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? STOP AND THINK - on the last question

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? After the TPS hand out the raw data sheet and the data/calculation sheet. Have them make any changes necessary to the raw datasheet. Also have them do them look at and do the sample calculations on the raw datasheet.

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

Homework PURPOSE: 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 II Energy 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). Part II is after students have collected data as homework the night before. You may want to give class time to look over their calculations. Either have students put their household/capita average on the board or give them to you to calculate the average, which you put on the board. You may want to speak to how pooling data or increasing sample size can increase data accuracy.

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 The website below gives you per capita or per country consumption rates and over several years. I chose the latest year with complete data 2011. If you have access to a computer, you can have students choose countries & data to compare. If you do not have computer access the data can be down loaded as an excel file. EF_T1_L1_Total_Primary_Energy_Consumption_per_Capita_Data http://www.eia.gov/cfapps/ipdbproject/iedindex3.cfm?tid=44&pid=45&aid=2&cid=regions&syid=2011&eyid=2011&unit=QBTU

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? These are questions on their calculation sheet, have them work on their own. There will be a class brainstorming later.

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 One British Thermal Unit (BTU) is the heat that will raise the temperature of one pound of water by one degree Fahrenheit. NOTE BTU is a million times smaller then MMBTU

Science as Process Class brainstorm: What are some reasons we differ from state and/or national averages? Some science as process reasons could include: Single day sample, small sample size of class, time of year

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? Some science as process reasons could include: Single day sample, small sample size of class, time of year

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 watts Elec. furnace, 2000sf, cold climate 7941 watts Elec. furnace, 1000sf, warm climate 1440 watts Electric space heater (high) 900 watts Electric space heater (medium) 600 watts Electric space heater (low) 750 watts Gas furnace (for the blower) Cooling 3500 watts Central Air Conditioner (2.5 tons) 1440 watts Window unit AC, huge 900 watts Window unit AC, medium 500 watts Tiny window unit AC 325-425 watts Fan only for central AC (no cooling) Have students estimate what is used in their home for heating and cooling on the day they gathered their other data and how many hours it is on per day. If they cannot estimate, they can ask or check when they get home the next day.

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.

Homework PURPOSE: To find out how much gasoline (fossil fuel) you use during a 48-hour (2-day) audit of all family transportation. 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: Use the Transportation Raw Data Sheet tonight to begin gathering data on all your vehicles and travel. 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.