Homework answers / question archive / Energy Efficiency | BIOL 106 | 20 points OBJECTIVES Students who complete this exercise will • calculate and compare the costs of efficient and inefficient light bulbs • discuss the rewards and difficulties of energy efficiency   MATERIALS   • Worksheet of 3 light bulbs that have equivalent wattage outputs, one halogen, one compact fluorescent, and one LED with original packaging showing the price tags of each • 1 recent utility bill for the campus or for a nearby residence, showing the price per kilowatt hour charged by the local utility company • Calculator   INTRODUCTION   Residents of the United States have the highest per capita consumptive energy use in the world

Energy Efficiency | BIOL 106 | 20 points OBJECTIVES Students who complete this exercise will • calculate and compare the costs of efficient and inefficient light bulbs • discuss the rewards and difficulties of energy efficiency   MATERIALS   • Worksheet of 3 light bulbs that have equivalent wattage outputs, one halogen, one compact fluorescent, and one LED with original packaging showing the price tags of each • 1 recent utility bill for the campus or for a nearby residence, showing the price per kilowatt hour charged by the local utility company • Calculator   INTRODUCTION   Residents of the United States have the highest per capita consumptive energy use in the world

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Energy Efficiency | BIOL 106 | 20 points

OBJECTIVES

Students who complete this exercise will
• calculate and compare the costs of efficient and inefficient light bulbs
• discuss the rewards and difficulties of energy efficiency
 
MATERIALS
 
• Worksheet of 3 light bulbs that have equivalent wattage outputs, one halogen, one compact fluorescent, and one LED with original packaging showing the price tags of each
• 1 recent utility bill for the campus or for a nearby residence, showing the price per kilowatt hour charged by the local utility company
• Calculator
 
INTRODUCTION
 
Residents of the United States have the highest per capita consumptive energy use in the world. We use commercial energy primarily for transportation, heating and cooling, and for electricity. Our high energy use leads to many problems, including expensive utility bills, dependence on other nations, air pollution, and depletion of resources. We could ease all of these problems if we conserved more energy. One way to conserve energy is to change our behaviors. For example, we could drive less and instead walk more or take public transportation. We could turn off lights when we don't need them, and lower thermostats in the winter.
 
Another way to conserve energy is to use more efficient machines. Energy efficiency is the percentage of energy used in a machine that actually performs useful work. For the most part, our machines have low energy efficiency, and the vast majority of commercial energy that we buy is wasted. For instance, most of the energy in the gasoline we pump into a car does not actually move the car forward. Instead, most of it creates waste heat that has to be blown away by a fan to prevent the car from overheating.
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Why is most of the energy wasted? First, as the second law of thermodynamics states, when you convert energy from one form to another (for example, from the potential energy in gasoline to the kinetic energy of a car moving forward), some of the energy is always converted to heat. This is a physical law that we cannot overcome-machines can never be 100% efficient. Second, manufacturers usually don't make machines that are as efficient as technology allows, in order to reduce production costs.
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Environmental scientists measure two different types of costs. Initial cost is simply the purchase
price you pay for an item at the store. Life cycle cost is the initial cost plus the price of using and
maintaining that item for as long as you own it. For example, the life cycle cost of a car includes the sticker price plus the amount you spend on gasoline, oil changes, and other maintenance. Often, highly efficient machines have a higher initial cost, but a lower life cycle cost than comparable low efficiency machines.
  
When working through this lab, show your work for all problems. Show all units!

PART 1: COMPARING THE ENERGY EFFICIENCY OF LIGHT BULBS
 
Look at the “Light Bulb Prices” handout. This handout compares three commonly purchased bulbs today: halogen, compact fluorescent, and LED. Not too long ago, homes used incandescent bulbs but those are largely out of production. However, we still compare modern light bulbs to incandescent bulbs when talking about wattage (w). For example, today’s bulbs will say “100w equivalent” meaning their brightness is equivalent to that of a 100 watt incandescent bulb, though it uses less watts to do so.
 
1. What is the initial cost of each individual light bulb? (1.5 points)
 
• Halogen initial cost =
• Fluorescent initial cost =
• LED initial cost =
 
2. What is the actual wattage of each light bulb as indicated on the packaging? This is a measure of how much power it uses when lit (and therefore is also related to how much energy you need to light it). (0.75 points)
 
• Halogen actual wattage =
• Fluorescent actual wattage =
• LED actual wattage =
 
3. What is the wattage that these bulbs are equivalent to? For example, it may be a 10 watt bulb, but it may produce the amount of light that a typical 60 watt incandescent bulb produces. (0.75 points)
 
• Halogen wattage equivalent =
• Fluorescent wattage equivalent =
• LED wattage equivalent =
 
4. If you turn on one of the lights for 10 hours a day, every day of the year (365 days), for how many hours is it lit during a year? (0.5 points)
 
5. Although light bulbs are advertised in ‘watts’, they are actually measuring a ‘watt-hour’ (wh), which is the amount of electricity used in one hour. Power companies charge using ‘kilowatt-hours’ (kwh), which is 1000 watts, because it is an easier unit to work with. Using your value in #4, how many kwh will each of the different light bulbs use in one year? Hint: first determine how many watt-hours it uses in a year, then convert to kwh. (1.5 points)
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• Halogen:
 
• Fluorescent:
 
• LED:
 
6. Examine the “Electric bill” handout. How much does the local utility charge per kwh? Pay careful attention to the units in this question. (0.5 points)
 
7. How much will the electricity cost to run one light bulb in each category for 10 hours a day, every day, for one year? Hint: use questions 5 & 6. (1.5 points)
 
• Halogen:
 
• Fluorescent:
 
• LED:
 
8. How much will it cost to buy one brand-new light bulb and run it for the year as described previously? Hint: use questions 1 & 7. (1.5 points)
 
• Halogen:
 
• Fluorescent:
 
• LED:
 
9. Not only do we consider how much energy a light bulb is using, but also how long that light bulb will last. Let’s use a time period of 10 years. For how many hours will a light bulb be used if it was on for 10 hours a day, every day of the year, for 10 years? Hint: use question 4. (1 point)
 
10. According to the website where these bulbs are being sold, halogen light bulbs last about 1,000 hours, CFL light bulbs last about 10,000 hours, and LED light bulbs last about 11,000 hours. How many light bulbs would need to be purchased in order to power a single lamp for 10 years? How much would this cost? (1.5 points)
 
• Halogen:
 
• Fluorescent:
 
• LED:
 
11. How much will the electricity cost to run a lamp at 10 hours a day, every day, for 10 years? (Hint: use question #7). (1.5 points)
 
• Halogen:
 
• Fluorescent:
 
• LED:
 
12. Estimate how many light fixtures you have in your home. Assuming there are currently no bulbs in them, how much would it cost you in bulbs and electricity to maintain them for 10 years? Hint: use questions 10 & 11. (1.5 points)
 
• Halogen:
 
• Fluorescent:
 
• LED:
 
13. Based on all the calculations you have done, which light bulb would you recommend for homeowners to buy? Why? (2 points)
 
14. Is this recommendation in line with what you think consumers currently purchase? Why or why not? (2 points)
 
15. Describe two other benefits, outside of monetary value, that you (or society) get from using more energy-efficient light bulbs. (2 points)