrow should have been pointing to the far right indicating this is a very inefficient model.
This is what this label should be:

                               

Click on the page forward to continue Lesson 4.

---