Exercises

E.7.1. If the embodied energies and CO2 used in the Alpure water case study in the chapter are uncertain by a factor of ±25%, do the conclusions change? Mark ±25% margins onto each bar in a copy of Figure 7.3 (you are free to copy it) and then state your case.

E.7.2. Alpure water has proved to be popular. The importers now want to move up-market. To do so they plan to market their water in 1 liter glass bottles of appealing design instead of the rather ordinary PET bottles with which we are familiar from the case study in the chapter. A single 1-liter glass bottle weighs 430 grams, much more than the 40 grams of those made of PET. Critics argue that this marketing-strategy is irresponsible because of the increased weight. The importers respond that glass has lower embodied energy than PET.

Use the methods of this chapter and the data available in Chapter 12 to analyze this situation. What do you conclude?

E.7.3. If the glass container of the coffeemaker of Section 7.4 is replaced by a double-walled stainless steel one weighing twice as much, how much does the total embodied energy of the product change? If this reduces the electric power consumed over the product life by 10%, is the energy balance favorable?

E.7.4. The figure shows a 1700 W steam iron. It weighs 1.3 kg, 98% of which is accounted for by the seven components listed in the table. The iron heats up on full power in 4 minutes and is then used, typi­cally, for 20 minutes on half power. At end of life the iron is dumped as landfill. Create an eco-audit for the iron, assuming that it is used once per week over a life of five years, using data from the data sheets of Chapter 12.

What conclusions can you draw? How might the energy be reduced?

E.7.5. The picture shows a 970 W toaster. It weighs 1.2 kg including 0.75 m of cable and plug. It takes 2 minutes, 15 seconds, to toast a pair of slices. It is used to toast, on average, eight slices per day, so it draws its full electrical power for 9 minutes (540 seconds) per day over its design life of three years. The toast­ers are made locally; transport energy and CO2 are negligible. At end of life it is dumped. Create an eco-audit for the toaster using data from the data sheets of Chapter 12.

Toaster: bill of materials

Component

Material

Shaping Process

Mass (kg)

Body

Polypropylene

Molded

0.24

Heating element

Nichrome

Drawn

0.03

Inner frame

Low carbon steel

Rolled

0.93

Cable sheath, 0.75 meter

Polyurethane

Molded

0.045

Cable core, 0.75 meter

Copper

Drawn

0.011

Plug body

Phenolic

Molded

0.037

Plug pins

Brass

Rolled

0.03

E.7.6. It is proposed to replace the steel bumper of Case Study 7.6 by one made of CFRP. It is anticipated that the CFRP will weigh 7 kg. Following the procedure of the text, drawing data from the data sheets of Chapter 12, estimate whether, over the life pattern used in the text, there is a net energy saving.

E.7.7. The production of a small car (mass 1000 kg) requires materi­als with a total embodied energy of 70 GJ, and a further 15 GJ for the manufacturing phase. The car is manufactured in Germany and deliv­ered to the U. S. showroom by sea freight (distance 10,000 km) followed by delivery by heavy truck over a further 250 km (Table 6.7 of the text both). The car has a useful life of 10 years and will be driven, on average, 25,000 km per year, consuming 2 MJ/km. Assume that recycling at end of life recovers 25 GJ per vehicle.

Make an energy-audit bar chart for the car with bars for material, manufacture, distribution, and use. Which phase of life consumes most energy? The inherent uncertainty of current data for embodied and processing energies is considerable; if both were in error by a factor of 2 either way, can you still draw firm conclusions from the data? If so, what steps would do most to reduce life-energy requirements?

E.7.8. The following table lists one European automaker’s summary of the material content of a midsized family car. Material proxies for the vague material descriptions are given in brackets and italicized. The vehicle is gasoline-powered and weighs 1800 kg. The data sheets of Chapter 12 provide the embodied energies of the materials; mean values are listed in the table. Table 6.7 gives the energy of use: 2.1 MJ/tonne. km, equating to 3.8 MJ/km for a car of this weight. Use this informa­tion to allow a rough comparison of embodied and use energies of the car, assuming it is driven 25,000 km per year for 10 years.

Material content of a family car, total weight 1800 kg

Material Mass (kg) Material energy, MJ/kg*

Steel (low alloy steel) 950 32

Aluminum (cast aluminum alloy)

E.7.9. Carry out an energy eco-audit for a product of your choosing. Pick something simple (a polypropylene washing-up bowl, for example) or, more ambitiously, something more complex. Dismantle it, weigh the parts, and use your best judgment to decide what they are made of and how they were shaped.

a CO2 eco-audit for the patio heater shown here. It is Southeast Asia and shipped 8,000 km to the United sold and used. It weighs 24 kg, of which 17 kg is rolled stainless steel, 6 kg is rolled carbon steel, 0.6 kg is cast brass, and 0.4 kg is unidentified injection-molded plastic (so use a proxy of your own choosing for this). In use it delivers 14 kW of heat ("enough to keep eight people warm"), consuming 0.9 kg of propane gas (LPG) per hour, releasing 0.059 kg of CO2/MJ. The heater is used for 3 hours per day for 30 days per year, over five years, by which time the owner tires of it and takes it to the recycling depot (only 6 miles/ 10 km away, so neglect the transport CO2), where the stainless steel is dismembered, and the steel and brass are sent for recycling.

Use data from the text and data sheets to construct