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May 11, 2010 / or4green

Sustainable Lighting

Lighting is often considered “low-hanging fruit” from a sustainability standpoint. It is not difficult to change to a more energy efficient light bulb that can significantly lower electricity usage, which in turn reduces cost and emissions. There can be other trade-offs, a well-known one being that the more energy efficient CFL bulbs often contain mercury, a hazardous material, requiring more careful and costly disposal. These and other factors lead to a nice O.R. problem on lighting.

This past semester we ran a student project on re-designing lighting in a classroom space. The problem was to determine the optimal locations of bulbs as well as the kinds of bulbs to use in order to minimize costs (bulb purchase, bulb disposal, and electricity) while meeting standard illumination thresholds.

There are fairly sophisticated computer programs that will do this for you (see DIALux). But having students develop their own model makes sense because it is something they can realistically complete in one semester, and the process can be eye-opening for them. There is another reason related to the discussion here on life-cycle assessment software from a while back. That post described a demonstration in which two different programs were used to calculate the carbon footprint of a simple construction and each subsequently came up with estimates that differed by three orders of magnitude. The models used by these programs will have underlying assumptions, some made clear in the program or its documentation, others buried more deeply. So a good part of the exercise in developing such a program from scratch is to then compare its results with off-the-shelf software, as well as its assumptions. Lighting is simpler than life-cycle assessment, so the challenge of aligning models should be within reason.

To formulate the problem, the ceiling and desk level (where the illumination is to be measured) were broken up into grid cells (see figure). Each ceiling cell can contain at most one bulb from a list of several types. The contribution to the illumination at a given desk level location from a ceiling bulb is calculated using the formula illuminance at desk (measured in lux) = light intensity of bulb (measured in lumens) / distance^2. The overall illumination at the desk location is found by summing these contributions over all of the ceiling cells.

src: Cassel, Donato and Mozolic

The students found the current room to be significantly over-illuminated. Their solution came in just above the illumination threshold with a smaller number of bulbs spaced across the ceiling.

A (somewhat paraphrased) portion of the formulation follows.


x_{i,j,k} = 1 if bulb type i is in location j,k; 0 otherwise

l_i = light intensity (in lumens) of bulb type i

c_i = purchase cost of bulb type i

d_i = disposal cost of bulb type i

p_i = power usage (in watts) of bulb type i

s_i = # of life-spans of bulb type i over the given time frame

b_i = \sum_{j,k} x_{i,j,k} \; \; : total # of bulbs of type i in the design

r_{j,k,l,m} = distance from ceiling cell (j,k) to desk cell (l,m)

T = illumination threshold (in lux)


Minimize \sum_i c_i b_i s_i \; \; : bulb purchase cost

Minimize \sum_i d_i b_i s_i \; \; : bulb disposal cost

Minimize \sum_i p_i b_i \; \; : bulb power usage


\sum_{i,j,k} \frac{x_{i,j,k} l_i}{r_{j,k,l,m}^2} \ge T for each desk cell (l,m) (illumination constraint)

\sum_{i} x_{i,j,k} \le 1 for each ceiling cell (j,k) (at most one bulb per cell)

Note the objectives are left somewhat vague here. For instance the power objective can be converted to cost using the price of electricity ($0.16/kwh in this region), or to emissions (1.2 lbs of CO2 per kwh here). The three objectives can be combined in a multiple objective optimization with weights as desired by the decision maker, some can be turned into constraints, etc. Many other considerations could be added such as lighting fixtures used, windows, occupancy timers, room obstructions, light tubes, maintenance issues, light quality, etc.

Another aspect of this project was that it was run in conjunction with similar ones from the Civil Engineering and Management Departments. The civil group focused more on general sustainable design in the room including but not limited to lighting. The interaction ended up not being extensive but exchanges of information (e.g. CAD drawings of the room) and ideas took place throughout the semester. These projects provide a great opportunity for multidisciplinary collaboration. That includes not only the academic disciplines but also the real-world operational side of the institution as well.

The reference is Analyzing Light Optimization at the United States Coast Guard Academy: Minimizing Cost and Environmental Impact by T. Cassel, A. Donato, and R. Mozolic, USCGA Dept. of Mathematics Capstone Report, Spring 2010, Advisors: I. Frommer and M. Case.

April 19, 2010 / or4green

CompSust 2010 – call for papers

The 2nd International Conference on Computational Sustainability has been announced.
Location: Massachusetts Institute of Technology in Cambridge, MA, USA
Date: June, 28th-30th, 2010

Computational Sustainability has do with applying computational methods to sustainability, and this can have overlap with O.R. I attended the 1st CompSust Conference last summer and wrote about it here and here, and also posted a guest commentary by U Conn OPIM professor Bob Day.

While generally impressed with last year’s conference, we both found the representation of sustainability areas to be uneven. Bob wrote:

…there was a disproportionate representation of biological/ecological areas (roughly two-thirds of the conference), and a relative lack of representation from the energy-sector and industrial applications focused on sustainability.

So it was a good sign to see the call for papers lead off with “human built systems and human impact”. This is followed by “ecosystem monitoring and modeling”, “ecosystem management”, “pollution production”, and “economics and human behavior”. If the organizers can fill each area with quality talks like some of the better ones from CompSust 2009, it should be a great conference.

April 14, 2010 / or4green

Recent Stories

I.B.M. Suppliers Must Track Environmental Data, by Todd Woody, NY Times Green Inc., April 14, 2010. See also IBM’s Smarter Planet website including the blog post “Smarter Sustainability”.

Building a Green Economy, by Paul Krugman, NY Times magazine, April 5, 2010. Pretty in-depth piece with a great introduction to environmental economics.

A bit older, but also interesting is In China, Wal-Mart presses suppliers on labor, environmental standards, by Steven Mufson, Washington Post, February 28, 2010. This received some attention from the Operations Room blog.

March 28, 2010 / or4green


Not all new, but potentially some interesting material…

Hybrid or electric vehicles? A real options perspective
by Nishihara Michi in Operations Research Letters, In Press, Accepted Manuscript, Available online 26 November 2009. Free version is available here.

A strategic and tactical model for closed-loop supply chains

by Maria Isabel Gomes Salema, Ana Paula Barbosa Póvoa, and Augusto Q. Novais
in OR Spectrum, Volume 31, Number 3 / June, 2009
Includes a case study.

Toward some operational principles of sustainable development
by Herman E. Daly in Ecological Economics, Volume (Year): 2 (1990), Issue (Month): 1 (April) Pages: 1-6.
Highly cited paper.

Games with Exhaustible Resources
by R. Sircar, C. Harris & S. Howison, August 2009
Understanding exhausting oil using a game theoretic approach. Described in Jan/Feb 09 issue of SIAM News.

Sometimes the list of papers citing an interesting paper has some good finds. This Google Scholar page lists a number of papers having to do with computer power saving. They cite the paper Idleness is not sloth by R. Golding et al from a 1995 USENIX conference proceedings.

Lastly, a couple of journals with some relevant material are:
The International Journal of Sustainable Society. Interesting sounding recent paper: An eco-efficiency analysis of the snowboard manufacturing industry

Natural Resource Modeling. Current issue (Feb 2010) has a paper applying MCDM (multi-criteria decision making) to organic coffee production. The journal is associated with a Resource Modeling Association.

March 17, 2010 / or4green


Here is a listing of some relevant institutes and centers, several of which have been mentioned on this blog before, others not. All have a sustainability focus. The O.R. connection is not explicit for most, but O.R. can be an important element in the work of pretty much each one. There is a wealth of information to be found on the various web sites.

[Quotations below come from the respective web sites of the institutes unless otherwise noted. This post will be recycled as a “page” for easy access from any part of the blog, and updated over time. It is not a comprehensive list; contributions are welcome.]

Yale University’s Center for Industrial Ecology

…established in September 1998 to provide an organizational focus for research in industrial ecology … Faculty research interests include, among others, the theoretical basis of industrial ecology, the cycles of materials, technological change and the environment, eco-industrial urban development, industrial symbiosis, and product and producer policy issues.

– Industrial Ecology has been mentioned several times here, see the category archive.

Institute of Computational Sustainability at Cornell University
– their mission has to do with applying computer science to sustainability
– I attended their inaugural conference, which included several green O.R. talks, and wrote about it here.

Global Institute of Sustainability at Arizona State University
– “The Institute conducts research, education, and problem-solving related to sustainability, with a special focus on urban environments.”
– mentioned in the article “A Threat So Big, Academics Try Collaboration,” NY Times, 12/25/07.

New Building Institute
– “NBI assesses technologies, promotes design approaches, and helps guide policies and programs that will significantly improve the energy efficiency of commercial buildings.”
– study of theirs on LEED buildings came up in posts here and here.

Rocky Mountain Institute
– “Our mission is to drive the efficient and restorative use of resources.”
– works with private sector and government
– follows the principles of Natural Capitalism
– key figure is Amory Lovins
– mentioned briefly in this post

Environmental and Energy Study Institute (EESI)
– Established “to provide timely information and develop innovative policy solutions that set us on a cleaner, more secure and sustainable energy path”. This information is aimed at Members of Congress.
– came up in a post about RPS

Sustainable Development Research Network (SDRN)
– “SDRN aims to facilitate and strengthen the links between providers of research and policymakers across government, in order to improve evidence-based policymaking to deliver the UK government’s objectives for sustainable development” (thanks daniel s. for letting me know)

Precourt Energy Efficiency Center at Stanford University

The mission of the Precourt Center is to promote energy efficient technologies, systems, and practices, emphasizing economically attractive deployment. PEEC works to understand and overcome market, policy, technology, and human behavioral barriers to economically efficient reductions of energy use and to inform public and private policymaking…

– The PEEC holds a number of conferences, the next one will be in November.

Robert Mondavi Institute at UC-Davis
– From a piece in the Santa Barbara Independent in June 2009:

UC-Davis’ to-be-built Robert Mondavi Institute, a 31,000-square-foot headquarters for the school’s winemaking, brewing, and food science studies. With state-of-the-art in sustainability that includes LEED certification, green cleaning chemistry, stormwater catchment, and the goal of zero net water, the institute intends to dramatically reduce use of water in wine and beer making.

Center for Sustainable Systems at the University of Michigan
– “leader in Industrial Ecology research and education specializing in life cycle assessment of human-built systems that rely on natural resources to provide for society’s needs.”

The Sustainability Institute
– “applies systems thinking, system dynamics modeling, and organizational learning to economic, environmental and social challenges.”
– connected to climateinteractive and c-roads, described here

The Mascaro Center for Sustainable Innovation at the University of Pittsburgh
– “center of excellence in sustainable engineering focusing on the design of sustainable neighborhoods”
– engineering oriented but likely relevant here
– had a summer school in ’08

February 23, 2010 / or4green

Green Analytics

Sustainability. Analytics. Trendy buzzwords or here to stay? INFORMS has sought to become identified with analytics (see its online magazine by that name). And there has been INFORMS conference activity related to sustainability going back at least to 1998 (see this post). The latest activity is at the upcoming practice conference (mentioned here too) with interesting-sounding talks on green (or sustainable) analytics:

Keeping Ford Green with Analytics
Erica Klampfl, Ford

Smart Water: Improving Water System Performance through Asset Management
Arun Hampapur, IBM

Green Technology and Sustainability Applications: Trends, Challenges and Opportunities
Bryan Guy, Cypress Venture Group

Real-Time Dispatching of Distributed Resources in the Smart Grid
Michael T. Ozog, Integral Analytics, Inc.

Smart Grid: Operation of Utility Distribution Systems
Avnaesh Jayantilal, AREVA T&D

Analytics Applications Opportunities in Sustainability
Dwight Collins (see this post) & Dariush Rafinejad, Presidio Graduate School

February 15, 2010 / or4green

Environmentally Conscious Manufacturing Survey and Book

An earlier post mentioned Dr. Surendra M. Gupta from Northeastern University and his group’s work on “Environmentally Conscious Manufacturing” (ECM), much of it utilizing O.R. methods. ECM is essentially about sustainable manufacturing from design to production to delivery through to end-of-life. Gupta and Mehmet Ali Ilgin have a new survey on ECM in the Journal of Environmental Management. This is a follow-up to a 1999 survey by Gungor and Gupta mentioned here, a paper with 350+ citations (as of Jan 2010). The new work surveys 540(!) references dividing them into four categories: environmentally conscious product design, reverse and closed-loop supply chains, remanufacturing, and disassembly. While many working in sustainability have to come to the field only recently, Gupta and his group have been involved for many years, as the 1999 survey suggests.

Skimming the survey, the design-for-recycling papers sounded interesting, some of which use the analytic hierarchy process (AHP) and neural nets, and many of which come from materials-related journals. Mixed integer programming (both linear (MILP) and nonlinear (MINLP)) was a common technique among the reverse logistics and closed loop supply chain papers. Section 3.1.1 (p567) lists a large number of applications in these areas such as construction waste, carpeting, copier machines, computers, home appliances, hazardous waste, and spent batteries (I wrote about this here). Some of the models combine genetic algorithms, tabu search, simulated annealing and other heuristics with MILP’s or MINLP’s. Dozens of papers are cited in this section.

The wide array of applications represented across the numerous papers suggests many of them require custom models. One would hope that down the road, some commonalities could be found (or designed into existence), so that, for example, the reverse logistics for a spent battery would not be all that different from those of worn carpeting. And extensive surveys like this one can be very helpful in this process. In a way, the actual practice of single-stream recycling has started on this path. But reverse logistics for products can be far more complicated. For one, the products may not yet be waste; they may just be in need of refurbishing or similar. Related to this, they do not all share a common reverse network the way waste often does. But perhaps that will change over time if some of the notions of technological and biological nutrient cycles become more wide-spread.

Getting back to the survey, Sec 3.3 (p569) about transportation in reverse logistics cites numerous papers that utilize the vehicle routing problem. And additional OR methods (such as MCDM) appear in later sections on product end-of-life (EOL) strategy; production planning/scheduling in remanufacturing, and more. The citation is as follows (click on the title to access the paper):

Ilgin, M. A. and Gupta, S. M., Environmentally Conscious Manufacturing and Product Recovery (ECMPRO): A Review of the State of the Art, Journal of Environmental Management, Vol. 91, No. 3, 563-591, 2010.

Dr. Gupta has also recently co-authored a book proposing the application of numerous OR techniques to the strategic planning of reverse and closed-loop supply chains:

Pochampally, K. K., Nukala, S. and Gupta, S. M., Strategic Planning Models for Reverse and Closed-loop Supply Chains, CRC Press, Boca Raton, Florida, ISBN: 9781420054781, 2009.

More information about the book is available at the CRC Press web site here, or through Amazon here (includes a fuller view of the table of contents.)

February 10, 2010 / or4green

More Conference Activity and a Summer School

1. EURO XXIV, Lisbon 11-14 July 2010. The big European OR conference has had a good amount of green O.R. for several years and this year is no different. One of the streams is “optimisation for sustainable development” offered by a group of that name from Ecole Polytechnique. They aim to develop stochastic multi-objective optimization techniques for dealing with problems in sustainable development. Appears to be somewhat new but could be very relevant.

2. INFORMS 2010 Optimization Society Conference: Energy, Sustainability and Climate Change – hosted by the Center for Applied Optimization and the Industrial and Systems Engineering Department of the University of Florida, Gainesville, Florida on 26-28 February 2010. I mentioned this a while back but now the program (pdf) is up along with additional conference details.

3. Summer Graduate School on Mathematics of Climate Change, National Center for Atmospheric Research (NCAR) in Boulder, Colorado, 12 – 23 July 2010. Sounds interesting, for graduate students, co-sponsored by MSRI.

January 26, 2010 / or4green

WSC 2009 Papers Available

It looks like the recent 2009 Winter Simulation Conference had a nice collection of sustainability related talks in the ” Energy And Material Applications Stream”. The session titles were:

  • Energy and Material Flow Business Processes
  • Energy Capacity and Logistics Planning
  • Monte-Carlo-Based Energy Simulations
  • Electric Power Generation and Distribution

Some topics covered were:

  • biofuels
  • emission reduction technologies
  • wind, solar and geothermal power
  • energy efficiency
  • the smart grid
  • hydrogen fuel

Warren Powell and Thomas Spengler, both mentioned elsewhere on this site, were among the authors.

The program with links to the papers is available here.

January 10, 2010 / or4green

Odds and Ends: CO2 data, OM blog, Nanotech.

NASA has made an extensive CO2 data set available. The data comes from the Atmospheric Infrared Sounder (AIRS), an instrument that travels on the Aqua spacecraft. More information is available from NASA here.

There are some sustainbility-related posts from the Operations Management side of the house on a blog called “The Operations Room”. It is written by Kellogg School (Northwestern U.) professors Martin Lariviere and Gad Alon. Check out their green ops and sustainability tags. Don’t miss the “pizza box” post with the Walmart video about closing the cardboard loop. And another post mentions SourceMap, an open source web site from the MIT Media Lab that allows one to document where materials in a product come from and the associated carbon footprint.

Back in July, I wrote about nanotech and OR ethics. Around that time, the OECD Conference on Potential Environmental Benefits of Nanotechnology was being held. (OECD is the Organization for Economic Co-operation and Development, more about them here.) The slides from the conference presentations are posted here. There are a number of interesting-sounding ones, such as:
– Are we willing to heed the lessons of the past? – Using the precautionary principle to foster safe, innovation-led growth (Steve Mullins (ACTU, Australia)
– Understanding the life-cycle environmental implications of nanotechnology in lithium-ion batteries for automobiles (Thomas Seager, Rochester Institute of Technology, United States)
– Sustainability and recycling issues (Amin Reller, University of Augsburg, Germany)
The content may not be explicitly O.R., but there is plenty of quantitative analysis coupled with decision making.