Tuesday, August 25, 2009

Dimensions and Metrics of Green Manufacturing

We will discuss this topic in two sections - first, dimensions and then metrics. They are linked, as we will see, but best described sequentially.

The dimensions of design, manufacturing and environment can be represented as follows (and see the figure.) Think of three axes defining a volume (a cube, one axis along each principle face.) Along one axis (x) we express manufacturing throughput (quality, yield, production rate, lead time, flexibility, "lean-ness, etc.), from low to high; Along the second axis (say the y axis) we show design related attributes (functionality, complexity, life, maintainability); and the third axis (say z) represents environmental impacts (including energy, consumables, waste, hazards, end of life, etc.) from low to high. In this volume space we can plot "cost" as a function of these three axes (meaning ... the particulars of the elements of each axis will drive the cost up or down, or, in some cases, have no effect.) Our challenge is to find the "sweet spot" in this domain where we maximize production (and all its features - specially quality), minimize environmental impact, and optimize design - all at the same time. This is not easy but is our goal.

We measure our success or failure in this space using measures of performance - for example amount of waste, materials used and resources consumed (recall the Interface Carpet example?), energy consumed in production (primary and secondary) often expressed as specific energy or energy per unit of volume/mass or product, and the production rate (inverse of production time per piece, feature, etc.). Increasing process yield is a green option of course but, as we discussed some blogs ago, is usually done in the normal course of continuous improvement. But, if motivated by reduction in use of some resource, certainly supports green manufacturing.

My friend from Cambridge University in the UK, Professor Julian Allwood, outlines five options for sustainable manufacturing which I have adapted towards "greening manufacturing":

  • Use less material and energy
  • Substitute input materials: non-toxic for toxic, renewable for non-renewable
  • Reduce unwanted outputs: cleaner production, industrial symbiosis
  • Convert outputs to inputs: recycling and all its variants
  • Changed structures of ownership and production: product service systems and supply chain structure

(see http://www.ifm.eng.cam.ac.uk/sustainability/seminar/documents/050216lo.pdf)

These are solid elements that, if pursued, can lead to a greener process, system, facility, enterprise. But, the question arises - how much "less material"? or "less energy". Or, how much substitution is needed? How much do I need to change my distribution or supply chain? Basically, how do I know how much is enough to really make a positive change?

To answer these questions we need metrics.

I define a metric as a type of "measurement used to gauge some quantifiable component" of performance, such as a return on investment (ROI) for a company's revenues, etc. These metrics are used by engineers and designers for accumulating and analyzing information and data to enable better decision making, including trade-offs among several alternatives. According to SearchCRM.com Definitions (a source I googled when defining 'metrics') these types of "systematic approaches ... can be employed to transform an organization's mission statement and business strategy into specific and quantifiable goals, and to monitor the organization's performance in terms of achieving those goals."

(see http://searchcrm.techtarget.com/sDefinition/0,,sid11_gci940481,00.html accessed 8/24/09).

For green manufacturing these metrics could include:

  • Global warming gases emission (CO2, methane CH4, N2O, CFC’s)

- per capita

- per GDP

- per area/nation

  • Recyclability (or percent recycled)
  • Reuse of materials
  • Energy consumption
  • Pollution (air, water, land)
  • Ecological footprint - “fair share” - footprint (discussed in an earlier blog)
  • Exergy (available energy) or other thermodynamic measures

And, these can be represented in terms of a "return on investment" - for example, greenhouse gas return on investment (GROI). Other forms of return measure include:

  • Energy payback time
  • Water (or materials, consumables) payback time
  • Carbon footprint
  • Efficiency improvement (for example, wrt exergy)

For green manufacturing these need to be linked to traditional design and manufacturing parameters. And they need to be assessed over all three scopes of ISO 14064 (1- direct emissions from on-site or company owned assets, 2- indirect emissions created on behalf of the company from energy generation or supply, 3- all others resulting from your business operation including business travel, shipping of goods, resource extraction and product disposal).

Some examples of how these links are set up and the application of these metrics will follow.

Reminder: "Why Green Manufacturing?" Join my webinar on September 17th - go to

https://www2.gotomeeting.com/register/187277227 to register.


  1. Hi Professor Dornfeld,

    What is the difference between recyclability and reuse of materials?

  2. Good question. I use the term recyclability to indicate the material can be reintroduced into the waste stream for recovery and conversion back into useful material whereas reuse indicates the component, part, material may be used again "as is" (or perhaps re-manufactured) without entering the waste stream. I would not use recyclability to indicate material recovered and then burned for energy. Of course, others may have a different take on this.


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