David Marrett, Murrieta High School, Murrieta Valley Unified School District

Overview

Students practice simple data collection, tabulation, graphing, and analysis in this energy awareness exercise. Next, they design a conservation plan. Finally, they study how to implement the plan.

• Objectives: Before effective conservation of resources can start, people need a good awareness of resource consumption patterns, including their own. This exercise will build awareness first then plan for conservation.
• Subjects: Environmental Science, Earth Science, Physics
• Suggested Grade Level: 10-12
• California Standards Addressed: Laws of thermodynamics, especially first and second laws (1st= conservation of energy; 2nd=entropy)
• Time: 6.5 hour lesson segments over 3 weeks

Materials

• Notebook
• Access to Internet for Research

Preparation and Background

As part of a unit on natural resource conservation, students learn the laws of thermodynamics that any "change" requires energy, energy is conserved, but constantly transformed and that nature moves toward higher disorder (entropy).

Procedure

Students note all "changes" and energy sources during one school day (6:30am to 9:00pm). Tabulate data and research sources of energy involved. All energy units will be converted to kilo joules (kJ)

For Discussion

After students submit first draft reports, energy expenditures are classified as falling into 1 of 3 categories:

1. Absolutely necessary
2. Convenient and useful, but not really needed
3. Wasteful

In small groups, then reporting out to the whole class, discuss how perceptions differ among the same activities.

Extensions

Each student writes an energy saving plan, calculating percentages. Students then attempt implementation and monitor successes and challenges.

Resources

Common Household Appliance Energy Use

Listed below are some common appliances, their wattage and an estimate of operating costs.

Appliance Wattages

Appliances and Approximate Wattages

Energy Use of Some Typical Home Appliances

If you want a general estimate of how much electricity your home appliances consume, you can refer to the list below, which provides the energy consumption (Wattage) of some typical home appliances. If you have appliances that are not listed in the table, or desire a more exact figure based on a specific appliance in your home, use the following formula to estimate the amount of energy a specific appliance consumes:

Wattage * Hours Used Per Day / 1000 = Daily Kilowatt Hour (kWh) Consumption

Note: 1 kilowatt (kW) = 1,000 Watts (W)

Multiply this by the number of days you use the appliance during the year for the annual consumption. You can then calculate the annual cost to run an appliance by multiplying the kWh per year by your local utility's rate per kWh consumed.

Examples:

You can usually find the wattage of most appliances stamped on the bottom or back of the appliance, or on its "nameplate." The wattage listed is the maximum power drawn by the appliance. Since many appliances have a range of settings (for example, the volume on a radio), the actual amount of power consumed depends on the setting used at any one time.

Here are some examples of the range of nameplate wattages for various household appliances:

Refrigerators, although turned "on" all the time, actually cycle on and off at a rate that depends on a number of factors. These factors include how well it is insulated, room temperature, freezer temperature, how often the door is opened, if the coils are clean, if it is defrosted regularly, and the condition of the door seals. To get an approximate figure for the number of hours that a refrigerator actually operates at its maximum wattage, divide the total time the refrigerator is plugged in by three.

If the wattage is not listed on the appliance, you can still estimate it by finding the current draw (in amperes) and multiplying that by the voltage used by the appliance. Most appliances in the United States use 120 volts. Larger appliances, such as clothes dryers and electric cooktops, use 240 volts. The amperes might be stamped on the unit in place of the wattage. If not, find a clamp-on ammeter—an electrician's tool that clamps around one of the two wires on the appliance—to measure the current flowing through it. You can obtain this type of ammeter in stores that sell electrical and electronic equipment. Take a reading while the device is running; this is the actual amount of current being used at that instant.

Note: When measuring the current drawn by a motor, in the first second that the motor starts, the meter will show about three times the current than when it is running smoothly.

Also note that many appliances continue to draw a small amount of power when they are switched "off." These "phantom loads" occur in most appliances that use electricity, such as VCRs, televisions, stereos, computers, and kitchen appliances. Most phantom loads will increase the appliance's energy consumption a few watts per hour. These loads can be avoided by unplugging the appliance or using a power strip and using the switch on the power strip to cut all power to the appliance.

Appliance Wattage Hours/Month

Electricity Consumption Score Card

• *Based on 1000 hours of operation per year. This figure will vary widely depending on geographical area and specific size of unit.
• **Thermostatically controlled units cycle on and off. Estimates of "hours of use" are based on the time the heat element is "on" and will be less than actual switch-on time.
• ***Number of hours used varies widely.

Typical Operating Costs of Electric Household Appliances

These figures are based on average use by a family of four at an electric rate of 13¢ per kilowatt hour.

Wattage for Home Appliances

See also: HEG78-94 Electrical Appliances and the Energy Dollar (100 kB PDF)