Factors Influencing Design: Energy, Lifespan and Maintenance
Energy Sources in Engineering Context
Every product an engineer designs relies on energy somewhere in its life cycle — in manufacture, in operation, or in disposal. Understanding where that energy comes from and what its environmental consequences are is now a core engineering responsibility. Energy sources divide into renewable energy and non-renewable energy (fossil fuels and nuclear power, which relies on finite uranium reserves).
Renewable: wind, solar (photovoltaic and thermal), tidal, wave, hydroelectric, biomass. Non-renewable: coal, oil, natural gas (fossil fuels that release carbon dioxide when burned) and nuclear (produces radioactive waste, not greenhouse gases). The distinction between the specific environmental impacts of these groups is a key exam point.
Environmental Impacts: Specific Mechanisms
Vague answers like “bad for the environment” or “hurts wildlife” earn zero marks. You must name the specific mechanism:
Fossil fuels (coal, oil, gas): combustion releases carbon dioxide, a greenhouse gas that accumulates in the atmosphere and contributes to global warming and climate change. It also releases sulfur dioxide (acid rain) and particulate matter (respiratory health impacts). Extraction involves mining and drilling, which cause habitat loss and risk of oil spills. Nuclear: does not release greenhouse gases during operation, but produces high-level radioactive waste that must be stored securely for thousands of years. A reactor accident (such as Chernobyl or Fukushima) can contaminate large areas with long-lived radioactive isotopes. Wind: no greenhouse gas emissions during operation, but wind turbines cause noise, affect local visual landscape and can kill birds and bats if sited on migration routes. Offshore wind has a smaller land-use impact. Solar: no operational emissions, but manufacturing photovoltaic panels uses energy and toxic chemicals. Land-use for large solar farms can displace habitats. Tidal: predictable and reliable (unlike wind and solar), no emissions, but tidal barrages can affect estuarine ecosystems and sediment transport. Biomass: burning biomass releases carbon dioxide, but if the biomass is regrown, the carbon is re-absorbed over the growth cycle — making it roughly carbon-neutral, though transport emissions add to the total.
Engineered lifespan is the design decision to build a product to last for a defined period — long enough to be useful, but not necessarily forever. A domestic washing machine might be designed for a 10-year service life; a commercial aircraft for 25 years or a specific number of pressurisation cycles. Designing for a finite lifespan allows engineers to optimise material use and cost, because they do not need to over-engineer components beyond what the expected service conditions demand.
Planned obsolescence takes this further — it is the deliberate design of a product so that it becomes obsolete or fails within a predictable time, driving replacement sales. There are two forms: functional obsolescence (the product stops working after the designed lifespan, for example sealed batteries or glued components that cannot be replaced) and aesthetic obsolescence (the design is made to look dated quickly so customers choose to upgrade). Critics argue that planned obsolescence increases waste and resource consumption. The UK and EU “right to repair” legislation is introducing requirements for manufacturers to supply spare parts and allow user repair for an extended period.
Maintenance Requirements in Engineering Design
Some products are designed for easy maintenance; others are designed to be sealed for life. The choice affects material selection, fastener choice and the design of access points. The main maintenance activities an engineer must consider are:
Lubrication. Moving parts in contact generate friction and wear. Sealed bearings (such as those in a bicycle hub) contain grease for the life of the bearing. Industrial gearboxes have oil-fill ports and oil-change service intervals. Nylon and PTFE components are self-lubricating and require no external oil or grease. Avoiding corrosion. Steel components in outdoor or marine environments must be protected: galvanising (zinc coating), painting, anodising (aluminium), use of stainless steel or plastic enclosures. For a coastal wind turbine nacelle, corrosion protection adds significantly to whole-life cost if not designed in from the start. Compensating for wear. Brake pads, tyres and conveyor belts wear in service. Design must allow these to be measured (indicator grooves on brake pads, tread-depth indicators on tyres) and replaced without dismantling the entire assembly. A service interval defines how often a product must be inspected and consumable parts replaced.
The three engineering maintenance categories are: lubrication (sealed bearings, oil-change intervals, self-lubricating materials like nylon), corrosion avoidance (galvanising, painting, stainless steel, anodising) and wear compensation (measurable wear indicators, replaceable consumables, defined service intervals). All three should be built into a design from the start, not retrofitted.
At the end of a product’s service life, the engineer’s responsibilities do not stop. Recovery of materials (recycling) is increasingly a legal requirement and a commercial priority. Metals are the most efficiently recycled engineering materials: steel and aluminium scrap can be remelted and re-rolled into new stock with a fraction of the energy needed to produce primary metal from ore. Aluminium recycling uses only about 5% of the energy of primary smelting. Thermoplastics can be remelted and granulated for re-moulding, though multiple recycling cycles degrade polymer chains and reduce quality. Thermosets and composites are difficult to recycle because they cannot be remelted; they are typically shredded for use as filler material or incinerated for energy recovery. Designing for disassembly (using screws rather than glue, labelling polymer types with recycling codes) makes end-of-life recovery easier.