Cumulative Exergy Demand

The indicator Cumulative Exergy Demand (CExD) is introduced to depict total exergy removal from nature to provide a product, summing up the exergy of all resources required. CExD assesses the quality of energy demand and includes the exergy of energy carriers as well as of non-energetic materials. The exergy concept was applied to the resources contained in the ecoinvent database, considering chemical, kinetic, hydro-potential, nuclear, solar-radiative and thermal exergies. Details on the CExD method may be found in Bösch et al. (2007).

In order to quantify the life cycle exergy demand of a product, the indicator Cumulative Exergy Demand (CExD) is defined as the sum of exergy of all resources required to provide a process or product.

Exergy is another way to express quality of energy rather than energy content. Both are expressed in MJ. Exergy is a measure for the useful “work” a certain energy carrier can offer. For instance natural gas has a high exergy value, as it can be used to create high temperatures and high pressured steam. If natural gas is used to heat a house in a highly efficient boiler, very little energy content is lost, but the exergy content is almost entirely lost (there is very little one can do with water between 50 and 80 degrees).

In this method exergy is used as a measure of the potential loss of “useful” energy resources. This method has been directly taken from ecoinvent 2.0. The amount of substances present is compatible with the EI 2.0 database and extended for other databases.

Characterisation

 

The impact category indicator is grouped into the eight resource categories fossil, nuclear, hydropower, biomass, other renewables, water, minerals, and metals. However, in SimaPro 10 different impact categories are presented:

- Non renewable, fossil
- Non renewable, nuclear
- Renewable, kinetic
- Renewable, solar
- Renewable, potential
- Non renewable, primary
- Renewable, biomass
- Renewable, water
- Non renewable, metals
- Non renewable, minerals

The assignment of the adequate type of exergy depends on resource use:

  • Chemical exergy is applied on all material resources, for biomass, water and fossil fuels (i.e. all materials that are not reference species in the reference state)
  • Thermal exergy is applied for geothermy, where heat is withdrawn without matter extraction
  • Kinetic exergy is applied on the kinetic energy in wind used to drive a wind generator
  • Potential exergy is applied on potential energy in water used to run a hydroelectric plant
  • Nuclear exergy is applied on nuclear fuel consumed in fission reactions
  • Radiative exergy is applied on solar radiation impinging on solar panels

 

Normalisation


Normalisation is not a part of this method.

Download the Methods Manual (PDF, 0.6 MB) for a concise overview of the methods in SimaPro.