Electricity Units and Calculations

Science as process• The scientific process is often collaborative to improve

ideas and understanding.

• I’ll be giving you a data sheet later for the home energy audit but want your input to see if anything is missing.

• We will be working together to brainstorm how to get an accurate assessment of home energy use.

• After we collect your data, we will compare our class per capita energy use to the U.S average and to people from other countries around the world.

Part 1-Electricity basics

• Electric power- The rate at which electric energy is transferred to other forms of energy– Example: An electric blender transfers electrical

energy to mechanical energy (blender spinning) and heat energy (friction from spinning blades)

• The way we use electricity is by transferring it into other forms

• What other examples of electrical energy transfer can you think of?

Power Units

• The unit used for Electrical power= Watt

• Abbreviated by capital letter W

• Watt=Amp X Volts

• 1 kW=1000 Watts

• Kilowatt hour (kWh) is the standard unit used by energy companies. Simply means amount of kilowatts used in an hour.

Home Energy Audit

Think-Pair-Share: Data needed???? (5 min)• What information do we need? – What energy units should we use?

• How do we get that information?

Home Energy Audit

• Some appliances may not have the wattage, but we can calculate it if we have amp and volts

• The amount of time the appliance is used per day in needed to calculate kWh

HomeworkPURPOSE: To find out how much electricity you use, you will need to determine what uses electricity in your home and how much power each electrical item requires for normal use. We will be comparing data in kWh, so you will need to convert all data to kWh.

USE: After you collect and convert your electricity data, you will compare your usage to local and national averages. This analysis will then inform the changes you suggest on your Family Proposal.

PROCEDURE: Use the Raw Data Sheet tonight to gather data on all your appliances and convert it to kWh. Use the sample problems we did in class as models. Be prepared to put some time into this work!

Electricity Units: Part IIEnergy use

• We have data that says the the average U.S. citizen uses 312.8 million Btu/person/year

• BTU=a standard unit of measurement to denote the amount of heat energy in fuels. A BTU is the amount of heat required to increase 1 pound of water by one degree Fahrenheit.

• Is that a lot or a little? How do you know?

• In order to compare our calculations, we will need to calculate the per capita (person) kWh use in our homes/year, find the class average and then convert to million Btu (MMBtu).

Dimensional Analysis• If the average U.S. person uses 312.8 million

BTU/person/year of energy, how many kWh does that person use per year?

• Conversion : 1 MMBtu = 293.29722222222 kWh

• Calculate the annual energy use in kWh for two other countries.

• Do Problem #5

How does our class compare?• Is our class above or below the national average?

• Do you have any hypotheses why?

• Do problem #6

• Do you think there would be differences per capita use in different states? Why? Where do you think our state would rank?

Consumption per person per state

• http://energy.gov/maps/2009-energy-consumption-person

• The average BTU used per person in Iowa/year is 472,000,000 in 2009.

• 1 kWh = 3412.14163312794 BTU

• Do problem #7

Science as Process

• Class brainstorm: What are some reasons we differ from state and/or national averages?

Science as Process

• Discuss with your partner: Did we account for all of our home energy use by looking at the appliances in our home? Why or why not?

Science as Process

Average U.S. Household in 2007: How Energy was consumed

Science as Process

• We need to account for heating water(We will do this during our water audit)

• We need to account for heating and cooling energy– Estimate with the wattage data on the next slide

Do Question #8: Estimate Your Home Energy Use

Heating

26,500 wattsElec. furnace, 2000sf, cold climate7941 wattsElec. furnace, 1000sf, warm climate1440 wattsElectric space heater (high)900 wattsElectric space heater (medium)600 wattsElectric space heater (low)750 wattsGas furnace (for the blower)

Cooling

3500 wattsCentral Air Conditioner (2.5 tons)1440 wattsWindow unit AC, huge900 wattsWindow unit AC, medium500 wattsTiny window unit AC325-425 wattsFan only for central AC (no cooling)

Homework• We will begin our 2-day transportation audit as

homework

• While collecting transportation data you also need to look around your home to figure out how you could measure flow rate (volume/time) and figure out volumes (laundry, dishwasher) as we will work on data collection as a class.

HomeworkPURPOSE: 1. To find out how much gasoline (fossil fuel) you use during a 48-hour (2-

day) audit of all family transportation. 2. Begin thinking about how to measure flow rate (volume/time) and figure

out appliances that use set volumes of water per load (laundry/dishwasher).

USE: After you collect and convert your data, we will compare your water and fossil fuel usage to local and national averages. This analysis will then inform the changes you suggest on your Family Proposal.

PROCEDURE: 1. Use the Transportation Raw Data Sheet tonight to begin gathering data on

all your vehicles and travel. 2. Use the Water Raw Data Sheet to think about how you will measure water

and figure out which appliances you can determine water volume per load data.