CORRESPONDENCE/REBUTTAL pubs.acs.org/est
Reply to Comment on “Remanufacturing and Energy Savings”
P
rof. Lund criticizes our article on three main points: (1) some of the products we analyzed are not remanufactured, (2) for some products there is no alternative to remanufacturing, and (3) some of the data we cited may be biased. These are generally points that have already been discussed in our paper with further details in the Supporting Information (SI). Perhaps we can clarify a possible misinterpretation of our study. This work did not set out to evaluate the remanufacturing industry. Nor did it claim that all of the products analyzed were remanufactured. For example, the analyses on clothing and computer equipment are clearly labeled as reuse. The original intent of this study was to evaluate the energy implications of remanufacturing as an end-of-life treatment that extends the useful life of a product. In doing so, we recognized that the analysis could be extended to other end-of-life scenarios such as refurbishment and reuse. This is clearly discussed in the paper. Even so, remanufacturing dominates our product categories (5 out of 8). The question then, would be, does this consideration of a range of end-of-life scenarios change the results of the analysis. If the results are categorized as (saves energy/too close to call/does not save energy), we obtained (8/11/6) for all eight product categories (25 case studies) as given in the paper. On the other hand, if only the five remanufacturing categories per Lund are included (14 case studies), the result is (2/11/1). The pattern appears the same; some save, some do not, and many are very close. There would be no change in our conclusion. In the paper we regarded a difference of (7% (or less) of the total life cycle energy as “too close to call.” If this constraint is removed, then one would get (12 save/13 do not save energy) for all eight categories, and (6 save/8 do not save energy) for the five remanufacturing categories per Lund. For these products there appears to be a good reason to question the common assumption that remanufacturing saves energy. Lund’s second point is that for some cases there is no new component available, so remanufacturing is the only option. We certainly understand this point, but if there is no alternative, then there does not seem to be any energy comparison to be made. It would be hard to claim an energy benefit or an energy penalty. On the other hand, one can always purchase a new product as an alternative to extending the life of the old product by remanufacturing. This kind of scenario will eventually occur in the life of a product, and does allow for an energy comparison. For each product we looked at a range of possible energy comparisons, several are in Table 1, most are in the SI. We were careful not to inappropriately place mismatched components in products. Lund’s third point suggests he may have misread our paper. In the paper we do discuss claims of performance degradation for remanufactured tires and refilled cartridges in detail, and we provide estimates of the potential energy increases if these claims were true. But we do not use these performance degradation claims in our analysis results given in Table 1, Figures 2 and 3, and the conclusions. We do use the performance degradation claims for rewound electric motors as suggested by the DOE:1 a 0.5% use phase energy increase for 22 kW rewound electric motors and a r 2011 American Chemical Society
1.0% use phase energy increase for 220 kW rewound electric motors. In summary, the current default view of remanufacturing is that it always saves energy. This is generally based upon an analysis that only considers the early stages of the life cycle. For products with no use phase or no change in energy efficiency over time, this view may be fine and we would generally agree that remanufacturing saves energy. But for products with a use phase, a claim of energy savings could not be made without comparing the use phases for the two alternatives. For the products we analyzed, the energy requirement from the use phase usually dominates the total life cycle energy requirements, and vastly exceeds any projected savings from remanufacturing or reuse. We lay out the conditions under which one can expect a savings or not. The results show examples of both, sometimes for the same product under slightly different scenarios. The paper also points out that remanufacturing can have other advantages to society that lay beyond the consideration of energy only. Timothy G. Gutowski,*,† Sahil Sahni,‡ Avid Boustani,† and Stephen C. Graves†,§ †
‡
Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
§
Sloan School of Management, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
’ AUTHOR INFORMATION Corresponding Author
*Phone: (617) 253-2034; fax: (617) 253-1556; e-mail: gutowski@ mit.edu.
’ REFERENCES (1) U. S. Department of Energy, Energy Efficiency and Renewable Energy, Industrial Technologies Program, Best Practices: MotorMaster+ Version 4, http://www1.eere.energy.gov/industry/bestpractices/software_ motormaster.html (accessed November 5 2009)
Published: July 22, 2011 7604
dx.doi.org/10.1021/es202450w | Environ. Sci. Technol. 2011, 45, 7604–7604
