HW3_Solutions

HW3_Solutions - DEPARTMENT OF CIVIL AND ENVIRONMENTAL...

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1 DEPARTMENT OF CIVIL AND ENVIRONMENTAL ENGINEERING UNIVERSITY OF CALIFORNIA, BERKELEY CE11 ENGINEERED SYSTEMS AND SUSTAINABILITY, SPRING 2009 H OMEWORK 3: NEP AND LCA DUE F RIDAY , F EBRUARY 18, 2009 (T OTAL : 100 POINTS ) ****SOLUTIONS**** Net Ecosystem Production (NEP) 1. Calculate the annual NEP of a tropical rain forest and desert scrub. Assume that the annual net primary productivity (NPP) of a tropical rain forest is 1.44 kg of C/m 2 , and that of desert scrub is 0.032 kg of C/m 2 . The amount of carbon stored in the tropical rain forest is 10.00 kg of C/m 2 and in the desert is 0.30 kg of C/m 2 . The mean annual temperature (MAT) in a tropical forest is 303 K and in the desert is 295 K. How many times more carbon is stored in a tropical rain forest versus in desert scrub? (20 points) Solution t C NPP NEP - = , where - - - - = 4 . 139 1 4 . 139 15 . 283 1 1921 exp 8 . 42 MAT t Rainforest Desert Givens Givens NPP RF 1.44 kgC/m 2 /yr NPP D 0.032 kgC/m 2 C RF 10.00 kgC/m 2 C D 0.30 kgC/m 2 MAT RF 303 K MAT D 295 K Calculations Calculations t RF 8.46 years t D 15.47 years C RF /t RF 1.18 kgC/m 2 /yr C D /t D 0.0194 kgC/m 2 /yr NEP RF 0.26 kgC/m 2 /yr NEP D 0.013 kgC/m 2 /yr How many times more carbon is absorbed (net) by the rain forest? NEP RF /NEP D = 0.26/0.030 = 20.4 times more C Sample Calculations: Rainforest years K t 46 . 8 4 . 139 ) 303 ( 1 4 . 139 15 . 283 1 1921 exp 8 . 42 = - - - - = 1 2 26 . 0 46 . 8 00 . 10 44 . 1 - - = - = yr kgCm NEP
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2 Life-Cycle Assessment (LCA) 2. Modified problem 7.9 from (Rubin 2001): Consider energy inputs and air pollution outputs from manufacturing paper and plastic (polyethylene) grocery bags. In what is thought as a fair comparison, the below table compares the inputs and outputs of 60,790 plastic bags and 30,395 paper bags (Graedel, 1998). Data are available from three studies. Material Allen and Bakshani, 1992 Graedel, 1998 Ciambrone, 1997 Plastic: for 60,790 sacks Energy (MJ): 42,000 42,000 36,000 Air pollution emissions (kg): 33 35 27 Paper: for 30,395 sacks Energy (MJ): 52,000 52,000 41,000 Air pollution emissions (kg): 89 90 22 (a) Why are different amounts of paper and plastic bags compared and not one plastic bag versus one paper bag? (3 points) The important parameter to compare is not the unit but the functional unit . And in the case of sacks, the functional unit is the transportation of goods from the supermarket to home, which in most of the cases uses twice more plastic sacks than paper sacks. (b)
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HW3_Solutions - DEPARTMENT OF CIVIL AND ENVIRONMENTAL...

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