How Green is That Product? An Introduction to Life Cycle Environmental Assessment

Homework #1

Goal: In this assignment, you’ll do the following:

practice working with the International System of Units (SI), which we’ll use extensively in this

course;

assemble flow data into the basic unit process inventory format that we’ll use in our plastic bag

and bottled soda LCA models; and

read and interpret a life-cycle energy analysis of bottled water to better understand the life-

cycle systems perspective.

Instructions: All questions below should be solved offline. Enter your answers to each question in the

answer boxes that have been provided, and be sure to follow any guidance for the required format(s) of

each answer. When you complete the assignment, return to the course page on the Coursera website.

Click on the “Homework Assignment” button. Then, click on the link to “Homework #1,” which will

allow you to enter your answers from each answer box below into a web form for automated grading.

Grading: This assignment is worth 100 points. The point values of each answer are listed below.

Numerical answers whose values are within +/- 5% of the correct values will be marked as correct.

Question 1: Working with SI units (8 points for each correct answer)

Tables 1a through 1d contain data on quantities of energy, mass, volume, and length, respectively, in

different US customary and SI units. In each table, convert the quantities in the first column into the SI

units specified in the second column. Next, compute the sum of all quantities in the second column.

Finally, enter the sum into the answer box in each table (note: answer boxes are shaded in gray). Use

the conversion factors provided below to perform all conversions.

Conversions of common units

Mass Energy 1 pound = 454 grams 1 British thermal unit = 1,055 joules 1 pound = 16 ounces 1 therm = 100,000 British thermal units 1 short ton = 2,000 pounds 1 kilowatt-hour = 3,600,000 joules 1 kg = 1,000 grams = 1,000,000 milligrams 1 gigajoule = 1,000 megajoules 1 megajoule = 1,000,000 joules Volume Length 1 liter = 1,000 milliliters 1 yard = 3 feet 1 pint = 16 fluid ounces 1 foot = 0.3 meters 1 gallon = 4 quarts = 8 pints 1 meter = 100 centimeters 1 fluid ounce = 0.03 liters 1 foot = 12 inches

Table 1a: Energy unit conversions

Original quantity Enter equivalent quantity in joules (J)

18.5 British thermal units (Btu)

0.05 therms

0.2 megajoules (MJ)

45 kilowatt-hours (kWh)

0.008 gigajoules (GJ)

Answer 1a (total joules)

Table 1b: Mass unit conversions

Original quantity Enter equivalent quantity in grams (g)

5 ounces (oz)

1.25 pounds (lb)

0.55 kilograms (kg)

0.02 short tons

88,500 milligrams (mg)

Answer 1b (total grams)

Table 1c: Volume unit conversions

Original quantity Enter equivalent quantity in liters (l)

1,450 milliliters (ml)

13 pints

2.5 quarts

10 gallons (gal)

155 fluid ounces (fl oz)

Answer 1c (total liters)

Table 1d: Length unit conversions

Original quantity Enter equivalent quantity in meters (m)

550 inches (in)

7 yards

16 feet (ft)

140 centimeters (cm)

Answer 1d (total meters)

Question 2: Constructing a simple unit process inventory (2 points for each correct answer)

Table 2a contains flow data for the unit process inventory associated with producing 1 kilogram (kg) of

widgets (a fictitious product). The flow data in Table 2a appear in random order. Your job is to organize

these flow data into the structured unit process inventory format we’ve discussed in the lectures this

week. You’ll do so by entering all flow data in Table 2a into the appropriate rows in Table 2b.

Additionally, in each section of Table 2b, list your flow names in alphabetical order. The shaded answer

box in each row of Table 2b should contain the value of the flow listed in that row. One example answer

has been provided.

Table 2a: Unit process inventory for producing 1 kg of widgets

Flow name Category Subcategory Value Units

Widgets Product 1,000 g

Carbon dioxide Air/elementary Low population 400 g

Water Resource/elementary 5 l

Natural gas Product 75 MJ

Methane Air/elementary Low population 15 g

Electricity Product 4 kWh

Sulfur dioxide Air/elementary Low population 68 g

Particulate matter Air/elementary Low population 2 g

Diesel fuel Product 15 MJ

Solid waste Soil/elementary 100 g

Chlorine Water/elementary Surface 3 g

Dissolved solids Water/elementary Surface 50 g

Coal Product 12 MJ

Nylon resin Product 1,100 g

Table 2b: Structured unit process inventory for producing 1 kg of widgets Answer number Inputs from

nature Flow name Category Subcategory Value Units

2b.1

Inputs from the technosphere

Flow name Category Subcategory Value Units

2b.2

2b.3

2b.4

2b.5

2b.6

Outputs to nature

Flow name Category Subcategory Value Units

Carbon dioxide Air/elementary Low population 400 g 2b.7

2b.8

2b.9

2b.10

2b.11

2b.12

2b.13

Outputs to the technosphere

Flow name Category Subcategory Value Units

2b.14

Question 3: Interpreting published life-cycle data (8 points for each correct answer)

To answer these questions, you’ll need to first download and read the following open-access journal

article by clicking on the link:

Gleick, P.H., and H.S. Cooley (2009). “Energy implications of bottled water.” Environmental

Research Letters, Volume 4, Issue 1. http://iopscience.iop.org/1748-9326/4/1/014009/

Question 3a: Which statement below is CORRECT?

1. This study considers all life-cycle stages and environmental impacts associated with bottled

water

2. This study considers all life-cycle stages but only one environmental impact (energy use)

associated with bottled water

3. This study considers some, but not all, life-cycle stages and all environmental impacts associated

with bottled water

4. This study considers some, but not all, life-cycle stages and only one environmental impact

(energy use) associated with bottled water

Answer 3a (enter the number of the correct answer here):

Question 3b: In the answer box below, enter the total manufacturing energy required to make PET and

form it into a typical 1 liter PET bottle weighing 38 grams.

Answer 3b (use units of MJ)

Question 3c: Which statement below BEST DESCRIBES the total transportation energy requirement for

bottled water?

1. The total transportation energy requirement depends mostly on the mode of transportation

2. The total transportation energy requirement depends on both the distance from the bottling

plant to the market and the mode of transportation

3. The total transportation energy requirement depends mostly on the distance from the bottling

plant to the market

4. The total transportation energy requirement is negligible

Answer 3c (enter the number of the correct answer here):

Question 3d: Select the TWO life cycle processes that contribute most to the energy implications of

bottled water. Enter both numbers in the answer box below using a space between the two numbers;

do not use a comma (for example: X Y). (Note that online, you’ll simply select two checkboxes!)

1. Manufacture of the PET plastic bottle

2. Treatment at bottling plant

3. Fill, label, and seal bottle

4. Transportation

5. Cooling

Answer 3d (enter two numbers separated by a space):

Question 3e: Which statement below BEST SUMMARIZES the authors’ conclusions about the energy

requirements of bottled water?

1. Producing bottled water requires 1,120 to 2,040 times the energy required for producing tap

water

2. Producing bottled water requires 2,000 times the energy required for producing tap water

3. Producing bottled water requires more energy than producing tap water

4. Producing bottled water requires a lot of energy

Answer 3e (enter the number of the correct answer here):