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University of Michigan - Ann Arbor
Civil And Environmental Engineering
CEE 265
Phillip Savage

CEE 265 November 14, 2013 LIFE CYCLE IMPACT ANALYSIS Recap: paper vs. plastic example of LCA  Calculated the energy input for a years worth of each type of bag o We found that the paper bags have higher energy intensity per functional unit o Then we drew a mass flow diagram and added recycling into the process  Recycling evaluations o For any recycled fractions you can see the air emissions per functional unit o You can draw conclusions based on the graph o If you recycle the same amounts, the plastic bags are the winner Interpretation step of the LCA  Was our analysis comprehensive? o We didn’t look at water footprint o We didn’t look at material depletion (renewable vs. non) o No global warming potential  Plastic bags are not favored worldwide o In some parts of the world there are taxes on plastic bags o Some parts of African they actually have a ban  We should think a little more about the economic and social factors o In terms of aesthetics, plastic wastes are harder to look at o Paper waste is biodegradable o Might sway which type of bag is favored  Life cycle cost: upstream and downstream o Visible costs includes costs that the retailer might pass on to the consumer o Invisible costs include things like how bags indirectly affect waste disposal costs  Returned bags on shopping costs  Collection and disposal of bags directly on city costs o Example. San Francisco  Charge $0.17 per grocery bag you use  Department of the environment came up with the amount to charge  Gives economic insensitive to use the cheaper bags In-Class Problem 20.2: buying a new refrigerator  Must evaluate from an environmental perspective and from a cost perspective o Buy a reused refrigerator  818 kWH/year electricity used  You use it for 10 years o Buy a second reused refrigerator  $200 spent  Use for 7 years o Need to think about discounting because this is now 17 years in the future o Also need to think about allocation  Acquiring two reused refrigerators that were used by other people  Each refrigerator had material energy used to build it  Determine how much of that assembly impact needs to be allocated o Or you can buy a brand new refrigerator  $500 spent  248 kWh/year electricity used  Used for 17 years o Either scenario, whatever the end-of-life impacts are we are responsible o So is reusing refrigerators more cost effective or is buying a new one?  Life cycle cost  Life cycle energy consumption  Life cycle greenhouse gases  Calculations for the life cycle cost: o New refrigerator (248 kWh/year)*($0.10/kWh) = $24.80/year on energy  Cash flow diagram of all 17 years  At year 0, you have the $500 purchase price  So the net present value (total cost of buying and using the fridge) has to take into account the effect of discounting  Total cost will not be ($24.80*17) + $500
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