Eco Audit Tool: Strategies for reducing environmental impact

Transcription

1 Page 1 of 10 Home > Data & Tools > Eco Audit > Strategies for Reducing Environmental Impact Eco Audit Tool: Strategies for reducing environmental impact Having identified the dominant life phase and component/s that contribute most to a product's environmental impact (using the Eco Audit tool), the next step is to identify the correct strategy for reducing that impact. As mentioned in the introduction, the appropriate strategies are highly dependent on both the type of product and the dominant life phase. Guidance on what impact reduction strategies, and material indices, to consider is accessed by clicking on the dominant life phase bars in the Summary chart (see Figure 4). Figure 4. Summary chart showing access to guidance on impact reduction The strategies for reducing the environmental impact of each life phase can be viewed by clicking on the links below: 1. Material phase 2. Manufacture phase 3. Transportation phase 4. Use phase 5. Disposal and end-of-life phase Strategies for reducing environmental impact 1. Material phase Minimize embodied energy or CO 2 footprint per unit of function.

2 Page 2 of 10 Select material with lowest embodied energy and CO 2 footprint per unit of function. Use as large a 'recycled content' in the material as possible. Use as little material as possible while retaining enough redundancy for safety. Watch out for conflict with the Use phase. The material with the lowest direct eco-impact may not be the lightest or the cheapest. Use trade-off methods to resolve the conflict. Relevant material indices to embodied energy (CO 2 footprint): Mode of loading Stiffness prescribed: Strength prescribed: E = Young's modulus, y = yield strength; = density, H m = embodied energy of material/kg (for indices to CO 2 footprint: replace H m by CO 2 = CO 2 footprint of material/kg) Charts for selecting materials that impact of Material phase Bubble chart of Modulus (y-axis) vs. Embodied energy Density (x-axis) Bubble chart of Yield strength (y-axis) vs. Embodied energy Density (x-axis) Bubble chart of Modulus (y-axis) vs. CO 2 footprint Density (x-axis) Bubble chart of Yield strength (y-axis) vs. CO 2 footprint Density (x-axis) Alternatively use the graph stage 'Advanced' function to create bar charts of the material index. Ashby, M. (2012) "Materials and the environment" 2nd edition, Elsevier, Chapter 6 Section 6.3 and Chapter 9 Sections MacKay, D. (2009) "Sustainable energy without the hot air" UIT press, Chapters 15 and H.

3 Page 3 of 10 Strategies for reducing environmental impact Manufacture phase Minimize process energy, CO 2 footprint and waste. Select processes with low energy and CO 2 footprint deformation processing rather than casting for example. Avoid processes with large processing waste net-shape processes rather than machining from solid for example. Check for quality loss on changing process. Relevant material indices. Select compatible process with lowest process energy H p or CO 2 footprint CO 2, p. Charts for selecting processes that impact of Manufacture phase Bar chart of Shaping energy Bar chart of Machining energy Ashby, M. (2012) "Materials and the environment" 2nd edition, Elsevier, Chapter 6 Section MacKay, D. (2009) "Sustainable energy without the hot air" UIT press, Chapters 15 and H. Strategies for reducing environmental impact Transportation phase Transportation is an energy-conversion process: primary energy (oil) is converted into mechanical power and this is used to

4 Page 4 of 10 provide motion. As in any energy-conversion process there are losses, here most conveniently expressed as the energy dissipated per tonne per kilometer transported (MJ/tonne.km), carrying with it an associated CO 2 footprint (kg/tonne.km). Sea, ground and air transport systems usually burn hydrocarbon fuel, so the CO 2 emission is approximately proportional to the energy. Transport dissipates energy in two ways: as work against drag exerted by air or water, and as work to accelerate the vehicle, lost on braking: Energy dissipated per unit distance = where and are constants, C d is the drag coefficient, A the frontal area of the vehicle, v the velocity and m the mass of the vehicle. The addition of one more unit of freight does not significantly change the frontal area or the drag coefficient, so it is the kinetic energy term that dominates. So the steps to reduce the energy for transport focus on mass, distance, velocity and mode of transport. Design for low-impact transport. Reduce the mass transported, m. Material-efficient design helps here. Rethink the transport mode. Reduce the distance of transport. Reduce the speed v. The motive for off-shore manufacture, incurring the need for long haul transport, is that the lower labor costs more than off-set the greater transport costs. Use the Eco Audit tool to explore the impact of different transport modes and distances. Charts for selecting processes that impact of Transport phase Material selection to mass can reduce the mass of both products and the vehicles themselves. See strategies for reducing environmental impact of Use phase. Explore alternative transport modes by specifying different options in the transport section of the Eco Audit product definition. Ashby, M. (2012) "Materials and the environment" 2nd edition, Elsevier, Chapter 6 Section 6.4.

5 Page 5 of 10 MacKay, D. (2009) "Sustainable energy without the hot air" UIT press, Chapters 3, 5, 15, A and C. Strategies for reducing environmental impact Use phase The strategies for reducing the environmental impact of the use phase are highly dependent on the type of product and whether the static or mobile use phase is dominant. These can be categorized into three main groups (click category for guidance on impact reduction): Static mode - mechanical devices Static mode - heating and cooling systems Mobile mode - transportation Static mode mechanical devices Rotating disks, drums and shafts have rotational inertia. Energy is dissipated when they are spun up to speed and down again. The energy loss is d by giving the component as small a rotational moment of inertia as possible. The same is true of oscillating components like connecting rods, weaving and printing equipment. Design for energy use. Select material with the lowest value of the appropriate index, listed below. The material choice that s mass may not embodied energy or cost. Use trade-off methods to resolve the conflict. Relevant material indices to use energy (CO 2 footprint), choose materials with the lowest values of the indices listed below. Mode of loading Stiffness prescribed: Strength prescribed:

6 Page 6 of 10 Charts for selecting materials that impact of Use phase (static appliances with moving parts) Bubble chart of Modulus (y-axis) vs. Density (x-axis) Bubble chart of Yield strength (y-axis) vs. Density (x-axis) Alternatively, use the graph stage 'Advanced' function to create bar charts of the material index. Ashby, M. (2012) "Materials and the environment" 2nd edition, Elsevier, Chapter 9 Sections MacKay, D. (2009) "Sustainable energy without the hot air" UIT press, Chapter 11. Static mode heating and cooling systems Refrigerators and freezers, ovens and kilns, space heating and air conditioning use energy to heat or cool space. Energy use is d by maximizing the thermal resistance of the walls of the product or building. These walls are usually multi-layers. The thermal resistance or R-value is a measure of thermal resistance of a window, wall, roof or floor unit. It is the temperature difference required to drive a unit flux of heat through the unit: where q is the heat flux through the unit, T is the temperature difference across it, t i are the thicknesses of the layers of the unit and i are the thermal conductivities of those layers. The U-value (the transmittance or conductance) is the reciprocal of the R-value. In the SI system the units of R-value are m 2 K/W, but the US still uses ft 2.F.h/Btu. Design for minimum thermal loss. Select material with the lowest value of the appropriate index, listed below.

7 Page 7 of 10 The material choice that s mass may not embodied energy or cost. Use trade-off methods to resolve the conflict. Relevant material indices. When the temperature difference across the wall is constant over long periods of time, choose the material with the largest R value (where R 1/ ). When, instead, the temperature difference across the wall fluctuates, choose the material with the lowest value of the index listed below. Temperature profile To heat loss: Thermal conductivity Combined thermal inertia and conductivity = thermal conductivity, C p = specific heat; = density Charts for selecting materials that impact of Use phase (static heating and cooling systems) Bubble chart of Thermal conductivity (y-axis) vs. Volume specific heat C p (x-axis) Alternatively, use the graph stage 'Advanced' function to create bar charts of the material index. Ashby, M. (2012) "Materials and the environment" 2nd edition, Elsevier, Chapter 10 Sections MacKay, D. (2009) "Sustainable energy without the hot air" UIT press, Chapters 7 and E. Mobile mode transportation The use energy of transport systems or of products that form part of them is largely dependent on their mass. The energy dissipated per unit distance is where and are constants, C d is the drag coefficient, A the frontal area of the vehicle, v the velocity and m the mass of the vehicle. Material substitution to reduce mass and refinement of shape to reduce frontal area and drag coefficient thus reduces the use energy of the product.

8 Page 8 of 10 Design for minimum mass. Select material with the largest value of the appropriate index, listed below, to reduce mass. Lean design: use as little material as possible. The material choice that s mass may not embodied energy or cost. Use trade-off methods to resolve the conflict. Relevant material indices to reduce mass: Mode of loading Stiffness prescribed: Strength prescribed: E = Young's modulus, y = yield strength; = density Charts for selecting materials that impact of Use phase (transportation products) Bubble chart of Modulus (y-axis) vs. Density Bubble chart of Yield strength (y-axis) vs. Density Alternatively, use the graph stage 'Advanced' function to create bar charts of the material index. Ashby, M. (2012) "Materials and the environment" 2nd edition, Elsevier, Chapter 9 Sections and Chapter 10 Sections MacKay, D. (2009) "Sustainable energy without the hot air" UIT press, Chapters 3, 20 and A.

9 Page 9 of 10 Strategies for reducing environmental impact Disposal and end-of-life phases There are six options for disposal of products at the end of their first life: Landfill Combust for energy recovery Downcycle Recycle Re-condition or re-engineer Reuse as is The first, landfill, is the least attractive. Combustion, properly carried out, recovers some of the embodied energy of the materials of the product, but the recovery-efficiency is low, the economics are unattractive and proposals to build combustion plants are often opposed by local residents. Recycling is the best way to extract value from waste and return materials to the supply-stream, preserving material stock. Re-conditioning or reengineering restores used products or recoverable components to as-new condition, but establishing a market and maintaining a supply chain of recondition products is not easy, and issues of warranty and responsibility for malfunction are deterrents. Reuse sounds the most attractive option; passing products from consumers who no longer want them to those willing to accept them in a used state. This requires a market place where seller and buyer can meet and negotiate (like ebay ) and an acceptance of used products rather than new. Increase end-of-life potential, design for recycling. Select material that have high recycle ratio (the 'Recycle fraction in current supply', listed on the material datasheets). Minimize the number of different materials in the product. Avoid combining materials that are incompatible if recycled together. Identify materials used in components, using recycle marks or color coding, preferably with grades, filler type and content. Design for ease of disassembly: snap fits, fasteners, releasable adhesives. The material choice that best suits end-of-life may not the use energy. Use trade-off methods to resolve the conflict. Charts for selecting materials that maximize end-of-life potential

10 Page 10 of 10 Bar chart of Recycle fraction in current supply Ashby, M. (2012) "Materials and the environment" 2nd edition, Elsevier, Chapter 4 and Chapter 7 Sections 7.2. MacKay, D. (2009) "Sustainable energy without the hot air" UIT press, Chapter 15 opyrig t ranta ign am ridge