Examine the LCA presented in Exhibit 6 of the case in the context of the EPA definition. Critique the analysis based on the following questions:

How does the assumption that the shipping distance is the same for each process affect the application of the LCA to Mark Jacobson's situation?

How might a change in another assumption alter the results?

How might the prioritization of other criteria (besides global warming potential) alter the assessment of the two processes?

Exhibit 6 Life Cycle Assessment of BONE Structure Class Project, School of Engineering, Stanford University Goal and Scope of Analysis The purpose of this analysis is to assess the life cycle impacts of a BONE Structure wall relative to a timber wall built to California's Title 24 Energy Code. Specically, a California Title 24 timber wall system provides an Rvalue of 13 and 3.0 air changes per hour at a pressure of SOPa.29 In contrast, the BONE Structure wall system provides an R-value of 28.5 and 0.8 air changes per hour at a pressure of 50Pa. The functional unit for this study is a wall unit of 25 feet by 10 feet (7.62 meters by 3.05 meters) with 15 percent of window space over 100 years. The boundaries of the analysis include fabrication and transportation of building materials, construction (including construction waste), and use. The lifetime of a BONE structure is assumed to be 100 years whereas lifetime of a conventional timber structure is 50 years, and the analysis accounts for impacts associated with replacement of the timber wall after 50 years. The analysis does not account for carbon sequestered during timber growth. End-of-life management and waste streams are not included because of associated high levels of uncertainty. Maintenance, renovation, and repair are not included. Assumptions and Liz Cycle Inventory Analysis We have assumed that transportation distances for the components of the Bone Structure system are the same as for the timber system, 250 km. Furthermore, the transport is by commercial truck, which produces 0.00435 kg C02 per kg cargo per km travel. Construction waste is zero for the BONE Structure system. A waste factor of 15 percent in cutting wood on the construction site is applied for the timber wall system, based on the industry average in conventional timber construction. All in-wall MEP (mechanical, electrical, plumbing) systems are assumed equal. All window assemblies are assumed identical. All exterior siding on both units is assumed equal. Thus, only structural elements and insulation materials differentiate the two walls. The BONE Structure wall section is comprised of steel structural elements, plywood window framing, polystyrene insulation panels, and a polyurethane insulation spray. The component quantities and fabrication processes are summarized in Table 1. BONE Structure OIT-113 p. 16 Table 1: BONE Structure System Component Quantities and Fabrication Processes Assembly Materials/Processes Amount Plywood, US PNW 23.377 kg Window Framing Power Sawing 10 min Polystyrene Foam Slab 46.6 kg Insulation Polyurethane Flexible Foam 100.4 kg Power Sawing 1 hr Galvanized Steel Sheet 460.86 kg Zinc Coat 197 sq. ft. Galvanized Steel Laser Machining 1 hr Metal Working 460.86 kg The timber wall section is comprised of Douglas Fir lumber, unfaced glass wool insulation, and an exterior plywood sheathing barrier. The component quantities and fabrication processes are summarized in Table 2. Table 2: Timber Wall System Component Quantities and Fabrication Processes Assembly Materials/Processes Amount 124 kg Timber Framing Douglas Fir Wood Power Sawing 1 hour Insulation Unfaced Glass Wool Insulation 21.6 kg Russian Birch Plywood 98 kg Sheathing Power Sawing 45 minutes Life Cycle Impact Assessment A comparison of life cycle environmental impacts, including global warming potential, acidification potential, eutrophication potential, and carcinogens is provided in Table 3. The life cycle global warming potential impact flow networks for the BONE Structure wall system and timber wall system are shown in Table 4 and Table 5, respectively. The life cycle global warming potential comparison is broken down further in Table 6.p. 17 BONE Structure OIT-113 Table 3: Life Cycle Environmental Impact Metrics for BONE Structure and Timber Wall Systems BONE Structure Wall System Conventional Timber Wall System 40,800 7,600 3.55 4.76 62.1 39.9 344 615 Global Warming Acidification Carcinogens Eutrophication Potential (kg Potential (kg (mg BaP) Potential CO,cq) SO,cq) (kg PO2 eq)BONE Structure OIT-113 p. 18 Table 4: Life Cycle Global Warming Potential Impact Flow Network for BONE Structure Wall System (with a 0.5% cutoff; only boxes with 2 0.5% of the total CO2-eq are displayed) 1p Bone Wall Functional Unit 7.5983 kg COZ 1p Galvaized steel 1p 1p Insulation Panel 1p Energy Use - Air Energy Use - Gas Conditioning 100 yr Heating 100yr 2. 9E3 kg CO2 663 kg CO2 1.7163 kg CO2 2.28E3 kg CO2 461 kg 531 p 18.3 m2 Galvanized steel 1461 kg Transportation Zinc coat, colls 146.6 kg | |I 100 kg 1. 158 4 MJ Metal working, 3.4584 MJ Polystyrene foam sheet, at Aggregate (GLO) | market for Polyurethane Electricity, at Grid, plant/RNA average for ste Heat, from reside (Typical for | slab {GLOy| | flexible foam E | Aloc Def, 5 WECC, 2008/RNA heating systems product market for | Allo U 1.2183 kg CO2 588 kg CO2 100 kg CO2 from NG, 934 kg CO2 168 kg CO2 428 kg CO2 1.7183 kg CO2 2.2883 kg CO2 Transport, freight 3.6983 MJ 3.5783 MJ light commercia Electricity, natural Electricity, |vehicle {GLO) gas, at power Bituminous coal, a plant/Us 686 kg CO2 power plant/US 689 kg Coz .03E3 kg CO2 323 m3 438 kg Natural gas, Bituminous coal, at processed, at mine/Us plant/US 182.4 kg CO2 46.6 kg CO2 333 m3 Natural gas, at extraction site/US 58 kg COZBONE Structure OIT-113 p. 19 Table 5: Life Cycle Global Warming Potential Impact Flow Network for Timber Wall System (with a 0.5% cutoff; only boxes with 2 0.5% of the total CO2-eq are displayed) 1 p Timber Wall - 2xFull Assembly + Energy 4_08E4 kg CO2 2p 2p 1 p 1 p Treated Plywood Wood Framing - Energy Use - Air Energy Use - Gas Sheathing Ind. Transport Conditioning 100yr Heating 100yr 346 kg CO2 317 kg CO2 3.9183 kg CO2 3.6E4 kg CO2 423 p 2.63E4 MJ 5.46E5 MJ Transport Aggregate Electricity, at Grid, Heat, from reside WECC, 2008/RNA U heating systems from NG, 548 kg CO2 3.9183 kg CO2 3.6E4 kg CO2 122 them1 1 8.4983 MJ 8.23E3 MJ Transport, freight, Electricity, natural Electricity, light commercial gas, at power bituminous coal, at vehide {GLO} plant/US power plant/US 530 kg CO2 1.58E3 kg CO2 2.3863 kg CO2