3.11 Reduce Consumption

Fromm states that we have changed from a society of “being” to a society of “having” [see reference 7]. This endless consumption is fuelled by companies providing the products, with ubiquitous advertising and selling techniques. The result of this is that much of production is consumer driven, and any major reduction in consumption will have to come from a systemic change in a consumer driven lifestyle.

Unfortunately this looks unlikely to change, and apart from changing their personal consumption patterns, not an area that an engineer can make a big change in. This section will therefore look at ways an engineer can make an impact – in the design and manufacture side of a product.

This is split into three parts –

• incorporating design ideas that use less material from the start by optimising components
• by extending the life of a product which will reduce the amount produced over time.
• the idea of increasing the efficiency of the manufacturing process (and why this won't necessarily lead to successful results)

Use less by design

A design specification for a product will include its purpose, size, shape and geometry. Also included will be material properties- strength, stiffness, lifetime as well as material available, and mainly, cost. It is usual that the factors of most importance will be suitability for the job and cost, with environmental factors low down the list.

It can be possible to optimise geometries of a component while still maintaining its strength and stiffness, thereby reducing the material content. An example of this is the “I” section steel beam often found in buildings. The cross section uses much less steel than a solid bar, but because of its shape it has the same strength properties as a full bar. The design could be optimised further by finding out where the principal loads will be, and making the bar thicker in these places, and thinner everywhere else.

However, to do this the structural engineer will have to order the bar specially made, and the supplier will no doubt charge a premium for this service. The reason for this is that is it usually easier (and therefore cheaper) to manufacture standardised components than bespoke designs.

Another example of designing for less material use can be found in concrete: currently rectangles and linear designs are used for ease and cost, but wasteful on concrete. Mould optimisation could save a huge amount of concrete, and therefore energy.

During manufacturing, metal goes through processes of trimming, cutting and machining to get to the final product. Metal lost in this way is known as “yield loss”. 25% of steel and nearly half of aluminium never makes it into a component, but is recycled into fresh sheets. There is a huge amount of wasted energy in this process. Component designers don't always consider these manufacturing processes when designing a product. If they did, they could make parts tessellate, which would save wastage in manufacture.

The barriers to these tools of sustainable material use will soon become familiar; it is possible if the engineer were to design for it from the beginning but not currently implemented due to cost considerations and lack of incentives.

Make longer life products

One way of reducing consumption is to create products with a longer life. In developed countries most of the demand for steel and aluminium is to replace end of life products, as opposed to building new ones for growth. If products were designed to last longer, less material would be used in creating new products. However, it is not always the case that longer life products reduce the overall energy used. When considering products that use energy (such as a car), we must calculate energy savings from producing a more efficient design and weight that up with the embodied energy of manufacturing a new product.

When looking at the economic case for making longer life products, it will almost always be more expensive to make something more durable. Manufacturers will be looking for a quick payback so the cheaper, shorter term option will be more likely to be considered. This is taken to the extreme in some cases, where companies will incorporate into the design a fault or flaw that will make the product unusable after a set amount of time. In other words the product is designed to fail after a set time limit forcing the consumer to throw it away and purchase another one, thereby increasing sales and profit margins. This is known as “manufacture for obsolescence” and is common in mobile phone manufacture.

Concepts to make longer life products include:

• durability – incorporating maintenance and restoration
• upgrading – including modular and adaptable design
• cascading – find new uses for the product in its current condition
• design for reuse and recycling when finished

(Source Sustainable Materials With Both Eyes Open [see reference 2])

Reduce Energy Consumption by Increasing Efficiency in Production

Figure 2.11.3 Energy and C02 Consumption of Global Steel Production Since 1975

Source: MIT Opencourseware [see reference 3]

Image sourced from MIT opencourseware under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License
http://dspace.mit.edu/bitstream/handle/1721.1/39134/1-964Fall-2004/NR/rdonlyres/Civil-and-Environmental-Engineering/1-964Fall-2004/C31B4488-55CE-461E-B18F-FCBECAA4A5EA/0/lec2_construction.pdf

The graph above shows how the energy consumption per tonne of steel in the EU has decreased by almost half in the last 25 years. The reason for this is that the main cost of steel production is energy; energy is required to extract ore by mining processes, and large amounts of energy is needed to convert the ore into a liquid ready for pouring or casting.

Steel manufacturers want to maximise profits and will achieve this by lowering costs. Investment is put into new technology that increases efficiency and therefore saves money. The energy consumption per tonne has decreased, but the number of tonnes produced has increased, resulting in a net increase of energy use and associated carbon emissions. The graph shows that production efficiency is already very high due to cost considerations, so very little energy reductions can be made from a sustainability point of view.

The same concepts are true for plastic, in that the manufacturing processes are already efficient. The IEA estimates it could be made 15% more efficient.