Imagine being able to complete your homework in a half an hour each night versus the usual two hours of homework! Which would you choose? When are you being most efficient?
What is energy? It fuels our cars, plays our radios, heats our water, and lights our homes. Energy is the ability to do work. We can use energy to put something in motion or produce light and heat. Think about how much energy you use each day. You wake up using an alarm clock, take a shower using hot water, use appliances in the kitchen to prepare your breakfast, and use a school bus as transportation to get to school. But how much energy do each of those use? How efficient are they?
Energy efficiency is the amount of useful energy you get from a system. Converting energy from one form to another always involves a loss of usable energy, usually in the form of heat. While it would be great to have a perfect energy efficient machine, it simply isn't possible. However, today we are making appliances that use less energy than they did many years ago. The National Appliance Energy Conservation Act was passed in 1990 and now requires appliances to meet energy efficiency standards.
When you buy appliances, they are labeled with a yellow EnergyGuide Label which gives you the Energy Use and Energy Efficiency Rating (EER). The EnergyGuide labels list the manufacturer, the model, the capacity, the features, the amount of energy the appliance will use a year on average, it's comparison with similar models, and the estimated yearly energy cost. Since many high-efficiency appliances cost more to buy, is buying the less energy efficient appliance the bargain? What you need to factor in is how much it costs each year to operate and how many years you will use it. The payback period is the amount of time you must use an appliance before you benefit from energy savings. The life cycle cost of an appliance is the purchase price plus the operating cost over the projected life of the appliance. Life cycle costs of efficient appliances are usually much less than cheaper appliances.
Calculating Life cycle CostsHow much will an appliance cost to buy and use over a lifetime?
purchase price + (annual energy cost x estimated lifetime x discount factor) = life cycle cost
Appliance Characteristics for Lifestyle Cost Comparisons
APPLIANCE ESTIMATED LIFETIME DISCOUNT FACTOR water heater 13 .83 refrigerators and freezers 20 .76 room air conditioner 15 .81 dishwasher 12 .84 clothes washer 18 .78
Calculating Payback PeriodHow long will it take to recover the extra money you spend for a more efficient appliance?
purchase price of more expensive model - purchase price of less expensive model = difference in purchase price
higher yearly operating cost - lower annual operating cost = difference in annual operating cost
difference in purchase price / difference in annual operating cost = payback period
Example: You are shopping for a refrigerator. There are two models. One casts $100 more than the other but uses $25 less electricity per year. Which refrigerator should you buy?
$1000 purchase price of more expensive model - $900 purchase price of less expensive model = $100
$100/$25 less electricity/yr = 4 yrs
It would take 4 years to realize the savings. However, since the payback period is only 4 years and your refrigerator will last much longer than that, you will save money over the life of the refrigerator and conserve natural resources.
Use these links to learn more:
- Energy Efficiency Guidelines
Did you see a word or two that you did not recognize? You might find it in the glossary below.
LINKS TO THE ENERGY AUDIT GLOSSARY
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Students: Click on the button at the left to connect to the Power Worksheet.
Created for the Fermilab LInC program sponsored by Fermi National Accelerator Laboratory Education Office and Friends of Fermilab, and funded by United States Department of Energy, Illinois State Board of Education, North Central Regional Technology in Education Consortium which is operated by North Central Regional Educational Laboratory (NCREL), and the National Science Foundation.
Authors: Sue Emmons, Powell Middle School, Littleton, CO; Kevin Lindauer, John F. Kennedy High School, Denver, CO; Linda Lung, National Renewable Energy Laboratory, Golden, CO; John Sepich, Scott Carpenter Middle School, Westminster, CO; ; Janet Stellema, Monarch K-8, Louisville, CO; Edited by Marge Bardeen NTEP II Project PI.
Created: September 9, 1998 revised September 27, 2001